PERFORMANCE OF A SINGLE-CRYSTAL DIGITAL GAMMA-CAMERA FOR 1ST PASS CARDIAC STUDIES

First pass radionuclide angiocardiography (FPRNA) has gained increasing interest because of the development of new Tc-99m-labelled perfusion agents and of new Os-191/Ir-191m generator systems. The aim of the study was to evaluate the performance capacities of a small field of view single crystal digital gamma camera for Tc-99m and Ir-191m at high count rates. The camera dead time for Tc-99m (window 30%) was well corrected up to 300 kcps in fast acquisition mode using the relative decrease of a small shielded reference source. Using the decaying activity method for Ir-191m the non-linearity response of the gamma camera was corrected by an Os-191 reference source up to 210 kcps at 70 keV, 75 kcps at 129 keV and 320 kcps including both peaks. Saturation count rates were respectively 270 kcps, 150 kcps and 420 kcps and high count rate resolution (FWHM) 9.0, 7.3 and 10.3 mm. Since the accuracy of first pass measurements is more sensitive to count rate than to spatial resolution the 50-150 keV window was chosen for clinical studies. In data obtained from 32 ECG gated FPRNA patient studies, the whole field of view count rate during the left ventricular phase ranged from 100 to 250 kcps with 80 to 120 mCi (2960-4400 MBq) of Ir-191m and 100 to 180 kcps with 20 to 25 mCi (750-925 MBq) of Tc-99m red blood cells permitting for both tracers accurate non-linearity correction.