夏目 貴弘

Several resolution recovery (RR) methods have been developed. This study was aimed to validate the following performance of the advanced RR methods: Evolution™, Astonish™, Flash3D™, and 3D-OSEM. We compared the advanced RR method with filtered back projection (FBP) and standard order-subset expectation maximization (OSEM) using resolution (RES), cylinder/sphere (CYS), and myocardial (MYD) digital phantoms. The RES phantom was placed in three spheres. Sixteen spheres (hot and cold) were then placed in a concentric configuration (diameter: 96-9.6 mm) inside the CYS phantom. The MYD phantom was created by computer simulation with the use of an electron γ-shower 4 (EGS4) and it included two left ventricular defects in the myocardium. The performance was evaluated at source-to-detector distances (R-distance) of 166, 200, and 250 mm with reconstruction parameters (product of subset and iteration: SI) with use of the resolution recovery factor, count recovery, normalized mean square error (NMSE), and %CV. According to increased SI updates, the value of the FWHM decreased, and the effect was more obvious as the R-distance increased. The spatial resolution of the advanced RR method was 20 % better than that of FBP and OSEM. The resolution recovery ratio was 80 %, and the count recovery was maintained only in objects with a diameter of &gt 30 mm in the advanced RR method. The NMSE and %CV was 50 and 30 % improved over FBP and OSEM, respectively. The advanced RR method caused overestimation due to Gibbs's phenomenon in the marginal region when the diameter of the sphere was 16-28.8 mm. © 2012 Japanese Society of Radiological Technology and Japan Society of Medical Physics.

Purpose: This study aims to evaluate the fundamental performance of four leading advanced resolution recovery methods. Method: To evaluate the performance of the resolution recovery algorithm, we carried out the computer simulation with the cone/sphere digital phantoms. These phantoms were used to investigate the basic properties of those algorithms. The software of four packages (advance) were also tested, specifically Astonish^TM (AST), Evolution^TM (EVL), Flash-3D^TM (FL3), and 3D-OSEM (3DOS). The performance was evaluated in the collimator systems (LEHR) reconstruction conditions using the full width at half maxi am (FWHM), aspect ratio (ASR), and artifacts of conical part. Result: In the "without BG," FWHM of the advance method indicated a true-FWHM with SI (subset×iteration)=20, 40. As SI increased, FWHM was composed with over estimate. Each advances of FWHM indicated only 5% of improvement as compared with reference FWHM in the "with BG." The ASR increased 20% to AST, FL3, and ASR of 3DOS remained in 10% in the outside. As for the reproducibility of the conical part, an artifact was caused by the FL3, EVL, and AST methods. This artifact did not occur in 3DOS. Discussions: An SI needs more than 150 to obtain an accurate compensation effect. As for the advance method, the major compensation effect was not demonstrated very much as compared with the OS-EM. The EVL, FL3, and AST overestimated values due to a Gibb's oscillation in the artifacts of the conical part.

負荷心筋パーフュージョンMRI画像を用いた定量解析の際、最も処理時間を必要とする左室心筋領域設定のための自動化アルゴリズムの開発を行い、得られた左室心筋の輪郭を手動にて設定した輪郭と比較し、両者の左室心筋輪郭より算出した心筋血流値を比較した。虚血性心疾患を疑い、薬剤負荷心筋パーフュージョンMRI検査を施行した17例を対象とした。5例において本法を適応することができなかった。視覚的評価では自動設定された左室心筋領域は左室および右室内腔や肺なとの心筋以外の組織を含むことなく、左室心筋領域内に設定されていた。設定した左室心筋領域の面積は手動よりも有意に大きくなった。開発した左室心筋領域の自動設定アルゴリズムは心筋パーフュージョンMRIの定量解析に要する時間を大幅に短縮し、再現性の高い定量解析を日常臨床に導入できる可能性が示唆された。