MRI装置における部分容積効果を用いた新しいスライス厚測定法の提案

摘要

Magnetic resonance imaging（MRI）装置の性能維持管理は，検査の安全性を担保することはもちろん，装置の適正使用のために必要不可欠である．この中で，装置の性能評価法はsignal-to-noise ratio（SNR）や画像不均一性といった比較的測定が容易なものから，幾何学的歪み，スライス厚測定のように特別なファントムが必要で煩雑なものがあり，一般ユーザが日常的に行えるものは限られているのが現状である．%The wedge and the slab methods are standard procedures as slice thickness mensuration of the MRI needs an expensive and exclusive phantom, and they are poor in versatility. We suggest a new method, that we call "differential edge response function method" . This is a modified version of the partial method which Higashida and others proposed. In this method, we use an original phantom which has an acrylic disk on the bottom, and take an image of it while moving a slice position so it includes the disk part. We established the region of interest on an image set up and got the edge response function (ERF) from the mean signal intensity and relations of the Z position of the image. In this method, the effective slice thickness is the half width of the slice profile, which is differentiated ERF. This method can be measured even if the linearity of the signal intensity is poor compared to the partial method. It is possible to correct the alignment. In this method the measurement accuracy was approximately equal to the wedge method. This method is minimally influenced by signal-to-noise ratio in comparison with the wedge method. Furthermore, versatility is high, because it is simple and relatively easy to use.