An Investigation into the Impact of Photon Scatter in the Detection of 67Ga Tumours using Channelized Hotelling and Human Observers

In 67Ga citrate SPECT imaging, significant downscatter may occur from higher energy photons into lower energy acquisition windows. As a result, it is possible that reconstructed image quality will be adversely affected. With these additional scattered photons, the effect of using more complex reconstruction strategies such as 3D detector response compensation (DRC) and attenuation correction (AC) is unclear. Through a combination of numerical Channelized Hotelling Observers (CHO) and human localization receiver operating characteristics (LROC) studies, an assessment is made of the degree to which tumour detection is affected in iterative SPECT reconstructions when scattered photons are included in the projection data. Decreased tumour detectability was observed when scattered photons are present in 67Ga projection data compared to primary photon only reconstructions. This decrease has been found to be statistically significant at the p < 10−6 level for both the human LROC and numerical observer studies. Furthermore, using numerical observer measurements, the addition of either AC or 3D DRC into the image reconstructiuon procedure is seen to improve lesion detectability compared to no compensation, but maximum lesion detectability occurs when both 3D DRC and AC are included.