脂肪抑制Magnetic Resonance Imageのためのポリスチレンボール弾を用いた静磁場不均一軽減補助具の試作と効果の検討

摘要

頭頚部領域は被写体断面積の変化が大きく，その形状が複雑であることから，magnetic resonance imaging（MRI）検査において静磁場（B_0）が不均一になりやすい．水と脂肪の共鳴周波数差を利用し，水の共鳴周波数から3.5ppmずれたradio frequency（RF）パルスを照射することで脂肪の信号を選択的に抑制するchemical shift saturation（CHESS）法では，B_0の不均一によって，脂肪抑制ムラが生じ，均一な脂肪抑制画像を得ることが困難な場合が多い．%Purpose: Homogeneity of static magnetic field (B_0) is unstable for head and neck magnetic resonance (MR) examination; consequently, chemical shift selective fat suppression becomes inhomogeneous. There is a commercially available additional pad to attenuate the B_0 inhomogeneity, but it is expensive. It has been reported that uncooked rice can be used as a material in the pad, but it has hygienic and weight problems. We searched for a material which can replace the uncooked rice, and evaluated its performance. Method: After filling various materials into the cylindrical phantom, each material was evaluated by image distortion of gradient filed echo and spin echo single-shot echo planar images. A prototype additional pad was made with a material which showed less image distortion in the phantom experiment and is easily available in clinical examination. For comparison, an uncooked rice pad with the same volume was also prepared. Fat suppressed head and neck magnetic resonance imaging (MRI) of normal volunteers were visually compared when the three additional pads, including the commercial product, were used or not. Result: The polystyrene ball bullet (BB bullet) was adopted as a material for the additional pad. The improvement of the fat suppression in the head and neck MRI was almost the same between the three additional pads. BB bullet pad was the lightest. Conclusion: BB bullet can be used as a material of additional pad attenuating the B_0 inhomogeneity instead of uncooked rice.