Optimization of the attenuation coefficient for Chang’s attenuation correction in ¹²³I brain perfusion single-photon emission computed tomography

Abstract

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