~(123)I-IMP脳血流SPECTにおける視野外ぺネトレーションの散乱線補正に関する検討:シミュレーション法とマルチウインドウ法の比較

摘要

N-Isopropyl-p-[123I] Iodoamphetamine (~(123)I-IMP)を 用いた腦血流single photon emission computed to- mography (SPECT) は， 他の蓄積型トレーサであ る~(99m)Tc製剤に比べ血流直線性が高く，~(133)Xeによる 脳血流測定と強く相関するため，脳血流定量シン千グ ラフィに非常に有用である.しかし，~(123)I-IMPは静 脈内に投与された後，ほとんどが肺に取り込まれるた め脳血流SPECT検査時において視野外に高い放射能 が存在する.視野外から放出される529 keVの高エ ネルギーγ線による散乱線成分（ダウンスキヤッタ）お よびコリメータの隔壁通過成分（ぺネトレーション） は，~(123)Iのメィンピークである159keVのウインドウ 内に混入するため，局所脳血流定量値に変化を及ぼす 可能性が生じる.%Purpose: The N-Isopropyl-p-[123I] Iodoamphetamine (~(123)I-IMP) SPECT imaging reduces the image quality and quantitative accuracy due to scatter and septal penetration occurred by radioactive uptake from outside of the field of view such as the lungs. We evaluated the influence of scatter and septal penetration using phantom-simulated radioactivity from outside of the field of view, and subsequently compared the effect of scatter and septal penetration corrections between the simulation-based effective scatter source estimation (ESSE) method and the multi-window method (ellipse approximation method). Methods: We used the phantom filled with 10 and 25 kBq/mL for the brain and lung parts corresponding to radioactive concentration in the clinical study. The SPECT images were acquired with and without lung phantom using low-energy high-resolution (LEHR) and cardiac high-resolution (CHR) collimators. We quantitatively evaluated a brain phantom by count analysis and coefficient of variation as reference data without lung phantom simulated the radioactivity from outside of the field of view, and compared between two scatter corrections by each collimator. Results: The brain count in cerebral base with the ESSE method using LEHR collimator was higher than that of the ellipse approximation method. The whole brain count with the ellipse approximation method using CHR collimator shows 28.8% lower than the ESSE method, so that it suggests that the ellipse approximation method for LEHR collimator and the ESSE method for CHR collimator was close to reference counts. The coefficient of variation of the ESSE method was lower than that of the ellipse approximation method for both two collimators. Conclusions: It was possible to correct the scatter and penetration from outside the field of view with high accuracy, by using the ellipse approximation method with LEHR collimator and the ESSE method with CHR collimator.