Mei Chang-Sheng, Chu Renxin, Hoge W Scott, Panych Lawrence P, Madore Bruno
Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
Department of Physics, Soochow University, Taipei, Taiwan, Republic of China.
Magn Reson Med. 2015 Jun;73(6):2142-51. doi: 10.1002/mrm.25338. Epub 2014 Jun 27.
To describe how B0 inhomogeneities can cause errors in proton resonance frequency (PRF) shift thermometry, and to correct for these errors.
With PRF thermometry, measured phase shifts are converted into temperature measurements through the use of a scaling factor proportional to the echo time, TE. However, B0 inhomogeneities can deform, spread, and translate MR echoes, potentially making the "true" echo time vary spatially within the imaged object and take on values that differ from the prescribed TE value. Acquisition and reconstruction methods able to avoid or correct for such errors are presented.
Tests were performed in a gel phantom during sonication, and temperature measurements were made with proper shimming as well as with intentionally introduced B0 inhomogeneities. Errors caused by B0 inhomogeneities were observed, described, and corrected by the proposed methods. No statistical difference was found between the corrected results and the reference results obtained with proper shimming, while errors by more than 10% in temperature elevation were corrected for. The approach was also applied to an abdominal in vivo dataset.
Field variations induce errors in measured field values, which can be detected and corrected. The approach was validated for a PRF thermometry application.
描述B0不均匀性如何在质子共振频率（PRF）位移测温法中导致误差，并校正这些误差。
在PRF测温法中，通过使用与回波时间TE成比例的比例因子，将测量的相移转换为温度测量值。然而，B0不均匀性会使磁共振回波发生变形、扩展和移位，这可能会使成像对象内的“真实”回波时间在空间上发生变化，并呈现出与规定的TE值不同的值。本文介绍了能够避免或校正此类误差的采集和重建方法。
在超声处理过程中，在凝胶体模中进行了测试，并在适当匀场以及故意引入B0不均匀性的情况下进行了温度测量。观察到了由B0不均匀性引起的误差，并通过所提出的方法进行了描述和校正。校正后的结果与在适当匀场情况下获得的参考结果之间未发现统计学差异，同时校正了温度升高超过10%的误差。该方法也应用于腹部体内数据集。
场变化会在测量的场值中引起误差，这些误差可以被检测和校正。该方法在PRF测温法应用中得到了验证。
