Accuracy evaluation of CT-based attenuation correction in SPECT with different energy of radioisotopes

Objectives In this study, we evaluated the accuracy of CT-based attenuation correction (AC) under the conventional CT protocol (140 kVp, on average 50-60 keV) by comparing the SPECT image qualities of different energy of radioisotopes, ²⁰¹Tl, ^99mTc and ¹³¹I.

Methods Using a cylindrical phantom, three different SPECT scans of ²⁰¹Tl (70 keV, 1.5 mCi), ^99mTc (140 keV, 7.6 mCi) and ¹³¹I (364 keV, 2.6 mCi) were performed. The CT image was obtained with 140 kVp and 2.5 mA in GE Hawkeye 4. The OSEM reconstruction algorithm was performed with 2 iterations and 10 subsets. "AC vs. non-AC" and "scatter correction (SC) vs. non-SC" were compared in terms of uniformity and center to peripheral ratio (CPR).

Results The uniformity was calculated from the uniform whole region in the reconstructed images. For ²⁰¹Tl and ^99mTc, the uniformities were improved by about 10% AC was applied, but these were decreased by about 2% as SC was applied. The uniformity of ¹³¹I was slightly increased as both AC and SC were applied. The CPR in the reconstructed image was close to one when AC was applied for ²⁰¹Tl and ^99mTc scans, and when SC was only applied for ¹³¹I scan.

Conclusions The image uniformity and CPR of ²⁰¹Tl and ^99mTc were affected by only AC without SC, and for ¹³¹I scan, SC more influenced the image quality than AC under the conventional CT protocol in SPECT/CT