Does CT-based attenuation correction alter lesion detection and diagnostic confidence in adrenal imaging?

Objectives Attenuation can significantly impact SPECT imaging. Imaging of the chest and abdomen may be particularly affected, especially when emission counts are low. We previously presented preliminary results on the benefit of CT based attenuation correction (CTAC). We now present further data examining the effect of CTAC on lesion detection, relative uptake and reporter confidence in adrenal imaging.

Methods A total of 75 SPECT/CT studies were performed in 41 consecutive patients who underwent [I-131] iodonorcholesterol or [I-123/I-131] MIBG scintigraphy. All SPECT studies were acquired on a Phillips Skylight gamma camera with an integrated single slice spiral CT and were reconstructed (OSEM) both with and without attenuation correction (AC and NAC respectively). All the images were evaluated blindly by 2 experienced Nuclear Medicine physicians with CT fusion. For each study, relative uptake of each lesion, the confidence of lesion detection and final diagnosis were assessed using a 5 point scale.

Results Overall, when SPECT imaging was interpreted with CT fusion: NAC identified 98 foci compared with 116 with AC (18% increase). 13 of these were adrenal glands. In the [I-131] MIBG therapy group, AC correction made no difference in lesion confidence, uptake or diagnostic confidence. However, for both the [I-123] MIBG and [I-131] iodonorcholesterol groups, there was a significant improvement in all three indices. The beneficial effect was greatest for the iodonorcholesterol group.

Conclusions CT-based attenuation correction in adrenal imaging leads to the enhanced visualization of the adrenal glands and metastases improving lesion detection, subjective lesion uptake and reporter confidence and offers the potential for quantification (e.g. SUV) in the future. This benefit is greatest for lower count studies