Patent Publication Number: US-11642092-B1

Title: Systems and methods for characterizing high risk plaques

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/662,762, filed May 10, 2022, which is a continuation of U.S. patent application Ser. No. 17/033,136, filed Sep. 25, 2020, which is a continuation of U.S. patent application Ser. No. 16/750,278, filed Jan. 23, 2020, now U.S. Pat. No. 10,813,612, which claims the benefit of U.S. Provisional Application No. 62/797,024, filed Jan. 25, 2019. Each of these disclosures is incorporated herein by reference in its entirety. Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57. 
    
    
     TECHNICAL FIELD 
     The systems and methods disclosed herein are directed to identifying high risk plaques in coronary arteries, and more particularly, to characterizing coronary plaque by using three-dimensional (3D) models of medical images of coronary arteries to calculate density ratios of the coronary plaque and surrounding tissues. 
     BACKGROUND 
     The heart is a muscle that receives blood from several arteries, including the left circumflex artery (LCX) and the left anterior descending artery (LAD), both of which branch off from the left main artery, and the right coronary artery. Coronary artery disease generally relates to a constriction or blockage of one of these arteries and may produce coronary lesions in the blood vessels providing blood to the heart, such as a stenosis (abnormal narrowing of a blood vessel) or ischemia (a deficient supply of blood to the body part due to obstruction of the inflow of arterial blood). As a result, blood flow to the heart may be restricted. A patient suffering from coronary artery disease may experience chest pain. A more severe manifestation of coronary artery disease may the lead to myocardial infarction, or a heart attack. 
     Patients suffering from chest pain and/or exhibiting symptoms of coronary artery disease may be subjected to one or more tests that may provide some indirect evidence relating to coronary lesions. For example, noninvasive tests may include electrocardiograms, blood tests, treadmill exercise tests, echocardiograms, single positron emission computed tomography (SPECT) and positron emission tomography (PET). Anatomic data may be obtained noninvasively using coronary computed tomography angiography (CCTA), which uses computed tomography (CT) scanning after an intravenous infusion of an iodinated contrast agent to examine the arteries that supply blood to the heart and determine whether they have been narrowed or blocked by plaque buildup. CCTA and CT scanning, as sometimes used herein, may be hereinafter referred to as CT scanning for brevity. Images generated from a CT scan can be reconfigured to create three-dimensional (3D) images that may be viewed on a monitor, printed on film, or transferred to electronic media. Invasive tests can include measuring the fractional flow reserve (FFR) of any given lesion in order to evaluate the functional significance of that lesion. FFR is defined as the ratio of the blood pressure downstream of a lesion to the blood pressure upstream of the lesion at hyperemia and requires cardiac catheterization to be measured. Another common invasive test is the invasive coronary angiogram, with heart disease severity scored through the SYNTAX scoring system, which involves assessing the coronary anatomy using angiograms and answering a series of questions. A score is generated based on the lesion characteristics and responses to the questions to determine the most appropriate course of treatment. This process is time-consuming and depends on an individual cardiologist&#39;s subjective characterizations of the coronary angiograms. Because of this limitation, the SYNTAX score is sometimes performed by multiple cardiologists to obtain an average score, which increases the time and resources required to perform the assessment. Further, as with any invasive medical procedures, FFR and SYNTAX scoring risk adverse effects and unnecessary medical costs. 
     Although plaque features, such as adverse plaque characteristics (APCs), have been investigated for prognostic value of major adverse cardiac events using both invasive and noninvasive techniques (such as intravascular ultrasound, optical coherence tomography, and coronary computed tomography data), a need exist for methods and systems for predicting adverse cardiac events by characterizing individual coronary plaque using noninvasive imaging techniques(atomic image data specific to a patient). 
     SUMMARY 
     Coronary artery disease (CAD) is a major cause of morbidity and mortality. Coronary computed tomographic angiography (CCTA, sometimes referred to simply as CT) has emerged as a non-invasive method for evaluation of CAD. Coronary atherosclerosis is the primary disease entity of CAD, with coronary stenosis and ischemia serving as secondary and tertiary consequences of the atherosclerotic process. The primary mechanisms for heart attack resulting from coronary atherosclerosis are rupture of the plaque, erosion of the plaque, or a calcified nodular protrusion that punctures the plaque. Coronary atherosclerosis may present in many different forms: focal or diffuse, at bifurcations or trifurcations/along straight segments of the artery; of different compositions, for example, plaque can be graded as necrotic core, fibrofatty, fibrous, calcified and densely calcified; and of different 3D shapes. Not all coronary plaque will be implicated in adverse cardiac events, and over-treatment of non-risky plaques can impose unnecessary health risks to patients and may result in unnecessary increased health care costs. Herein is described methods and systems of using images generated by scanning a patient&#39;s arteries (e.g., CCTA) to identify coronary artery plaques that are at higher risk of causing future heart attack or acute coronary syndrome. While it cannot necessarily be determined whether these plaques will rupture, erode or protrude, it can be noted that these plaques will likely be the future culprits of heart attack or acute coronary syndrome (ACS). 
     Scientific evidence reported to date that examine “high risk plaque” features have focused on plaques alone and have identified certain atherosclerotic plaque features as associated with future risk of heart attack or ACS, such as aggregate plaque volume (APV), low attenuation plaque (LAP), positive arterial remodeling (PR) and napkin ring signs (NRS). Such studies, however, have failed to consider the relationship between the plaque and adjoining vascular structures, most notably the coronary lumen and the perivascular coronary fat/tis sue. 
     “Radiodensity” as used herein is a broad term that refers to the relative inability of electromagnetic relation (e.g., X-rays) to pass through a material. In reference to an image, radiodensity values refer to values indicting a density in image data (e.g., film, print, or in an electronic format) where the radiodensity values in the image corresponds to the density of material depicted in the image. “Attenuation” as used herein is a broad term that refers to the gradual loss of intensity (or flux) through a medium. “Hypo-attenuation” is a term that may be used to indicate, in an image, portions of materials having low density that appear darker. “Hyper-attenuation” is a term that may be used to indicate, in an image, portions of materials having high density that appear lighter in the image. Antoniades reported a fat attenuation index, FAI, which could identify high risk plaques by characterizing the radiodensity gradient of fat tissue (e.g., perivascular adipose tissue) near or surrounding such plaque. (See, Antonopoulos et al., “Detecting human coronary inflammation by imaging perivascular fat,”  Sci. Transl. Med ., Vol. 9, Issue 398, Jul. 12, 2017.) The attenuation density of fat cells closer to the density of water (e.g., Hounsfield unit (HU) density=0) contrast with fat cells of a lower HU density (closer to −100), with the former associated with more inflamed fat cells and achieving higher attenuation due to cholesterol efflux from those cells. This was assumed to identify areas where there are coronary artery atherosclerotic lesions that are more inflamed. 
     No study to date, however, has considered the relationship of the densities of the coronary lumen, the plaque itself and the perivascular coronary fat. As summarized below and described herein, methods and systems are described for identifying a coronary plaque that is at increased susceptibility to be implicated in future ACS, heart attack or death. In some embodiments, a ratio method is described where the plaque serves as the central fulcrum point between the lumen or perivascular coronary fat. 
     One innovation includes a method for characterization (e.g., volumetric characterization) of coronary plaque using data from images of the coronary plaque and perivascular tissue gathered from a computed tomography (CT) scan along a blood vessel, the image information including radiodensity values of coronary plaque and perivascular tissue located adjacent to the coronary plaque. In some embodiments, the perivascular tissue may include the vessel lumen and/or the perivascular fat. In some embodiments, the method can include creating three dimensional (3D) models from CT images prior to determining radiodensity values. In some embodiments, the method can include quantifying, in the image data, the radiodensity in regions of coronary plaque, quantifying, in the image data, radiodensity in at least one region of corresponding perivascular tissue adjacent to the coronary plaque, determining gradients of the quantified radiodensity values within the coronary plaque and the quantified radiodensity values within the corresponding perivascular tissue, determining a ratio of the quantified radiodensity values within the coronary plaque and the corresponding perivascular tissue, and characterizing the coronary plaque based on at least the radiodensity values and/or ratios. In some examples, the plaque may be characterized by analyzing one or more of a minimum radiodensity value of the plaque and/or the perivascular tissue and a maximum radiodensity value of the plaque and/or the perivascular tissue. In some embodiments, the perivascular tissue may include at least one of coronary artery lumen, fat or coronary plaque. Such methods are performed by one or more computer hardware processors configured to execute computer-executable instructions on a non-transitory computer storage medium. Such methods may include one or more other aspects, or the aspects of the methods may be characterized in various ways, in different embodiments, some of which are described below. 
     In some embodiments, the method further comprises receiving, via a network, the image data at a data storage component. In some embodiments, the network is one of the Internet or a wide area network (WAN). In some embodiments, the image data from a CT scan includes at least ten images, or at least 30 images, or more. In some embodiments, the method further includes generating a patient report comprising at least one of a diagnosis, a prognosis, or a recommended treatment for a patient based on the characterization of the coronary plaque. 
     Adipose tissue (or simply “fat”) is a type of connective tissue that plays an important role in the functioning of the body by storing energy in the form of lipids and cushioning and insulating the body. It is a loose connective tissue composed mostly of adipocytes, but also may contain a stromal vascular fraction (SVF) of cells including preadipocytes (the predecessor cells to adipocytes), fibroblasts, and vascular endothelial cells, and a variety of immune cells. Quantifying radiodensity in at least one region of perivascular tissue can include quantifying radiodensity of coronary plaque and adipose tissue in one or more regions or layers of vascular and/or perivascular tissue. In some embodiments, the radiodensity of the scan information is quantified for water (e.g., as a control or reference point) in each of one or more of the regions of coronary plaque and perivascular tissue. In some embodiments, radiodensity of the scan information is quantified for necrotic core plaque in the each of one or more regions or layers of coronary plaque. In some embodiments, the coronary plaque radiodensity values and the perivascular tissue radiodensity values are an average radiodensity. In some embodiments, the coronary plaque radiodensity values and the perivascular tissue radiodensity values are a maximum radiodensity. In some embodiments, the coronary plaque radiodensity values and the perivascular tissue radiodensity values are a minimum radiodensity. The quantified radiodensities may be characterized as numerical values. In some embodiments, the quantified radiodensities account for CT scan- and patient-specific parameters, including but not limited to one or more of iodinated contrast agent, contrast type, injection rate, aortic contrast opacification, left ventricular blood pool opacification, signal-to-noise, contrast-to-noise, tube voltage, milliamps, method of cardiac gating, CT scanner type, heart rate, heart rhythm, or blood pressure. 
     Such methods may also include reporting the quantified radiodensities of the coronary plaque and the perivascular tissue as a gradient of such radiodensities. In some embodiments, the quantified radiodensities of the coronary plaque and the perivascular tissue are determined and reported as a ratio of the slopes of the radiodensity gradients of the coronary plaque and perivascular tissue adjacent to the coronary plaque. In some embodiments, the quantified (maximum or minimum) radiodensities of the coronary plaque and the perivascular tissue determined and each are reported as the differences in radiodensity values of the coronary plaque and the perivascular tissue. In some embodiments, the image data is gathered from a CT scan along a length of at least one of a right coronary artery, left anterior descending artery, left circumflex artery, aorta, carotid arteries, or, femoral arteries, or their branches. In some embodiments, the data is gathered from a CT scan along a length of a non-coronary reference vessel, which can be, for example, the aorta. The radiodensity of the image data can be expressed in a variety of measurement units. In one example, the radiodensity is quantified in Hounsfield units. In another example, the radiodensity is quantified in absolute material densities, for example, when multi-energy CT is performed, which uses spectral data allowing differentiation and classification of tissues to obtain material-specific images. 
     In some embodiments of the method for characterization (e.g., volumetric characterization) of coronary plaque, one or more regions (or layers) of perivascular tissue extend to an end distance from the outer wall of the blood vessel. In some embodiments of the method, one or more regions (or layers) of the coronary plaque tissue extend to an end distance from the outer wall of the blood vessel, the end distance being the fixed distance where the radiodensity of adipose tissue (i) reaches a maximum value within the plaque, or (ii) increases by a relative percent (e.g., ≥10%); (iii) or changes by a relative percent versus the lowest radiodensity value in the plaque. In some embodiments, the end distance may be defined as being the fixed distance where the radiodensity of adipose tissue (i) reaches a minimum value within the scanned anatomical area in a healthy vessel, or (ii) drops by a relative percent (e.g., ≥10%); or (iii) drops by a relative percent versus a baseline radiodensity value in a vessel of the same type free of disease. In some embodiments, the baseline radiodensity value is the radiodensity quantified in a layer of adipose tissue lying within a fixed layer or region surrounding the outer vessel wall, measured by a thickness, area or volume. In some embodiments, the baseline perivascular tissue radiodensity is the radiodensity quantified for a layer of adipose tissue lying proximal to the outer wall of the blood vessel. In some embodiments, the baseline adipose tissue radiodensity is the radiodensity quantified for water (as a reference or control point) in a layer of adipose tissue lying proximal to the outer wall of the blood vessel. The baseline radiodensity may be generated in various ways. In some embodiments, the baseline radiodensity is an average radiodensity. In some embodiments, the baseline radiodensity is a maximum radiodensity. In some embodiments, the baseline radiodensity is a minimum radiodensity. In some embodiments, a baseline coronary plaque radiodensity value is the average radiodensity quantified in a layer of coronary plaque tissue within a fixed layer or region within the plaque and is measured by a thickness, area or volume. In some embodiments, the baseline coronary plaque radiodensity is the radiodensity quantified for all coronary plaques in the measured vessels. 
     In some embodiments, the method may further include determining a plot of the change in quantified radiodensity relative to baseline radiodensity in each of one or more concentric layers of perivascular tissue with respect to distance from the outer wall of the blood vessel up to an end distance, determining the area of the region bound by the plot of the change in quantified radiodensity and a plot of baseline radiodensity with respect to distance from the outer wall of the blood vessel up to the end distance, and dividing said area by the quantified radiodensity measured at a distance from the outer wall of the blood vessel, wherein the distance is less than the radius of the vessel or is a distance from the outer surface of the vessel above which the quantified radiodensity of adipose tissue drops by more than 5% compared to the baseline radiodensity of adipose tissue in a vessel of the same type free of disease. Some embodiments of the method may further comprise determining a plot of the change in quantified radiodensity relative to baseline radiodensity in each of one or more concentric layers of coronary plaque tissue with respect to distance from the outer wall of the blood vessel up to the inner surface of the plaque, determining the area of the region bound by the plot of the change in quantified radiodensity and a plot of baseline radiodensity with respect to distance from the outer wall of the blood vessel up to the inner surface of the plaque, and dividing said area by the quantified radiodensity measured at a distance from the outer wall of the blood vessel, wherein the distance is less than the radius of the vessel or is a distance from the outer surface of the vessel above which the quantified radiodensity of adipose tissue drops by more than 5% compared to the baseline radiodensity of adipose tissue in a vessel of the same type free of disease. In some embodiments, the quantified radiodensity is the quantified radiodensity of adipose tissue in the each of one or more regions or layers of perivascular tissue or coronary plaque. In some embodiments, the quantified radiodensity is the quantified radiodensity of water in the each of one or more regions or layers of perivascular tissue. In some embodiments, the quantified radiodensity is an average radiodensity. In some embodiments, the quantified radiodensities are a maximum radiodensity. In some embodiments, the quantified radiodensities are a minimum radiodensity. 
     In some embodiments of the methods described herein, the methods may further comprise normalizing the quantified radiodensity of the coronary plaque and the perivascular tissue to CT scan parameters (patient- and CT-specific parameters), which include but are not limited to one or more of iodinated contrast agent, contrast type, injection rate, aortic contrast opacification, left ventricular blood pool opacification, signal-to-noise, contrast-to-noise, tube voltage, milliamps, method of cardiac gating, CT scanner type, heart rate, heart rhythm, or blood pressure. In some embodiments, the methods may also include normalizing the quantified radiodensity of the coronary plaque-associated perivascular fat to remote perivascular fat and/or normalizing the quantified radiodensity of the coronary plaque to remote coronary plaques. 
     Embodiments of the method may further comprise quantifying other high risk plaque features, such as remodeling, volume, spotty calcifications, and further characterizing the high risk plaque based on one or more of high risk plaque features. In some embodiments, characterization of the coronary plaque includes analyzing plaque heterogeneity, specifically the presence of calcium and non-calcified plaque admixtures. In some embodiments, characterizing the coronary plaque comprises identifying the coronary plaque as a high risk plaque if it is prone to be implicated as culprit lesions in future acute coronary events, based on comparison with previously classified patient image data which may include image data from scans taken for the same patient and/or image data from scans taken from other patients. In some embodiments, characterizing the coronary plaque comprises identifying the coronary plaque as a high-risk plaque if it is likely to cause ischemia (e.g., restriction in blood supply to tissue) based on a comparison with previously classified patient image data. In some embodiments, characterizing the coronary plaque comprises identifying the coronary plaque as a high-risk plaque if it is likely to show aberrations in shear stress (e.g., low shear stress) based on a comparison with previously classified patient image data. 
     A vasospasm is the narrowing of the arteries caused by a persistent contraction of the blood vessels, which is known as vasoconstriction. This narrowing can reduce blood flow. Vasospasms can affect any area of the body including the brain (cerebral vasospasm) and the coronary artery (coronary artery vasospasm). In some embodiments of the method, characterizing the coronary plaque comprises identifying the coronary plaque as a high risk plaque if it is likely to cause a vasospasm based on a comparison with previously classified patient image data. In some embodiments, characterizing the coronary plaque comprises identifying the coronary plaque as a high risk plaque if it is likely to rapidly progress based on a comparisons with previously classified patient image data. In some cases, coronary plaque may calcify, hardening by deposition of or conversion into calcium carbonate or other insoluble calcium compounds. In some embodiments, characterizing the coronary plaque comprises identifying the coronary plaque as a high risk plaque if it is likely not to calcify, based on a comparisons with previously classified patient image data. In some embodiments, characterizing the coronary plaque comprises identifying the coronary plaque as a high risk plaque if it is likely not to respond, regress or stabilize to medical therapy based on a comparisons with previously classified patient image data. In some embodiments, characterizing the coronary plaque comprises identifying the coronary plaque as a high risk plaque if it is progresses rapidly in volumetric size. In some embodiments, characterizing the coronary plaque comprises identifying the coronary plaque as a high risk plaque if it is associated with complications at the time of revascularization (such as by inducing no-reflow phenomenon) based on a comparisons with previously classified patient image data. 
     Another innovation includes a system for characterization of coronary plaque tissue (e.g., volumetric characterization) using image data gathered from one or more computed tomography (CT) scans along a blood vessel, the image information including radiodensity values of coronary plaque and perivascular tissue located adjacent to the coronary plaque. The system can include a first non-transitory computer storage medium configured to at least store the image data, a second non-transitory computer storage medium configured to at least store computer-executable instructions, and one or more computer hardware processors in communication with the second non-transitory computer storage medium. The one or more computer hardware processors are configured to execute the computer-executable instructions to at least quantify, in the image data, the radiodensities in regions of coronary plaque, and quantify, in the image data, radiodensities in at least one region of corresponding perivascular tissue adjacent to the coronary plaque, determine gradients of the quantified radiodensity values within the coronary plaque and the quantified radiodensity values within the corresponding perivascular tissue, determine a ratio of the quantified radiodensity values within the coronary plaque and the corresponding perivascular tissue, and characterize the coronary plaque by analyzing one or more of the gradients of the quantified radiodensity values in the coronary plaque and the corresponding perivascular tissue, or the ratio of the coronary plaque radiodensity values and the radiodensity values of the corresponding perivascular tissue. 
     Another innovation includes a non-transitory computer readable medium including instructions that, when executed, cause one or more hardware computer processors of an apparatus to perform a method, the method including quantifying, in the image data, the radiodensities in regions of coronary plaque. The method may further include quantifying, in the image data, radiodensities in at least one region of corresponding perivascular tissue adjacent to the coronary plaque, determining gradients of the quantified radiodensity values within the coronary plaque and the quantified radiodensity values within the corresponding perivascular tissue. The method may further include determining a ratio of the quantified radiodensity values within the coronary plaque and the corresponding perivascular tissue. The method may further include characterizing the coronary plaque by analyzing one or more of the gradients of the quantified radiodensity values in the coronary plaque and the corresponding perivascular tissue, or the ratio of the coronary plaque radiodensity values and the radiodensity values of the corresponding perivascular tissue. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosed aspects will hereinafter be described in conjunction with the accompanying drawings, which are incorporated in and constitute a part of this specification, and are provided to illustrate and provide a further understanding of example embodiments, and not to limit the disclosed aspects. In the drawings, like designations denote like elements unless otherwise stated. 
         FIG.  1    depicts a schematic of an example of an embodiment of a system  100  that includes a processing system  120  configured to characterize coronary plaque. 
         FIG.  2    is a schematic illustrating an example of a heart muscle and its coronary arteries. 
         FIG.  3    illustrates an example of a set of images generated from scanning along a coronary artery, including a selected image of a portion of a coronary artery, and how image data may correspond to a value on the Hounsfield Scale. 
         FIG.  4 A  is a block diagram that illustrates a computer system  400  upon which various embodiments may be implemented. 
         FIG.  4 B  is a block diagram that illustrates computer modules in a computer system  400  which may implement various embodiments. 
         FIG.  5 A  illustrates an example of a flowchart of a process for analyzing coronary plaque. 
         FIG.  5 B  illustrates an example of a flowchart that expands on a portion of the flowchart in  FIG.  5 A  for determining characteristics of coronary plaque. 
         FIG.  6    illustrates a representation of image data depicting an example of a portion of a coronary artery  665  (sometimes referred to herein as a “vessel” for ease of reference). 
         FIG.  7    illustrates the same vessel  665  and features of plaque and fat as illustrated in  FIG.  6    and further illustrates additional examples of areas of an artery, and the plaque and/or perivascular fat that is near an artery, that may be analyzed to determine characteristics of a patient&#39;s arteries. 
         FIG.  8    illustrates examples of regions that may be evaluated to characterize plaque, the regions including a portion of a coronary artery and perivascular tissue disposed adjacent to the coronary artery. 
         FIG.  9    illustrates an example of an overview of a representation of image data of a coronary artery (vessel)  905 . 
         FIG.  10    illustrates another view of the representation of image data of the coronary artery (vessel)  905  illustrated in  FIG.  9   , showing examples of certain features of plaque, perivascular tissue (e.g., fat) and lumen that can be evaluated to characterize coronary plaque determine health characteristics of a patient&#39;s arteries. 
         FIG.  11    illustrates another example of determining radiodensity values of regions of the perivascular fat and plaque to determine metrics, as described herein. 
         FIG.  12    illustrates a representation of image data showing a coronary artery  905 , plaque  915 , and perivascular fat  920  located adjacent to the plaque (as similarly shown in  FIG.  11   ). 
         FIG.  13    is a table illustrating an example of a set of patient information. 
         FIG.  14    is a table  1400  illustrating an example of a set of scan information. 
         FIG.  15    is a table  1500  illustrating an example of a set of cardiac information. 
         FIG.  16    is an example of a cross section of a coronary artery  1600 . The coronary artery includes an inside lumen of the artery and an outer vessel wall with gradient radiodensities exhibited in the lumen, within the plaque and perivascular tissue outside of the vessel. 
         FIG.  17    is an image showing an example of a longitudinal straightened rendering of a coronary artery  1708  that shows a buildup of plaque between an inner portion and an outer portion of the coronary artery  1708 . This figure demonstrates the different compartments of lumen, plaque and perivascular tissue. 
         FIG.  18    is a chart of plots illustrating the compartment areas of cross-sections of plaque  1801 , lumen  1802 , and fat  1803  along the length of a coronary artery. Different ratios of these compartments can be calculated by area or by summated volume. 
         FIG.  19    is another chart of plots illustrating the compartment areas of cross-sections of plaque  1901 , lumen  1902 , and fat  1903  along the length of a coronary artery. 
     
    
    
     DETAILED DESCRIPTION OF CERTAIN INVENTIVE ASPECTS 
     Introduction 
     Disclosed are methods for identification of high-risk plaques using volumetric characterization of coronary plaque and perivascular adipose tissue data by computed tomography (CT) scanning. The volumetric characterization of the coronary plaque and perivascular adipose tissue allows for determination of the inflammatory status of the plaque by CT scanning. This is of use in the diagnosis, prognosis and treatment of coronary artery disease. While certain example embodiments are shown by way of example in the drawings and will herein be described in detail, these embodiments are capable of various modifications and alternative forms. It should be understood that there is no intent to limit example embodiments to the particular forms disclosed, but on the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of example embodiments. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” and the like may be used herein for ease of description to describe the relationship of one component and/or feature to another component and/or feature, or other component(s) and/or feature(s), as illustrated in the drawings. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The figures are intended to depict example embodiments and should not be interpreted to limit the intended scope of the claims. The accompanying figures are not to be considered as drawn to scale unless explicitly noted. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. In this specification, the term “and/or” picks out each individual item as well as all combinations of them. 
     Example embodiments are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures). As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of example embodiments. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. 
     When it is determined that a detailed description related to a related known function or configuration may make the purpose of example embodiments unnecessarily ambiguous, the detailed description thereof may be omitted. Also, terms used herein are defined to appropriately describe example embodiments and thus may be changed depending on a user, the intent of an operator, or a custom. Accordingly, the terms must be defined based on the following overall description within this specification. 
     In the drawings, the dimensions of layers and regions are exaggerated for clarity of illustration. It will also be understood that when a layer (or tissue) is referred to as being “on” another layer or tissue, it can be directly on the other layer or substrate, or intervening layers may also be present. Further, it will be understood that when a layer is referred to as being “under” another layer, it can be directly under, and one or more intervening layers may also be present. In addition, it will also be understood that when a layer is referred to as being ‘between’ two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. Like reference numerals refer to like elements throughout. 
     Overview of Example Processing System to Characterize Coronary Plaque 
     This disclosure includes methods and systems of using data generated from images collected by scanning a patient&#39;s arteries to identify coronary artery plaques that are at higher risk of causing future heart attack or acute coronary syndrome. In particular, the characteristics of perivascular coronary fat, coronary plaque, and/or the coronary lumen, and the relationship of the characteristics of perivascular coronary fat, coronary plaque, and/or the coronary lumen are discussed to determine ways for identifying the coronary plaque that is more susceptible to implication in future ACS, heart attack and death. The images used to generate the image data may be CT images, CCTA images, or images generated using any applicable technology that can depict the relative densities of the coronary plaque, perivascular fat, and coronary lumen. For example, CCTA images may be used to generate two-dimensional (2D) or volumetric (three-dimensional (3-D)) image data, and this image data may be analyzed to determine certain characteristics that are associated with the radiodensities of the coronary plaque, perivascular fat, and/or coronary lumen. In some implementations, the Hounsfield scale is used to provide a measure of the radiodensity of these features. A Hounsfield unit, as is known, represents an arbitrary unit of x-ray attenuation used for CT scans. Each pixel (2D) or voxel (3D) of a feature in the image data may be assigned a radiodensity value on the Hounsfield scale, and then these values characterizing the features may be analyzed. 
     In various embodiments, processing of image information may include: (1) determining scan parameters (for example, mA (milliampere), kvP (peak kilovoltage)); (2) determining the scan image quality (e.g., noise, signal-to-noise ratio, contrast-to-noise ratio); (3) measuring scan-specific coronary artery lumen densities, for example, (from a point distal to a coronary artery wall to a point proximal to the coronary artery wall to distal to the coronary artery, and from a central location of the coronary artery to an outer location (e.g., outer relative to radial distance from the coronary artery): (4) measuring scan-specific plaque densities (e.g., from central to outer, abruptness of change within a plaque from high-to-low or low-to-high) as a function of their 3D shape; and (5) measuring scan-specific perivascular coronary fat densities (from close to the artery to far from the artery) as a function of its 3D shape. 
     From these measurements, which are agnostic to any commonly known features of ischemia-causing atherosclerosis, we can determine a number of characteristics, including but not limited to:
         1. A ratio of lumen attenuation to plaque attenuation, wherein the volumetric model of scan-specific attenuation density gradients within the lumen adjusts for reduced luminal density across plaque lesions that are more functionally significant in terms of risk value.   2. A ratio of plaque attenuation to fat attenuation, wherein plaques with high radiodensities are considered to present a lower risk, even within a subset of plaques considered “calcified,” where there can be a gradation of densities (for example, 130 to 4000 HU) and risk is considered to be reduced as density increases.   3. A ratio of lumen attenuation/plaque attenuation/fat attenuation.   4. A ratio of #1-3 as a function of 3D shape of atherosclerosis, which can include a 3D texture analysis of the plaque.   5. The 3D volumetric shape and path of the lumen along with its attenuation density from the beginning to the end of the lumen.   6. The totality of plaque and plaque types before and after any given plaque to further inform its risk.   7. Determination of “higher plaque risks” by “subtracting” calcified (high-density) plaques to obtain a better absolute measure of high risk plaques (lower-density plaques). In other words, this particular embodiment involves identifying calcified plaque and excluding it from further analysis of plaque for the purpose of identifying high risk plaques.       

     The above listed metrics and others can be analyzed together to assess the risk of the plaque being implicated in future heart attack, ACS, ischemia or death. This can be done through development and/or validation of a traditional risk score or through machine learning methods. Factors for analysis from the metrics, that are likely to be associated with heart attack, ACS, ischemia or death, may include: (1) a ratio of [bright lumen:dark plaque]; (2) a ratio of [dark plaque:light fat]; (3) a ratio of [bright lumen:dark plaque: light fat]; and (4) a low ratio of [dark lumen:dark myocardium in 1 vessel area]/[lumen:myocardium in another vessel area]. Some improvements in the disclosed methods and systems include: (1) using numerical values from ratios of [lumen: plaque], [plaque: fat] and [lumen: plaque: fat] instead of using qualitative definitions of atherosclerotic features; (2) using a scan-specific [lumen: plaque attenuation] ratio to characterize plaque; (3) using a scan-specific [plaque: fat attenuation] ratio to characterize plaque; (4) using ratios of [lumen: plaque: fat circumferential] to characterize plaque; and (5) integration of plaque volume and type before and after as a contributor to risk for any given individual plaque. 
     Atherosclerotic plaque features may change over time with medical treatment (colchicine and statin medications) and while some of these medications may retard progression of plaque, they also have very important roles in promoting the change in plaque. While statin medications may have reduced the overall progression of plaque they may also have actually resulted in an increased progression of calcified plaque and a reduction of non-calcified plaque. This change will be associated with a reduction in heart attack or ACS or death, and the disclosed methods can be used to monitor the effects of medical therapy on plaque risk over time. Also, this method can also be used to identify individuals whose atherosclerotic plaque features or [lumen: plaque]/[plaque: fat]/[lumen: plaque: fat] ratios indicate that they are susceptible to rapid progression or malignant transformation of disease. In addition, these methods can be applied to single plaques or to a patient-basis wherein whole-heart atherosclerosis tracking can be used to monitor risk to the patient for experiencing heart attack (rather than trying to identify any specific plaque as being causal for future heart attack). Tracking can be done by automated co-registration processes of image data associated with a patient over a period of time. 
       FIG.  1    depicts a schematic of an example of an embodiment of a system  100  that includes a processing system  120  configured to characterize coronary plaque. The processing system  120  include one or more servers (or computers)  105  each configured with one or more processors. The processing system  120  includes non-transitory computer memory components for storing data and non-transitory computer memory components for storing instructions that are executed by the one or more processors data communication interfaces, the instructions configuring the one or more processors to perform methods of analyzing image information. A more detailed example of a server/computer  105  is described in reference to  FIG.  4   . 
     The system  100  also includes a network. The processing system  120  is in communication with the network  125 . The network  125  may include, as at least a portion of the network  125 , the Internet, a wide area network (WAN), a wireless network, or the like. In some embodiments, the processing system  120  is part of a “cloud” implementation, that can be located anywhere that is in communication with the network  125 . In some embodiments, the processing system  120  is located in the same geographic proximity as an imaging facility that images and stores patient image data. In other embodiments, the processing system  120  is located remotely from where the patient image data is generated or stored. 
       FIG.  1    also illustrates in system  100  various computer systems and devices  130  (e.g., of an imaging facility) that are related to generating patient image data and that are also connected to the network  125 . One or more of the devices  130  may be at an imaging facility that generates images of a patient&#39;s arteries, a medical facility (e.g., a hospital, doctor&#39;s office, etc.) or may be the personal computing device of a patient or care provider. For example, as illustrated in  FIG.  1   , an imaging facility server (or computer)  130 A may be connected to the network  125 . Also, in this example, a scanner  130 B in an imaging facility maybe connected to the network  125 . One or more other computer devices may also be connected to the network  125 . For example, a mobile wireless device including, for example, a tablet, smart phone, watch, or laptop  130 C (or any other mobile computer device), a personal computer  130 D, and/or and an image information storage system  130 E may also be connected to the network  125 , and communicate with the processing system  120 , and each other, via the network  125 . 
     The information communicated from the devices  130  to the processing system  120  via the network  125  may include image information  135 . In various embodiments, the image information  135  may include 2D or 3D image data of a patient, scan information related to the image data, patient information, and other imagery or image related information that relates to a patient. For example, the image information may include patient information including (one or more) characteristics of a patient, for example, age, gender, body mass index (BMI), medication, blood pressure, heart rate, height, weight, race, whether the patient is a smoker or non-smoker, body habitus (for example, the “physique” or “body type” which may be based on a wide range of factors), medical history, diabetes, hypertension, prior coronary artery disease (CAD), dietary habits, drug history, family history of disease, information relating to other previously collected image information, exercise habits, drinking habits, lifestyle information, lab results and the like. One example of a set of patent information is illustrated in a table  1300  in  FIG.  13   . In some embodiments, the image information includes identification information of the patient, for example, patient&#39;s name, patient&#39;s address, driver&#39;s license number, Social Security number, or indicia of another patient identification. Once the processing system  120  analyzes the image information  135 , information relating to a patient  140  may be communicated from the processing system  120  to a device  130  via the network  125 . The patient information  140  may include for example, a patient report. Also, the patient information  140  may include a variety of patient information which is available from a patient portal, which may be accessed by one of the devices  130 . 
     In some embodiments, image information comprising a plurality of images of a patient&#39;s coronary arteries and patient information/characteristics may be provided from one or more of the devices  130  to the one or more servers  105  of the processing system  120  via a network  125 . The processing system  120  is configured to generate coronary artery information using the plurality of images of the patient&#39;s coronary arteries to generate two-dimensional and/or three-dimensional data representations of the patient&#39;s coronary arteries. Then, the processing system  120  analyzes the data representations to generate patient reports documenting a patient&#39;s health conditions and risks related to coronary plaque. The patient reports may include images and graphical depictions of the patient&#39;s arteries in the types of coronary plaque in or near the coronary arteries. Using machine learning techniques or other artificial intelligent techniques, the data representations of the patient&#39;s coronary arteries may be compared to other patients&#39; data representations (e.g., that are stored in a database) to determine additional information about the patient&#39;s health. For example, based on certain plaque conditions of the patient&#39;s coronary arteries, the likelihood of a patient having a heart attack or other adverse coronary effect can be determined. Also, for example, additional information about the patient&#39;s risk of CAD may also be determined. 
       FIG.  2    is a schematic illustrating an example of a heart muscle  225  and its coronary arteries. The coronary vasculature includes a complex network of vessels ranging from large arteries to arterioles, capillaries, venules, veins, etc.  FIG.  1    depicts a model  220  of a portion of the coronary vasculature that circulates blood to and within the heart and includes an aorta  240  that supplies blood to a plurality of coronary arteries, for example, a left anterior descending (LAD) artery  215 , a left circumflex (LCX) artery  220 , and a right coronary (RCA) artery  230 , described further below. Coronary arteries supply blood to the heart muscle  225 . Like all other tissues in the body, the heart muscle  225  needs oxygen-rich blood to function. Also, oxygen-depleted blood must be carried away. The coronary arteries wrap around the outside of the heart muscle  225 . Small branches dive into the heart muscle  225  to bring it blood. The examples of methods and systems described herein may be used to determine information relating to blood flowing through the coronary arteries in any vessels extending therefrom. In particular, the described examples of methods and systems may be used to determine various information relating to one or more portions of a coronary artery where plaque has formed which is then used to determine risks associated with such plaque, for example, whether a plaque formation is a risk to cause an adverse event to a patient. 
     The right side  230  of the heart  225  is depicted on the left side of  FIG.  2    (relative to the page) and the left side  235  of the heart is depicted on the right side of  FIG.  2   . The coronary arteries include the right coronary artery (RCA)  205  which extends from the aorta  240  downward along the right side  230  of the heart  225 , and the left main coronary artery (LMCA)  210  which extends from the aorta  240  downward on the left side  235  of the heart  225 . The RCA  205  supplies blood to the right ventricle, the right atrium, and the SA (sinoatrial) and AV (atrioventricular) nodes, which regulate the heart rhythm. The RCA  205  divides into smaller branches, including the right posterior descending artery and the acute marginal artery. Together with the left anterior descending artery  215 , the RCA  205  helps supply blood to the middle or septum of the heart. 
     The LMCA  210  branches into two arteries, the anterior interventricular branch of the left coronary artery, also known as the left anterior descending (LAD) artery  215  and the circumflex branch of the left coronary artery  220 . The LAD artery  215  supplies blood to the front of the left side of the heart. Occlusion of the LAD artery  215  is often called the widow-maker infarction. The circumflex branch of the left coronary artery  220  encircles the heart muscle. The circumflex branch of the left coronary artery  220  supplies blood to the outer side and back of the heart, following the left part of the coronary sulcus, running first to the left and then to the right, reaching nearly as far as the posterior longitudinal sulcus. 
       FIG.  3    illustrates an example of a set of images generated from scanning along a coronary artery, including a selected image of a portion of a coronary artery, and how image data may correspond to a value on the Hounsfield Scale. As discussed in reference to  FIG.  1   , in addition to obtaining image data, scan information including metrics related to the image data, and patient information including characteristics of the patient may also be collected. 
     A portion of a heart  225 , the LMCA  210 , and the LAD artery  215  is illustrated in the example of  FIG.  3   . A set of images  305  can be collected along portions of the LMCA  210  and the LAD artery  215 , in this example from a first point  301  on the LMCA  210  to a second point  302  on the LAD artery  215 . In some examples, the image data may be obtained using noninvasive imaging methods. For example, CCTA image data can be generated using a scanner to create images of the heart in the coronary arteries and other vessels extending therefrom. Collected CCTA image data may be subsequently used to generate three-dimensional image models of the features contained in the CCTA image data (for example, the right coronary artery  205 , the left main coronary artery  210 , the left anterior descending artery  215 , the circumflex branch of the left coronary artery  220 , the aorta  240 , and other vessels related to the heart that appear in the image data. 
     In various embodiments, different imaging methods may be used to collect the image data. For example, ultrasound or magnetic resonance imaging (MRI) may be used. In some embodiments, the imaging methods involve using a contrast agent to help identify structures of the coronary arteries, the contrast agent being injected into the patient prior to the imaging procedure. The various imaging methods may each have their own advantages and disadvantages of usage, including resolution and suitability of imaging the coronary arteries. Imaging methods which may be used to collect image data of the coronary arteries are constantly improving as improvements to the hardware (e.g., sensors and emitters) and software are made. The disclosed systems and methods contemplate using CCTA image data and/or any other type of image data that can provide or be converted into a representative 3D depiction of the coronary arteries, plaque contained within the coronary arteries, and perivascular fat located in proximity to the coronary arteries containing the plaque such that attenuation or radiodensity values of the coronary arteries, plaque, and/or perivascular fat can be obtained. 
     Referring still to  FIG.  3   , a particular image  310  of the image data  305  is shown, which represents an image of a portion of the left anterior descending artery  215 . The image  310  includes image information, the smallest point of the information manipulated by a system referred to herein generally as a pixel, for example pixel  315  of image  310 . The resolution of the imaging system used to capture the image data will affect the size of the smallest feature that can be discerned in an image. In addition, subsequent manipulation of the image may affect the dimensions of a pixel. As one example, the image  310  in a digital format, may contain 4000 pixels in each horizontal row, and 3000 pixels in each vertical column. Pixel  315 , and each of the pixels in image data  310  and in the image data  305 , can be associated with a radiodensity value that corresponds to the density of the pixel in the image. Illustratively shown in  FIG.  3    is mapping pixel  315  to a point on the Hounsfield scale  320 . The Hounsfield scale  320  is a quantitative scale for describing radiodensity. The Hounsfield unit scale linear transformation of the original linear attenuation coefficient measurement into one in which the radiodensity of distilled water at standard pressure and temperature is defined as zero Hounsfield units (HU), while the radiodensity of air at standard pressure and temperature is defined as −1000 HU. Although  FIG.  3    illustrates an example of mapping pixel  315  of image  310  to a point on the Hounsfield scale  320 , such an association of a pixel to a radiodensity value can also be done with 3D data. For example, after the image data  305  is used to generate a three-dimensional representation of the coronary arteries. 
     Once the data has been obtained and rendered into a three-dimensional representation, various processes can be performed on the data to identify areas of analysis. For example, a three-dimensional depiction of a coronary artery may be segmented to define a plurality of portions of the artery and identified as such in the data. In some embodiments, the data may be filtered (e.g., smoothed) by various methods to remove anomalies that are the result of scanning or other various errors. Various known methods for segmenting and smoothing the 3D data may be used, and therefore for brevity of the disclosure will not be discussed in any further detail herein. 
       FIG.  4 A  is a block diagram that illustrates a computer system  400  upon which various embodiments may be implemented. Computer system  400  includes a bus  402  or other communication mechanism for communicating information, and a hardware processor, or multiple processors,  404  coupled with bus  402  for processing information. Hardware processor(s)  404  may be, for example, one or more general purpose microprocessors. 
     Computer system  400  also includes a main memory  406 , such as a random access memory (RAM), cache and/or other dynamic storage devices, coupled to bus  402  for storing information and instructions to be executed by processor  404 . Main memory  406  also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor  404 . Such instructions, when stored in storage media accessible to processor  404 , render computer system  400  into a special-purpose machine that is customized to perform the operations specified in the instructions. The main memory  406  may, for example, include instructions that analyze image information to determine characteristics of coronary features (e.g., plaque, perivascular fat and coronary arteries) to produce patient reports containing information that characterizes aspects of the patients health relating to their coronary arteries. For example, one or more metrics may be determined, the metrics including one or more of a slope/gradient of a feature, a maximum density, minimum density, a ratio of a slope of one feature to the slope of another feature, a ratio of a maximum density of one feature to the maximum density of another feature, a ratio of a minimum density of a feature to the minimum density of the same feature, or a ratio of the minimum density of a feature to the maximum density of another feature. 
     Computer system  400  further includes a read only memory (ROM)  408  or other static storage device coupled to bus  402  for storing static information and instructions for processor  404 . A storage device  410 , such as a magnetic disk, optical disk, or USB thumb drive (Flash drive), etc., is provided and coupled to bus  402  for storing information and instructions. 
     Computer system  400  may be coupled via bus  402  to a display  412 , such as a cathode ray tube (CRT) or LCD display (or touch screen), for displaying information to a computer user. An input device  414 , including alphanumeric and other keys, is coupled to bus  402  for communicating information and command selections to processor  404 . Another type of user input device is cursor control  416 , such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor  404  and for controlling cursor movement on display  412 . This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane. In some embodiments, the same direction information and command selections as cursor control may be implemented via receiving touches on a touch screen without a cursor. 
     Computing system  400  may include a user interface module to implement a GUI that may be stored in a mass storage device as computer executable program instructions that are executed by the computing device(s). Computer system  400  may further, as described below, implement the techniques described herein using customized hard-wired logic, one or more ASICs or FPGAs, firmware and/or program logic which in combination with the computer system causes or programs computer system  400  to be a special-purpose machine. According to one embodiment, the techniques herein are performed by computer system  400  in response to processor(s)  404  executing one or more sequences of one or more computer readable program instructions contained in main memory  406 . Such instructions may be read into main memory  406  from another storage medium, such as storage device  410 . Execution of the sequences of instructions contained in main memory  406  causes processor(s)  404  to perform the process steps described herein. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. 
     Various forms of computer readable storage media may be involved in carrying one or more sequences of one or more computer readable program instructions to processor  404  for execution. For example, the instructions may initially be carried on a magnetic disk or solid state drive of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system  400  can receive the data on the telephone line and use an infra-red transmitter to convert the data to an infra-red signal. An infra-red detector can receive the data carried in the infra-red signal and appropriate circuitry can place the data on bus  402 . Bus  402  carries the data to main memory  406 , from which processor  404  retrieves and executes the instructions. The instructions received by main memory  406  may optionally be stored on storage device  410  either before or after execution by processor  404 . 
     Computer system  400  also includes a communication interface  418  coupled to bus  402 . Communication interface  418  provides a two-way data communication coupling to a network link  420  that is connected to a local network  422 . For example, communication interface  418  may be an integrated services digital network (ISDN) card, cable modem, satellite modem, or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface  418  may be a local area network (LAN) card to provide a data communication connection to a compatible LAN (or WAN component to communicate with a WAN). Wireless links may also be implemented. In any such implementation, communication interface  418  sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information. 
     Network link  420  typically provides data communication through one or more networks to other data devices. For example, network link  420  may provide a connection through local network  422  to a host computer  424  or to data equipment operated by an Internet Service Provider (ISP)  426 . ISP  426  in turn provides data communication services through the world wide packet data communication network now commonly referred to as the “Internet”  428 . Local network  422  and Internet  428  both use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on network link  420  and through communication interface  418 , which carry the digital data to and from computer system  400 , are example forms of transmission media. 
     Computer system  400  can send messages and receive data, including program code, through the network(s), network link  420  and communication interface  418 . In the Internet example, a server  430  might transmit a requested code for an application program through Internet  428 , ISP  426 , local network  422  and communication interface  418 . 
     The received code may be executed by processor  404  as it is received, and/or stored in storage device  410 , or other non-volatile storage for later execution. 
     Accordingly, in an embodiment, the computer system  105  comprises a non-transitory computer storage medium storage device  410  configured to at least store image information of patients. The computer system  105  can also include non-transitory computer storage medium storage that stores instructions for the one or more processors  404  to execute a process (e.g., a method) for characterization of coronary plaque tissue data and perivascular tissue data using image data gathered from a computed tomography (CT) scan along a blood vessel, the image information including radiodensity values of coronary plaque and perivascular tissue located adjacent to the coronary plaque. Executing the instructions, the one or more processors  404  can quantify, in the image data, the radiodensity in regions of coronary plaque, quantify in the image data, radiodensity in at least one region of corresponding perivascular tissue adjacent to the coronary plaque, determine gradients of the quantified radiodensity values within the coronary plaque and the quantified radiodensity values within the corresponding perivascular tissue, determine a ratio of the quantified radiodensity values within the coronary plaque and the corresponding perivascular tissue, and characterizing the coronary plaque by analyzing one or more of the gradients of the quantified radiodensity values in the coronary plaque and the corresponding perivascular tissue, or the ratio of the coronary plaque radiodensity values and the radiodensity values of the corresponding perivascular tissue. 
     Various embodiments of the present disclosure may be a system, a method, and/or a computer program product at any possible technical detail level of integration. The computer program product may include a computer readable storage medium (or mediums) having computer readable program instructions thereon for causing a processor to carry out aspects of the present disclosure. For example, the functionality described herein may be performed as software instructions are executed by, and/or in response to software instructions being executed by, one or more hardware processors and/or any other suitable computing devices. The software instructions and/or other executable code may be read from a computer readable storage medium (or mediums). 
     The computer readable storage medium can be a tangible device that can retain and store data and/or instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device (including any volatile and/or non-volatile electronic storage devices), a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of the computer readable storage medium includes the following: a portable computer diskette, a hard disk, a solid state drive, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or raised structures in a groove having instructions recorded thereon, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire. 
     Computer readable program instructions described herein can be downloaded to respective computing/processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and/or a wireless network. The network may comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and/or edge servers. A network adapter card or network interface in each computing/processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing/processing device. 
     Computer readable program instructions (as also referred to herein as, for example, “code,” “instructions,” “module,” “application,” “software application,” and/or the like) for carrying out operations of the present disclosure may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, configuration data for integrated circuitry, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++, or the like, and procedural programming languages, such as the “C” programming language or similar programming languages. Computer readable program instructions may be callable from other instructions or from itself, and/or may be invoked in response to detected events or interrupts. Computer readable program instructions configured for execution on computing devices may be provided on a computer readable storage medium, and/or as a digital download (and may be originally stored in a compressed or installable format that requires installation, decompression or decryption prior to execution) that may then be stored on a computer readable storage medium. Such computer readable program instructions may be stored, partially or fully, on a memory device (e.g., a computer readable storage medium) of the executing computing device, for execution by the computing device. The computer readable program instructions may execute entirely on a user&#39;s computer (e.g., the executing computing device), partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user&#39;s computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present disclosure. 
     Aspects of the present disclosure are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer readable program instructions. 
     These computer readable program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer readable program instructions may also be stored in a computer readable storage medium that can direct a computer, a programmable data processing apparatus, and/or other devices to function in a particular manner, such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function/act specified in the flowchart(s) and/or block diagram(s) block or blocks. 
     The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process, such that the instructions which execute on the computer, other programmable apparatus, or other device implement the functions/acts specified in the flowchart and/or block diagram block or blocks. For example, the instructions may initially be carried on a magnetic disk or solid state drive of a remote computer. The remote computer may load the instructions and/or modules into its dynamic memory and send the instructions over a telephone, cable, or optical line using a modem. A modem local to a server computing system may receive the data on the telephone/cable/optical line and use a converter device including the appropriate circuitry to place the data on a bus. The bus may carry the data to a memory, from which a processor may retrieve and execute the instructions. The instructions received by the memory may optionally be stored on a storage device (e.g., a solid state drive) either before or after execution by the computer processor. 
     The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the blocks may occur out of the order noted in the Figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. In addition, certain blocks may be omitted in some implementations. The methods and processes described herein are also not limited to any particular sequence, and the blocks or states relating thereto can be performed in other sequences that are appropriate. 
     It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions. For example, any of the processes, methods, algorithms, elements, blocks, applications, or other functionality (or portions of functionality) described in the preceding sections may be embodied in, and/or fully or partially automated via, electronic hardware such application-specific processors (e.g., application-specific integrated circuits (ASICs)), programmable processors (e.g., field programmable gate arrays (FPGAs)), application-specific circuitry, and/or the like (any of which may also combine custom hard-wired logic, logic circuits, ASICs, FPGAs, etc. with custom programming/execution of software instructions to accomplish the techniques). 
     Any of the above-mentioned processors, and/or devices incorporating any of the above-mentioned processors, may be referred to herein as, for example, “computers,” “computer devices,” “computing devices,” “hardware computing devices,” “hardware processors,” “processing units,” and/or the like. Computing devices of the above-embodiments may generally (but not necessarily) be controlled and/or coordinated by operating system software, such as Mac OS, iOS, Android, Chrome OS, Windows OS (e.g., Windows XP, Windows Vista, Windows 7, Windows 8, Windows 10, Windows Server, etc.), Windows CE, Unix, Linux, SunOS, Solaris, Blackberry OS, VxWorks, or other suitable operating systems. In other embodiments, the computing devices may be controlled by a proprietary operating system. Conventional operating systems control and schedule computer processes for execution, perform memory management, provide file system, networking, I/O services, and provide a user interface functionality, such as a graphical user interface (“GUI”), among other things. 
       FIG.  4 B  is a block diagram that illustrates examples of representative instructions which may be executed by one or more computer hardware processors in one or more computer modules in a representative processing system (computer system)  120  which may implement various embodiments described herein. As illustrated in  FIG.  1   , the processing system  120  can be implemented in one computer (for example, a server) or in 2 or more computers (two or more servers). Although the instructions are represented in  FIG.  4 B  as being in seven modules  450 ,  455 ,  460 ,  465 ,  470 ,  475 ,  480 , in various implementations the executable instructions may be in fewer modules, including a single module, or more modules. 
     The processing system  120  includes image information stored on a storage device  410 , which may come from the network  125  illustrated in  FIG.  1   . The image information may include image data, scan information, and/or patient data. In this example, the storage device  410  also includes stored plaque information of other patients. For example, the stored plaque information of other patients may be stored in a database on the storage device  410 . In other examples, stored plaque information of other patients is stored on a storage device that is in communication with processing system  120 . The other patients&#39; stored plaque information may be a collection of information from one, dozens, hundreds, thousands, tens of thousands, hundreds of thousands, or millions of patients, or more. 
     The information for each patient may include characterizations of that patient&#39;s plaque, such as densities and density gradients of the patient&#39;s plaque, and the location of the plaque relative to the perivascular tissue near or adjacent to the plaque. The information for each patient may include patient information as illustrated in  FIG.  13   . For example, the information may include one or more of sex, age, BMI (body mass index), medication, blood pressure, heart rate, weight, height, race, body habitus, smoking history, history or diagnosis of diabetes, history or diagnosis of hypertension, prior coronary artery disease, family history of coronary artery disease and/or other diseases, or one or more lab results (e.g., blood test results). The information for each patient may include scan information as illustrated in  FIG.  14   . For example, the information may include one or more of contrast-to-noise ratio, signal-to-noise ratio, tube current, tube voltage, contrast type, contrast volume, flow rate, flow duration, slice thickness, slice spacing, pitch, vasodilator, beta blockers, recon option whether it&#39;s iterative or filter back projection, recon type whether it&#39;s standard or high resolution, display field-of-view, rotation speed, gating whether it&#39;s perspective triggering or retrospective gating, stents, heart rate, or blood pressure. The information for each patient may also include cardiac information as illustrated in  FIG.  15   . For example, the information may include characterizations of plaque including one or more of density, volume, geometry(shape), location, remodeling, baseline anatomy (for diameter, length), compartments (inner, outer, within), stenosis (diameter, area), myocardial mass, plaque volume, and/or plaque composition, texture, or uniformity. 
     The processing system  120  also includes memory  406 ,  408 , which may be main memory of the processing system or read only memory (ROM). The memory  406 ,  408  stores instructions executable by one or more computer hardware processors  404  (groups of which referred to herein as “modules”) to characterize coronary plaque. The memory  406 ,  408  will be collectively referred to, in reference to this diagram, as memory  406  for the sake of brevity. Examples of the functionality that is performed by the executable instructions are described below. 
     Memory  406  includes module  450  that generates, from the image data stored on the storage device  410 , 2-D or 3-D representations of the coronary arteries, including plaque, and perivascular tissue that is located adjacent to or in proximity of the coronary arteries in the plaque. The generation of the 2-D or 3-D representations of the coronary arteries may be done from a series of images  305  (e.g., CCTA images) is described above in reference to  FIG.  3   . Once the representation of the coronary arteries are generated, different portions or segments of the coronary arteries can be identified for evaluation. For example, portions of interest of the right coronary artery  205 , the left anterior descending artery  215 , or the circumflex branch of the left coronary artery  220  may be identified as areas of analysis (areas of interest) based on input from a user, or based on a feature determined from the representation of the coronary artery (plaque). 
     In module  460 , the one or more computer hardware processors quantify radiodensity in regions of coronary plaque. For example, the radiodensity in regions of coronary plaque are set to a value on the Hounsfield scale. In module  465 , the one or more computer hardware processors quantify radiodensity of perivascular tissue that is adjacent to the coronary plaque, and quantify radiodensity value of the lumen of the vessel of interest. In module  470 , the one or more computer hardware processors determine gradients of the radiodensity values of the plaque the perivascular tissue and/or the lumen. In module  475 , the one or more computer hardware processors determine one or more ratios of the radiodensity values in the plaque, perivascular tissue, and/or the lumen. Next, in module  480 , the one or more computer hardware processors characterize the coronary plaque using the gradients of the plaque, the perivascular tissue, and/or the lumen, and/or characterize ratio of the radiodensity values of the coronary plaque to perivascular tissue and/or the lumen including comparing the gradients and/or ratios to a database containing information of other patients plaque gradients and ratios. For example, the gradients and/or the ratios are compared to patient data that stored on storage device  410 . Determining gradients and ratios of the plaque the perivascular tissue and the lumen are described in more detail with reference to  FIGS.  6 - 12   . 
       FIG.  5 A  illustrates an example of a flowchart of a process  500  for analyzing coronary plaque. At block  505 , the process  500  generates image information including image data relating to coronary arteries. In various embodiments, this may be done by a scanner  130 B ( FIG.  1   ). At block  510 , a processing system may receive image information via a network  125  ( FIG.  1   ), the image information including the image data. At block  515 , the process  500  generates a 3D representation of the coronary arteries including perivascular fat and plaque on the processing system. The functionality of blocks  505 ,  510 , and  515 , can be performed, for example, using various scanning techniques (e.g., CCTA) to generate image data, communication techniques to transfer data over the network, and processing techniques to generate the 3D representation of the coronary arteries from the image data. 
     At block  520 , the processing system performs a portion of the process  500  to analyze the coronary plaque, which is described in further detail in reference to process  550  of  FIG.  5 B . Additional details of this process to analyze the coronary plaque in particular in reference to  FIGS.  6 - 12   . 
       FIG.  5 B  illustrates an example of a flowchart that expands on a portion of the flowchart in  FIG.  5 A  for determining characteristics of coronary plaque. Referring now to  FIG.  5 B , at block  555 , process  550  can utilize the one or more processors  404  to quantify the radiodensity in regions of coronary plaque. At block  560 , the process  550  can utilize the one or more processors  404  to quantify, in the image data, radiodensity in at least one region of corresponding perivascular tissue, meaning perivascular tissue that is adjacent to the coronary plaque. At block  565 , the process  550  determines gradients of the quantified radiodensity values within the coronary plaque and the quantified radiodensity values within the corresponding perivascular tissue. The one or more processors  404  can be the means to determine these gradients. At block  570 , the process  550  may determine a ratio of the quantified radiodensity values within the coronary plaque and the corresponding perivascular tissue. For example, the perivascular tissue that is adjacent to the coronary plaque. The one or more processors  404  can determine these ratios. At block  575 , process  550  can utilize the one or more processors  404  to characterize the coronary plaque by analyzing one or more of the gradients of the quantified radiodensity values in the coronary plaque and the corresponding perivascular tissue, or the ratio of the coronary plaque radiodensity values and the radiodensity values of the corresponding perivascular tissue. The process  550  can then return back to process  500  as illustrated by the circle A. 
     Referring again to  FIG.  5 A , at block  525 , the process  500  may compare determined information of a particular patient&#39;s coronary plaque to stored patient data, for example patient data stored on storage device  410 . An example of the coronary plaque information of a particular patient that can be compared to stored patient data is illustrated in  FIG.  15   . To better understand the particular patient&#39;s coronary plaque information, and/or to help determine the particular patient&#39;s coronary plaque information, one or more of the scan information illustrated in  FIG.  14    may be used. Also, when comparing a particular patient&#39;s coronary plaque information to previously stored coronary plaque information, one or more characteristics of the patient may be compared, including, for example, one or more of the characteristics of a patient that are shown in  FIG.  13   . In some examples, the coronary plaque information of the particular patient being examined may be compared to or analyzed in reference to a patient who has one or more of the same or similar patient characteristics. For example, the patient being examined may be compared to a patient that has the same or similar characteristics of sex, age, BMI, medication, blood pressure, heart rate, weight, height, race, body habitus, smoking, diabetes, hypertension, prior coronary artery disease, family history, and lab results. Such comparisons can be done through various means, for example machine learning and/or artificial intelligence techniques. In some examples, neural network is used to compare a patient&#39;s coronary artery information to numerous (e.g., 10,000+) other patients&#39; coronary artery information. For such patients that have similar patient information and similar cardiac information (for example, the characteristics shown in  FIG.  15   ), risk assessments of the plaque of the patient being examined may be determined. 
       FIG.  6    illustrates a representation of image data depicting an example of a portion of a coronary artery  665  (sometimes referred to herein as a “vessel” for ease of reference). Although  FIG.  6    is a two-dimensional (2D) illustration, the image data analyzed maybe two dimensional or three dimensional (e.g., volumetric).  FIG.  6    also illustrates examples of plaque located in the vessel  665  and perivascular fat located adjacent to the vessel  665 .  FIG.  6    further illustrates examples of areas (shown on  FIG.  6    as rectangles) that may contain at least a portion of the vessel  665 , plaque that is in the vessel  665 , or perivascular fat that is adjacent to the vessel  665 , where these areas indicate portions of one or more of the vessel  665 , plaque, or perivascular fat that may be analyzed to determine densities, density gradients, and/or density ratios of the vessel  665 , plaque, or perivascular fat to determine one or more characteristics of a patient&#39;s coronary arteries. As illustrated in  FIG.  6   , the vessel  665  includes a vessel wall  661  and a vessel wall  663  which are depicted as boundary lines to provide a graphical reference of where plaque and fat are located relative to the vessel  665  in  FIG.  6   . The vessel wall  661  and the vessel wall  662  may sometimes be referred to herein as a first vessel wall and a second vessel wall, or vice versa. The line delineating the vessel walls  661 ,  663  indicate an outer boundary of the vessel walls  661 ,  663 . In the example illustrated in  FIG.  6   , all of the fat  625 ,  640  is located outside of the vessel walls  661 ,  663 , and all of the plaque  610 ,  620 ,  635 ,  650  is located within the vessel walls  661 ,  663 . 
     Plaque can be characterized by its attenuation that is exhibited in images of the coronary arteries. For example, plaque can be characterized as being low attenuation plaque, a medium attenuation plaque, a high attenuation plaque, or very high attenuation plaque. In some cases, these characterizations are not exactly precise and may be affected by the methods and processes used to collect the images of the coronary arteries. In some examples, low attenuation plaque can have a density of about 0 to about 70. In some examples, medium attenuation plaque can have a density of about 70 to about 350 In some examples, high attenuation plaque can have a density of about 350 to about 1000. In some examples, very high attenuation plaque can have a density of more than 1000. 
       FIG.  6    illustrates examples of different types of plaque that may be contained within the vessel walls  661  and  663  of the vessel  665 , according to some embodiments. In an example, the plaque may be fibrous plaque  610  having a medium attenuation characteristic, inside the vessel wall  663  and extending towards the interior of the vessel  665 . In this example the fibrous plaque  610  has other types of plaque adjacent to it within the vessel wall  663 , and fat disposed outside of the vessel  665  juxtaposed or adjacent to the fibrous plaque  610 . As illustrated in  FIG.  6   , disposed adjacent to the fibrous plaque  610  is necrotic core plaque  615  which has a low attenuation characteristic.  FIG.  6    also illustrates an example of a plaque  620  having medium-high attenuation characteristics, that is also disposed (or located) adjacent to the fibrous plaque  610 . In this example, plaque  620  is also disposed adjacent to necrotic core plaque  615 , such that plaque  620  is at least partially between the plaque fibrous  610  and the necrotic core plaque  615 , and the outside boundary of the vessel wall  663 .  FIG.  6    also illustrates an example of a very high attenuation plaque  635  disposed within vessel wall  663 , but protruding out of the vessel  665  such that vessel wall  663  extends outward (i.e., away from the center of the vessel  665 ) around plaque  635 . In another example,  FIG.  6    illustrates a fibrous plaque  650  having a medium attenuation characteristics (i.e., the attenuation characteristics not being as high as fibrous plaque  610 ) that is disposed adjacent to and within the vessel wall  661 . As illustrated in  FIG.  6   , the fibrous plaque  650  generally extends towards the center of the vessel  665 . 
       FIG.  6    further illustrates examples of fat that is outside of the vessel adjacent to (or at least in proximity of) the vessel  665 . The fat illustrated in  FIG.  6    is also in proximity to and/or adjacent to one or more of the plaques  610 ,  615 ,  620 ,  635 . In one example, fat  625  is along a portion of the vessel wall  663 , adjacent to the vessel wall  663 , and juxtaposed to the plaque  620 , such that it is adjacent to plaque  620  and in the proximity of plaque  610  and  615 . In another example illustrated in  FIG.  6   , fat  640  as shown outside of the vessel wall  662  and adjacent to plaque  635 . In this example, fat  640  at least partially surrounds the portion of plaque  635  extending from the vessel  665  such that a portion of fat  640  is adjacent to the vessel wall  663  on two or more sides of plaque  635 . 
     Identifying high risk plaques may be dependent upon the interplay between contrast attenuation&#39;s in the coronary lumen, attenuation patterns of plaque, and fat attenuation patterns. As mentioned above,  FIG.  6    also illustrates boxes indicating examples of areas that include all or portions vessel  665 , perivascular fat, and/or plaque, for analysis of density gradients and density ratios. In the illustrated boxes in  FIG.  6   , as well as similar boxes illustrated in  FIGS.  7 ,  10 ,  11 , and  12   , the boxes are shown as two-dimensional rectangles the cover portions of the representation of the image data depicting a portion of a coronary artery (vessel  665 ), plaque, and fat. As will be discussed below in reference to  FIGS.  11  and  12   , the portion of the image data that is analyzed may be, in some examples, data representing a one-dimensional vector of pixels that is in the rectangular box. In other words, image data along the line that is in the rectangular box. In other examples, the portion of the image data that is analyzed may be a two dimensional vector of pixels that is in the rectangular box. In other words, image data contained in two or more adjacent lines that are in the rectangular box. In some cases for the two dimensional vector of pixels, the image data in the two or more adjacent lines may be processed to form a one dimensional vector. For example, the image data in the two or more adjacent lines of image data may be averaged, which may help reduce the effect of noise. In some cases, the image data may be filtered to reduce the effect of noise. In some examples, filtering may occur before the image data is analyzed for gradient, ratios, slope, minimum density, maximum density, etc. 
       FIG.  6    illustrates an example of an area, indicated by box  605 , where contrast attenuation patterns in a proximal portion of the coronary lumen can be analyzed, box  605  extending from a central area of the vessel  665  towards the vessel wall  661 .  FIG.  6    illustrates another example of an area, indicated by box  652 , where contrast attenuation patterns in a portion of the coronary lumen of vessel  665  can be analyzed, box  652  extending longitudinally relative to vessel  665  from a central area of the vessel  665  towards the vessel wall  661 .  FIG.  6    further illustrates an example of an area, indicated by box  662 , where contrast attenuation patterns of a portion of the lumen, a portion of fibrous plaque  610  and plaque  620  can be analyzed, box  662  thus covering a portion of the vessel  665  and a portion of fibrous plaque  610  and plaque  620 .  FIG.  6    further illustrates an example of an area indicated by box  642 , where contrast attenuation patterns of a portion of plaque  635  and a portion of fat  640  positioned adjacent to plaque  635  can be analyzed, box  642  extending over a portion of plaque  635  and a portion of fat  640 . Information determined by analyzing various aspects of the density of coronary artery features (e.g., the lumen, the plaque, and/or the perivascular fat) can be combined with other information to determine characteristics of a patient&#39;s arteries. In some examples, the determined information may include for any of the lumen, plaque or perivascular fat, one or more of a slope/gradient of a feature, a maximum density, a minimum density, a ratio of a slope of the density of one feature to the slope of the density of another feature, a ratio of a maximum density of one feature to the maximum density of another feature, a ratio of a minimum density of a feature to the minimum density of the same feature, a directionality of the density ratios, e.g., a density ratio between features facing one way or direction and features facing in an opposite direction (for example, the radiodensity ratio of features facing inwards towards the myocardium and features facing outwards toward the pericardium), or a ratio of the minimum density of a feature to the maximum density of another feature. Such determined information may indicate distinct differences in risks of plaque in a patient. In some examples, determined information (for example as listed above) may be used with a percentage diameter of stenosis to determine characteristics of a patient&#39;s arteries. Additional information regarding examples of analysis of the attenuation patterns in the coronary lumen attenuation patterns of plaque, and attenuation patterns of fat are described in reference to  FIGS.  9 - 12   . 
     Still referring to  FIG.  6   , in an example of the directionality of radiodensity ratios, the density of a portion of the necrotic core plaque  615  to the density of a portion of the vessel  665  (e.g., plaque:vessel inward facing ratio) can be determined and may indicate a certain risk of plaque. In another example of the directionality of radiodensity ratios, the density of a portion of a portion of the vessel  665  to the density of the necrotic core plaque  615  (e.g., vessel:plaque outward facing) can be determined and may indicate a certain risk of plaque. In another example, the density ratio of the necrotic core plaque  615  to the density of a portion of the vessel  665  (e.g., plaque:vessel inward facing ratio) can be compared to the density ratio of the necrotic core plaque  615  to the fibrous plaque  620  (e.g., plaque:plaque outward facing) may indicate a certain risk of plaque. In other examples, features that are adjacently positioned can be used to determine inward and/or outward directional radiodensity values that may be used to indicate a risk associated with plaque. Such ratios may provide distinct differences in risk of plaque. Various embodiments of directional radiodensity values and/or directional radiodensity ratios can be included with any of the other information described herein to indicates plaque risk. 
     The size of a compartment may be used to also indicate a risk associated with plaque. For example, determination of risk associated with a plaque may be based at least partially on the size of the compartments, such that the ratio of the radiodensities affects the determination of risk and the function of the size of the compartments can also affect the determination of risk. While the presence of plaque in a patient where the ratio of plaque:fat may indicate a high risk plaque, if there is only a small amount of plaque (e.g., a small compartment of plaque), it would be of risk than if there was a larger compartment of the same plaque with the same radiodensity ratio of plaque to fat. In one implementation, the size (e.g., a volume) of the compartment a feature (e.g., of lumen, plaque, perivascular tissue (fat), and myocardium) can be determined, and a radiodensity ratio can also be determined, and then the ratio can be weighted based on the size of the compartment. For example, a large compartment can increase the weight of a ratio to make the ratio more indicative of a risk associated with the plaque. Similarly, a small compartment can decrease the weight of a ratio to make the ratio less indicative of a risk associated with the plaque. In an implementation, only the compartment size of the plaque is used to weight (or adjust) the ratio. In an implementation, the compartment size of both of the features that are used in the radiodensity ratio can be used to weight the ratio to determine a resulting risk. In an implementation, the compartment size of one of plaque, lumen, perivascular tissue, or myocardium is used to weight (or adjust) the risk associated with the radiodensity ratio. In an implementation, the compartment size of more than one of plaque, lumen, perivascular tissue, or myocardium is used to weight the risk associated with the radiodensity ratio. Various embodiments of determining plaque risk using compartment size can be included with any of the other information described herein to indicate plaque risk. Using a compartment size to weight other information, or otherwise adjust a risk associated with the radiodensity ratio, can be done in the examples as described in reference to  FIGS.  7 - 12  and  16 - 19   . 
       FIG.  7    illustrates the same vessel  665  and features of plaque and fat as illustrated in  FIG.  6    and further illustrates additional examples of areas of an artery, and plaque and/or perivascular fat near the artery, that may be analyzed to determine characteristics of a patient&#39;s arteries. Such areas are indicated in  FIG.  7    by rectangular boxes, similar to the illustrations in  FIG.  6   . Although particular locations of the rectangular boxes are illustrated in  FIG.  6    and  FIG.  7   , these are only examples of areas that may be analyzed. In one example,  FIG.  7    illustrates box  660  which includes a portion of the vessel  665 , a portion of necrotic core plaque  615 , a portion of fibrous plaque  610 , a portion of plaque  620 , and a portion of fat  625 . In another example,  FIG.  7    illustrates box  655  which includes a portion of the vessel  665 , a portion of the fibers plaque  610  a portion of the plaque  620  the portion of the necrotic core plaque  615 , and a portion of fat  625 . Box  655  may, in some cases, illustrate the general area for analysis due to the existence of 3 different types of plaque  610 ,  615 ,  620 , and adjacently disposed fat  625 . Particular portions of a general area for analysis may be analyzed to better understand the characteristics formed by adjacent features. For example,  FIG.  7    illustrates the general area  665  containing box  660  (described above), box  673 , which extends across a portion of fibrous plaque  610  and plaque  620 , and box  674  which extends across a portion of plaque  620  and perivascular fat  625 . As another example,  FIG.  7    also illustrates another box  672  that extends across a portion of the vessel  655  and necrotic core plaque  615 . As a further example,  FIG.  7    illustrates box  671  that extends across a portion of the vessel  665  and fat  640  juxtaposed to the vessel  665 . As a further example,  FIG.  7    illustrates box  670  that extends across a portion of the vessel  665  and plaque  635 . Characteristics of a patient&#39;s arteries that can be analyzed based on these features can include:
         1. A ratio of lumen attenuation to plaque attenuation, wherein the volumetric model of scan-specific attenuation density gradients within the lumen adjusts for reduced luminal density across plaque lesions that are more functionally significant in terms of risk value.   2. A ratio of plaque attenuation to fat attenuation, wherein plaques with high radiodensities are considered to present a lower risk, even within a subset of plaques considered “calcified,” where there can be a gradation of densities (for example, 130 to 4000 HU) and risk is considered to be reduced as density increases.   3. A ratio of lumen attenuation/plaque attenuation/fat attenuation.   4. A ratio of #1-3 as a function of 3D shape of atherosclerosis, which can include a 3D texture analysis of the plaque.   5. The 3D volumetric shape and path of the lumen along with its attenuation density from the beginning to the end of the lumen.   6. The totality of plaque and plaque types before and after any given plaque to further inform its risk.   7. Determination of “higher plaque risks” by “subtracting” calcified (high-density) plaques to obtain a better absolute measure of high risk plaques (lower-density plaques). In other words, this particular embodiment involves identifying calcified plaque and excluding it from further analysis of plaque for the purpose of identifying high risk plaques.       

       FIG.  8    illustrates an example of an image of a heart  800  and certain regions of a coronary artery  805 . In this example, at region  810 , contrast attenuation in the proximal portion of the vessel is high. At region  820 , contrast attenuation in the distal portion of the vessel is low. At region  830 , contrast attenuation in the heart muscle is low, that is, in that region of the heart muscle that is close to the distal portion of the vessel. The radiodensity values in these regions may be determined and compared. In some examples a ratio of the radiodensity values of regions  830  and  820  (i.e., radiodensity values  830 : radiodensity values  820 ) and/or the radiodensity values of regions  830  and  810  (i.e., radiodensity values  830 : radiodensity values  810 ) can be used to determine whether there is ischemia or not. 
       FIG.  9    illustrates an example of an overview of a representation of image data of a coronary artery (vessel)  905 . In this example, vessel  905  includes a lumen walls  910 ,  911  (the lines indicating the outer boundary of the lumen wall), and plaque  915  which is within the vessel  905 , that is, plaque  915  is within lumen wall  910 , and extends outward away from the center of the vessel  905  as well as extending inward towards the center of the vessel  905 .  FIG.  9    also illustrates perivascular fat  920  that is disposed adjacent to plaque  915  and outside of the vessel  905 . That is, lumen wall  910  is between perivascular fat  920  and plaque  915 . Both the plaque  915  in the perivascular fat dietary  920  include contrast attenuation patterns that may be analyzed to determine characteristics of the coronary artery  905 .  FIG.  9    also includes spotty calcification  925  located in plaque  915 . In this example, G1 represents a portion of the perivascular fat  920  and the plaque  915 , from the inner surface  930  of the plaque  915  to the outer surface  935  of the perivascular fat  920 , where the gradient the gradient of the density of the contrast attenuation may be determined and evaluated, described in more detail in  FIG.  10   . 
       FIG.  10    illustrates another view of the representation of image data of the coronary artery (vessel)  905  illustrated in  FIG.  9   , showing examples of certain features of plaque, perivascular tissue (e.g., fat) and lumen that can be evaluated to characterize coronary plaque determine health characteristics of a patient&#39;s arteries. Plaque  915  and perivascular fat  920  that were shown in  FIG.  9    are also shown in  FIG.  10   . The image data in  FIG.  10    demonstrates a gradient the transitions from lighter density values to darker density values along a line in the image data that extends from an edge of the plaque  915 , that is closest to the center of the vessel  905 , to the edge  935  of the perivascular fat  920 . 
     The density of portions of the image data depicting the perivascular fat  920 , plaque  915 , and/or the lumen of the vessel  905  may be evaluated to characterize coronary plaque into determine health characteristics of a patient&#39;s arteries. As mentioned above, information determined by analyzing various aspects of the density of the lumen, the plaque, and/or the perivascular fat can include, but is not limited to, one or more of a slope/gradient of a feature, a maximum density, minimum density, a ratio of a slope of one feature to the slope of another feature, a ratio of a maximum density of one feature to the maximum density of another feature, a ratio of a minimum density of a feature to the minimum density of the same feature, or a ratio of the minimum density of a feature to the maximum density of another feature. Any of this information can be combined with other information to determine characteristics of a patient&#39;s arteries. 
       FIG.  10    illustrates several examples of regions of features in image data that may be evaluated, other regions of evaluation may also be selected in other examples. A first example is a region  931  of perivascular fat  920  delineated by a rectangular box indicating perivascular fat  920 . Region  931  extends from an edge of the perivascular fat region  920  to the plaque  915 , and the image data evaluated may be in one or more dimensions (for example two dimensions). Another example is a region  941  that extends across plaque  915 . Region  941  is adjacent to the perivascular fat region  931  on one side, and adjacent to lumen region  939  on the opposite side. Lumen region  939  extends from plaque  915  across a portion of the vessel  905 . In this configuration, perivascular fat region  931 , plaque region  941 , and lumen region  939 , are aligned and span the lumen of the vessel  905 , the plaque  915 , and the perivascular fat region  920 . The densities of the image data in a portion of, or all of, these regions may be evaluated relating to their maximum density, minimum density, gradient, or ratio of one of these characteristics, as described herein. 
     In another example, plaque—lumen region  937  is delineated by rectangular box that extends from the lumen wall  911  across the vessel  905  and across the plaque  915 . Plaque—lumen region  937  represents a two dimensional set densities of image data that all, or portion of, may be evaluated. 
     In another example, as illustrated in  FIG.  10   , perivascular fat—plaque region  933  is an evaluation region delineated by retainer boxes that extends from the edge  930  of the plaque  915  to the edge  935  of the perivascular fat  920 . This example illustrates that in some cases, two or more adjacent vectors (or “lines”) of image data across features in the image data that may include one or more features (e.g., fat, plaque, lumen) may be evaluated. Evaluation of two or more adjacent vectors of image data may result in more robust metrics that are less affected by noise in the image data. 
     In another example, perivascular fat—plaque region  938  is delineated by a rectangular box that extends from the edge  930  of the plaque  915 , that extends into the vessel  905 , to the edge  935  of the perivascular fat  920  disposed distal to the plaque  915 . Perivascular fat—plaque region  938  represents a one dimensional set of densities of image data that all, or a portion of, may be evaluated. As an example of metrics of the features depicted in  FIG.  10    (using mere examples of radiodensity values), the slope of the gradient of the image density values in the plaque  915  in the perivascular fat—plaque region  938  may be −3, the maximum density of the plaque  915  may be 98 and the minimum density of the plaque  915  may be −100. The slope of the gradient of the perivascular fat  920  and the perivascular fat—plaque region  938  may be −5, the maximum density of the perivascular fat  920  in the perivascular fat—plaque region  938  may be 180, and a minimum density of the perivascular fat  920  in the perivascular fat—plaque region  938  may be 102. Other metrics of the perivascular fat—plaque region  938  may include: a ratio of the slopes of the plaque  915  to the perivascular fat  920  {−3/−5}, a ratio of the maximum density of the plaque  915  to the maximum density of the perivascular fat  920  {98/180}; a ratio of the minimum density of the plaque  915  to the minimum density of the perivascular fat  920  {−100/102}; a ratio of the minimum density of the plaque  915  to the maximum density of the perivascular fat  920  {−100/180}; a ratio of the maximum density of the plaque  915  and the minimum density of the perivascular fat  920  {98/102}; and the gradient across the entire perivascular fat—plaque region  938  (e.g., −4). 
       FIG.  11    illustrates another example of determining radiodensity values of regions of the perivascular fat and plaque to determine metrics, as described herein.  FIG.  11    shows coronary artery  905 , coronary plaque  915  located in a lumen wall  910  of the coronary artery  905 , and perivascular fat  920  located outside of the lumen wall  910  and adjacent to the coronary plaque  915 , similarly as shown in  FIG.  10   . 
       FIG.  11    further illustrates an example of two regions where radiodensity data that may be evaluated to characterize the plaque. The two regions include a first region (or a perivascular fat  1131  region) in the perivascular fat  920  and a second region (or a plaque region)  1141 , adjacent to the first region  1131  and in the coronary plaque  915 . In this example, the coronary artery  905  and the lumen wall  910  are depicted as being aligned generally vertically on the page. The plaque  915  and the fat  920  are illustrated as extending laterally from the artery  905  (e.g., to the left relative to the figure orientation). The plaque  915  is within the lumen wall  910  of the artery  905 , such that the lateral extent of the lumen wall  910  is shown as coincident with the leftmost boundary  950  of the plaque  915 . Dashed line  1125  indicates the alignment of the coronary artery  905  at this location, and in this example indicates a center line of the artery  905  which is aligned with the artery  905  at this location. 
     As illustrated in  FIG.  11   , the fat region  1131  and the plaque region  1141  represent areas of radiodensity information (e.g., 3D or 2D) of image data, generated from one or more images, that are evaluated to characterize plaque  915 . As described above, in some examples, one or more images can be used to generate a 3D data set that represents a coronary artery, plaque in the artery, and perivascular tissue that is located near or adjacent to the artery and/or the plaque. Once a data set is generated, it can be used to characterize the relationship between one or more of plaque, perivascular tissue and lumen tissue. In some embodiments of evaluating plaque, the data set is used as a 3D data set (which may also be referred to as a 3D model). In some embodiments of evaluating plaque, the data set is used as a 2D data set where information in the data set is looked at in XY (2D) region. In the example illustrated in  FIG.  12   , the image data can present 2D or 3D data. 
     In some embodiments of evaluating plaque, a region of radiodensity values can be used that are along a line in the image data, whether the data evaluated is a 2D or 3D representation of an artery. A region radiodensity values along a line can be referred to as a “linear region.” The linear region may indicate data that includes, or goes across, part or all of one or more types of tissues, for example, plaque, perivascular tissue, and/or lumen tissue of the coronary artery. That is, the region may be referred to as indicating a portion of one or more type of tissue (e.g., plaque, perivascular tissue, and/or lumen tissue of the coronary artery) which indicates that some information in the data set is included in the particular region. The radiodensity data in a linear region is a vector with dimensions 1×n, where n represents the number of discrete points of radiodensity data along the vector. Some examples of regions which may be linear regions are illustrated and described in  FIG.  10   . For example, lumen region  939  ( FIG.  10   ) which includes part of the vessel  905  tissue, coronary plaque region  941  which includes a portion of the coronary plaque  915 , perivascular fat region  931  which includes a portion of the perivascular fat  920 , perivascular fat-plaque region  935  which includes a portion of the perivascular fat  920  and the plaque  915 , and plaque-lumen region  937  which includes a portion of the plaque  915  and the lumen of the vessel  905 . 
     In the example illustrated in  FIG.  11   , the plaque region  1141  delineates a portion of the plaque  915  and extends in a lateral (or substantially lateral) direction relative to the alignment of the coronary artery as indicated by centerline  1125  of the vessel  905 . The plaque region  1141  extends from a proximal end  1115  that is closest to the center of the artery  905 , to a distal end  1120  that extends laterally away from the center line  1125  of the artery  905 . The perivascular fat region  931  extends from a proximal end  1105  that is closer to the artery  905  to a distal end  1110 , farthest from the artery  905 . Also shown in  FIG.  11   , the perivascular fat region  1131  is aligned (or substantially aligned) with the plaque region  1141 . The proximal end  1105  of the perivascular fat region  1131  is near, or adjacent to, the distal end  1120  of the plaque region  1141 . 
     Radiodensity data in the perivascular fat region  931  is represented by radiodensity values  951 . Radiodensity data in the plaque region  941  is represented by radiodensity values  961 . These radiodensity values  951 ,  961  may be in Hounsfield Units, described above. Once the regions  1131 ,  1141  are determined, and the radiodensity values in the regions are determined, the radiodensity values  951  representing the density of a portion the perivascular fat  920  and the radiodensity values  961  representing the radiodensity values of a portion of the plaque  915  maybe analyzed to determine characterizations of the plaque and help assess its risk. 
     Analysis of the radiodensity values of each linear region can be performed to determine metrics that indicate the radiodensity values in a region, or the relationship of the cardio density values in one region as compared to another region. The plaque can be characterized by analyzing metrics that are determined by one or more of the maximum density, minimum density, and/or the slope of the gradients (sometimes referred to simply as “slope” for ease of reference) for a region or several regions, for example, adjacent regions. In some examples, determining metrics can include determining one or more of a maximum density of the radiodensity values, a minimum density of the radiodensity values, and/or a slope of the gradient of the radiodensity values, one or more of a slope/gradient of a feature, a maximum density, minimum density, a ratio of a slope of one feature to the slope of another feature, a ratio of a maximum density of one feature to the maximum density of another feature, a ratio of a minimum density of a feature to the minimum density of the same feature, or a ratio of the minimum density of a feature to the maximum density of another feature. 
     In one particular example, referring to  FIG.  11   , the plaque  915  may be characterized by analyzing one of more of the maximum density, minimum density, and slope of the radiodensity values in the perivascular fat region  1131  and the adjacent plaque regions  1141 . For example, in the illustrated examples of radiodensity values in regions  1131 ,  1141 , the maximum and minimum density of the perivascular fat  920  is 120 and 34, respectively, and the maximum and minimum density of the plaque  915  is 30 and −79 respectively. The gradient of the radiodensity values in plaque region  1141  is −2. The gradient the cardio density values in perivascular fat region  1131  is −3. The determined metrics may include, for example:
         (a) a ratio of the gradient of the perivascular fat region  1131  and the gradient of the plaque region  1141 : {−2:−3};   (b) a ratio of the maximum density of the perivascular fat region  1131  and the maximum density of the plaque region  1141 : {120:30};   (c) a ratio of the minimum density of the perivascular fat region  1131  and the minimum density of the plaque region  1141 : {34:−79};   (d) a ratio of the minimum density of the perivascular fat region  1131  and the maximum density of the plaque region  1141 : {34:30};   (e) a ratio of the maximum density of the perivascular fat region  1131  and the minimum density of the plaque region  1141 : {120:−79}; and   (f) the gradient from the proximal end  1115  of the plaque region  1141  (e.g., the inner surface of the plaque  915 ) to the distal end  1110  of the perivascular fat region  1131  (e.g., the outer surface of the perivascular fat  920 ): −2.       

     A maximum or a minimum density of the radiodensity values in a regions may be determined several ways, according to various embodiments. In one example, simply the maximum/minimum radiodensity value can be selected as the maximum or minimum value. However, some data sets may include outliers that indicate erroneous data. If it can be determined that an outlying radiodensity value is in fact erroneous (e.g., using statistical methods), then the outlying value may be deleted from the analysis, or corrected if possible. Outliers may be due to random variation or may indicate something scientifically interesting. In any event, we typically do not want to simply delete the outlying observation. However, if the data contains significant outliers, robust statistical techniques or alternatively, imaging techniques, can be used to filter the image data to improve the accuracy of the metrics. 
       FIG.  12    illustrates a representation of image data showing a coronary artery  905 , plaque  915 , and perivascular fat  920  located adjacent to the plaque (as similarly shown in  FIG.  11   ).  FIG.  12    also illustrates a perivascular fat region  1231  and the perivascular fat  920 , and a plaque region  1241  in the plaque  915 . The perivascular fat region and  1231  and the plaque region  1241  differ from the fat region  1131  and the plaque region  1141  illustrated in  FIG.  11    in that the radiodensity values in these regions are in the form of a two dimensional vector. That is, if each of the regions  1231 ,  1241  contains rows (e.g., lateral with reference to the page) and columns (e.g., vertical with reference to the page) of cardio representing the image data in regions  1231 ,  1241 , density values in regions  1231 ,  1241  includes two or more adjacent rows of radiodensity values. In one example, the two or more adjacent rows of radiodensity values may be used to generate minimum and maximum density values, for example, by taking the maximum and minimum density value from any of the two or more rows. In another example, the two or more adjacent rows of radiodensity values may be used to generate minimum and maximum density values by averaging the information in the two or more rows, for example, by averaging the maximum radiodensity values in each of the rows to determine a maximum radiodensity value for the region, and by averaging the minimum radiodensity values in each of the rows to determine a minimum cardio density value for the region. Similarly, the gradient of the radiodensity values in each of the regions may be calculated based on the radiodensity values in two or more rows. For example the gradient of the radiodensity value in each row of the region may be calculated, and the gradient can be determined by averaging each of the calculated gradient values. It is contemplated to use other statistical techniques to average multiple radiodensity values in a region to determine characteristics and metrics of the region. Such techniques may be particularly useful to minimize the effect of noise (inaccurate data) in a region. 
       FIG.  13    is a table  1300  illustrating an example of a set of patient information. In this example, the table  1300  includes two columns, a first column  1305  labeled “Item” and a second column  1310  labeled “Importance or Value.” 
     In this example, the items of patient information in the first column  1305  includes information of a patient&#39;s sex, age, BMI, medication, blood pressure, heart rate, weight, height, race, body habitus, smoking, diabetes, hypertension, prior CAD, family history, and labs. In other examples, more or fewer items may be included, and/or different items may be included. 
     The second column  1310  can include a numeric assessment of the importance or value of each item in the first column  1305 . The numeric assessment can be provided by a risk score and used to bias the analysis based on one or items that are deemed to be more important. In some examples, each item has the same assigned value. In other examples, different values can be assigned to one or more of the items. In some example, the values can be normalized to add up to 1.0, or 100%, or another value. 
       FIG.  14    is a table  1400  illustrating an example of a set of scan information. The table  1400  includes a first column  1405  labeled “Item” listing scan related items, and a second column  1410  labeled “Importance or Value.” In this example, the items of scan information in the first column  1405  includes contrast to noise ratio, signal-to-noise ratio, tube current, tube voltage, contrast type, contrast volume, flow rate, flow duration, slice thickness, slice spacing, pitch, vasodilator, beta blockers, recon option whether it&#39;s iterative or filter back projection, recon type whether it&#39;s standard or high resolution, display field-of-view, rotation speed, gating whether it&#39;s perspective triggering or retrospective gating, stents, heart rate, or blood pressure. In other examples, more or fewer items may be included, and/or different items may be included. 
     The second column  1410  can include a numeric assessment of the importance or value of each item in the first column  1405 . The numeric assessment can be provided by a risk score and used to bias the analysis based on one or items that are deemed to be more important. In some examples, each item has the same assigned value. In other examples, different values can be assigned to one or more of the items. In some example, the values can be normalized to add up to 1.0, or 100%, or another value. 
       FIG.  15    is a table  1500  illustrating an example of a set of cardiac information. The table  1500  includes a first column  1505  labeled “Item” listing scan related items, and a second column  1510  labeled “Importance or Value.” In this example, the items of cardiac information in the first column  1504  includes contrast to density, volume, geometry-shape, location, remodeling, baseline anatomy (for diameter, length), compartments (inner, outer, within), stenosis (diameter, area), myocardial mass, plaque volume, plaque composition, texture, or uniformity. In other examples, more or fewer items may be included, and/or different items may be included. 
     The second column  1510  can include a numeric assessment of the importance or value of each item in the first column  1505 . The numeric assessment can be provided by a risk score and used to bias the analysis based on one or items that are deemed to be more important. In some examples, each item has the same assigned value. In other examples, different values can be assigned to one or more of the items. In some examples, the values can be normalized to add up to 1.0, or 100%, or another value. 
       FIG.  16    is an example of a cross section of a coronary artery  1600 . In  FIG.  16    illustrates the inside lumen wall  1606  of the artery  1600  having an interior portion  1602  and the outer vessel wall  1608  with gradient radiodensities exhibited in the lumen within the plaque  1604  between the lumen wall  1606  and perivascular tissue  1620  outside of the vessel. The line  1612  indicates a line through a diameter of the artery  1600 . 
       FIG.  17    is an image showing an example of a longitudinal straightened rendering of a coronary artery  1708  that shows a buildup of plaque between an inner portion and an outer portion of the coronary artery  1708 . As illustrated in  FIG.  17   , the coronary artery  1708  includes an inner lumen  1710  having a cavity  1702  within the inner lumen  1710  for transporting blood. The coronary artery  1708  also includes an outer vessel  1706  extending from the left side (relative to the orientation of  FIG.  17   ) of the coronary artery  1708 . Plaque  1704  buildup is between the outer vessel  1706  and the inner lumen  1710 . This figure demonstrates the different compartments of the lumen, the plaque and perivascular tissue outside of the inner lumen  1710  and plaque  1702 . 
       FIG.  18    is a chart of plots illustrating the compartment areas of cross-sections of plaque  1801 , lumen  1802 , and fat  1803  along the length of a coronary artery. Such plots  1801 ,  1802 ,  1803  can be generated for the left and/or right coronary artery. A plurality of cross-sectional areas of plaque of a coronary artery can be determined along a length of the coronary artery. The distance from the ostium of each plaque, lumen, and fat cross-section can also be determined. The ratios of cross-sections of the plaque, lumen and fat at one or more portions of one or more coronary arteries may be indicative of a patient&#39;s risk associated with plaque.  FIG.  18    illustrates an example of plots of the plaque cross-sections  1801 , lumen cross-sections  1802 , and fat cross-sections  1803 , where the distance from the ostium of the plaque, lumen, and fat cross-sections  1801 ,  1802 ,  1803  are plotted on the x-axis, and area of the respective plaque, lumen, and fat cross-sections  1801 ,  1802 ,  1803  are plotted on the y-axis. In some embodiments, the distance scale along the x-axis can be in millimeters, although other scales can be used in other embodiments. In some embodiments, the areas of the cross-sections can be in mm 2 , although another area unit of measurement can be used in other embodiments. Ratios of these compartments along portions of a coronary artery can be calculated based on one or more or the plaque cross-sections  1801 , the lumen cross-sections  1802 , and the fat cross-sections  1803  at one or more corresponding distances from the ostium, and the calculated ratios can be included in a generated display or in a report. 
     In the example illustrated in  FIG.  18   , along the entire distance from the ostium, the cross-sections of the lumen  1802  are generally smaller than the cross-sections of the plaque  1801  and the cross-sections of the fat  1803 , and the cross-sections of the plaque  1   801  are smaller than the cross-sections of the lumen  1802 . At some distances from the ostium (for example, from about distances 7 to 9 along the x-axis) one or more of the cross-sectional areas of the plaque, the lumen, and/or the fat are substantially similar, or nearly the same, although even in these areas the cross-sections of the lumen  1802  are smaller than the cross-sections of the plaque  1801 , and the cross-sections of the plaque  1801  are smaller than the cross-sections of the fat  1803 . However, at other distances from the ostium the cross-sections differ greatly and this difference is clearly visible from the plaque cross-section plot  1801 , the lumen cross-section plot  1802 , and the fat cross-section plot  1803 . For example, in a section of the coronary from about the distance 16 (indicated by line “A”) to about the distance 25 (indicated by line “B”) along the x-axis, the cross-section area of the fat  1803  is visibly greater the cross-section of the plaque  1801 , and the cross-section area of the plaque  1801  is visibly greater than the cross-section area of the lumen  1802 . As a general example, at one specific distance “20” indicated by the line “C” the cross-sectional area of the lumen  1802  is about 9 units, the cross-sectional area of the plaque  1801  is about 18 units 2 , and the cross-sectional area of the fat is about 24 units 2 . As a specific example, at the specific distance 20 mm indicated by the line C, the cross-sectional area of the lumen  1802  is about 9 mm 2 , the cross-sectional area of the plaque  1801  is about 18 mm 2 , and the cross-sectional area of the fat is about 24 mm 2 . Accordingly, at distance “20” the ratio of the fat:plaque=1.33, the ratio of the fat:lumen=2.67, and the ratio of the plaque:fat=2.00. In some embodiments, the ratios of one or more of fat:plaque, fat:lumen, and/or plaque:fat are calculated as a plurality of distances in this data can be provided on a display or in a report as numbers or in a plot of the ratios. In an example, ratios that exceed a certain threshold can be flagged for further investigation of the portion or the coronary artery that corresponds to where the ratio exceeds a certain threshold. In another example, ratios that exceed a certain threshold for a certain distance (portion of the coronary artery) can be flagged for further investigation of the corresponding portion of the coronary artery. Such compartmental ratios may be used to indicate distinct differences in risks associated with plaque. 
     Ratios of compartments of the plaque, lumen and fat along a coronary artery can also be calculated based on summated volume (e.g., based on the cross-sectional area of the plaque, lumen, and fat over a certain distance) and the summated volume can be included in a generated display or in a report. The ratios of compartments of the plaque, lumen and fat along a coronary artery calculated based on summated volume may be indicative of a patient&#39;s risk associated with plaque. In an example, a plurality of portions of the coronary artery can be used to calculate a plurality of summated volumes. In an example, for a point where a cross-section area ratio (e.g., fat:plaque, fat:lumen, and/or plaque:fat) is exceeds a certain threshold (or is above a certain threshold for a certain distance), this can mark a starting point to calculate the summated volume of the coronary artery. In an example, the point where cross-sectional area ratio (e.g., fat:plaque, fat:lumen, and/or plaque:fat) falls back below a certain threshold (or falls below a certain threshold for a certain distance) this can mark and ending point to calculate the summated volume of the coronary artery. An example using the plots in  FIG.  18   , at about line A one or more of the cross section area ratios (e.g., fat:plaque, fat:lumen, and/or plaque:fat) may exceed a certain threshold and thus line a can mark a starting point to calculate this made volume of the coronary artery; and then at about line B one or more of the cross section area ratios (e.g., fat:plaque, fat:lumen, and/or plaque:fat) may fall below a certain threshold and thus line B may mark the ending point to calculate this made volume of the coronary artery. Although the portion of the plots corresponding to distances 16-25 generally shows the largest ratios, in some examples smaller ratios may indicate the beginning/ending of summated volume calculations. For example, beginning at a distance 34, the plots of the plaque cross-section  1801 , lumen cross-section  1802 , and fat cross-section  1803  vary consistently (although not greatly) to distance 46, and then again continue to vary consistently (although not greatly) to distance 56. In some examples, the summated volume may be determined to be calculated for a portion of the coronary artery when one or more of the cross section area ratios (e.g., fat:plaque, fat:lumen, and/or plaque:fat) such that they exceed a certain threshold for a certain distance, and the results flagged for further investigation of the corresponding part of the coronary artery either on a display or in a generated report. Such compartmental ratios may be used to indicate distinct differences in risks associated with plaque. 
     In some implementations, other compartmental ratios (e.g., fat:plaque, fat:lumen, and/or plaque:fat) may be calculated and provided on a display, or in a report, to provide additional information about a patient&#39;s coronary arteries. Such information may indicate a portion of an artery for further investigation, or may indicate a condition of a patient. One or more compartmental ratios may be determined at a first point in time (e.g., at a start date), and then determined again at a subsequent (second) point in time (e.g., 2 months later, 6 months later, 1 year later, 2 years later, and the like) to track any changes that occur in the patient over the theme period. The period of time can be, for example, from 1 week or two weeks, to months or years. In an example, one or more compartmental ratios may be determined at a first point in time (e.g., when a patient is 50 years old), and then determined again that a second point in time (e.g., when a patient is 60 years old) to track any changes that occur in the patient over a certain time period. In an example, for a patient that has a family history of coronary artery issues, such testing may be conducted when the patient is 40 years old, and then subsequently every 5 or 10 years to collect information on the patient&#39;s coronary arteries that may indicate changes to the coronary arteries that may indicate the onset of coronary artery issues/diseases. 
     In some implementations, compartmental ratios may be determined for coronary segments. For example, compartmental ratios of one or more of the right coronary artery proximal segment, the right coronary artery middle segment, right coronary artery distal segment, a posterior intraventricular branch of the right coronary artery, the left coronary artery (main stem), the interior intraventricular branch of the left coronary artery, the interior intraventricular branch of the left coronary artery middle segment, interior intraventricular branch left coronary artery distal segment, the first diagonal branch, the second diagonal branch, the circumflex branch of the left coronary artery proximal segment, the first marginal branch, circumflex branch of the left coronary artery middle segment, second marginal branch, the circumflex branch of the left coronary artery distal segment, the posterior left intraventricular branch the right coronary artery, and/or the intermediate atrial branch for the right coronary artery. In some implementations, compartmental ratios may be determined for any coronary vessels. Information relating to compartmental ratios that are determined for a patient may be presented on one or more paper or electronic reports, plots, graphs and the like. In some implementations, two or more compartmental ratios for a particular patient are determined and presented as a patient summation of compartmental ratios. For example, compartmental ratios of two or more portions of a patient&#39;s right coronary artery may be presented and report on a display to indicate the compartmental ratios of these portions of the right coronary artery. In some examples, compartmental ratios of all of the portions of the right coronary artery are determined presented for evaluation. In some examples, compartmental ratios of all the portions of the left coronary artery are determined and presented for evaluation. In some examples, compartmental ratios of corresponding parts of the left coronary artery and the right coronary artery are determined and presented for evaluation. Various embodiments of compartmental ratios can be included with any of the other information described herein to indicates plaque risk. 
       FIG.  19    is another chart of plots illustrating the compartment areas of cross-sections of plaque  1901 , lumen  1902 , and fat  1903  along the length of a coronary artery. Similar to  FIG.  18   , the distances of a measured cross-section of plaque, lumen, and fat from the ostium of a coronary artery are plotted on the x-axis, and areas of the respective cross-section of the plaque are plotted on the y-axis. The coronary artery in  FIG.  19    illustrates an example of different compartmental ratios than the artery in  FIG.  18   . 
     EXAMPLES OF CERTAIN EMBODIMENTS 
     The following are non-limiting examples of certain embodiments of systems and methods of characterizing coronary plaque. Other embodiments may include one or more other features, or different features, that are discussed herein. 
     Embodiment 1: A method for characterization of coronary plaque tissue data and perivascular tissue data using image data gathered from a computed tomography (CT) scan along a blood vessel, the image information including radiodensity values of coronary plaque and perivascular tissue located adjacent to the coronary plaque, the method comprising: quantifying, in the image data, the radiodensity in regions of coronary plaque; quantifying, in the image data, radiodensity in at least one region of corresponding perivascular tissue adjacent to the coronary plaque; determining gradients of the quantified radiodensity values within the coronary plaque and the quantified radiodensity values within the corresponding perivascular tissue; determining a ratio of the quantified radiodensity values within the coronary plaque and the corresponding perivascular tissue; and characterizing the coronary plaque by analyzing one or more of: the gradients of the quantified radiodensity values in the coronary plaque and the corresponding perivascular tissue, or the ratio of the coronary plaque radiodensity values and the radiodensity values of the corresponding perivascular tissue, wherein the method is performed by one or more computer hardware processors configured to execute computer-executable instructions on a non-transitory computer storage medium. 
     Embodiment 2: The method of embodiment 1, wherein the perivascular tissue comprises at least one of coronary artery lumen, fat, coronary plaque or myocardium. 
     Embodiment 3: The method of any one of embodiments 1 and 2, further comprising receiving, via a network, the image data at a data storage component. 
     Embodiment 4: The method of embodiment 3, wherein the network is one of the Internet or a wide area network (WAN). 
     Embodiment 5: The method of any one of embodiments 1-4, wherein the image data from the CT scan includes at least ten images. 
     Embodiment 6: The method of any one of embodiments 1-4, wherein the image data from the CT scan includes at least 30 images. 
     Embodiment 7: The method of any one of embodiments 1-6, further comprising generating a patient report comprising at least one of a diagnosis, a prognosis, or a recommended treatment for a patient based on the characterization of the coronary plaque. 
     Embodiment 8: The method of any one of embodiments 1-7, wherein quantifying radiodensity in at least one region of perivascular tissue comprises quantifying radiodensity, of the scan information, for coronary plaque and adipose tissue in each of one or more regions or layers of perivascular tissue. 
     Embodiment 9: The method of any one of embodiments 1-8, wherein the radiodensity of the scan information is quantified for water in each of one or more of the regions of coronary plaque and perivascular tissue. 
     Embodiment 10: The method of any one of embodiments 1-9, wherein radiodensity of the scan information is quantified for low radiodensity plaque in the each of one or more regions or layers of coronary plaque. 
     Embodiment 11: The method of any one of embodiments 1-10, wherein the coronary plaque radiodensity values and the perivascular tissue radiodensity values are an average radiodensity. 
     Embodiment 12: The method of any one of embodiments 1-10, wherein the wherein the coronary plaque radiodensity values and the perivascular tissue radiodensity values are a maximum radiodensity. 
     Embodiment 13: The method of any one of embodiments 1-10, wherein the wherein the coronary plaque radiodensity values and the perivascular tissue radiodensity values are a minimum radiodensity. 
     Embodiment 14: The method of any one of embodiments 1-13, wherein the quantified radiodensities are transformed numerical radiodensity values of the image data. 
     Embodiment 15: The method of any one of embodiments 1-14, wherein the quantified radiodensities account for patient- and CT-specific parameters, including one or more of iodinated contrast agent, contrast type, injection rate, aortic contrast opacification, left ventricular blood pool opacification, signal-to-noise, contrast-to-noise, tube voltage, milliamps, method of cardiac gating, single and multiple energy image acquisition, CT scanner type, heart rate, heart rhythm, or blood pressure. 
     Embodiment 16: The method of any one of embodiments 1-15, further comprising reporting the quantified radiodensities of the coronary plaque and the perivascular tissue as a gradient. 
     Embodiment 17: The method of any one of embodiments 1 and 16, wherein the quantified radiodensities of the coronary plaque and the perivascular tissue are reported as a ratio of the slopes of the gradients from the coronary plaque to perivascular tissue adjacent to the coronary plaque. 
     Embodiment 18: The method of any one of embodiments 1-17, wherein the quantified radiodensities of the coronary plaque and the perivascular tissue are reported as the difference in radiodensity values from the coronary plaque to the perivascular tissue. 
     Embodiment 19: The method of any one of embodiments 1-18, wherein the image data is gathered from a CT scan along a length of at least one of a right coronary artery, left anterior descending artery, left circumflex artery, or their branches, or aorta, or carotid arteries, or femoral arteries, or renal arteries. 
     Embodiment 20: The method of any one of embodiments 1-18, wherein the data is gathered from a CT scan along a length of a non-coronary reference vessel. 
     Embodiment 21:The method of embodiment 20, wherein the non-coronary reference vessel is the aorta. 
     Embodiment 22: The method of any one of embodiments 1-21, wherein the radiodensity is quantified in Hounsfield units. 
     Embodiment 23: The method of any one of embodiments 1-21, wherein radiodensity is quantified in absolute material densities when multienergy CT is performed. 
     Embodiment 24: The method of any one of embodiments 1-24, wherein one or more regions or layers of perivascular tissue extend to an end distance from the outer wall of the blood vessel, the end distance being the fixed distance where the radiodensity of adipose tissue (i) reaches a minimum value within the scanned anatomical area in a healthy vessel, or (ii) drops by a relative percent (e.g., ≥10%); or (iii) drops by a relative percent versus a baseline radiodensity value in a vessel of the same type free of disease. 
     Embodiment 25: The method of any one of embodiments 1-25, wherein one or more regions or layers of the coronary plaque extend to an end distance from the outer wall of the blood vessel, the end distance being the fixed distance where the radiodensity of adipose tissue (i) reaches a maximum value within the plaque, or (ii) increases by a relative percent (e.g., ≥10%); (iii) or changes by a relative percent vs the lowest radiodensity value in the plaque. 
     Embodiment 26: The method of embodiment 24, wherein the baseline radiodensity value is the average radiodensity quantified in a layer of perivascular tissue lying within a fixed layer or region surrounding the outer vessel wall is measured by a thickness, area or volume. 
     Embodiment 27: The method of embodiment 24, wherein the baseline perivascular tissue radiodensity is the radiodensity quantified for adipose tissue in a layer of perivascular tissue lying proximal to the outer wall of the blood vessel. 
     Embodiment 28: The method of embodiment 24, wherein the baseline perivascular tissue radiodensity is the radiodensity quantified for water in a layer of perivascular tissue lying proximal to the outer wall of the blood vessel. 
     Embodiment 29: The method of embodiment 24, wherein the baseline radiodensity is an average radiodensity. 
     Embodiment 30: The method of embodiment 24, wherein the baseline radiodensity is a maximum radiodensity. 
     Embodiment 31: The method of embodiment 24, wherein the baseline radiodensity is a minimum radiodensity. 
     Embodiment 32: The method of embodiment 24, wherein the baseline radiodensity value is the average radiodensity quantified in a layer of coronary plaque tissue within a fixed layer or region within the plaque and is measured by a thickness, area or volume. 
     Embodiment 33: The method of embodiment 24, wherein the baseline coronary plaque radiodensity is the radiodensity quantified for all coronary plaques in the measured vessels. 
     Embodiment 34: The method of any one of embodiments 1-33, further comprising: determining a plot of the change in quantified radiodensity relative to baseline radiodensity in each of one or more concentric layers of perivascular tissue with respect to distance from the outer wall of the blood vessel up to an end distance; determining the area of the region bound by the plot of the change in quantified radiodensity and a plot of baseline radiodensity with respect to distance from the outer wall of the blood vessel up to the end distance; and dividing said area by the quantified radiodensity measured at a distance from the outer wall of the blood vessel, wherein the distance is less than the radius of the vessel or is a distance from the outer surface of the vessel above which the quantified radiodensity of adipose tissue drops by more than 5% compared to the baseline radiodensity of adipose tissue in a vessel of the same type free of disease. 
     Embodiment 35: The method of any one of embodiments 1-34, further comprising: determining a plot of the change in quantified radiodensity relative to baseline radiodensity in each of one or more concentric layers of coronary plaque tissue with respect to distance from the outer wall of the blood vessel up to the inner surface of the plaque; determining the area of the region bound by the plot of the change in quantified radiodensity and a plot of baseline radiodensity with respect to distance from the outer wall of the blood vessel up to the inner surface of the plaque; and dividing said area by the quantified radiodensity measured at a distance from the outer wall of the blood vessel, wherein the distance is less than the radius of the vessel or is a distance from the outer surface of the vessel above which the quantified radiodensity of adipose tissue drops by more than 5% compared to the baseline radiodensity of adipose tissue in a vessel of the same type free of disease. 
     Embodiment 36: The method of embodiment 25, wherein the quantified radiodensity is the quantified radiodensity of adipose tissue in the each of one or more regions or layers of perivascular tissue or coronary plaque. 
     Embodiment 37: The method of embodiment 25, wherein the quantified radiodensity is the quantified radiodensity of water in the each of one or more regions or layers of perivascular tissue. 
     Embodiment 38: The method of embodiment 25, wherein the quantified radiodensity is an average radiodensity. 
     Embodiment 39: The method of embodiment 25, wherein the quantified radiodensities are a maximum radiodensity. 
     Embodiment 40: The method of embodiment 25, wherein the perivascular tissue extends to an end distance from the outer wall of the blood vessel, the end distance being the fixed distance where the radiodensity of adipose tissue (i) reaches a minimum value within the scanned anatomical area in a healthy vessel; (ii) or drops by a relative percent (e.g., 10%); or (iii) drops by a relative percent vs the baseline radiodensity value in a vessel of the same type free of disease. 
     Embodiment 41: The method of any one of embodiments 1-40, wherein one or more regions or layers of coronary plaque tissue extend to an end distance from the outer wall of the blood vessel, the end distance being the fixed distance where the radiodensity of adipose tissue (i) reaches a maximum value within the plaque; or (ii) increases by a relative percent (e.g., ≥10%); (iii) or changes by a relative percent vs the lowest radiodensity value in the plaque. 
     Embodiment 42: The method of any one of embodiments 1-41, further comprising normalizing the quantified radiodensity of the coronary plaque and the perivascular tissue to CT scan parameters (patient- and CT-specific parameters), which include one or more of iodinated contrast agent, contrast type, injection rate, aortic contrast opacification, left ventricular blood pool opacification, signal-to-noise, contrast-to-noise, tube voltage, milliamps, method of cardiac gating, single and multiple energy image acquisition, CT scanner type, heart rate, heart rhythm, or blood pressure; normalize the quantified radiodensity of the coronary plaque-associated perivascular fat to remote perivascular fat; and normalize the quantified radiodensity of the coronary plaque to remote coronary plaques. 
     Embodiment 43: The method of any one of embodiments 1-42, further comprising quantifying other high risk plaque features, such as remodeling, volume, spotty calcifications, and further characterizing the high risk plaque based on one or more of the high risk plaque features. 
     Embodiment 44: The method of any one of the preceding embodiments, wherein characterizing the coronary plaque is based in part on plaque heterogeneity comprising calcium and non-calcified plaque admixtures. 
     Embodiment 45: The method of any one of the preceding embodiments, wherein characterizing the coronary plaque comprises identifying the coronary plaque as a high risk plaque if it is prone to be implicated as culprit lesions in future acute coronary events, based on comparison with previously classified patient image data. 
     Embodiment 46: The method of any one of the preceding embodiments, wherein characterizing the coronary plaque comprises identifying the coronary plaque as a high risk plaque if it is likely to cause ischemia based on a comparison with previously classified patient image data. 
     Embodiment 47: The method of any one of the preceding embodiments, wherein characterizing the coronary plaque comprises identifying the coronary plaque as a high risk plaque if it is likely to cause vasospasm based on a comparison with previously classified patient image data. 
     Embodiment 48: The method of any one of the preceding embodiments, wherein characterizing the coronary plaque comprises identifying the coronary plaque as a high risk plaque if it is likely to rapidly progress based on a comparisons with previously classified patient image data. 
     Embodiment 49: The method of any one of the preceding embodiments, wherein characterizing the coronary plaque comprises identifying the coronary plaque as a high risk plaque if it is likely not to calcify, based on a comparisons with previously classified patient image data. 
     Embodiment 50: The method of any one of the preceding embodiments, wherein characterizing the coronary plaque comprises identifying the coronary plaque as a high risk plaque if it is likely not to respond, regress or stabilize to medical therapy based on a comparisons with previously classified patient image data. 
     Embodiment 51: The method of any one of the preceding embodiments, wherein characterizing the coronary plaque comprises identifying the coronary plaque as a high risk plaque if it is associated with complications at the time of revascularization (such as by inducing no-reflow phenomenon) based on a comparisons with previously classified patient image data. 
     Embodiment 52: A system for volumetric characterization of coronary plaque tissue data and perivascular tissue data using image data gathered from one or more computed tomography (CT) scans along a blood vessel, the image information including radiodensity values of coronary plaque and perivascular tissue located adjacent to the coronary plaque, comprising: a first non-transitory computer storage medium configured to at least store the image data; a second non-transitory computer storage medium configured to at least store computer-executable instructions; and one or more computer hardware processors in communication with the second non-transitory computer storage medium, the one or more computer hardware processors configured to execute the computer-executable instructions to at least: quantify, in the image data, the radiodensity in regions of coronary plaque; quantify, in the image data, radiodensity in at least one region of corresponding perivascular tissue adjacent to the coronary plaque; determine gradients of the quantified radiodensity values within the coronary plaque and the quantified radiodensity values within the corresponding perivascular tissue; determine a ratio of the quantified radiodensity values within the coronary plaque and the corresponding perivascular tissue; and characterize the coronary plaque by analyzing one or more of: the gradients of the quantified radiodensity values in the coronary plaque and the corresponding perivascular tissue, or the ratio of the coronary plaque radiodensity values and the radiodensity values of the corresponding perivascular tissue. 
     Embodiment 53: A non-transitory computer readable medium comprising instructions that, when executed, cause an apparatus to perform a method comprising: quantifying, in the image data, the radiodensity in regions of coronary plaque; quantifying, in the image data, radiodensity in at least one region of corresponding perivascular tissue adjacent to the coronary plaque; determining gradients of the quantified radiodensity values within the coronary plaque and the quantified radiodensity values within the corresponding perivascular tissue; determining a ratio of the quantified radiodensity values within the coronary plaque and the corresponding perivascular tissue; and characterizing the coronary plaque by analyzing one or more of: the gradients of the quantified radiodensity values in the coronary plaque and the corresponding perivascular tissue, or the ratio of the coronary plaque radiodensity values and the radiodensity values of the corresponding perivascular tissue. 
     Embodiment 54: A system comprising a processor and a non-transient storage medium including processor executable instructions implementing a processing system for characterizing coronary plaque configured to: quantify, in the image data, radiodensity in regions of coronary plaque; quantify, in the image data, radiodensity in at least one region of corresponding perivascular tissue adjacent to the coronary plaque; characterize one or more medical conditions based on the quantified radiodensity properties of coronary plaque and the radiodensity in at least one region of corresponding perivascular tissue adjacent to the coronary plaque using at least one of a ratio of the quantified radiodensity values within the coronary plaque and the corresponding perivascular tissue, or at least one gradient of the quantified radiodensity values in the coronary plaque and the corresponding perivascular tissue. 
     Embodiment 55: A non-transitory computer readable medium comprising instructions that, when executed, cause an apparatus to perform a method comprising: quantifying, in the image data, radiodensity in regions of coronary plaque; quantifying, in the image data, radiodensity in at least one region of corresponding perivascular tissue adjacent to the coronary plaque; characterizing one or more medical conditions based on the quantified radiodensity properties of coronary plaque and the radiodensity in at least one region of corresponding perivascular tissue adjacent to the coronary plaque using at least one of a ratio of the quantified radiodensity values within the coronary plaque and the corresponding perivascular tissue, or at least one gradient of the quantified radiodensity values in the coronary plaque and the corresponding perivascular tissue. 
     Implementing Systems and Terminology 
     Implementations disclosed herein provide systems, methods and apparatus for mask-less phase detection autofocus. One skilled in the art will recognize that these embodiments may be implemented in hardware, software, firmware, or any combination thereof. 
     In some embodiments, the circuits, processes, and systems discussed above may be utilized in a wireless communication device, for example, a mobile wireless device. The wireless communication device may be a kind of electronic device used to wirelessly communicate with other electronic devices. Examples of wireless communication devices include cellular telephones, smart phones, Personal Digital Assistants (PDAs), e-readers, gaming systems, music players, netbooks, wireless modems, laptop computers, tablet devices, etc., for example, the mobile wireless device  130 C ( FIG.  1   ). 
     The wireless communication device may include one or more image sensors, one or more image signal processors, and a memory including instructions or modules for carrying out the process discussed above. The device may also have data, a processor loading instructions and/or data from memory, one or more communication interfaces, one or more input devices, one or more output devices such as a display device and a power source/interface. The wireless communication device may additionally include a transmitter and a receiver. The transmitter and receiver may be jointly referred to as a transceiver. The transceiver may be coupled to one or more antennas for transmitting and/or receiving wireless signals. 
     The wireless communication device may wirelessly connect to another electronic device (e.g., base station) to communicate information. For example, to communicate information received from the processing system  120  ( FIG.  1   ) to/from another device  130  ( FIG.  1   ). A wireless communication device may alternatively be referred to as a mobile device, a mobile station, a subscriber station, a user equipment (UE), a remote station, an access terminal, a mobile terminal, a terminal, a user terminal, a subscriber unit, etc. Examples of wireless communication devices include laptop or desktop computers, cellular phones, smart phones, tablet devices, etc. Wireless communication devices may operate in accordance with one or more industry standards. Thus, the general term “wireless communication device” or “mobile device” may include wireless communication devices described with varying nomenclatures according to industry standards (e.g., access terminal, user equipment (UE), remote terminal, etc.). 
     The functions described herein may be stored as one or more instructions on a processor-readable or computer-readable medium. For example, on the processing system  120  or any of the devices  130 . The term “computer-readable medium” refers to any available medium that can be accessed by a computer or processor. By way of example, and not limitation, such a medium may comprise RAM, ROM, EEPROM, flash memory, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray® disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. It should be noted that a computer-readable medium may be tangible and non-transitory. The term “computer-program product” refers to a computing device or processor in combination with code or instructions (e.g., a “program”) that may be executed, processed or computed by the computing device or processor. As used herein, the term “code” may refer to software, instructions, code or data that is/are executable by a computing device or processor. 
     The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is required for proper operation of the method that is being described, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims. 
     It should be noted that the terms “couple,” “coupling,” “coupled” or other variations of the word couple as used herein may indicate either an indirect connection or a direct connection. For example, if a first component is “coupled” to a second component, the first component may be either indirectly connected to the second component or directly connected to the second component. As used herein, the term “plurality” denotes two or more. For example, a plurality of components indicates two or more components. 
     The term “determining” encompasses a wide variety of actions and, therefore, “determining” can include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” can include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory) and the like. Also, “determining” can include resolving, selecting, choosing, establishing and the like. 
     The phrase “based on” does not mean “based only on,” unless expressly specified otherwise. In other words, the phrase “based on” describes both “based only on” and “based at least on.” 
     In the foregoing description, specific details are given to provide a thorough understanding of the examples. However, it will be understood by one of ordinary skill in the art that the examples may be practiced without these specific details. For example, electrical components/devices may be shown in block diagrams in order not to obscure the examples in unnecessary detail. In other instances, such components, other structures and techniques may be shown in detail to further explain the examples. Thus, the present invention is not intended to be limited to the implementations shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.