Experience with the EEC phantom and test procedures in two block detector scanners.
Physical performance characteristics of two modern commercial positron scanners have been compared using a phantom and test procedures defined by the Instrumentation Task Group of the EEC Concerted Action on PET Investigation of Cellular Regeneration and Degeneration. The tomographs were (a) a whole body scanner with 8 detector rings (102 cm diam) and (b) a brain scanner with 16 detector rings (76 cm diam). Each consisted of bismuth germanate block detectors. Both tomographs acquired transaxial image planes with interplane septa inserted but the unique feature of the brain devices is the ability to automatically retract septa and acquire coincidences between the two rings, thus increasing efficiency. Transaxial resolution and recovery coefficients were similar for the two devices, as expected from the equal transaxial detector widths (5.6 mm). With septa, the normalized volume sensitivity (scatter subtracted) was found to be 7% higher for the brain scanner. This reflects the combined effects of different ring diameters, numbers of coincidence lines of response, energy threshold and septa geometry. With septa retracted, the efficiency (scatter subtracted) increases by about a factor of 5. Scatter fractions measured in the reconstructed image were significantly lower than those obtained from sinograms (within the diameter of the phantom). This is indicative of the redistribution of counts in the reconstruction process since total counts are preserved. Count rate tests showed good accuracy of on-line dead time correction schemes at activities (in the FOV) of at least 480 MBq (13 mCi).
Spinks
T J
TJ
MRC Cyclotron Unit, Hammersmith Hospital, London, UK.
D001921:Brain / Q000000981:diagnostic imaging; D004867:Equipment Design; D005060:Europe; D005069:Evaluation Studies as Topic; D006801:Humans; D008954:Models, Biological; D008961:Models, Structural; D012680:Sensitivity and Specificity; D014055:Tomography, Emission-Computed / Q000295:instrumentation*