Optimization of the Attenuation Coefficient for Chang Attenuation Correction in ¹²³I Brain Perfusion SPECT

N-isopropyl-p-¹²³I-iodoamphetamine brain perfusion SPECT has been used with various attenuation coefficients (μ-values); however, optimization is required. This study aimed to determine the optimal μ-value (μ_opt-value) for Chang attenuation correction (AC) using clinical data by comparing the Chang method and CT-based AC. Methods: We used 100 patients (reference group, 60; disease group, 40) who underwent N-isopropyl-p-¹²³I-iodoamphetamine SPECT. SPECT images of the reference group were obtained to calculate the AC using the Chang method (μ-values, 0.07-0.20; 0.005 interval) and the CT-based method, both without scatter correction (SC) and with SC. The μ_opt-value with the smallest mean percentage error for the brain regions of the reference group was calculated. Agreement between the Chang and CT-based methods applying the μ_opt-value was evaluated using Bland-Altman analysis. Additionally, the percentage error in the region of hypoperfusion in the diseased group was compared with the percentage error in the same region in the reference group when the μ_opt-value was applied. Results: The μ_opt-values were 0.140 for Chang without SC and 0.160 for Chang with SC. In the Chang method, with the μ_opt-value applied, fixed and proportional biases were observed in the Bland-Altman analysis (both P < 0.05), and there was a tendency for the percentage error to be underestimated in the limbic regions and overestimated in the central brain regions. There was no significant difference between the disease group and the reference group in the region of hypoperfusion in either Chang without SC or Chang with SC. Conclusion: The present study revealed that the μ_opt-values of the Chang method are 0.140 without SC and 0.160 with SC.