A study of the effects of attenuation correction on tumor detection in SPECT oncology

The effects of attenuation correction (AC) on tumor detection in SPECT oncology have not been studied as intensively as in PET oncology. The different attenuation mechanism in SPECT compared to PET imaging may lead to different effects of AC on tumor detection for the two modalities. Using the theory of filtered-backprojection reconstruction algorithm, we analyzed how the reconstructed images may appear when AC is not performed (non-AC) so that we can reveal the effects of AC on tumor detection. We then designed and performed a series of simulation studies to evaluate the results of the theoretical analysis. Finally, we analyzed the effects of Chang\´s post-reconstruction AC technique on tumor detection. Our results show that (1) for lung tumors, when the tumor-to-lung uptake ratio is above a threshold, tumors are visible in both AC and non-AC images; around this threshold, tumors "disappear" in non-AC images, and below this threshold, tumors appear photophenic in non-AC images. These effects are similar to those in PET oncology. (2) In mediastinum and abdomen areas, non-AC images have lower tumor-to-background ratio (TBR) than the true uptake ratio. This effect is opposite to that in PET oncology. (3) Chang\´s post-reconstruction AC technique does not improve TBR as compared with non-AC. As a conclusion, accurate AC can improve TBR as compared with non-AC, and thus can potentially improve tumor detectability. Chang\´s AC technique does not improve TBR as compared to non-AC, and is thus not likely to improve tumor detection in SPECT oncology