Orzada Stephan, Fiedler Thomas M, Ladd Mark E
Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany.
Magn Reson Med. 2024 Dec;92(6):2696-2706. doi: 10.1002/mrm.30235. Epub 2024 Jul 26.
This study proposes faster virtual observation point (VOP) compression as well as post-processing algorithms for specific absorption rate (SAR) matrix compression. Furthermore, it shows the relation between the number of channels and the computational burden for VOP-based SAR calculation.
The proposed new algorithms combine the respective benefits of two different criteria for determining upper boundedness of SAR matrices by the VOPs. Comparisons of the old and new algorithms are performed for head coil arrays with various channel counts. The new post-processing algorithm is used to post-process the VOP sets of nine arrays, and the number of VOPs for a fixed median relative overestimation is compared.
The new algorithms are faster than the old algorithms by a factor of two to more than 10. The compression efficiency (number of VOPs relative to initial number of SAR matrices) is identical. For a fixed median relative overestimation, the number of VOPs increases logarithmically with the number of RF coil channels when post-processing is applied.
The new algorithms are much faster than previous algorithms. Post-processing is very beneficial for online SAR supervision of MRI systems with high channel counts, since for a given number of VOPs the relative SAR overestimation can be lowered.
本研究提出了更快的虚拟观测点（VOP）压缩算法以及用于比吸收率（SAR）矩阵压缩的后处理算法。此外，还展示了通道数量与基于VOP的SAR计算的计算负担之间的关系。
所提出的新算法结合了通过VOP确定SAR矩阵上界的两种不同标准的各自优点。对具有不同通道数的头部线圈阵列进行新旧算法的比较。使用新的后处理算法对九个阵列的VOP集进行后处理，并比较固定中位数相对高估情况下的VOP数量。
新算法比旧算法快两到十倍以上。压缩效率（VOP数量相对于SAR矩阵初始数量）相同。应用后处理时，对于固定的中位数相对高估，VOP数量随射频线圈通道数量呈对数增加。
新算法比以前的算法快得多。后处理对于具有高通道数的MRI系统的在线SAR监测非常有益，因为对于给定数量的VOP，可以降低相对SAR高估。
