磁共振测温用于椎体肿瘤热疗的可行性研究

A feasibility study of MR thermometry in vertebra tumor thermotherapy

目的对磁共振测温在椎体环境不同组织中测温的难点初步分析。方法在3 T Phillips磁共振仪器中,分别采集T1、T2图像,根据椎体肿瘤热疗的临床需求,结合解剖图分割出手术关心的区域;再用PRF（proton resonance frequency）和谱估计两种方法分别对含水较多和水脂混合的组织区域进行温度测量,并以肌肉区域的温度对其余区域作场漂修正。结果在重点关注区域中,分别选取80-300个像素点,对于PRF方法,脊髓和椎间盘的温度误差平均值均〈0.2℃,温度标准差〈1.5℃;主动脉和上下腔静脉的温度误差平均值在0.9℃-1.8℃,标准差〈1.7℃;椎体部分的温度误差平均值约0.9℃,但标准差接近12℃;对于谱估计方法,在水脂混合的椎体部分,温度标准差仍〉12℃。结论磁共振测温在含水较多、均匀且流动较少的组织脊髓和椎间盘测温效果较好,在主动脉和静脉血管里的血液的温度因血液流动的干扰而难以用磁共振直接测得,椎体内由松质骨所引起的磁化率干扰会给磁共振测温带来较大偏差。

Objective To analyze difficulties of temperature measuring by MR thermometry in different types of tissues near vertebra. Method Regions of interest（ ROI） were segmented into several parts based on clinical needs and T1 / T2 maps were acquired in a 3T Phillips scanner. Proton Resonance Frequency（ PRF） and spectrum estimation were used separately to measure the temperature in water-domain and water-fat mixed tissues, with field drift correction using muscles as background tissues. Results Eighty-three hundred pixels were chosen in each ROI for PRF method. The mean error value of the spinal cord and intervertebral disk was below 0.2 ℃, and the standard deviation was below 1.5 ℃. The mean error value of the aorta and vena cava was 0.9 ℃-1.8 ℃, while the standard deviation was below 1.7 ℃. The mean error value of the vertebra was around 0.9 ℃, while the standard deviation was near 12 ℃. The standard deviation of the vertebra water-fat mixed region was still above 12 ℃ by using spectrum estimation method. Conclusions MR thermometry nas good performances in regions of water-domain and less blood flow, while the blood flow in aorta and vena caca can induce disturbances in temperature measuring. Susceptibility caused by cancellous bone can also bring errors into temperature results.