コリメータ開口補正OSEM再構成法の局所脳血流量定量への応用

摘要

Single photon emission computed tomography（SPECT）を用いた脳血流シンチグラフィにおいて，散乱線補正にtriple energy window（TEW）法，減弱補正にX線CTの減弱マップによるChang法（X線CTAC），再構成法にフィルタ補正逆投影（filtered back projection；FBP）法を用いることによって定量的放射能分布が求められる．%Autoradiography (ARG) has been used for quantitative analysis of the cerebral blood flow using ~(123)I-IMP, and the regional cerebral blood flow (rCBF) can be assessed more accurately with scatter and attenua tion correction. Currently, the filtered back projection (FBP) method is generally used for image reconstruc tion. However, we anticipate obtaining more accurate rCBF by the ordered subsets expectation maximization method with collimator broad correction three dimensional ordered subsets expectation maximization (3D-OSEM). In the present study, we optimized the processing conditions to quantify rCBF using the 3D-OSEM method and compared them with the FBP method. Regarding the method, we determined the subsets and iteration, compared rCBF values using a profile curve, and compared them with the rCBF values obtained by the XeCT (Xenon-enhanced computed tomography)/CBF method. We found that in the 3D-OSEM method using 90 direction collection and 1.72 mm/pixel, the most accurate image was obtained around subset 9 and iteration 10. In addition, as compared to the profile curve and the XeCT/CBF method, the thalamus rCBF was high in the 3D-OSEM method with a good correlation with that of the XeCT/CBF. Accordingly, we concluded that the 3D-OSEM method can improve the decrease in rCBF due to blurring of the distance between the source (i.e., a structure located in the central part of the brain such as the thalamus and the collimator).