表面线圈接受信号对磁共振波谱化学位移成像分析的影响

目的探讨表面线圈接受信号对磁共振波谱分析的影响.方法实验研究采用含有0.1% Gd-DTPA(0.5 mmol/ml)的500 ml 生理盐水模型:一是将其直接放置在柔性线圈表面上,横断面、冠状面T1加权成像,然后对中心层面图像Profile测定;MR检查后对同一模型进行多体素化学位移成像氢波谱检查.二是将同一模型包绕在线圈内,采用上述同样方法进行检查.另对1例人体肩背部脂肪瘤进行活体多体素化学位移成像氢波谱检查,柔性表面线圈贴近肩背部病灶部位进行信号采集.结果水模型直接放在表面线圈上,等中心层面横断面图像Profile显示中心明显低于左右两侧,远离线圈侧明显低于靠近线圈侧,波谱亦显示感兴趣区内远离线圈侧波谱信号幅度明显低于靠近线圈侧.水模型包绕在线圈内,等中心层面横断面图像Profile在左右、前后方向基本均匀分布;MRS波谱信号幅度大小分布与距离线圈远近无关.水模型冠状面Profile显示靠近线圈中心明显高于两侧.人体脂肪瘤波谱图像示感兴趣区内靠近表面线圈侧波谱信号幅度明显高于远离线圈侧.结论表面线圈接受信号不均匀性会对磁共振波谱定量分析产生直接影响;将检查对象放置在线圈中心并包绕在柔性线圈内可以基本排除其对波谱定量分析的影响.

Effect of sensitivity of surface coils on quantification of MR spectroscopy

Objective To evaluate the analysis of MR spectroscopy(MRS) influenced by the sensitivity of surface coils as receivers of MR signals.Methods A phantom containing solutions of 0.1% Gd-DTPA(0.5 mmol/ml) in saline was examined: Firstly,the reception profile of surface coils were measured by using the transaxial and coronal T1-weighted sequences and the proton MR spectroscopy using 2D CSI SE sequence were performed on the phantom which was positioned freely on the surface of a small flex coil.Secondly,section profiles and MRS were achieved with the same parameters as used for the first on the phantom which was positioned within the same coil.A patient with a lipoma in the shoulder was examined with the similar parameters of MR spectroscopy as used for the phantom by using a large flex coil adapted to the shoulder shape.Results The transaxial isocenter image section profile showed that the pixel values of the center area was much lower than the right and the left areas and that of the posterior area near the small flex coil was much higher than the anterior area;which correlated with the represent of MRS.As the phantom was placed within the small flex coil,there were not markedly difference between the center and the right or the left area;or the anterior and the posterior area on the transaxial isocenter image section profile;the water map of 2D CSI also showed distributed uniformly.The coronal isocenter image section profile showed that the pixel values of the isocenter area were the highest and that of the inner and the external areas decreased greatly.The map of the patient's lipoma showed that the signal intensities close to the large flex coil were stronger than that farther away from the coil.Conclusion The quantification of MRS is easily affected by the inhomogeneous reception of surface coil;This problem can be excluded by positioning the subjects within the coil's center as a flex surface coil used.