Physical aspects of cardiac scanning with a block detector positron tomograph

Physical aspects relating to cardiac scanning are described for an eight ring (15 plane) positron tomograph consisting of BGO block detectors (CTI/Siemens 931-08/12). Performance parameters were derived from a cylindrical heart phantom having a "myocardial" wall of thickness varying from 3 mm to 27 mm. This phantom was inserted into a chest phantom consisting of simulated chest wall, lungs, and arms. Recovery coefficients for myocardial thicknesses of 10 mm and 15 mm were 0.75 and 0.9, respectively. Division by the transmission minus "blood pool" (extravascular density) image was found to give a variation of corrected myocardial counts within +/- 5% when transmission data were smoothed. The on-line dead time correction algorithm was found to be accurate to within 5% up to 20 mCi (740 MBq) in the axial field of view (FOV) (10.8 cm) in the central chamber of the heart phantom. However, the correction factor at this rate is approximately 3, which would imply poor use of administered dose. Counts in the image due to scatter are approximately 2% in the (cold) central cavity of the heart phantom relative to counts/pixel in the active myocardium. The presence of phantom arms in the FOV was found to have only a small effect on mean pixel counts and noise in the heart phantom image, as did movement of the arms within a reasonable range.