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- W190064434 abstract "As part of an ECT quality assurance program, the authors have investigated the effect of Anger camera orientation on system linearity, sensitivity, and pulse height stability. Data have been acquired from two Siemens ZLC 7500 cameras using 2'' photomultiplier tubes from two different vendors. Each PMT is individually shielded with mu-metal. Point source sensitivity and position stability were studied using 1 mm Co-57 point sources mounted within tantalum well-collimators fixed onto the crystal facing. Measured variations in sensitivity as a function of rotation were 0.35% RMS and 1.2% peak-peak. Centroid position variations were 0.27 mm RMS and 1.0 mm peak-peak. The observed sensitivity variations increased markedly (approx. =x4) if the camera was not shielded from backscatter. The position variation, however, was only weakly affected (approx. =x1.15). Pulse height stability and flood uniformity variations with orientation were studied by fixing a Co-57 flood source to the collimator and acquiring 20 million count flood images. Images corresponding to the average energy signal at each pixel (Z-map) were simultaneously recorded. The variation in regional flood count density, analyzed over 1'' x 1'' regions of interest, was comparable to that found in the point source experiments. Regional and global Z-map data varied approximately sinusoidallymore » with angle - 0.6% (RMS) and 1.7% (peak-peak). Direct measurement of the pulse height spectra versus angle yielded similar results. These data imply that variations of camera sensitivity and linearity during gantry rotation are small and relatively uniform over the detector area. Recent simulations in this laboratory indicate that ECT reconstructions are insensitive to such variations.« less" @default.
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- W190064434 date "1984-01-01" @default.
- W190064434 modified "2023-09-28" @default.
- W190064434 title "A study of Anger camera sensitivity and linearity as a function of spatial orientation" @default.
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