Method and software for improving coronary calcium scoring consistency

#The present invention generally relates to medical imaging software, methods, and databases. Specifically, the present invention relates to improving machine-to-machine and temporal (e.g., inter and intra-machine) consistency of coronary calcium scoring by using an algorithm that can either sharpen or smooth the image, so as to return the spatial resolution of the processed image to a certain reference value.

#Coronary artery calcium quantitation is a major focus in the effort to assess risk for coronary heart disease, to monitor progression of plaque development, and to potentially assess therapies and interventions designed to reduce mortality from coronary heart disease. (See Rumberger J. A. et al, “Electron Beam Computed Tomographic Coronary Calcium Scanning: A Review and Guidelines for Use in Asymptomatic Persons,” Mayo Clinic Proc. 1999; 74:243–252 and Schmermund A., et al, “An Algorithm for Noninvasive Identification of Angiographic Three-Vessel and/or left Main Coronary Artery Disease in Symptomatic Patients,” J. Am. Coll. Cardiology 1999; 33:444–452, the complete disclosure of which are incorporated herein by reference). Although the current orthodoxy is that the rupture of soft plaque and subsequent thrombus formation is the major precursor of acute coronary events, in most individuals it is believed that coronary calcium burden is also a valid surrogate or indicator of total plaque burden, including soft plaque.

#The assessment of risk from coronary calcium is generally a two-step process: First, calcium burden is quantitated by a “scoring” algorithm, most commonly with the Agatston scale. (See Agatston A. S. et al, “Quantification of Coronary Artery Calcium Using Ultrafast Computed Tomography,” J. Am. Coll. Cardiology 1990; 15:827–832, the complete disclosure of which is incorporated herein by reference). Second, the measured calcium burden, age, and gender of the individual are used to rank the individual against his or her age-matched cohort.

#FIG. 1 illustrates a peak signal for a 1 mm-diameter cylindrical lesion spanning a whole slice as a function of CT scanner resolution;

#FIG. 2 illustrates an exemplary system of the present invention;

#FIG. 3 illustrates an exemplary computer system of the present invention;

#The present invention provides methods, systems, and software for monitoring the spatial resolution of an imaging device so as to improve the consistency of calcium scoring. A filtering algorithm can be used to sharpen or smooth the images obtained by the imaging device so as to alter the spatial resolution of the image to that of a predetermined reference value so as to allow for a more accurate comparison to other filtered images and data stored in a calcium scoring database which have a similar reference spatial resolution.

#In calcium scoring a patient, a supine subject is typically asked to hold their breath and multiple scans can be performed while the table moves the subject through the x-ray beam. In an electron beam CT scanner (EBCT) an ECG signal is used to trigger the scanner acquisition at desired points in the cardiac cycle, with or without overlap of slices (prospective gating). In a helical CT scanner, there typically is a higher degree of overlap, and the scanner may be triggered so as to obtain data only during certain parts of the cardiac cycle (which requires that images be reconstructed from data obtained during different heartbeats, and in multi-detector scanners, from different detector rows), or the scanner can operate continuously and the data will be reconstructed and sorted afterwards (retrospective gating). One exemplary retrospective gating methodology is described in co-pending Provisional Patent Application Ser. No. 60/306,311 filed Jul. 17, 2001, the complete disclosure of which is incorporated herein by reference.

#The ability to quantify the amount of calcium in a lesion depends on two major factors. The first factor is the spatial resolution of the image, which can be defined as a full width at half maximum or “FWHM” of the device. The full width half maximum is the full width of a spectral band at a height equal to half of the height at the band maximum. The FWHM of the CT scanners will generally be between approximately 1 mm and 2 mm FWHM. It should be appreciated however, that the present invention is equally applicable to CT scanners and other imaging devices having a FWHM outside of this range, however, it is generally not desirable to have large FWHM and blurred images.