# Patent

## Title
Methods, systems and computer program products for non-invasive determination of blood flow distribution using speckle imaging techniques and hemodynamic modeling

## Abstract

A non-invasive method for measuring blood flow in principal vessels of a heart of a subject is provided. The method includes illuminating a region of interest in the heart with a coherent light source, wherein the coherent light source has a wavelength of from about 600 nm to about 1100 nm; sequentially acquiring at least two speckle images of the region of interest in the heart during a fixed time period, wherein sequentially acquiring the at least two speckle images comprises acquiring the at least two speckle images in synchronization with motion of the heart of the subject; and electronically processing the at least two acquired speckle images based on the temporal variation of the pixel intensities in the at least two acquired speckle images to generate a laser speckle contrast imaging (LSCI) image and determine spatial distribution of blood flow rate in the principal vessels and quantify perfusion distribution in tissue in the region of interest in the heart from the LSCI image.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application is a 35 U.S.C. §371 national stage application of PCT International Application No. PCT/US2012/020626, filed on Jan. 9, 2012, which claims priority to U.S. Provisional Application No. 61/431,161, filed Jan. 10, 2011; and U.S. Provisional Application No. 61/476,854, filed Apr. 19, 2011, the disclosures and content of which are incorporated by reference herein as if set forth in their entirety. The above-referenced PCT International Application was published in the English language as International Publication No. WO 2012/096878 on Jul. 19, 2012.


RESERVATION OF COPYRIGHT
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner, East Carolina University of Greenville, N.C., has no objection to the reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
FIELD
The present inventive concept relates generally to determination of blood flow distribution and, more particularly, to the use of speckle imaging techniques for non-invasive determination of blood flow distribution.
BACKGROUND
Revascularization is an interventional procedure for the provision of a new, additional, or augmented blood supply to a body part or organ. Revascularization typically involves a thorough analysis and/or diagnosis and treatment of the existing diseased vasculature of the affected organ. In some instances, revascularization can be aided by the use of different imaging modalities, such as magnetic resonance imaging (MRI), positron emission tomography (PET) scan, computed tomography (CT) scan, and X ray fluoroscopy.
Revascularization is designed to improve blood flow to tissues perfused by the principal arterial vessel(s) supplying that tissue. Revascularization may be needed, for example, due to an obstruction in the native arterial vessel supplying that tissue. Coronary artery bypass grafting (CABG) is a revascularization procedure that may be used to increase blood flow to ischemic myocardium by bypassing the native coronary obstructions.
There are two measurement components to the revascularization evaluation, blood flow in the principal arterial supply and quantitative perfusion in the tissue. Conventional methods for measurement of blood flow and perfusion are limited, despite the benefit these measurements would bring to the clinical evaluation of the quality of the revascularization procedure.
Some conventional interoperative methods of measuring blood flow are based on ultrasound detection of blood flow in the graft conduits, but not the native principal arterial vessel(s). Some conventional angiographic evaluation methods include conventional coronary angiography performed in a hybrid operating room setting at the time of surgery. Recently, Novadaq Technologies, Inc. of Toronto, Canada has introduced fluorescence imaging that uses both angiographic image evaluation and quantitative perfusion evaluation to CABG.
However, ultrasound detection typically requires physical contact between the graft vessel and a probe. Furthermore, ultrasound detection typically relies on proper placement of the probe around the vessel to obtain accurate measurement of flow speed and can be unreliable, measurement to measurement.
Coronary angiography typically requires radiation and administration of toxic image contrast agent. Furthermore, hybrid operating rooms used for coronary angiography can be relatively expensive, making this method unavailable to many patients undergoing CABG.
Fluorescence imaging typically requires injection of non-toxic dye into the patient. Furthermore, fluorescence imaging typically cannot provide information to directly determine the speed of blood flow in principal vessels. Despite the above, there remains a need for alternative methods of determining blood flow.
SUMMARY
Some embodiments of the present inventive concept provide a non-invasive method for measuring blood flow in principal vessels of a heart of a subject, the method including illuminating a region of interest in the heart with a coherent light source, wherein the coherent light source has a wavelength of from about 600 nm to about 1100 nm; sequentially acquiring at least two speckle images of the region of interest in the heart during a fixed time period, wherein sequentially acquiring the at least two speckle images comprises acquiring the at least two speckle images in synchronization with motion of the heart of the subject; and electronically processing the at least two acquired speckle images based on the temporal variation of the pixel intensities in the at least two acquired speckle images to generate a laser speckle contrast imaging (LSCI) image and determine spatial distribution of blood flow speed in the principal vessels and perfusion distribution in tissue in the region of interest in the heart from the LSCI image.
In further embodiments, sequentially acquiring the at least two speckle images may include electronically monitoring an EKG cardiac cycle of the subject; and electronically synchronizing acquisition of speckle images with the EKG signals.
In still further embodiments, the sequentially acquiring and the electronically evaluating may be performed before a procedure performed on a subject and after the procedure performed on the subject. The method may further include comparing the determined blood flow speed in the principal vessels and perfusion distribution in tissue in the region of interest in the heart before the procedure with the determined blood flow speed in the principal vessels and perfusion distribution in tissue in the region of interest in the heart after the procedure to access success of the procedure.
In some embodiments, the method further includes calculating a velocity field for the region of interest in the heart; calculating blood flow speed in the region of interest in the heart based on the calculated velocity field; and comparing the calculated blood flows speed in the region of interest to the blood flow speed determined using the acquired at least two speckle images of the region of interest in the heart to verify results obtained using the at least two speckle images.
In further embodiments, the velocity field is calculated using equations (9) and (10) set out below.
In still further embodiments, the coherent light source may have a wavelength of from about 600 nm to about 1100 nm and may allow relatively deep penetration of light into tissues to thereby allow an accurate determination of blood flow speed in the principal vessels and the perfusion distribution.
In some embodiments, the coherent light source may include a laser configured to illuminate the region of interest with a substantially constant intensity. The laser may have a fixed or variable wavelength of from about 600 nm to about 1100 nm. The laser may generate a laser beam having a substantially constant intensity within a field-of-view (FOV) of an imaging unit. The laser may be a low power and continuous-wave laser such that the subject does not require any protective apparatus to shield the subject from effects of the laser.
In further embodiments, data acquisition may include sequentially acquiring from about 50 to about 1000 speckle images using the camera during the fixed time period of from about 1 ms to about 200 ms.
In still further embodiments, sequentially acquiring may include acquiring from about 200 to about 500 speckle images during the fixed time period.
In some embodiments, the fixed time period may be selected based on in situ acquisition of blood flow speed of the subject in the region of interest.
Further embodiments of the present inventive concept provide a non-invasive method for measuring blood flow in principal vessels of a subject, the method including illuminating a region of interest with a coherent light source, wherein the coherent light source has a wavelength of from about 600 nm to about 1100 nm; sequentially acquiring at least two speckle images of the region of interest during a fixed time period; electronically processing the at least two acquired speckle images based on the temporal variation of the pixel intensities in the at least two acquired speckle images to generate a laser speckle contrast imaging (LSCI) image and determine spatial distribution of blood flow speed in the principal vessels and quantify perfusion distribution in tissue in the region of interest from the LSCI image; calculating a velocity field for the region of interest; calculating blood flow rate in the region of interest based on the calculated velocity field; and comparing the calculated blood flow speed in the region of interest to the blood flow speed determined using the acquired at least two speckle images of the region of interest to verify results obtained using the at least two speckle images.
Still further embodiments of the present inventive concept provide a non-invasive system for measuring blood flow in principal vessels in a heart of a subject, the system including a coherent light source configured to illuminate a region of interest in the heart of the subject, the coherent light source having a wavelength of from about 600 nm to about 1100 nm. A camera in communication with the coherent light source is provided that is configured to sequentially acquire at least two speckle images of the region of interest in the heart during a fixed time period, wherein acquisition of the at least two speckle images is synchronized with motion of the heart of the subject. A data processing circuit is also provided that is configured to evaluate the temporal variation of the pixel intensities in the at least two acquired speckle images to generate an LSCI image and determine spatial distribution of blood flow speed in the principal vessels and quantify perfusion distribution in tissue in the region of interest in the heart from the LSCI image.
Some embodiments of the present inventive concept provide a computer program product for measuring blood flow in principal vessels in a heart of a subject, the computer program product comprising a non-transitory computer-readable storage medium having computer-readable program code embodied in the medium. The computer-readable program code includes computer readable program code configured to electronically evaluate temporal variation of the pixel intensities in the at least two acquired speckle images to generate an LSCI image and determine spatial distribution of blood flow speed in the principal vessels and quantify perfusion distribution in tissue in the region of interest in the heart from the LSCI image, wherein the at least two speckle images are sequentially acquired using a camera during a fixed time period when the region of interest of the subject is illuminated by a coherent light source having a wavelength of from about 600 nm to about 1100 nm; and computer readable program code configured to sequentially acquire the at least two speckle images in synchronization with motion of the heart of the subject.
It is noted that aspects of the inventive concept described with respect to some embodiments, may be incorporated in different embodiments although not specifically described relative thereto. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination. Applicant reserves the right to change any originally filed claim and/or file any new claim accordingly, including the right to be able to amend any originally filed claim to depend from and/or incorporate any feature of any other claim or claims although not originally claimed in that manner. These and other objects and/or aspects of the present inventive concept are explained in detail in the specification set forth below. Further features, advantages and details of the present inventive concept will be appreciated by those of ordinary skill in the art from a reading of the figures and the detailed description of the embodiments that follow, such description being merely illustrative of the present inventive concept.



BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a block diagram of a non-invasive system for measuring blood flow in principal vessels of a subject in accordance with some embodiments of the present inventive concept(s).
FIG. 2A is a block diagram of a data processing system according to embodiments of the present inventive concept(s).
FIG. 2B is a more detailed block diagram of the data processing system illustrated in FIG. 2 in accordance with some embodiments of the present inventive concept(s).
FIGS. 3 and 4 are flowcharts illustrating operations for measuring blood flow in principal vessels in accordance with various embodiments of the present inventive concept(s).
FIG. 5 is a digital photograph of a system for measuring flow of blood phantom used in an experiment performed in accordance with some embodiments of the present inventive concept(s).
FIGS. 6 through 9 are close up digital photographs of certain elements in the system illustrated in FIG. 5 in accordance with some embodiments of the present inventive concept(s).
FIGS. 10 and 11 are digital photographs of an exemplary flow generation system used in some embodiments of the present inventive concept(s).
FIG. 12 is a graph illustrating the change in height (cm) vs. flow rate (ml/min) in the flow generation system in accordance with some embodiments of the present inventive concept(s).
FIGS. 13A through 13D are digital images illustrating a “no flow” case in accordance with some embodiments of the present inventive concept(s).
FIGS. 14A through 14D are images illustrating a “flow 1” case in accordance with some embodiments of the present inventive concept(s).
FIGS. 15A through 15D are images illustrating a “flow 2” case in accordance with some embodiments of the present inventive concept(s).
FIGS. 16A through 16D are images illustrating a “flow 3” case in accordance with some embodiments of the present inventive concept(s).
FIGS. 17A through 17D are images (averaged over a number of frames) illustrating a speckle image for each of four flow cases illustrated in FIGS. 13 through 16 in accordance with some embodiments of the present inventive concept(s).
FIGS. 18A through 18D are inverted speckle contrast images illustrating each of the four flow cases illustrated in FIGS. 13 through 16 in accordance with some embodiments of the present inventive concept(s).
FIGS. 19A through 19D are graphs illustrating a vertical profile of inverted speckle contrast images for each of the four flow cases in FIGS. 13 through 16 in accordance with some embodiments of the present inventive concept(s).
FIG. 20 is a graph illustrating predicted flow rate (ml/min) vs. inverted speckle image pixel intensity in accordance with some embodiments of the present inventive concept(s).
FIG. 21 is a digital photograph of an exemplary system for measuring flow of blood phantom in accordance with some embodiments of the present inventive concept(s).
FIGS. 22 through 27 are close up photographs of the elements in the system illustrated in FIG. 21 in accordance with some embodiments of the present inventive concept(s).
FIG. 28 is a graph illustrating flow rate (ml/min), flow speed (cm/min) and corresponding LAD flow rate vs. inverted speckle contrast image pixel intensity in accordance with some embodiments of the present inventive concept(s).
FIG. 29 is a graph illustrating flow speed vs. inverted speckle contrast image pixel intensity in accordance with some embodiments of the present inventive concept(s).
FIG. 30 is a graph illustrating average flow speed determined from speckle contrast images vs. flow speed determined from the pump flow rate in accordance with some embodiments of the present inventive concept(s).
FIGS. 31A, 31C and 31D are images illustrating effect of specular reflectance on acquired speckle image data in accordance with some embodiments of the present inventive concept(s).
FIG. 31B is a graph illustrating effect of specular reflectance on acquired speckle image data in accordance with some embodiments of the present inventive concept(s).
FIGS. 32A, 32C and 32D are images illustrating removal of specular reflectance of FIGS. 31A, 31C and 31D in accordance with some embodiments of the present inventive concept(s).
FIG. 32B is a graph illustrating removal of specular reflectance of FIGS. 31A, 31B and 31D in accordance with some embodiments of the present inventive concept(s).
FIG. 33 is a digital photograph of an exemplary system for measuring blood flow including a reservoir used in an experiment performed in accordance with some embodiments of the present inventive concept(s).
FIGS. 34A through 34D are digital images illustrating a “tube clamped” situation in accordance with some embodiments of the present inventive concept(s).
FIGS. 35A through 35D are images illustrating a “pump reading 100 mL” situation in accordance with some embodiments of the present inventive concept(s).
FIGS. 36A through 36D are images illustrating a “pump reading 500 mL” situation in accordance with some embodiments of the present inventive concept(s).
FIGS. 37A through 37D are images illustrating a “pump reading 1000 mL” situation in accordance with some embodiments of the present inventive concept(s).
FIGS. 38A through 38D are averaged speckle images (averaged over a number of frames) for each of the four flow cases illustrated in FIGS. 33 through 37 in accordance with some embodiments of the present inventive concept(s).
FIGS. 39A through 39D are colorized inverted speckle contrast images illustrating each of the four flow case illustrated in FIGS. 33 through 37 in accordance with some embodiments of the present inventive concept(s).
FIGS. 40A through 40D are graphs illustrating a vertical line profile of the inverted speckle contrast images for each of the four flow cases in FIGS. 33 through 37 in accordance with some embodiments of the present inventive concept(s).
FIG. 41 is a graph illustrating flow speed (cm/min) vs. inverted speckle contrast image pixel intensity in accordance with some embodiments of the present inventive concept(s).
FIG. 42 is a graph illustrating flow speed (cm/min) vs. inverted speckle contrast image pixel intensity in accordance with some embodiments of the present inventive concept.
FIGS. 43A through 43D are images illustrating a “pump reading 0 mL” situation in accordance with some embodiments of the present inventive concept(s).
FIGS. 44A through 44D are images illustrating a “clamped pump” situation in accordance with some embodiments of the present inventive concept(s).
FIG. 45 is a diagram of a blood vessel having a narrowing in the middle thereof that can be accessed using methods and systems in accordance with some embodiments of the present inventive concept.
FIG. 46 is a diagram illustrating velocity profiles of various locations in the blood vessel illustrated in FIG. 45 obtained using flow hemodynamic modeling in accordance with some embodiments of the present inventive concept.
FIG. 47 is a graph illustrating shear rate (which is related to flow rate) and horizontal coordinate (diameter) across the blood vessel illustrated in FIGS. 45 and 46 when the shear stress is about 1.0 second in accordance with some embodiments of the present inventive concept.
FIG. 48 is a flowchart illustrating operations for measuring blood flow in principal vessels in accordance with various embodiments of the present inventive concept(s).



DETAILED DESCRIPTION OF EMBODIMENTS
Embodiments of the present inventive concept will now be described more fully hereinafter with reference to the accompanying figures, in which preferred embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Like numbers refer to like elements throughout. In the figures, layers, regions, elements or components may be exaggerated for clarity. Broken lines illustrate optional features or operations unless specified otherwise.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the inventive concept. 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” and/or “comprising,” when used in this specification, 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. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. As used herein, phrases such as “between X and Y” and “between about X and Y” should be interpreted to include X and Y. As used herein, phrases such as “between about X and Y” mean “between about X and about Y.” As used herein, phrases such as “from about X to Y” mean “from about X to about Y.”
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 this inventive concept 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 specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well-known functions or constructions may not be described in detail for brevity and/or clarity.
It will be understood that when an element is referred to as being “on”, “attached” to, “connected” to, “coupled” with, “contacting”, etc., another element, it can be directly on, attached to, connected to, coupled with or contacting the other element or intervening elements may also be present. In contrast, when an element is referred to as being, for example, “directly on”, “directly attached” to, “directly connected” to, “directly coupled” with or “directly contacting” another element, there are no intervening elements present. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed “adjacent” another feature may have portions that overlap or underlie the adjacent feature.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the inventive concept. The sequence of operations (or steps) is not limited to the order presented in the claims or figures unless specifically indicated otherwise.
Spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. 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. For example, if a device in the figures is inverted, elements described as “under” or “beneath” other elements or features would then be oriented “over” the other elements or features. Thus, the exemplary term “under” can encompass both an orientation of over and under. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. Similarly, the terms “upwardly”, “downwardly”, “vertical”, “horizontal” and the like are used herein for the purpose of explanation only unless specifically indicated otherwise.
As will be appreciated by one of skill in the art, embodiments of the present inventive concept may be embodied as a method, system, data processing system, or computer program product. Accordingly, the present inventive concept may take the form of an embodiment combining software and hardware aspects, all generally referred to herein as a “circuit” or “module.” Furthermore, the present inventive concept may take the form of a computer program product on a non-transitory computer usable storage medium having computer-usable program code embodied in the medium. Any suitable computer readable medium may be utilized including hard disks, CD-ROMs, optical storage devices, or other electronic storage devices.
Computer program code for carrying out operations of the present inventive concept may be written in an object oriented programming language such as Matlab, Mathematica, Java, Smalltalk, C or C++, However, the computer program code for carrying out operations of the present inventive concept may also be written in conventional procedural programming languages, such as the “C” programming language or in a visually oriented programming environment, such as Visual Basic.
Certain of the program code may execute entirely on one or more of a user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer. In the latter scenario, the remote computer may be connected to the user's computer through 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).
The inventive concept is described in part below with reference to flowchart illustrations and/or block diagrams of methods, devices, systems, computer program products and data and/or system architecture structures according to embodiments of the inventive concept. It will be understood that each block of the illustrations, and/or combinations of blocks, can be implemented by computer program instructions. These computer 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 block or blocks.
These computer program instructions may also be stored in a computer-readable memory or storage that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory or storage produce an article of manufacture including instruction means which implement the function/act specified in the block or blocks.
The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the block or blocks.
As discussed above, there is a need for effective non-invasive methods for determining blood flow distribution. It is believed that none of the existing methods offer a fully non-invasive cost effective solution to the problem of flow speed determination. Accordingly, some embodiments of the inventive concept provide methods, systems and computer program products for determining speed distribution of blood flow without requiring the use of dye injection, contrast agent or a contact probe. Some embodiments of the inventive concept use speckle imaging techniques to determine blood flow distribution. As used herein, a “speckle” image acquisition refers to the recording of elastically scattered light, i.e. the scattered light has a wavelength that is the same as the incident light, from an object illuminated by a coherent light such as the output from a coherent light source. In particular, the “speckle” is actually a diffraction pattern, which is highly correlated to the morphology of the object being imaged. If certain parts of the object are in translational motion, i.e. blood stream flowing in a coronary artery, the corresponding part or pixels of the speckle image will vary with time in fashions different from those parts not undergoing such translational motion. This difference in the temporal variation of pixel intensity in the speckle image provides a mechanism to non-invasively measure flow speed (m/s or cm/min) in principal vessels. With knowledge of the diameters of the principal vessels that can be determined from the same set of acquired speckle images, the blood flow rate (ml/min) within FOV may be determined. The combined information of blood flow rates and their distribution in different vessels provide critical data for evaluating the effectiveness of Coronary artery bypass grafting (CABG) and other surgical procedures in improving patients' revascularization status and clinical prognosis. Speckle image acquisition is generally discussed, for example, in Velocity measurement of a diffuse object by using a time-varying speckle by Ohtsubo et al.
Thus, some embodiments of the present inventive concept provide a non-invasive technique for measuring blood flow that provides the ability to quantatively measure blood flow in principal vessels and perfusion distribution in areas perfused by one or more of those principal vessels as will be discussed further below with respect to FIGS. 1 through 44.
Furthermore, the data acquired from the obtained set of speckle images can be verified using flow hemodynamic modeling in accordance with some embodiments of the present inventive concept. In particular, using the Navier-Stokes equation, which provides the governing equation for fluid dynamics, a velocity field associated with the FOV (in the principal vessels) can be obtains. As used herein, “velocity field” refers to a distribution of fluid velocity in space and time. This velocity field may then be used to calculate flow rate as well as other quantities of interest, such as pressure. These quantities of interest, for example, flow rates, can then be compared with the experimental data calculated using the obtained set of speckle images. Thus, the hemodynamic modeling may be used to validate the experimental data as well as the success of the procedure as will be discuss further below with respect to FIGS. 45 through 48.
Referring first to FIG. 1, a non-invasive system for measuring blood flow in principal vessels of a subject in accordance with some embodiments of the present inventive concept will be discussed. As discussed above, “non-invasive” refers to a system or method that does not require the subject to be injected with a dye, penetrated with an object or touched with an intrabody probe or probes. Thus, as used herein, the term non-invasive refers to a system or method that makes minimal contact with the subject. As used herein, “subject” refers to the person or thing being imaged. It will be understood that although embodiments of the present inventive concept are discussed herein with respect to measuring blood flow in principal vessels of the subject, embodiments of the present inventive concept are not limited to this configuration. The subject can be any subject, including a veterinary, cadaver study or human subject. As used herein, “perfusion” refers to blood flow at the tissue perfusion distribution level detected with speckle imaging.
As illustrated in FIG. 1, the system 100 includes a communications device 110, a coherent light source unit 120, a camera 130, a synchronization module 170 and an EKG device 180. Although the system of FIG. 1 is depicted as only including these elements, it will be understood that other elements may also be present in the system without departing from the scope of the present inventive concept. For example, the systems illustrated in the photographs of FIGS. 5 and 21 include additional elements not present in the system illustrated in FIG. 1.
Referring again to FIG. 1, in some embodiments, the coherent light source unit 120 may be a laser unit, which may include a laser 123 and a beam shaping lens 125. The laser unit 120 may provide a coherent light source that illuminates a region of interest 140. The coherent light source provided by the laser unit 120 may have a wavelength of from about 600 nm to about 1100 nm. As used herein, the “region of interest” refers to the region of the subject that is being imaged, for example, the principal vessels and tissue, organs, etc. to determine blood flow therein. Although embodiments of the present inventive concept are discussed primarily herein with respect to blood flow distribution in the principal vessels, embodiments of the present inventive concept are not limited to this configuration. For example, blood flow in organs may be determined without departing from the scope of the present inventive concept.
The laser unit 120 may have light output at a fixed or variable wavelength of from about 600 nm to about 1100 nm without departing from the scope of the present inventive concept. The laser 120 can be configured to illuminate the region of interest 140 with a laser beam 127 having substantially constant intensity within FOV of an imaging unit. In some embodiments, the constant or near constant intensity of the laser beam can facilitate acquiring speckle images with a high signal-to-noise (SNR) ratio. The laser 120 can be a low power continuous-wave laser. Thus, the subject does not need to wear any protective apparatus, for example, clothing or goggles, to shield the subject from potential adverse effects of the laser. In some embodiments, for example, the laser 120 may be of 633 nm in wavelength and 1 mW in power.
Use of a laser or other coherent light source having a wavelength of from about 600 nm to about 1100 nm allows relatively deep penetration of light into tissue and can provide an accurate determination of blood flow speed in the principal vessels and the perfusion distribution as will be discussed further below.
In some embodiments, the laser unit 120 may be used to illuminate the coronary artery and be triggered by the electrocardiogram (EKG) provided by EKG device 180 through the synchronization module 170 and measurements can be taken from the same point outside the heart and the same point on the heart itself. In other words, the FOV is fixed by two parameters, the point on the heart and the distance from the camera outside the heart. The FOV is kept the same so that the synchronization can be performed.
Referring again to FIG. 1, the camera 130 communicates with the laser unit 120 and the communications device 110. The camera 130 is configured to sequentially acquire at least two speckle images of the region of interest during a fixed time period. The faster the camera 130, the shorter the fixed time period has to be for acquiring the same number of speckle images. In some embodiments, the camera 130 may be a CCD camera, for example, a Lumenera Lm075 or similar devices.
As used herein, the fixed time period is typically short enough to reduce or possibly minimize motion effects, but long enough to obtain sufficient light signals. Several examples of this fixed timer period are discussed throughout the specification, for example, the fixed time period may be from about 1.0 to about 200 ms, or within a single EKG cardiac cycle. However, it will be understood that the fixed time period is not limited to the specific time periods discussed herein. For example, the fixed time period may be greater than a single EKG cardiac cycle without departing from embodiments discussed herein.
The camera 130 may be configured to acquire from about 50 to about 1000 speckle images during the fixed time period. In some embodiments, the camera may only need to acquire from about 50 to about 500 speckle images to provide a meaningful result. The fixed time period may be selected based on data associated with in situ determined blood flow speed. In some embodiments, the fixed time period is relatively short, typically less than 1 second, or from about 1.0 ms to about 200 ms.
The acquisition of the speckle images can be synchronized with the motion of the heart of the subject. For example, in some embodiments, acquisition of the speckle images may be synchronized with the EKG of the subject such that the motion of the heart will have minimal effect on determination of blood flow speed. Thus, the fixed time period would be located within a single EKG cardiac cycle.
Referring again to FIG. 1, the communications device 110 is configured to process the at least two acquired speckle images based on temporal variation of pixel intensities among the acquired speckle images to determine spatial distribution of blood flow speed in the principal vessels and perfusion distribution in tissue in the region of interest. The at least two acquired speckle images can be electronically evaluated and/or processed using an image processing algorithm that combines temporal and spatial calculations of the at least two acquired speckle images. The at least two acquired speckle images have a direct relationship to the blood flow speed in the principal vessels and the perfusion distribution.
In particular, some embodiments of the present inventive concept use speckle imaging techniques to yield blood flow speed in the principal vessels and perfusion distribution over the FOV. As used herein, FOV refers to the area of the imaged object that can be viewed by the imaging sensor. Due to the coherence among the scattered light from different parts of the illuminated region of the imaged object, the intensity of the scattered light arriving at a detecting element of an imaging sensor depends on the relative spatial relation among the different parts. The dependency leads to a “speckle” appearance of the acquired image since intensity of scattered light having an optical wavelength of from about 200 nm to about 2000 nm can vary quickly over a small spatial domain with a size of about 10 cm. These concepts will be discussed further below.
Referring now to FIGS. 2A and 2B, a data processing system 200 that may be used in the system 100 illustrated in FIG. 1 in accordance with some embodiments of the inventive concept will be discussed. The data processing system 200 may be included in the communications device 110, the camera 130 or split between various elements of the system 100 without departing from the scope of the present inventive concept. As illustrated in FIG. 2, an exemplary embodiment of a data processing system 200 suitable for use in the system 100 of FIG. 1 includes a user interface 244 such as a keyboard, keypad, touchpad or the like, I/O data ports 246 and a memory 236 that communicates with a processor 238. The I/O data ports 246 can be used to transfer information between the data processing system 200 and another computer system or a network. These components may be conventional components, such as those used in many conventional data processing systems, which may be configured to operate as described herein.
Referring now to FIG. 2B, a more detailed block diagram of the data processing system 200 in accordance with some embodiments of the present inventive concept will be discussed. The processor 238 communicates with a display 345 via and address/data bus 347, the memory 236 via an address/data bus 348 and the I/O data ports 246 via an address/date bus 349. The processor 238 can be any commercially available or custom microprocessor or ASICs. The memory 236 is representative of the overall hierarchy of memory devices containing the software and data used to implement the functionality of the data processing system 200. The memory 236 can include, but is not limited to, the following types of devices: cache, ROM, PROM, EPROM, EEPROM, flash memory, SRAM, and DRAM.
As shown in FIG. 2B, the memory 236 may include several categories of software and data used in the data processing system 200: an operating system 352; application programs 354; input/output (I/O) device drivers 358; and data 356. As will be appreciated by those of skill in the art, the operating system 352 may be any operating system suitable for use with a data processing system, such as OS/2, AIX or zOS from International Business Machines Corporation, Armonk, N.Y., Windows95, Windows98, Windows2000, WindowsXP, or Vista from Microsoft Corporation, Redmond, Wash., Unix, Linux, LabView, or a real-time operating system such as QNX or VxWorks, or the like. The I/O device drivers 358 typically include software routines accessed through the operating system 352 by the application programs 354 to communicate with devices such as the I/O data port(s) 246 and certain memory 236 components. The application programs 354 are illustrative of the programs that implement the various features of the data processing system 200 included a system in accordance with some embodiments of the present inventive concept and preferably include at least one application that supports operations according to some embodiments of the present inventive concept. Finally, the data 356 represents the static and dynamic data used by the application programs 354, the operating system 352, the I/O device drivers 358, and other software programs that may reside in the memory 236.
As illustrated in FIG. 2B, the data 356 according to some embodiments of the present inventive concept may include acquired speckle images 360, intermediate data 361, calculated blood flow rates 363 and modeling data 364. Although the data 356 illustrated in FIG. 2B includes three different files 360, 361, 363 and 364, embodiments of the present inventive concept are not limited to this configuration. Two or more files may be combined to make a single file; a single file may be split into two or more files and the like without departing from the scope of the present inventive concept.
As further illustrated in FIG. 2B, the application programs 354 may include a light source trigger module 351, an image capture module 352, a processing module 353 and a modeling module 354 in accordance with some embodiments of the inventive concept. While the present inventive concept is illustrated, for example, with reference to the light source trigger module 351, the image capture module 352, the processing module 353 and the modeling module 354 being application programs in FIG. 2B, as will be appreciated by those of skill in the art, other configurations may also be utilized while still benefiting from the teachings of the present inventive concept. For example, the light source trigger module 351, the image capture module 352 the processing module 353 and the modeling module 354 may also be incorporated into the operating system 352 or other such logical division of the data processing system 300. Thus, the present inventive concept should not be construed as limited to the configuration of FIG. 2B, but is intended to encompass any configuration capable of carrying out the operations described herein.
Furthermore, while the light source trigger module 351, the image capture module 352 the processing module 353 and the modeling module 354 are illustrated in a single data processing system, as will be appreciated by those of skill in the art, such functionality may be distributed across one or more data processing systems. Thus, the present inventive concept should not be construed as limited to the configuration illustrated in FIGS. 2A and 2B, but may be provided by other arrangements and/or divisions of function between data processing systems.
In particular, the light source trigger module 351 may be configured to illuminate a region of interest with a coherent light source. The coherent light source may have a wavelength of from about 600 nm to about 1100 nm as discussed above. The image capture module 352 may be configured to sequentially acquire at least two speckle images of the region of interest during a fixed time period. The processing module 353 may be configured to process the at least two acquired speckle images based on a diffraction pattern of each the at least two speckle images to determine spatial distribution of blood flow speed in the principal vessels and perfusion distribution in tissue in the region of interest.
The modeling module 354 may be configured to calculate a velocity field for the region of interest; calculate blood flow speed in the region of interest based on the calculated velocity field; and compare the calculated blood flow in the region of interest to the blood flow speed determined using the acquired at least two speckle images of the region of interest to verify results obtained using the at least two speckle images. In some embodiments, the modeling module 354 is configured to calculate the velocity field using Equations 9 and 10 set out below.
Thus, blood flow speed as well as other quantities may be calculated using both the speckle method and the velocity field method before a procedure is performed on a subject and after a procedure is performed on the subject to verify that the procedure was successful. By comparing the measurements/quantities before and after the procedure, the success of the procedure may be determined, which will be discussed further below.
Referring now to the flowcharts of FIGS. 3 and 4, operations of a non-invasive method for measuring blood flow in principal vessels of a subject will be discussed. As illustrated in FIG. 3, operations begin at block 315 by illuminating a region of interest in the heart with a coherent light source. The coherent light source may have a wavelength of from about 600 nm to about 1100 nm. Providing a coherent light source with a wavelength of from about 600 nm to about 1100 nm may allow for non-invasive, deep penetration of light into tissues and provides an accurate determination of blood flow speed in the principal vessels and the perfusion distribution within the layer of light penetration.
In some embodiments, the coherent light source may be provided by a laser configured to illuminate the region of interest. The laser may have a fixed or variable wavelength. The laser may produce a beam having substantially constant intensity within a FOV of an imaging unit. The laser may be a low energy and continuous-wave laser such that the subject does not require any protective apparatus to shield the subject from effects of the laser.
Referring again to FIG. 3, operations continue at block 325 by sequentially acquiring at least two speckle images of the region of interest during a fixed time period. The fixed time period may be selected based on data associated with in situ determined blood flow speed. In some embodiments, the at least two speckle images may be acquired in synchronization with motion of a heart of the subject such that the motion of the heart will have minimal effect on determination of blood flow speed using the acquired at least two speckle images. For example, the fixed time period can correspond to a single EKG cardiac cycle or defined portion thereof cycle.
The camera may be configured to acquire the at least two speckle images during the fixed time period. In some embodiments, from about 50 to about 1000 speckle images may be acquired using the camera during the fixed time period of from about 1 ms to about 200 ms. In some embodiments, about 200 to about 500 speckle images may be acquired. Higher numbers of speckle images typically allow better signal-to-noise ratios in the calculated LSCI image but take longer time to acquire.
Referring again to FIG. 3, operations continue at block 335 by electronically processing the acquired speckle images based on the temporal variation of the pixel intensities in the acquired speckle images to generate a laser speckle contrast imaging (LSCI) image and determine spatial distribution of blood flow speed in the principal vessels and perfusion distribution in tissue in the region of interest from the LSCI image.
In some embodiments, electronically evaluating speckle image data may include electronically evaluating the acquired speckle images using an image processing algorithm that combines temporal and spatial calculations of the acquired speckle images to generate a LSCI image and determine spatial distribution of blood flow speed. The at least two speckle images may have a direct relationship to the blood flow speed in the principal vessels and the perfusion distribution which are utilized in generating an LSCI image for determination of the spatial distribution of blood flow speed. For example, following equations can be used to obtain the intensity at each pixel of the LSCI image K (i, j) from the acquired speckle image set {In} with n=1, 2, . . . , N, i.e.,




  
    
      
        
          
            K
            ⁡
            
              (
              
                i
                ,
                j
              
              )
            
          
          =
          
            
              σ
              ⁡
              
                (
                
                  i
                  ,
                  j
                
                )
              
            
            
              μ
              ⁡
              
                (
                
                  i
                  ,
                  j
                
                )
              
            
          
        
        ,
        where
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        
          (
          1
          )
        
      
    
  
  
    
      
        
          
            μ
            ⁡
            
              (
              
                i
                ,
                j
              
              )
            
          
          =
          
            
              1
              N
            
            ⁢
            
              
                ∑
                
                  n
                  =
                  1
                
                N
              
              ⁢
              
                
                  I
                  n
                
                ⁡
                
                  (
                  
                    i
                    ,
                    j
                  
                  )
                
              
            
          
        
        ,
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        
          (
          2
          )
        
      
    
  
  
    
      
        
          σ
          ⁡
          
            (
            
              i
              ,
              j
            
            )
          
        
        =
        
          
            
              
                1
                N
              
              ⁢
              
                
                  ∑
                  
                    n
                    =
                    1
                  
                  N
                
                ⁢
                
                  
                    (
                    
                      
                        
                          I
                          n
                        
                        ⁡
                        
                          (
                          
                            i
                            ,
                            j
                          
                          )
                        
                      
                      -
                      
                        μ
                        ⁡
                        
                          (
                          
                            i
                            ,
                            j
                          
                          )
                        
                      
                    
                    )
                  
                  2
                
              
            
          
          .
        
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        
          (
          3
          )
        
      
    
  




In the above calculations, In(i, j) refers to the pixel at (i, j) location in a speckle image acquired at nth time point and N (>1) is the total number of acquired speckle images.

It will be understood that the operations of blocks 315, 325 and 335 may be performed before and after a procedure performed on the subject. The results before and after the procedure may be compared to verify the success of the procedure in the subject.
Referring now to FIG. 4, operations for a non-invasive method for measuring blood flow in principal vessels of a subject in accordance with some embodiments will be discussed. Operations begin at block 415 by illuminating a region of interest in the heart with a coherent light source, wherein the coherent light source has a wavelength of from about 600 nm to about 1100 nm. At least two speckle images of the region of interest are sequentially acquired during a fixed time period (block 425) in synchronization with the motion of the heart. Temporal and spatial variation of pixel intensities of the at least two acquired speckle images are electrically evaluated to determine spatial distribution of blood flow speed in the principal vessels and perfusion distribution in tissue in the region of interest of the heart (block 435).
A velocity field for the region of interest in the heart is calculated (block 445). In some embodiments, the velocity field is calculated using equations (9) and (10) set out below. Blood flow speed in the region of interest of the heart based on the calculated velocity field is calculated (block 455). The calculated blood flow speed in the region of interest in the heart is compared to the blood flow speed determined using the acquired at least two speckle images of the region of interest to verify results obtained using the at least two speckle images (block 465). Thus, embodiments of the present inventive concept may be used to verify experimental results as will be discussed further below.
It will be understood that the operations of blocks 415, 425, 435, 445, 455 and 465 may be performed before and after a procedure performed on the subject. The results before and after the procedure may be compared to verify the success of the procedure in the subject.
The following non-limiting examples are provided by way of example.
EXAMPLES
Referring to FIG. 5, a digital photograph of a prototype system 500 to detect flow speed using laser speckle contrast imaging (LSCI) technology in accordance with some embodiments of the present inventive concept will be discussed. As illustrated in FIG. 5, the system includes a communication device 510, such as a laptop computer, a laser unit 520 including a laser generator and a focusing lens, a camera 530, a flow generator 580, flow liquid 590 and a flow target 585. Table 1 set out below summarizes the actual equipment/devices used in this experiment.








TABLE 1





Devices used in Experiment 1
Notes







CCD camera (530)
Lumenera Lm075


Laser (520)
633 nm in wavelength, 1 mW in power


Liquid used in flow (590)
20% Intralipid 1 to 4 ratio mixed with



water plus fruit color


Computer/Communications
Laptop PC


Device (510)









As discussed above, the faster the camera 530, the smaller the fixed time period has to be to obtain an adequate number of speckle images to provide a meaningful result. Thus, the limitation of the frame rate of the camera 530 in the prototype system may have impacted the final result of this experiment. The laser 520 is a low power continuous-wave laser providing a single-wavelength coherent light source. Thus, the subject of the imaging does not typically require any protection from such a laser, such as protective clothing or eyewear. The laser 520 produces a beam having a wavelength of from about 600 nm to about 1100 nm in some embodiments. During the experiment, the laser beam produced by the laser 520 is used to illuminate the region of interest with substantially constant intensity with the FOV of the imaging unit. This is an important aspect of the experiment because it allows the resulting images to have a high SNR.
Colored intralipid was used as the flow liquid 590 during the experiment due to the fact that a light scattering characteristics of the colored intralipid is similar to those of mammalian blood. Thus, the colored intralipid mimics the blood flowing in the human body. The communications device 510 used was a laptop computer, although embodiments of the present inventive concept are not limited to the use of a laptop computer. The acquired speckle images are provided to the communications device 510 and are used to calculate blood flow in according with some embodiments of the present inventive concept. As discussed above, the data is calculated using an image processing algorithm that combines temporal and spatial calculations of the acquired speckle images. Thus, spatial distribution of blood flow speed in principal vessels and perfusion distribution can be determined.
Referring now to FIGS. 6 through 9, close up photographs of the devices illustrated in FIG. 5 used during the first experiment are provided. In particular, FIG. 6 is a close up photograph of the laser unit 520; FIG. 7 is a close up photograph of the camera 530; FIG. 8 is a close up photograph of the communications device 510; and FIG. 9 is a close of the flow liquid 590.
Table 2 set out below summarizes parameters for the camera 530 used during the first experiment. The parameters are for the camera 530 while the image sequence is acquired.










TABLE 2









Length of image sequence
~1 second



Frame rate
~95 frames/second



Image resolution
320*240 pixels



Exposure time per frame
3 ms



Gain
1










The upper limit (Vlimit) of flow that can be detected based on the setup of the first experiment can be summarized by the following equation:




  
    
      
        
          V
          limit
        
        =
        
          
            Δ
            ⁢
            
              
            
            ⁢
            L
          
          
            10
            ⁢
            τ
          
        
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        
          (
          4
          )
        
      
    
  




In Equation 1, ΔL is the diameter of the tube, which was 0.26 cm in the first experiment;





  τ
  =
  
    
      0.4
      ⁢
      T
    
    =
    
      0.4
      f
    
  




is the estimated exposure time, 3.0 ms in the first experiment; and f is the frame rate. Thus, in the first experiment Vlimit can be roughly estimated at about 9.0 cm/second.

Referring now to FIGS. 10 and 11, photographs of the flow generation system used in the first experiment will be discussed. FIG. 10 illustrates the flow generation system 580. The higher the bottle in the flow generation system 580, the faster the flow of the flow liquid 590. FIG. 11 is a close up photograph of the tube target 585 used as the flow target for the first experiment. Table 3 below summarizes the relationship between the change in height of the bottle and the flow of liquid in the flow generation system in accordance with the first experiment. The change in height is measured from the height of the bottle to the end of the tube.












TABLE 3





Time
Volume
delta height
flow rate
flow rate
predicted flow


(secs)
(cm3)
(cm)
(cm3/sec)
(ml/min)
rate (ml/min)




















68
100
108
1.5
88.2
90.6


73
100
98
1.4
82.2
83.0


80
100
88
1.3
75.0
75.4


90
100
78
1.1
66.7
67.6


103
100
68
1.0
58.3
59.8


120
100
58
0.8
50.0
51.8


136
100
48
0.7
44.1
43.7


173
100
38
0.6
34.7
35.4









Thus, as illustrated by the delta height (cm) and flow columns of Table 3, the higher the bottle, the faster the flow rate of the colored intralipid liquid.
The estimated relationship between delta height (cm) and flow rate (ml/min) is represented by Equation (2) set out below:

flow rate=1.34×0.9√{square root over (Δh)}  Equation (5);

Where Δh is the change in height of the bottle relative to the vertical position of the tube end. FIG. 12 summarizes the data in Table 3 and is a graph illustrating delta height (cm) vs. flow rate (ml/min).

Four cases of flow rate were measured by the LSCI method in the first experiment setup, no flow, flow 1, flow 2 and flow 3. The details of each of the flow rates are summarized in Table 4 set out below. The first experiment was repeated three times for each case to ensure accuracy and repeatability. FIGS. 13A through 13D illustrate resultant images obtained for the “no flow” state. FIG. 13A is an averaged image obtained by averaging in a pixel-to-pixel fashion 97 frames for the “no flow” case; FIG. 13B is a vertical line profile image in the middle of inverted speckle contrast image for the “no flow” case; FIG. 13C is an inverted speckle contrast image for the “no flow” case; and FIG. 13D is a colorized inverted speckle contrast image for the “no flow” case.
FIGS. 14A through 14D illustrate resultant images obtained for the “flow 1” case, FIG. 14A is an averaged image obtained by averaging in a pixel-to-pixel fashion 97 frames for the “flow 1” case; FIG. 14B is a vertical line profile image in the middle of the inverted speckle contrast image for the “flow 1” case; FIG. 14C is an inverted speckle contrast image for the “flow 1” case; and FIG. 14D is a colorized inverted speckle contrast image for the “flow 1” case.
FIGS. 15A through 15D illustrate resultant images obtained for the “flow 2” case. FIG. 15A is an averaged image obtained by averaging in a pixel-to-pixel fashion 89 frames for the “flow 2” case; FIG. 15B is a vertical line profile image in the middle of an inverted speckle contrast image for the “flow 2” case; FIG. 15C is an inverted speckle contrast image for the “flow 2” case; and FIG. 15D is a colorized inverted speckle contrast image for the “flow 2” case.
FIGS. 16A through 16D illustrate resultant images obtained for the “flow 3” case. FIG. 16A is an averaged image obtained by averaging in a pixel-to-pixel fashion 89 frames for the “flow 3” case; FIG. 16B is a vertical line profile image in the middle of an inverted speckle contrast image for the “flow 3” case; FIG. 16C is an inverted speckle contrast image for the “flow 3” case; and FIG. 16D is a colorized inverted speckle contrast image for the “flow 3” case.
FIGS. 17A through 17D are the averaged images for each of the cases, “no flow”, “flow 1”, “flow 2”, and “flow 3,” respectively. FIGS. 18A through 18D are colorized inverted speckle contrast images for each of the cases, “no flow”, “flow 1”, “flow 2”, and “flow 3,” respectively. FIGS. 19A through 19D are vertical line profile images for each of the cases, “no flow”, “flow 1”, “flow 2”, and “flow 3,” respectively.
Table 4 set out below, summarizes the data for all four flow cases. In particular, the relationship between delta height and predicted flow is readily apparent. FIG. 20 is a graph illustrating predicted flow rate (ml/min) vs. inverted speckle contrast image pixel intensity as set out in Table 4.












TABLE 4








delta

inverted speckle




height
predicted flow
contrast image



Status
(cm)
rate (ml/min)
pixel intensity





















No flow
0
0
15



Flow 1
10
10.6
67



Flow 2
100
84.5
88



Flow 3
193
150.7
108










To summarize the first experiment, the laser speckle contrast imaging setup is clearly able to differentiate between a no flow state and the three flow speed cases. However, the sensitivity and precision were not ideal and the point of “no flow” was not consistent with the other three flow points as illustrated in FIG. 20. Some of the imprecision may be due to using a bottle for the flow speed generation method. This may have caused variation and lack of constant flow. Furthermore, frame rate of the camera may have limited to number of speckle images that could be obtained. The laser beam intensity used during the experiment was uneven in the FOV, i.e. there are dark spots in the FOV.
However, even given this imprecision, the results shown that the higher the frame rate the better the LSCI image quality and it was discovered that the exposure time should be as long as it can in the condition that the same frame rate can be achieved.
Referring first to FIG. 21, a photograph of the system 2100 for a second experiment to detect flow speed using the LSCI technology in accordance with some embodiments of the present inventive concept will be discussed. As illustrated in FIG. 21, the system includes a communications device 2110, such as a laptop computer, a laser unit 2120 including a laser generator and a beam shaping lens, a camera 2130, a flow generator 2181 provided by a biomedical pump, flow liquid 2190, a flow target 2185 and an electromagnetic flow detector 2191. Table 5 set out below summarizes the actual equipment/devices used in this experiment.








TABLE 5





Devices used in Experiment 2
Notes







CCD camera (2130)
Lumenera Lm075


Laser (2120)
633 nm in wavelength, 1 mW in power


Liquid used in flow (2190)
20% Intralipid


Saline water
0.9%


Biomedical pump (2181)
With electromagnetic flow detector (2191)


Communications Device/
Laptop PC


Computer(2110)









As discussed above, the faster the camera 2130, the smaller the fixed time period has to be to obtain an adequate number of speckle images to provide a meaningful result. Thus, the limitation of the frame rate on the camera 2130 may have impacted the final result of this experiment. The laser 2120 is a low power laser providing a single coherent light source. Thus, the subject of the imaging does not typically require any protection from the laser, such as protective clothing or eyewear. The laser 2120 produces a beam having a wavelength of from about 600 nm to about 1100 nm in some embodiments. During the experiment, the laser beam produced by the laser 2120 is used to illuminate the region of interest with substantially constant intensity with the FOV of the imaging unit. This may allow the speckle contrast images to have a high signal-to-noise ratio.
Colored intralipid was used as the flow liquid 2190 during the experiment due to the fact that light scattering characteristics of intralipid are similar to those of mammalian blood. Thus, the colored intralipid will mimic the blood flowing in the human body. The communications device 2110 used was a laptop computer, although embodiments of the present inventive concept are not limited to the use of a laptop computer. The acquired speckle images are provided to the communications device 2110 and are used to calculate blood flow in according with some embodiments of the present inventive concept. As discussed above, the data are calculated using an image processing algorithm that combines temporal and spatial calculations of the acquired speckle images. Thus, spatial distribution of blood flow speed in principal vessels and perfusion distribution can be determined.
Referring now to FIGS. 22 through 27, close up photographs of the devices illustrated in FIG. 21 used during the second experiment are provided. In particular, FIG. 22 is a close up photograph of the laser unit 2120; FIG. 23 is a close up photograph of the camera 2130; FIG. 24 is a close up photograph of the communications device 2110; FIG. 25 is a close up photograph of the biomedical pump 2181; FIG. 26 is a close up photograph of the electromagnetic flow detector 2191; and FIG. 27 is a close up photograph of the flow target 2185.
Table 6 set out below summarizes parameters for the camera 530 used during the second experiment. The parameters are for the camera 2130 while the image sequence is acquired.








TABLE 6







Length of image sequence
~1 second


Frame rate
~95 frames/second


Image resolution
320*240


Exposure time per frame
3 ms (split into 3 part to calculate std and



average every 3 continuous frames)


Gain
1


Working distance
~1.5 m


Aperture
2~4


Length of the video loop
3*1 second









Estimation of the blood flow rate and speed in accordance with the second experiment will be discussed. Since the LSCI technology measures the flow speed (cm/min) rather than flow rate (ml/min), the range of the flow speed of blood in the main branches of coronary artery can be established. The second experiment focused on this range. It is contemplated that the flow rate can be calculated using the flow speed and a cross sectional area of the vessel at the same location. Table 7 set out below illustrates the estimated blood flow rate and speed range in LAD.









TABLE 7





Average diameter
flow rate range
flow speed range


of LAD (cm)
(ml/min, cm3/min)
(cm/min)







0.4
0~100
0~796









Procedures used for in accordance with the second experiment will now be discussed. The biomedical pump was calibrated by comparing measured liquid volume during a certain time with the reading from the electromagnetic flow detector 2591 as illustrated in Table 8 set out below. In particular, pump calibration using 20% Intralipid solution mixed by saline water with 1:4 ratio (volume was measured from 100 mL to 300 mL and reading from the detector was recorded when liquid reaches 200 mL).














TABLE 8








flow rate
flow rate








reading
reading
Calculated


Time
Time
Volume
from pump
from pump
flow rate
Percentage
flow speed


(s)
(min)
(mL)
(L/min)
(mL/min)
(ml/min)
Error
(cm/min)






















15
0.25
200
0.78
780
800
3%
1095


18
0.30
200
0.65
650
667
3%
913


22
0.37
200
0.55
550
545
1%
772


26
0.43
200
0.45
450
462
3%
632


30
0.50
200
0.39
390
400
3%
548


49
0.82
200
0.24
240
245
2%
337


62
1.03
200
0.18
180
194
7%
253


111
1.85
200
0.11
110
108
2%
154









Three Intralipid solutions with different concentrations were measured to simulate light scattering characteristics of blood as will be discussed below and to examine the stability of the LSCI technology. The three intralipid concentrations are summarized below in Table 9. Table 10 summarizes the volume and linear flow rate range measured during the second experiment.










TABLE 9





Ratio of 20%





Intralipid to
Intralipid


saline water
concentration
repeat
Note







1:39
0.5%  
3
Tube surface is processed by





sand paper and collimated





reflectance lights were greatly





reduced. Aperture of the





camera was large. ~2.5


1:19
1%
3
Tube surface is processed by





sand paper and collimated





reflectance lights were greatly





reduced. Aperture of the





camera was medium. ~3


1:9 
2%
3
Same as above



















TABLE 10








Estimated


flow rate reading

Corresponding flow
maximum


in 3/8 inch
Calculated
rate in 4 mm
flow rate in


diameter tube
flow speed
diameter LAD
coronary artery







0~1000 mL/min
0~1404 cm/min
0~176 mL/min
100 mL/min









Results of the second experiment will now be discussed. Table 11 set out below summarizes the results for (1): 0.5% Intralipid solution (1:39); (2): 1% Intralipid solution (1:19); (3) 2% Intralipid solution (1:9) in accordance with the second experiment.







TABLE 11







(Std is standard deviation, L is the inversed speckle contrast see Equation 6 for details)















flow rate

Corresponding








reading from
flow speed
LAD flow rate

Std of

Std of

Std of


pump (mL/min)
(cm/min)
(mL/min)
L (1)
L (1)
L (2)
L (2)
L (3)
L (3)


















0
0
0
56
0.6
51
0.5
44
0.1


100
140
18
88
4.7
88
1.0
75
2.0


200
281
35
97
4.6
94
2.0
92
1.0


300
421
53
105
4.3
110
2.1
104
1.1


400
562
71
111
5.5
112
0.9
109
0.3


500
702
88
113
2.9
117
2.8
117
1.4


600
842
106
121
4.0
118
2.2
121
2.8


700
983
123
120
1.0
113
3.4
127
0.3


800
1123
141
115
5.6
109
3.1
128
0.7


900
1264
159
113
3.8
113
2.1
123
5.7


1000
1404
176
112
3.8
106
6.2
124
3.8









Referring now to FIG. 28, flow speed and corresponding LAD flow rate vs. the inverted speckle contrast image pixel intensity 1/K; Results obtained with ratio of 20% Intralipid to saline water of (1) 1:39; (2) 1:19; (3) 1:9 will be discussed. As illustrated in FIG. 28, the more diluted Intralipid solution has a larger background noise while flow reading is zero; after the flow speed exceeds 800 cm/min, the 1/K begins to saturate and has become less sensitive to the flow speed change; and compared to the huge concentration rage of the Intralipid solution, there is only very small change in the curves.
The quantitative relation between laser speckle contrast image pixel intensity and the flow speed will now be discussed. To make a positive correlation between the flow speed and the calculated image pixel intensity, the following equation is used to construct the inverted speckle contrast image L:




  
    
      
        
          L
          ⁡
          
            (
            
              i
              ,
              j
            
            )
          
        
        =
        
          
            1
            
              K
              ⁡
              
                (
                
                  i
                  ,
                  j
                
                )
              
            
          
          =
          
            
              μ
              ⁡
              
                (
                
                  i
                  ,
                  j
                
                )
              
            
            
              σ
              ⁡
              
                (
                
                  i
                  ,
                  j
                
                )
              
            
          
        
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        
          (
          6
          )
        
      
    
  




The quantitative relationship between laser speckle contrast image pixel K(i,j) and the flow speed have been derived as the following

K(i,j)∝√{square root over (τc(i,j)|T)}  Equation (7)

where T is the camera integration time, τc is a correlation time of scattering particles undergoing motion of speed v and given by





  
    
      τ
      c
    
    =
    
      λ
      
        2
        ⁢
        π
        ⁢
        
          
        
        ⁢
        v
      
    
  
  ,




λ is laser light wavelength. Based on the above relation, the inverted speckle image pixel intensity can be written as

L(i,j)=L0+a√{square root over (v(i,j))}  Equation (8)

where L0 is an added term to account for background noise and should be zero after the baseline has been removed; a is a constant related to the imaging parameters, laser parameters, time/spatial smoothing parameters for obtaining K and the components of the liquid. Thus, after removing the baseline from the data of “zero flow” case from each single measurements in case (1) ̃(3), the Equation (8) can be used to fit the measured data.

FIG. 29 is a graph illustrating flow speed vs. the L with curve fitting based on Equation (8). Table 12 summarizes the results of curve fitting, with R as the value of confidence of fitting (R=1 means perfect fitting).











TABLE 12







Case (1)
case (2)
case (3)





















L0
0
0
0



α
2.3149
2.5413
2.7606



R
0.9906
0.9797
0.9974










Based on the prediction model (curve fitting), flow speed in measurements (1) ̃(3) were obtained to compare with the flow speed calculated from the pump readings. The results are depicted in FIG. 30, a graph illustrating the average of calculated flow speed (cm/min) from L in case (1) ̃(3) vs. the flow speed determined from the pump readings.
To summarize the second experiment, the experiment showed that the inverted speckle image pixel intensity L acquired with the current imaging system can correlate to the speed of the flow within certain range, (flow speed <800 cm/min or LAD flow rate<100 mL/min), which corresponds to the maximum blood flow rate in average main branch of coronary artery. Compared to the huge concentration range of the Intralipid solution, there is only very small change in the curves. The light scattering parameters of blood might fall in between case (1) and (3) as illustrated in Table 13 set out below, where μa is absorption coefficient, μs is scattering coefficient, g is anisotropy factor and μs′=(1−g)μs is the reduced scattering coefficient.











TABLE 13








oxygenated




λ = 633 nm
blood
10% Intralipid




















ua (1/mm)
0.2
0.0003



us (1/mm)
31
34.75



g
0.99
0.83



us′ (1/mm)
0.31
5.98










When bubbles are trapped in the biomedical pump, they may affect the accuracy of the flow reading from electromagnetic flow meter and might affect results of measurement. Specular reflectance from the smooth surface of the tube will cause saturation of the camera and overwhelm the speckle information as shown in FIGS. 31A through 31D. In the second experiment, sand paper was used to create rough surface on the tube to eliminate this influence, the results of which are illustrated in FIGS. 32A through 32D, i.e. specular reflectance is removed by roughening the surface of the tube. The speed detection limit of L depends on the frame rate and the number of frames used to generate the speckle contrast image somehow is related to the signal-to-noise ratio of L. Smoothing of the original images with a moving window of 3 to 5 frames helps increase the signal-to-noise ratio.
Further experiments performed in accordance with some embodiments of the present inventive concept will now be discussed with respect to FIGS. 33 through 43. FIG. 33 is a digital photograph of a prototype system setup used to detect blood flow speed using the LSCI technology in accordance with some embodiments of the present inventive concept. The experiment discussed with respect to FIGS. 33 through 43 is similar to the experiment discussed above with respect to FIGS. 21 through 32, but an extra reservoir 3397 is present to add red blood cells into the circulation from a blood bag 3398 (expired and for research use only), which is acquired from the Red Cross. Thus, many of the details of the experiment will not be repeated herein.
Table 14 set out below summarizes the actual equipment/devices used in this experiment.








TABLE 14





Device
Parameters







CCD camera
Lumenera Lm075


Laser
633 nmin wavelength, 1 mW in power


Liquid used in
Blood (1 unit of red blood cells with hematocrit 70%


flow
+ 1000 mL saline water)


Saline water
0.9%


Biomedical pump
With electromagnetic flow rate detector


Computer
Laptop PC









Table 15 set out below summarizes parameters for the camera used during the second experiment. The parameters are for the camera while the image sequence is acquired.








TABLE 15







Length of image sequence
1 second


Frame rate
~95 frames/second


Image resolution
320*240


Exposure time per frame
3 ms


Gain
1


working distance
1.5~4 m


Aperture
2


Length of the video loop
3*1 second (split into 3 part to calculate std



and average every 3 continuous frames)









Four flow cases were measured by LSCI using the setup in FIG. 33 and each situation was performed three times to test the repeatability. The flow cases tested are “tube is clamped”, “pump is reading 100 mL”, “pump is reading 500 mL” and “pump is reading 1000 mL.” Table 16 set out below summarized the blood flows measured and the results for each situation.







TABLE 16







(Std is standard deviation, L is the inversed speckle contrast


see Equation 6 for details)











flow rate reading

Corresponding




from pump
flow speed
LAD flow rate
L
std of L


(mL/min)
(cm/min)
(mL/min)
(blood)
(blood)












Tube clamped
35
2











 0
0
0
84
1


100
140
18
144
2


200
281
35
153
4


300
421
53
156
6


400
562
71
164
6


500
702
88
168
4


600
842
106
174
3


700
983
123
179
3


800
1123
141
180
10


900
1264
159
188
1


1000 
1404
176
191
4









FIGS. 34A through 34D illustrate resultant images obtained for the “tube is clamped” case. FIG. 34A is an averaged image of 90 frames for the “tube is clamped” case; FIG. 34B is a vertical line profile image in the middle of inverted speckle contrast image for the “tube is clamped” case; FIG. 34C is an inverted speckle contrast image for the “tube is clamped” case; and FIG. 34D is a false-color inverted speckle contrast image for the “tube is clamped” case.
FIGS. 35A through 35D illustrate resultant images obtained for the “pump reads 100 mL” case. FIG. 35A is an averaged image of 97 frames for the “100 mL” case; FIG. 35B is a vertical line profile in the middle of an inverted speckle contrast image for the “100 mL” case; FIG. 35C is a n inverted speckle contrast image for the “100 mL” case; and FIG. 35D is a false-color inverted speckle contrast image for the “100 mL” case.
FIGS. 36A through 36D illustrate resultant images obtained for the “pump reads 500 mL” case. FIG. 36A is an averaged image of 97 frames for the “500 mL” case; FIG. 36B is a vertical line profile image in the middle of an inverted speckle contrast image for the “500 mL” case; FIG. 36C is a n inverted speckle contrast image for the “500 mL” case; and FIG. 36D is a false-color speckle contrast image for the “500 mL” case.
FIGS. 37A through 37D illustrate resultant images obtained for the “pump reads 1000 mL” case. FIG. 37A is an averaged image of 98 frames for the “1000 mL” case; FIG. 37B is a vertical line profile image in middle of an inverted speckle contrast image for the “1000 mL” case; FIG. 37C is an inverted speckle contrast image for the “1000 mL” case; and FIG. 37D is a false-color inverted speckle contrast image for the “1000 mL” case.
FIGS. 38A through 38D are averaged images for each of the cases, “pump clamped”, “100 mL”, “500 mL”, and “1000 mL,” respectively. FIGS. 39A through 39D are colorized inverted speckle contrast images for each of the cases, “pump clamped”, “100 mL”, “500 mL”, and “1000 mL,” respectively. FIGS. 40A through 40D are vertical line profile images for each of the cases, “pump clamped”, “100 mL”, “500 mL”, and “1000 mL,” respectively.
FIG. 41 of a graph of flow speed vs. L with to the line fitting the data based on Equation (8). Table 17 set out below summarized the curve fitting parameters using Equation (8).









TABLE 17







L (1)



















L0
100



α
3.0



R
0.96










The laser speckle imaging setup illustrated in FIG. 33 is clearly able to differentiate different flow speeds of human blood. In particular, when the reading from the pump is zero, the LSCI image still has contrast related to flow speed as illustrated in FIGS. 43A through 43D. Until the tube is clamped, the contrast disappears as shown in FIGS. 44A through 44D. Thus, when the flow speed is very low, is the pump reading still accurate? The power of the speed term v in Equation (8) after curve fitting was found not equal to 0.5, which is different from the Intralipid solution as discussed above with respect to FIGS. 21-32. If the data related to “no flow” case is discarded, one can see that the rest of data fit the Equation (8) well, the result is summarized in the graph of FIG. 42 illustrating flow speed vs. L with Equation (8) after the baseline removed. Thus, the Equation (6) with the power factor of 0.5 will fit the data well. Table 18 set out below summarizes the curve fitting parameters.









TABLE 18







L (1)



















L0
120



α
1.86



R
0.994










As discussed above, the data obtained using the speckle images discussed above can be verified using hemodynamic modeling as will be discussed with respect to FIGS. 45 through 47. The Navier-Stokes equation provides the governing equation for fluid dynamics.
The Navier-Stokes equation is set out below in Equations (9) and (10):




  
    
      
        
          ρ
          ·
          
            (
            
              
                
                  ∂
                  u
                
                
                  ∂
                  t
                
              
              +
              
                u
                ⁢
                
                  ∇
                  
                    ·
                    u
                  
                
              
            
            )
          
        
        =
        
          
            -
            
              ∇
              p
            
          
          +
          
            μ
            ·
            
              
                ∇
                2
              
              ⁢
              u
            
          
          +
          F
        
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        
          (
          9
          )
        
      
    
  
  
    
      
        
          
            
              ∂
              ρ
            
            
              ∂
              t
            
          
          +
          
            ∇
            
              ·
              
                (
                
                  ρ
                  ⁢
                  
                    
                  
                  ⁢
                  u
                
                )
              
            
          
        
        =
        0
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        
          (
          10
          )
        
      
    
  




where ρ is the density (kg/m3), u is the velocity vector (m/s), p is the pressure (m/s), F is the volume force vector (N/m3) and m is the viscosity.
Solving the Navier-Stokes equations produces a velocity field, i.e. a distribution of fluid velocity in space and time. Once this velocity field is obtained, other quantities of interest, such as flow rate and drag force, can be calculated. These calculated quantities can then be compared to the experimental data obtained using the speckle images discussed above to validate the data.
Furthermore, these quantities may be calculated before a procedure is performed on a subject and after a procedure is performed on the subject to verify that the procedure was successful. For example, measurements, images and calculations discussed above may be performed before a subject undergoes a carotid endarterectomy (CEA), which is a surgical procedure used to reduce the likelihood, or possibly prevent stroke, by correcting stenosis (narrowing) in the common carotid artery. Endarterectomy is the removal of material on the inside (end-) of an artery. A blood vessel 4501 including a narrowing 4597 is illustrated, for example, in FIG. 45. A velocity field/profile may be calculated at various point in the blood vessel as illustrated in FIG. 46 before and after the carotid endarterectomy to correct the narrowing 4597. Thus, by comparing the measurements/quantities before and after the procedure, the success of the procedure may be determined. FIG. 47 is a graph illustrating fluid rate estimate along the diameter of the blood vessel 4501 illustrated in FIGS. 45 and 46.
Although uses of the methods and systems discussed herein are discussed specifically with respect to carotid endarterectomies, it will be understood that embodiments of the present inventive concept are not limited to this configuration. For example, embodiments of the present inventive concept may be used for the brain, colon, or any other applicable part of the subject that may benefit from the techniques discussed herein.
Operations for a non-invasive method for measuring blood flow in principal vessels of a subject in accordance with some embodiments will be discussed with respect to FIG. 48. Operations begin at block 4816 by illuminating a region of interest with a coherent light source, wherein the coherent light source has a wavelength of from about 600 nm to about 1100 nm. At least two speckle images of the region of interest are sequentially acquired during a fixed time period (block 4826). Temporal and spatial variation of pixel intensities of the at least two acquired speckle images are electrically evaluated to determine spatial distribution of blood flow speed in the principal vessels and perfusion distribution in tissue in the region of interest (block 4836).
A velocity field for the region of interest is calculated (block 4846). In some embodiments, the velocity field is calculated using equations (9) and (10) set out below. Blood flow speed in the region of interest based on the calculated velocity field is calculated (block 4856). The calculated blood flow speed in the region of interest is compared to the blood flow speed determined using the acquired at least two speckle images of the region of interest to verify results obtained using the at least two speckle images (block 4866). Thus, embodiments of the present inventive concept may be used to verify experimental results as will be discussed further below.
It will be understood that the operations of blocks 4816, 4826, 4836, 4846, 4856 and 4866 may be performed before and after a procedure performed on the subject. The results before and after the procedure may be compared to verify the success of the procedure in the subject.
The foregoing is illustrative of the present inventive concept and is not to be construed as limiting thereof. Although a few exemplary embodiments of the present inventive concept have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this inventive concept. Accordingly, all such modifications are intended to be included within the scope of the inventive concept as defined in the claims. In the claims, means-plus-function clauses, where used, are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Therefore, it is to be understood that the foregoing is illustrative of the present inventive concept and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims. The inventive concept is defined by the following claims, with equivalents of the claims to be included therein.

## Claims

1. A non-invasive method for measuring blood flow distribution in principal vessels of a heart of a subject, the method comprising:
passively illuminating a region of interest in the heart with a coherent light source, wherein the coherent light source has a wavelength of from about 600 nm to about 1100 nm and a field of view including the region of interest is at least about 2 square centimeters;
sequentially acquiring at least two speckle images of the region of interest in the heart during a fixed time period, wherein sequentially acquiring the at least two speckle images comprises acquiring the at least two speckle images in synchronization with motion of the heart of the subject and the acquisition being triggered by the motion of the heart of the subject; and
electronically processing the at least two acquired speckle images based on the temporal variation of the pixel intensities in the at least two acquired speckle images to generate a laser speckle contrast imaging (LSCI) image and determine spatial distribution of blood flow speed in the principal vessels and quantify perfusion distribution in tissue in the region of interest in the heart from the LSCI image.

2. The method of claim 1, wherein sequentially acquiring the at least two speckle images in synchronization with motion of the heart of the subject further comprises:
electronically monitoring an EKG cardiac cycle of the subject to identify a pattern in the EKG cardiac cycle that differentiates between at least systolic and diastolic phases; and
electronically synchronizing acquisition of speckle images with the EKG signals.

3. The method of claim 1, wherein the sequentially acquiring and the electronically evaluating are performed before a procedure performed on a subject and after the procedure performed on the subject, the method further comprising:
comparing the determined blood flow speed in the principal vessels and perfusion distribution in tissue in the region of interest in the heart before the procedure with the determined blood flow speed in the principal vessels and perfusion distribution in tissue in the region of interest in the heart after the procedure to access success of the procedure.

4. The method of claim 1, further comprising:
quantification of tissue perfusion by calculating blood flow rate distribution in the region of interest in the heart based on a calculated velocity field; and
comparing the calculated blood flows speed in the region of interest to the blood flow speed determined using the acquired at least two speckle images of the region of interest in the heart to verify results obtained using the at least two speckle images.

5. The method of claim 4, wherein the fields of velocity and flow rate are calculated based on the following equations with appropriate boundary and initial conditions:



  
    
      
        ρ
        ·
        
          (
          
            
              
                ∂
                u
              
              
                ∂
                t
              
            
            +
            
              u
              ⁢
              
                ∇
                
                  ·
                  u
                
              
            
          
          )
        
      
      =
      
        
          -
          
            ∇
            p
          
        
        +
        
          μ
          ·
          
            
              ∇
              2
            
            ⁢
            u
          
        
        +
        F
      
    
    ,
    and
  




  
    
      
        
          
            ∂
            ρ
          
          
            ∂
            t
          
        
        +
        
          ∇
          
            ·
            
              (
              
                ρ
                ⁢
                
                  
                
                ⁢
                u
              
              )
            
          
        
      
      =
      0
    
    ;
  



wherein ρ is the fluid density (kg/m3), u is the velocity vector (m/s), p is the pressure (m/s), F is the volume force vector (N/m3) and μ is the viscosity.

6. The method of claim 1, wherein the coherent light source has a wavelength of from about 600 nm to about 1100 nm and allows relatively deep penetration of light into tissues to thereby allow an accurate determination of blood flow speed in the principal vessels and the perfusion distribution under surface.

7. The method of claim 1, wherein the coherent light source comprises a laser configured to illuminate the region of interest with a substantially constant intensity.

8. The method of claim 7, wherein the laser has a fixed or variable wavelength of from about 600 nm to about 1100 nm.

9. The method of claim 7, wherein the laser generates an output beam having a substantially constant intensity within a field-of-view (FOV) of an imaging unit.

10. The method of claim 7, wherein the laser comprises a low power and continuous-wave laser such that the subject does not require any protective apparatus to shield the subject from effects of the laser.

11. The method of claim 7, wherein the laser produces a single beam of light of a wavelength within a spectral region from the ultraviolet to the infrared.

12. The method of claim 11, wherein the sequentially acquiring comprises sequentially acquiring from about 50 to about 1000 speckle images using the camera during the fixed time period of from about 1 ms to about 200 ms.

13. The method of claim 12, wherein sequentially acquiring comprises acquiring from about 200 to about 500 speckle images during the fixed time period.

14. The method of claim 11, wherein the fixed time period is selected based on in situ acquisition of blood flow speed of the subject in the region of interest.

15. A non-invasive method for measuring blood flow distribution in principal vessels of a subject, the method comprising:
passively illuminating a region of interest with a coherent light source, wherein the coherent light source has a wavelength of from about 600 nm to about 1100 nm and a field of view including the region of interest is at least about 2 square centimeters;
sequentially acquiring at least two speckle images of the region of interest during a fixed time period;
electronically processing the at least two acquired speckle images based on the temporal variation of the pixel intensities in the at least two acquired speckle images to generate a laser speckle contrast imaging (LSCI) image and determine spatial distribution of blood flow speed in the principal vessels and quantify perfusion distribution in tissue in the region of interest from the LSCI image;
calculating a velocity field for the region of interest;
calculating blood flow rate distribution in the region of interest based on the calculated velocity field; and
comparing the calculated blood flow speed in the region of interest to the blood flow speed determined using the acquired at least two speckle images of the region of interest to verify results obtained using the at least two speckle images.

16. The method of claim 15, wherein the fields of velocity and flow rate are calculated based on the following equations with appropriate boundary and initial conditions:



  
    
      
        ρ
        ·
        
          (
          
            
              
                ∂
                u
              
              
                ∂
                t
              
            
            +
            
              u
              ⁢
              
                ∇
                
                  ·
                  u
                
              
            
          
          )
        
      
      =
      
        
          -
          
            ∇
            p
          
        
        +
        
          μ
          ·
          
            
              ∇
              2
            
            ⁢
            u
          
        
        +
        F
      
    
    ,
    and
  




  
    
      
        
          
            ∂
            ρ
          
          
            ∂
            t
          
        
        +
        
          ∇
          
            ·
            
              (
              
                ρ
                ⁢
                
                  
                
                ⁢
                u
              
              )
            
          
        
      
      =
      0
    
    ;
  



wherein ρ is the fluid density (kg/m3), u is the velocity vector (m/s), p is the pressure (m/s), F is the volume force vector (N/m3) and μ is the viscosity.

17. The method of claim 16, wherein the sequentially acquiring, the electronically evaluating, calculating the velocity field, calculating the blood flow rate based on the calculated velocity field and the comparing are performed before a procedure performed on a subject and after the procedure performed on the subject, the method further comprising comparing the results before and after the procedure to access success of the procedure.

18. A non-invasive system for measuring blood flow distribution in principal vessels in a heart of a subject, the system comprising:
a coherent light source configured to passively illuminate a region of interest in the heart of the subject, the coherent light source having a wavelength of from about 600 nm to about 1100 and a field of view including the region of interest is at least about 2 square centimeters;
a camera in communication with the coherent light source that is configured to sequentially acquire at least two speckle images of the region of interest in the heart during a fixed time period, wherein acquisition of the at least two speckle images is synchronized with and trigger by motion of the heart of the subject; and
a data processing circuit configured to evaluate the temporal variation of the pixel intensities in the at least two acquired speckle images to generate a laser speckle contrast imaging (LSCI) image and determine spatial distribution of blood flow speed in the principal vessels and quantify perfusion distribution in tissue in the region of interest in the heart from the LSCI image.

19. The system of claim 18, wherein the data processing circuit is further configured to:
electronically monitor an EKG cardiac cycle of the subject to identify a pattern in the EKG cardiac cycle that differentiates between at least systolic and diastolic phases; and
electronically synchronize acquisition of speckle images with the EKG signals.

20. The system of claim 18, further comprising a modeling module configured to:
calculate a velocity field for the region of interest in the heart;
calculate blood flow rate in the region of interest in the heart based on the calculated velocity field; and
compare the calculated blood flow in the region of interest to the blood flow speed determined using the acquired at least two speckle images of the region of interest in the heart to verify results obtained using the at least two speckle images.

21. The system of claim 20, wherein modeling module is configured to calculate the fields of velocity and rate based on the following equations with appropriate boundary and initial conditions:



  
    
      ρ
      ·
      
        (
        
          
            
              ∂
              u
            
            
              ∂
              t
            
          
          +
          
            u
            ⁢
            
              ∇
              
                ·
                u
              
            
          
        
        )
      
    
    =
    
      
        -
        
          ∇
          p
        
      
      +
      
        μ
        ·
        
          
            ∇
            2
          
          ⁢
          u
        
      
      +
      
        
          F
          ,
        
        ⁢
        
          
        
        ⁢
        and
      
    
  




  
    
      
        
          
            ∂
            ρ
          
          
            ∂
            t
          
        
        +
        
          ∇
          
            ·
            
              (
              
                ρ
                ⁢
                
                  
                
                ⁢
                u
              
              )
            
          
        
      
      =
      0
    
    ;
  



wherein ρ is the fluid density (kg/m3), u is the velocity vector (m/s), p is the pressure (m/s), F is the volume force vector (N/m3) and μ is the viscosity.

22. The system of claim 18, wherein the coherent light source has a wavelength of from about 600 nm to about 1100 nm and is configured to allow deep penetration of light into tissues and to provide an accurate determination of blood flow speed in the principal vessels and the perfusion distribution under surface.

23. The system of claim 18, wherein the coherent light source comprises a laser configured to illuminate the region of interest with a substantially constant intensity.

24. The system of claim 23, wherein the laser has a fixed or variable wavelength of from about 600 nm to about 1100 nm.

25. The system of claim 23, wherein the laser is configured to illuminate the region of interest with a laser beam having substantially constant intensity within a field-of-view (FOV) of an imaging unit.

26. The system of claim 23, wherein the laser comprises a low power and continuous-wave laser such that the subject does not require any protective apparatus to shield the subject from effects of the laser.

27. The system of claim 23, wherein the laser is configured to produce a single beam of light in a wavelength within a spectral region from the ultraviolet to the infrared.

28. The system of claim 18, wherein the camera is configured to acquire from about 50 to about 1000 speckle images during the fixed time period of from about 1 ms to about 200 ms.

29. The system of claim 28, wherein the camera is configured to acquire from about 200 to about 500 speckle images during the fixed time period.

30. The system of claim 18, wherein the fixed time period is selected based on in situ acquisition of blood flow speed of the subject in the region of interest.

31. The system of claim 18, wherein the camera is configured to acquire at least two speckle images in synchronization with motion of a heart of the subject.

32. A computer program product for measuring blood flow distribution in principal vessels in a heart of a subject, the computer program product comprising:
a non-transitory computer-readable storage medium having computer-readable program code embodied in the medium, the computer-readable program code comprising:
computer readable program code configured to electronically evaluate temporal variation of the pixel intensities in the at least two acquired speckle images to generate a laser speckle contrast imaging (LSCI) image and determine spatial distribution of blood flow speed in the principal vessels and perfusion distribution in tissue in a region of interest in the heart from the LSCI image, wherein and a field of view including the region of interest is at least about 2 square centimeters and the at least two speckle images are sequentially acquired using a camera during a fixed time period when the region of interest of the subject is passively illuminated by a coherent light source having a wavelength of from about 600 nm to about 1100 nm; and
computer readable program code configured to sequentially acquire the at least two speckle images in synchronization with motion of the heart of the subject trigger the acquisition responsive to the motion of the heart of the subject.

33. The computer program product of claim 32, further comprising:
computer readable program code configured to calculate a velocity field for the region of interest in the heart;
computer readable program code configured to calculate blood flow rate in the region of interest in the heart based on the calculated velocity field; and
computer readable program code configured to compare the calculated blood flow speed in the region of interest to the blood flow speed determined using the acquired at least two speckle images of the region of interest in the heart to verify results obtained using the at least two speckle images.

34. The computer readable program code of claim 33, wherein the computer readable program code configured to calculate the velocity field further comprises computer readable program code configured to calculate the fields of velocity and rate based on the following equations with appropriate boundary and initial conditions:



  
    
      ρ
      ·
      
        (
        
          
            
              ∂
              u
            
            
              ∂
              t
            
          
          +
          
            u
            ⁢
            
              ∇
              
                ·
                u
              
            
          
        
        )
      
    
    =
    
      
        -
        
          ∇
          p
        
      
      +
      
        μ
        ·
        
          
            ∇
            2
          
          ⁢
          
            u
            ,
          
        
      
      +
      
        F
        ⁢
        
          
        
        ⁢
        and
      
    
  




  
    
      
        
          
            ∂
            ρ
          
          
            ∂
            t
          
        
        +
        
          ∇
          
            ·
            
              (
              
                ρ
                ⁢
                
                  
                
                ⁢
                u
              
              )
            
          
        
      
      =
      0
    
    ;
  



wherein ρ is the fluid density (kg/m3), u is the velocity vector (m/s), p is the pressure (m/s), F is the volume force vector (N/m3) and μ is the viscosity.

35. The method of claim 1, wherein sequentially acquiring the at least two speckle images comprises:
triggering acquisition of the at least two speckle images with the motion of the heart of the subject; and
synchronizing in real time the triggered acquisition of the at least two speckle images with the motion of the heart of the subject.

36. The method of claim 35, wherein triggering further comprises recognizing a pattern in the motion of the heart of the subject and differentiating between diastolic and systolic phases of the heart.

37. The method of claim 1, wherein acquiring the at least two speckle images in synchronization with motion of the heart of the subject further comprises:
calculating a surrogate EKG signal from acquired images at different phases of a cardiac cycle; and
electronically synchronizing acquisition of speckle images with the surrogate EKG signal.

38. The method of claim 1, wherein the motion of the heart comprises physical motion of the heart.