mDIXONにおけるFlip AngleおよびEcho Timeの組み合わせによる水・脂肪分離効果およびコントラストの検討

摘要

脂肪の存在診断や造影剤を使用したコントラスト増強のために脂肪抑制法を併用した撮像方法が利用されている．その代表的な方法として，周波数選択脂肪抑制法や水周波数選択励起法がある．後者は直接脂肪信号を抑制するのではなく，水を選択的に励起することで脂肪信号を抑えるものである．%The method known as DIXON is imaging from two different echo times (TE), using the opposite phase of water and fat. Modified DIXON (mDIXON) is the method that is calculated from changing the opposing phases 'in' and 'opposed' phases of the actual measurement, to fit the theoretical value. We reviewed that the effect of the water-fat separation and contrast depended on the different flip angles (FA) and echo times (TE). The diluted gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) (from 0 to 5 mmol/1) and liver model was stabilized by lard. In order to measure the SNR and %CV of the lard, the various combinations of TE and FA (from 5 to 20 degrees) were changed. The suitable range for the measurement of the SNR and %CV of the lard, and the contrast of gadolinium Gd-EOB-DTPA and the liver model, in the axial view (including 50% fat), was around the 'opposed' phase in the first TE (TE1) and around the 'in' phase in the second TE (TE2) and FA: 15degrees (TE1: 2.0-2.9 ms, TE2: 4.1-5.0 ms). In order to avoid phase dispersion, shorter TE range is more desirable (TE1: 2.0-2.25 ms, TE2: 4.1-4.5 ms). It is our understanding that the water-fat separation is better in these ranges and under these circumstances, good contrast was obtained.