SPECT/CT에서 CT를 기반으로 한 Attenuation Correction의 정확도 평가

Accuracy Evaluation of CT-Based Attenuation Correction in SPECT with Different Energy of Radioisotopes

Purpose: 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. Materials and Methods: Using a cylindrical phantom, three different SPECT scans of ²⁰¹Tl (70 keV, 55.5 MBq), ⁹⁹ᵐTc (140 keV, 281.2 MBq) and ¹³¹I (364 keV, 96.2 MBq) 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. The experiments were performed in the 4 different conditions; non-AC and non-scatter correction (SC), only AC, only SC, AC and SC 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 10-20% 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 of the reconstructed image was close to one, when AC was applied for ²⁰¹Tl and ⁹⁹ᵐTc scans and ¹³¹I was distant from 1 and that is only AC. Conclusion: The image uniformity improved by AC on low energy likely to ²⁰¹Tl and ⁹⁹ᵐTc. However, image uniformity of high energy such as ¹³¹I was improved, when both AC and SC was applied.