Assessment of Infarct Size and Severity by Quantitative Myocardial SPECT: Results from a Multicenter Study Using a Cardiac Phantom

The aim of this study was to determine the reproducibility of measurements of the size and severity of myocardial defects from 99mTc sestamibi cardiac phantom studies performed on multiple different gamma camera systems. A total of 250 gamma camera systems were evaluated over a 5-y period as part of the validation process of multiple multicenter trials. Each laboratory performed 9 acquisitions of a cardiac phantom. Small myocardial defects (0%-30% of myocardial mass) were placed in the inferobasal region, whereas larger defects (40%-70%) were located in the anterior wall. Five representative short-axis slices were analyzed to determine defect size and severity (i.e., contrast in defect region) using circumferential short-axis count profiles. Defect size and severity were analyzed as a function of the type of collimator, gamma camera system, and type of orbit (180degrees versus 360degrees). Of the 250 systems, image data were acquired correctly and showed an acceptable correlation between true and measured defect size in 198 systems. For these systems, the slope of the regression line between true and measured defect size was 1.03 +/- 0.03, with an average absolute error in estimating defect size of 1.7% +/- 0.5% and a correlation coefficient r = 0.99 +/- 0.01. Results were independent of the gamma camera system, type of collimator, and orbit. Contrast in the defect region (minimum count/maximum count) showed a small dependence on collimator resolution and pixel size but was altered significantly by the type of acquisition orbit, with a 360 degrees orbit showing better contrast for defects located in the inferobasal wall than a 180degrees orbit. Measurement of defect size is independent of the gamma camera system, type of collimator, and orbit. Contrast in small defects located in the inferobasal wall of the heart is affected significantly by the type of acquisition orbit but not by the type of collimator.