OBJECT AND DETECTOR SCATTER FUNCTION DEPENDENCE ON ENERGY AND POSITION IN HIGH-RESOLUTION PET

We have shown in previous works that distinct non-stationary analytica l scatter kernels can be extracted from line source measurements and u sed to independently subtract object scatter and subtract or restore d etector scatter in high resolution PET. In this work, the dependence o f the scatter components on energy threshold and source position was i nvestigated. Line source measurements were acquired in multispectral m ode using the Sherbrooke PET simulator. Scatter parameters were extrac ted from data summed in energy windows with a lower threshold varying from 129 keV to 516 keV in steps of 42 keV, and a fixed upper threshol d of 644 keV. Decreasing the lower threshold from 344 keV to 129 keV i ncreases the trues by only 25%, but increases object scatter by 136% a nd almost triples detector scatter. A gain in efficiency by a factor o f 2 or more would result from recovering the latter by restoration in the broad window. The intensity and shape of the scatter functions for both object and detector are shown to have a significant dependence o n energy and position. This dependence needs to be taken into account in the design of kernels for accurate scatter correction over a broad energy range.