Abstract:
A method and system for performing coronary artery calcification scoring using an imaging system including obtaining image data; examining the image data so as to identify a plurality of discrete pixel elements, wherein each of the pixel elements includes a pixel value; dividing the pixel elements into a scorable region so as to create a plurality of scorable pixel elements; processing the scorable pixel elements so as to identify a center scorable pixel element and determine a median pixel value; and replacing the pixel value for the center scorable pixel element with the median pixel value. Also claimed is a medium encoded with a machine-readable computer program code for performing coronary artery calcification scoring, the medium including instructions for causing controller to implement the aforementioned method.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates generally to a method and system for performing coronary artery calcification scoring and more particularly to a method and system for performing coronary artery calcification scoring using an imaging system.  
           [0002]    In at least one known computed tomography (CT) imaging system configuration, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system, wherein the X-Y plane is generally referred to as an “imaging plane”. An array of radiation detectors, wherein each radiation detector includes a detector element, are within the CT system so as to received this fan-shaped beam. An object, such as a patient, is disposed within the imaging plane so as to be subjected to the x-ray beam wherein the x-ray beam passes through the object. As the x-ray beam passes through the object being imaged, the x-ray beam becomes attenuated before impinging upon the array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is responsive to the attenuation of the x-ray beam by the object, wherein each detector element produces a separate electrical signal responsive to the beam attenuation at the detector element location. These electrical signals are referred to as x-ray attenuation measurements.  
           [0003]    In addition, the x-ray source and the detector array may be rotated, with a gantry within the imaging plane, around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a “view”. A “scan” of the object comprises a set of views made at different gantry angles during one revolution of the x-ray source and the detector array. In an axial scan, the projection data is processed so as to construct an image that corresponds to a two-dimensional slice taken through the object.  
           [0004]    One method for reconstructing an image from a set of projection data is referred to as the “filtered back-projection technique”. This process converts the attenuation measurements from a scan into discrete integers, ranging from −2047 to +2047, called “CT numbers” or “Hounsfield Units” (HU). These HU&#39;s are used to control the brightness of a corresponding pixel on a cathode ray tube or a computer screen display in a manner responsive to the attenuation measurements. For example, an attenuation measurement for air may convert into an integer value of −2047 HU&#39;s (corresponding to a dark pixel) and an attenuation measurement for very dense bone matter may convert into an integer value of +2000 (corresponding to a bright pixel), whereas an attenuation measurement for water may convert into an integer value of OHU&#39;s (corresponding to a gray pixel). This integer conversion, or “scoring” allows a physician or a technician to determine the density of matter based on the intensity of the computer display.  
           [0005]    However, because the objects to be imaged may vary in size and mass, undesirable signal anomalies, such as noise, may be present in the constructed image. For example, in order to perform a coronary artery scan of a patient, the incident x-ray beam needs to have enough power to penetrate the patients&#39; body, become attenuated by different masses within the patients&#39; body and have still have enough energy remaining so as to allow the detector array to receive the x-ray beam and generate accurate signals responsive to the beam attenuation. If the patient is of average size, an accurate image may be constructed using a standard dose of x-ray energy. However, as the patient increases in size and mass, the x-ray energy needed to construct an accurate image increases as well, thus requiring larger size patients to be exposed to larger amounts of x-ray energy. If the beam energy is not increased for larger patients&#39; a large amount of noise may be present in the images and in some situations the images cannot be used for calcium scoring. Therefore, the x-ray beam intensity must be increased to compensate for the larger body mass, which is undesirable because of the health consequences of being exposed to large amounts of x-ray radiation. This is also undesirable because of the increased energy costs to produce larger x-ray beam intensities.  
           [0006]    Therefore, there is a need for a low-cost method for reliably performing calcification scoring wherein the method is easily and inexpensively implemented and wherein the method would expose patients&#39; to lower doses of x-ray radiation then is currently occurring. The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.  
         SUMMARY OF INVENTION  
         [0007]    The above discussed and other drawbacks and deficiencies are overcome or alleviated by a method for performing coronary artery calcification scoring using an imaging system comprising: obtaining image data; examining the image data so as to identify a plurality of discrete pixel elements, wherein each of the pixel elements includes a pixel value; dividing the pixel elements into a scorable region so as to create a plurality of scorable pixel elements; processing the scorable pixel elements so as to identify a center scorable pixel element and determine a median pixel value; and replacing the pixel value for the center scorable pixel element with the median pixel value.  
           [0008]    In an alternative embodiment a system for performing coronary artery calcification scoring comprising: a gantry having an x-ray source and a radiation detector array, wherein the gantry defines a patient cavity and wherein said x-ray source and the radiation detector array are rotatingly associated with the gantry so as to be separated by the patient cavity; a patient support structure movingly associated with the gantry so as to allow communication with the patient cavity; and a processing device having an enhancing filter, wherein the enhancing filter, obtains image data; examines the image data so as to identify a plurality of discrete pixel elements, wherein each of the pixel elements includes a pixel value; divides the pixel elements into a scorable region so as to create a plurality of scorable pixel elements; processes the scorable pixel elements so as to identify a center scorable pixel element and determine a median pixel value; and replaces the pixel value for the center scorable pixel element with the median pixel value.  
           [0009]    In another alternative embodiment, a medium encoded with a machine-readable computer program code for performing coronary artery calcification scoring, the medium including instructions for causing controller to implement the aforementioned method.  
           [0010]    The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0011]    Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures:  
         [0012]    [0012]FIG. 1 is a perspective view of a CT imaging system and a patient disposed for imaging in accordance with an exemplary embodiment;  
         [0013]    [0013]FIG. 2 is a block schematic diagram of a CT imaging system in accordance with an exemplary embodiment;  
         [0014]    [0014]FIG. 3 is a flow diagram describing a method for performing coronary artery calcification scoring in accordance with an exemplary embodiment;  
         [0015]    [0015]FIG. 4 illustrates an output device that includes a display screen having a plurality of discrete pixel element in accordance with an exemplary embodiment;  
         [0016]    [0016]FIG. 5 illustrates a 3×3 matrix having scorable pixel elements with individual pixel values in accordance with an exemplary embodiment;  
         [0017]    [0017]FIG. 6 illustrates a 3×3 matrix having scorable pixel elements with the center scorable pixel element after pixel value replacement in accordance with an exemplary embodiment;  
         [0018]    [0018]FIG. 7 illustrates a 3×3 matrix wherein the center scorable pixel element is undergoing pixel value replacement in accordance with an exemplary embodiment; and  
         [0019]    [0019]FIG. 8 illustrates a 3×3 matrix wherein the center scorable pixel element is undergoing pixel value replacement in accordance with an alternative embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0020]    Referring to FIG. 1 and FIG. 2 a representative CT imaging system  1  is shown and preferably includes a gantry  2  having an x-ray source  4 , a radiation detector array  6 , a patient support structure  8  and a patient cavity  10 , wherein x-ray source  4  and radiation detector array  6  are opposingly disposed so as to be separated by patient cavity  10 . A patient  12  is preferably dispose upon patient support structure  8  which is then disposed within patient cavity  10 . X-ray source  4  projects an x-ray beam  14  toward radiation detector array  6  so as to pass through patient  12 . X-ray beam  6  is preferably collimated by a collimate (not shown) so as to lie within an X-Y plane of a Cartesian coordinate system referred to as an “imaging plane”. After passing through and becoming attenuated by patient  12 , attenuated x-ray beam  16  is preferably received by radiation detector array  6 . Radiation detector array  6  preferably includes a plurality of detector elements  18  wherein each of said detector elements  18  receives attenuated x-ray beam  16  and produces an electrical signal responsive to the intensity of attenuated x-ray beam  16 .  
         [0021]    In addition, x-ray source  4  and radiation detector array  6  are preferably rotatingly disposed relative to gantry  2  and patient support structure  8 , so as to allow x-ray source  4  and radiation detector array  6  to rotate around patient support structure  8  when patient support structure  8  is disposed within patient cavity  10 . X-ray projection data is obtained by rotating x-ray source  4  and radiation detector array  6  around patient  10  during a scan. X-ray source  4  and radiation detector array  6  are preferably communicated with a control mechanism  20  associated with CT imaging system  1 . Control mechanism  20  preferably controls the rotation and operation of x-ray source  4  and radiation detector array  6 .  
         [0022]    Control mechanism  20  preferably includes an x-ray controller  22  communicated with x-ray source  4 , a gantry motor controller  24 , and a data acquisition system (DAS)  26  communicated with radiation detector array  6 , wherein x-ray controller  22  provides power and timing signals to x-ray source  4 , gantry motor controller  24  controls the rotational speed and angular position of x-ray source  4  and radiation detector array  6  and DAS  26  receives the electrical signal data produced by detector elements  18  and converts this data into digital signals for subsequent processing. CT imaging system  1  also preferably includes an image reconstruction device  28 , a data storage device  30  and a processing device  32 , wherein processing device  32  is communicated with image reconstruction device  28 , gantry motor controller  24 , x-ray controller  22 , data storage device  30 , an input device  34  and an output device  36 . Moreover, CT imaging system  1  also preferably includes a table controller  38  communicated with processing device  32  and patient support structure  8 , so as to control the position of patient support structure  8  relative to patient cavity  10 .  
         [0023]    In accordance with an exemplary embodiment, patient  12  is preferably disposed on patient support structure  8 , which is then positioned by an operator via processing device  32  so as to be disposed within patient cavity  10 . Gantry motor controller  24  is operated via processing device  32  so as to cause x-ray source  4  and radiation detector array  6  to rotate relative to patient  12 . X-ray controller  22  is operated via processing device  32  so as to cause x-ray source  4  to emit and project a collimated x-ray beam  14  toward radiation detector array  6  and hence toward patient  12 . X-ray beam  14  passes through patient  12  so as to create an attenuated x-ray beam  16 , which is received by radiation detector array  6 .  
         [0024]    Detector elements  18  receive attenuated x-ray beam  16 , produces electrical signal data responsive to the intensity of attenuated x-ray beam  16  and communicates this electrical signal data to DAS  26 . DAS  26  then converts this electrical signal data to digital signals and communicates both the digital signals and the electrical signal data to image reconstruction device  28 , which performs high-speed image reconstruction. This information is then communicated to processing device  32 , which stores the image in data storage device  30  and displays the digital signal as an image via output device  36 .  
         [0025]    In accordance with an exemplary embodiment, output device  36  preferably includes a display screen  40  having a plurality of discrete pixel elements  42 . An operator visually examines the image via output device  36  and determines if the image contains an unacceptable amount of signal noise. If the amount of signal noise is unacceptable, the operator filters out the unwanted noise by activating an enhancing filter  100  via input device  34 .  
         [0026]    Referring to the figures, a flow diagram describing a method for performing coronary artery calcification scoring is shown and discussed. In accordance with an exemplary embodiment, image data is obtained as shown in step  102 . In accordance with an exemplary embodiment, image data is preferably obtained using CT imaging system  1  and displayed to an operator as an image via output device  36  as described hereinabove. The operator then examines the image and if it is determined that an unacceptable amount of signal noise is present, the operator may apply enhancing filter  100  to the image data via input device  34 .  
         [0027]    Once enhancing filter  100  is activated, processing device  32  examines the image data so as to identify a plurality of discrete pixel elements  42  as shown in step  104 . The plurality of discrete pixel elements  42  are then preferably divided into a plurality of 3×3 matrices  200 , as shown in step  106 . In accordance with an exemplary embodiment, each 3×3 matrix  200  preferably includes nine scorable pixel elements  202  divided into three rows (I−1, I, I+1) and three columns (J−1, J, J+1), as shown in FIG. 5. In accordance with an exemplary embodiment, each of the scorable pixel elements  202  includes a pixel value responsive to the intensity of attenuated x-ray beam  16  received by detector elements  18 . Scorable pixel elements  202  are then processed so as to identify a median pixel value PV5, as shown in step  108 . This is preferably done by arranging scorable pixel elements  202  in ascending or descending order base on the pixel value of each scorable pixel element  202 . The median pixel element  204  is then determined by identifying the scorable pixel element  202  that has the fifth largest pixel value. The scorable pixel element  202  having the fifth largest pixel value is then identified as the median pixel element  204 .  
         [0028]    In accordance with an exemplary embodiment, median pixel element  204  is then examined so as to identify median pixel value PV5. This is preferably accomplished by determining the pixel value of median pixel element  204  and assigning this pixel value to median pixel value PV5. Once median pixel value PV5 is identified the pixel value for a center scorable pixel element  210  disposed in position (I, J) of 3×3 matrix  200  is replaced by median pixel value PV5 so as to create a filtered pixel matrix  208 , as shown in step  110 . Once this is complete, each of the scorable pixel elements  202  of 3×3 matrix  200  has its original pixel value and the center scorable pixel element  210  disposed in position (l, J) of 3×3 matrix  200  has a pixel value equal to median pixel value PV5, as shown in FIG. 6. The image data is then stored as a new filtered image so as to reflect this pixel value replacement and this new image information is then stored in data storage device  30 .  
         [0029]    For example, referring to FIG. 7 a 3×3 matrix  200  is shown having scorable pixel elements  202  wherein each scorable pixel element  202  includes an individual pixel value identified as pixel value 1 through pixel value 9. In this example, pixel value 1 through pixel value 9 are assigned random pixel values for demonstration purposes only. In accordance with an exemplary embodiment, pixel value 1 through pixel value 9 are in fact responsive to obtained image data. Scorable pixel elements  202  are then processed so as to identify a median pixel value PV5, as shown in step  108 . This is preferably done by arranging scorable pixel elements  202  in ascending or descending order  206 . The median pixel element  204  is then determined by identifying the scorable pixel element  202  having the fifth largest pixel value. This scorable pixel element  202  is then selected as the median pixel element  204 . The pixel value for median pixel element  204  is then selected as the median pixel value PV5, in this case PV5 equals 796 HU. The pixel value for the center scorable pixel element  210  disposed in position (I, J) of 3×3 matrix  200  is then replaced by PV5 so as to have a value of 796 HU. The pixel values of the remaining scorable pixel elements  202  in 3×3 matrix  200  retain their original pixel value, so as to create a filtered pixel matrix  208 .  
         [0030]    It should be understood that the exemplary embodiment described hereinabove may be applied using any N×N matrix, where N is an odd integer, such as 7, 9, 11. In accordance with an exemplary embodiment median pixel element  204  has the [((N*N)/2)+0.5] largest pixel value, wherein N is the number of rows and the number of columns.  
         [0031]    Referring to FIG. 8 an alternative embodiment is discussed. In accordance with an alternative embodiment, scorable pixel elements  202  are processed so as to identify a median pixel value PV5, as shown in step  108 . This is preferably done by arranging scorable pixel elements  202  in ascending or descending order base on the pixel value of each scorable pixel element  202 . The median pixel element  204  is then determined by discarding the scorable pixel elements  202  having the largest and the smallest pixel values. The pixel values of the remaining scorable pixel elements  202  are then added together. This sum is then divided by the number of remaining scorable pixel elements  202  so as to obtain an average pixel value. This average pixel value is then selected as the median pixel value PV5. In this case, PV5 is equal to 872 HU.  
         [0032]    Once median pixel value PV5 is identified the pixel value for the center scorable pixel element  210  disposed in position (I, J) of 3×3 matrix  200  is then replaced by PV5 so as to have a value of 872 HU. The pixel values of the remaining scorable pixel elements  202  in 3×3 matrix  200  retain their original pixel value, so as to create a filtered pixel matrix  208 , as shown in step  110 . Once this is complete, each of the scorable pixel elements  202  of 3×3 matrix  200  has its original pixel value and center scorable pixel element  210  has a pixel value equal to median pixel value PV5. The image data is then stored as a new filtered image so as to reflect this pixel value replacement and this new image information is then stored in data storage device  30 . It should be understood that the alternative embodiment described hereinabove may be applied using any N×N matrix, where N is an odd integer, such as 7, 9, 11.  
         [0033]    This invention advantageously allows for objects, such as a patient  12 , to be scanned using lower dose scans, thus reducing the energy required to generate larger radiation doses. In addition, potential health problems may be avoided by reducing the patients&#39; exposure to x-ray radiation to more acceptable levels.  
         [0034]    In accordance with an exemplary embodiment, enhancing filter  100  may be applied to image data obtained by any imaging system suitable to the desired end purpose, such as a magnetic resonance imaging (MRI) system.  
         [0035]    In accordance with an exemplary embodiment, processing of FIG. 3 may be implemented through processing device  32  operating in response to a computer program. In order to perform the prescribed functions and desired processing, as well as the computations therefore (e.g., the execution of fourier analysis algorithm(s), the control processes prescribed herein, and the like), the controller may include, but not be limited to, a processor(s), computer(s), memory, storage, register(s), timing, interrupt(s), communication interfaces, and input/output signal interfaces, as well as combinations comprising at least one of the foregoing. For example, the controller may include signal input signal filtering to enable accurate sampling and conversion or acquisitions of such signals from communications interfaces. It is also considered within the scope of the invention that the processing of FIG. 3 may be implemented by a controller located remotely from processing device  32 .  
         [0036]    As described above, the present invention can be embodied in the form of computer-implemented processes and apparatuses for practicing those processes. The present invention can also be embodied in the form of computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, or any other computer-readable storage medium, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. Existing systems having reprogrammable storage (e.g., flash memory) can be updated to implement the invention. The present invention can also be embodied in the form of computer program code, for example, whether stored in a storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, such as electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits.  
         [0037]    While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another.