Assessment of scatter compensation strategies for 67Ga tumor SPECT using numerical observers and human LROC studies

Ga-67 citrate SPECT imaging is often used for oncological studies in order to diagnose or stage patient lymphomas. Because the decay of Ga-67 involves multiple emission energies, it is possible that many down-scattered photons will be present in photopeak acquisition data. We have previously shown through human observer LROC studies, that the inclusion of these scattered photons significantly degrades lesion detectability in simulations. We have investigated the use of six different scatter compensation methods representing different strategies. These consist of i) perfect scatter rejection, ii) no scatter compensation, iii) ideal scatter compensation, iv) triple energy window estimation, v) effective scatter source estimation, and vi) post-reconstruction scatter subtraction. Each method has first been optimized using a channelized hotelling numerical observer, then ranked through the use of a human LROC study and by using a newly devised LROC numerical observer. Both human LROC and LROC numerical observer results indicate that both TEW and ESSE scatter compensation methods are able to improve lesion detectability over no compensation, but fail to achieve similar detectability to using perfect scatter rejection. Excellent agreement between the LROC numerical observer and human LROC studies indicate that the LROC observer may be good predictor of human performance in Ga-67 SPECT.