Magnetization Transfer Ratio of Brain Tissue: Normal Value and Effect of TR/TE

ABSTRACT

PURPOSE: Magnetization transfer imaging(MTI) is a new imaging contrast technique. Our MT pulse sequence is designed as fixed time interval between echo and MT pulse. This study was peformed to evaluate the influence of variations in TR/TE on MTR in T1 weighted image of normal brain tissue on this kind of MT pulse sequence. MATERIALS AND METHODS: Seven healthy volunteers in twenties of age as the objectives, MRI was taken under various TR/TE(TR/TE ;700/14, 650/14, 750/14, 700/20 and 1500/20 msec). MTR was calculated from signal intensities measured at the same point in both pre and post MT images and statisticslly analyzed. The MR imager used in this study was 1.0T Magnetom 42SP(Siemens, Erlangen, Germany) and the parameters of additional MT pulse sequence were offset 1000Hz and bandwidth 250Hz, and posteriorly located to echo with 7.7 msec fixed interval. Offset of this MT pulse was variable. RESULT: In white matter of brain tissue from a normal person, MTR was 34-39%(average 37%) for TR and TE of 700/14 in T1WI and 33-36%(average 35%) for TR/TE of 650/14, and 34-38%(average 35%) for TR/TE of 750/14 which showed no statistical difference. However, in case of 1500/20 of TR/TE, MTR was 26-28%(average 26%) which is statistically significant. With TR/TE of 700/14 as the standrd value, the MTR of gray and white matter were 37% and 29% respectively, showing a definite difference of statistical means. Signal from CSF in ventricles is rarely influenced by MT pulse. CONCLUSION: Conclusively, a subtle variation in TR/TE in T1WI has little influence on MTR but wide range of variation in TR/TE as in proton density image induces significant difference in MTR on this kind of MT pulse sequence. Therefore, the exchangeable usage of MTR data would be possible in narrow range of TR/TE change but difficult in wide range of variation.