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

Purpose : Magnetization transfer imaging(MTI) is a new imaging contrast technique. Our MT pulse sequence isdesigned as fixed time interval between echo and MT pulse. This study was performed to evaluate the influence ofvariations 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 variousTR/TE( TR/TE ; 700/14, 650/14, 750/14, 700/20 and 1500/20msec). MTR was calculated from signal intensities,measured at the same point in both pre and post MT images and statisticslly analized. The MR imager used in thisstudy was 1.0T Magnetom 42SP(Siemens, Erlangen, Germany) and the parameters of additional MT pulse sequence wereoffset 1,000Hz and bandwidth 250Hz, and posteriorly located to echo with 7.7 msec fixed interval. Offset of thisMT 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/TEof 750/14 which showed no statistical difference. However, in case of 1500/20 of TR/TE, MTR was 26-28%(average26%) which is statistically significant. With TR/TE of 700/14 as the standrd value, the MTR of gray and whitematter were 37% and 29% irespectively, showing a definiate difference of statistical means. Signal from CSF inventricles is rarely influenced by MT pulse. Conclusion : Conclusively, a subtle variation in TR/TE in T1WI haslittle influence on MTR but wide range of variation in TR/TE as in proton density image induces significantdifference in MTR on this kind of MT pulse sequence. Therefore, the exchangeable usage of MTR data would bepossible in narrow range of TR/TE change but difficult in wide range of variation.ope