X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1998-11-25
2001-05-15
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S015000
Reexamination Certificate
active
06233304
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to computed tomography (CT) imaging and more particularly, to generating a CT image calcification score.
In at least one known CT 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 and generally referred to as the “imaging plane”. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and 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 detector. In an axial scan, the projection data is processed to construct an image that corresponds to a two dimensional slice taken through the object.
One method for reconstructing an image from a set of projection data is referred to in the art as the filtered backprojection technique. This process converts the attenuation measurements from a scan into integers called “CT numbers” or “Hounsfield units”, which are used to control the brightness of a corresponding pixel on a cathode ray tube display.
To reduce the total scan time required for multiple slices, a “helical” scan may be performed. To perform a “helical” scan, the patient is moved while the data for the prescribed number of slices is acquired. Such a system generates a single helix from a one fan beam helical scan. The helix mapped out by the fan beam yields projection data from which images in each prescribed slice may be reconstructed. In addition to reduced scanning time, helical scanning provides other advantages such as improved image quality and better control of contrast.
In helical scanning, and as explained above, only one view of data is collected at each slice location. To reconstruct an image of a slice, the other view data for the slice is generated based on the data collected for other views. Helical reconstruction algorithms are known, and described, for example, in C. Crawford and K. King, “Computed Tomography Scanning with Simultaneous Patient Translation,”
Med. Phys
. 17(6), Nov/Dec 1990.
At least one known imaging system, known as an electron beam imaging system, is used to identify evidence of coronary atherosclerosis by detecting coronary artery calcification (CAC). In identifying CAC in the image data, a calcification level is determined. However, the electron beam imaging systems are very expensive and located in a limited number of geographical locations. To date, the use of general purpose CT imaging systems have been unable to generate stable and consistent calcification levels. One factor of the inconsistent results is the uneven and/or non-contiguous, spacing of the image data.
It would be desirable to generate a stable and consistent calcification score using image data from a general purpose CT imaging system. It also would be desirable to correct the calcification score for unevenly and/or non-contiguously spaced slices of image data.
BRIEF SUMMARY OF THE INVENTION
These and other objects may be attained by a calcification scoring algorithm that generates a calcification level using a general purpose CT imaging system. In accordance with one embodiment of the present invention, the patient is scanned to generate projection data. The projection data is processed to generate image data. The image data is then processed to determine a calcification score representative of coronary artery calcification. The calcification score is determined by identifying a scorable region in the image data, defining at least one region of interest in the scorable region, and determining a density score. After determining a calcium score for each region of interest, a total calcium score is determined by summing the calcium score from each region of interest. The total calcium level represents the calcification level of the image data.
In one embodiment, the total calcium score is corrected for non-evenly and/or non-contiguously spaced slices of image data. More specifically, where the image data represents unevenly and/or non-contiguously spaced slices of data, the algorithm weights the calcium score from each region of interest to correct for the slice spacing problem.
The above described algorithm generates a calcification score of image data generated from a general purpose CT imaging system. In addition, the algorithm corrects for non-evenly and/or non-contiguously spaced slices of image data.
REFERENCES:
patent: 4837686 (1989-06-01), Sones et al.
patent: 5864146 (1999-01-01), Karellas
patent: WO 99/09887 (1999-03-01), None
Ukai et al., “A coronary calcification diagnosis system based on helical CT images,” IEEE Nuclear Science Symposium Conference Record, Albuquerque, NM, Nov. 9-15, 1997, pp. 1208-1212.
Akinami Ohhashi et al., “Application of a neural network to automatic gray-level adjustment for medical images,” Proc of the International Joint Conf. on Neural Networks, New York, IEEE., Nov. 18, 1991 pp. 974-980.
Wilson et al., “Automated detection of microcalcifications in mammograms through application of image pixel remapping and statistical filter,” Proc. 11th IEEE Symp. on Computer-Based medical Systems, Lubbock, TX, Jun. 12-14, 1998, pp. 270-274.
Measurement of Coronary Artery Calcium with Dual-Slice Helical CT Commpared with Coronary Angiography: Evaluation of CT Scoring Methods, interobserver Variations, and Reproducibility, L. Broderick et al.,AJR Am J Roentgenaol1996 Aug;167 (2); pp. 439-444.
Cornary Artery Calcium: Alternate Methods for Accurate and Reproducible Quantitation, H. Yoon, M.D. et al,Acad Radiol1997 Oct;4(10): pp. 666-73.
Quantifications of Coronary Artery Calcium using Ultrafact Computed Tomogaphy, A. Agatston, M.D. et al.,J Am Coll Cardiol, 1990 Mar. 15;15(4): pp. 827-32.
Buchanan Robert A.
Hu Hui
Mitsa Theophano
Armstrong Teasdale LLP
Bruce David V.
Cabou Christian G.
General Electric Company
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