1.5Tおよび3.0 T-MR検査における人体の一部で形成されたループのRF発熱に関する検討: 人体等価ループファントムを用いた温度測定

摘要

Thermal injuries have been sometimes reported due to a closed conducting loop formed in a part of the patient's body during magnetic resonance imaging (MRI). In recent years, 3.0 T-MRI scanner has been widely used. However, it is considered that the specific absorption rate (SAR) of 3.0 T-MRI can affect the heat of the loop because its own SAR becomes approximately 4 times as much as that of the 1.5 T-MRI scanner. With this, the change in temperature was measured with human body-equivalent loop phantom in both 1.5 T-MRI and 3.0 T-MRI. In the two scanners, the temperature during 20 min of scanning time was measured with three types of sequences such as field echo (FE), spin echo (SE), and turbo SE (TSE) set up with the same scanning condition. It was found from the result that rise in temperature depended on SAR of the scanning condition irrespective of static magnetic field intensity and any pulse sequences. Furthermore, the increase of SAR and rise in temperature were not only in proportion to each other but also were indicated to have good correlation. However, even low SAR can occasionally induce serious thermal injuries. It was found from result that we had to attempt not to form a closed conducting loop with in a part of the patient's body during MRI.%近年，3.0 T-magnetic resonance(MR)装置が普及し，全身のあらゆる部位の撮像が行われている．MR装置の高磁場化，高性能化は診断情報，画質，代謝情報などの飛躍的な向上をもたらす．一方で高磁場になるほどradio frequency(RF)による人体への発熱の影響も大きくなり，3.0 T-MR検査における全身平均specific absorption rate(SAR)は単純計算で1.5 T-MR装置の約4倍となる．現在MR装置の安全に関する国際規格は国際電気標準会議（International Electrotechnical Commission;IEC）60601-2-33第2版にまとめられており，国内では日本工業規格（Japanese Industrial Standards;JIS）がこの方針に従って，IEC60601-2-33の完全翻訳版（JIS Z4951改訂版：2004年発行）となっている．