【摘要】 目的:探讨MR灌注成像过程中信号强度——时间曲线始端下挫现象产生的原因。材料与方法:在不注射造影剂的情况下,分别采用FLASH序列和EPI序列对正常人脑及水膜进行实验扫描。保持其它参数不变,单独改变TR或TD,观察曲线的形态变化,并分别计算始端下挫值、始端下挫率以及后续图像上ROI的平均信号强度(SI_m)。结果:所有受试序列均出现始端下挫现象,而且EPI序列比FLASH序列明显。相同扫描序列正常脑实验比水模实验明显。延长TR或TD可以使后续图像的平均信号也有不同程度的增加,始端下挫的幅度减小以至完全校正。在FLASH序列,延长TR对始端下挫的校正效果比延长TD明显。结论:导致灌注曲线始端下挫现象产生的主要原因是饱和现象和失相,而与注射造影剂无关;始端下挫现象的存在会在一定程度上降低了灌注成像的质量,可以通过延长TR或TD的方法加以校正;在始端下挫现象存在时,信号强度的基线水平的计算不应包括首幅图像。更多还原

【Abstract】 Objective To study the reasons of the defealing phenomenon at the beginning ofsignal intensity- -time curve (DPB) during perfusion weighted MR imaging. Methods Normal human brain and water model underwent experimental MR scannings with prolonging TRs or TDs respectively, while the other parameters were not changed, without contrast medium injection. The figure of the SI - T curves was observed, and parameters were calculated, such as the value of DPB, the rate of DPB(R△SI)and the average signal intensity on the rear images (SIm). Result DPB were seen in all of the sequences we tested, The amplitude of DPB(△SI) on EPI sequence was much higher than that on FLASH sequence, and △SI of normal brain was higher than that of water model when the same sequence was used. By prolonging TR or TD, SIm could be increased, and PDB could be adjusted. In FLASH sequencl, the effect to adjust the PDB phnomenon by prolonging TR was more remarkable than by prolonging TD. Conclusion The main reasons of DPB are not the injection of contrast medium, but the saturation and dephasing of proton. DPB could be adjusted by prolonging TR or TD. When DPB exist, the quality of periusion weighted imaging will be reduced, and the first imaging should be excluded while the baseline of the signal intensity was calculated.更多还原