自旋回波序列参数TR的选择对低场磁共振测温准确性的影响

Influence of SE sequence parameter TR on the thermometry accuracy of low-field MRI

目的在肿瘤热疗过程中,磁共振成像技术可以进行热疗组织的温度监测,而基于纵向弛豫时间(longitudinal relaxation time,T1)加权成像的测温方法的准确性受到自旋回波序列(spin-echo sequence,SE)参数的影响。为给临床磁共振测温提供参考并提高测温的准确性,本文将探讨自旋回波序列参数重复时间(TR)的选取对基于纵向弛豫时间加权成像的测温方法的测温准确性的影响。方法基于T1加权成像测温的原理,通过改变SE序列的参数重复时间(TR),在0.4 T磁共振设备下对不同温度的猪肝组织进行扫描,找到T1加权图像信号强度值与温度的拟合关系,计算不同TR值下的理论温度,将其与数字温度计测量的参考温度进行比较,以此量化参数TR对测温准确性的影响。结果参数TR的设置会一定程度上影响测温准确性。在本实验条件下,当参数TR为400 ms(回波时间TE=18ms)测温的准确性最高,利用该SE序列测得的猪肝组织温度与实际温度最为接近,测温误差基本在±1℃左右。结论核磁测温过程中,SE序列参数TR值的恰当选择,对提升测温准确性具有明显的作用,本文的研究对临床热疗中的核磁测温具有一定参考和指导价值。

Objective In the process of tumor thermotherapy,MRI scanner can monitor the temperature changes of the heated area. The measurement accuracy of T1-weighted imaging thermometry involves the parameters of imaging sequences. To supply more references for clinical MRI thermometry and improve the accuracy of MRI thermometry,this article investigates the influences of the parameter of spin-echo（ SE）sequence： repetition time（ TR） on the accuracy of MRI thermometry based on the theory of T1-weighted imaging. Methods Based on the theory of T1-weighted imaging thermometry,this study scans the porcine liver tissue of different temperatures under a 0. 4 T MRI scanner with SE sequence with different TR. In order to quantify the influence of TR on the thermometry accuracy of MRI,the fitting relationship of the signal intensity of T1-weighted image and temperature should be figured out. Subsequently the theoretical temperatures measured by different SE sequences are compared with actual temperatures measured by digital thermometer.Results Parameter TR can affect the accuracy of the MRI thermometry to a large extent. Under the condition of the experiment,when TR is 400 ms（ TE is fixed at 18ms）,the temperatures measured by this SE sequence are most close to the actual temperatures. The temperature deviation remains around ± 1℃. Conclusions In theprocess of MRI thermometry,proper TR of SE sequence can improve the thermometry accuracy to a large extent. This study has certain reference value and important directive significance for clinical thermotherapy.