Department of Radiation Oncology, Dana-Farber Cancer Institute, Brigham and Women's Hospital, and Harvard Medical School, Boston, Massachusetts, United States of America.
Siemens Medical Solutions USA Inc., Boston, Massachusetts, United States of America.
Phys Med Biol. 2022 Mar 11;67(6). doi: 10.1088/1361-6560/ac508e.
In MRI-based radiation therapy planning, mitigating patient-specific distortion with standard high bandwidth scans can result in unnecessary sacrifices of signal to noise ratio. This study investigates a technique for distortion detection and mitigation on a patient specific basis.Fast B0 mapping was performed using a previously developed technique for high-resolution, large dynamic range field mapping without the need for phase unwrapping algorithms. A phantom study was performed to validate the method. Distortion mitigation was validated by reducing geometric distortion with increased acquisition bandwidth and confirmed by both the B0 mapping technique and manual measurements. Images and contours from 25 brain stereotactic radiosurgery patients and 95 targets were analyzed to estimate the range of geometric distortions expected in the brain and to estimate bandwidth required to keep all treatment targets within the ±0.5 mm iso-distortion contour.The phantom study showed, at 3 T, the technique can measure distortions with a mean absolute error of 0.12 mm (0.18 ppm), and a maximum error of 0.37 mm (0.6 ppm). For image acquisition at 3 T and 1.0 mm resolution, mean absolute distortion under 0.5 mm in patients required bandwidths from 109 to 200 Hz pxfor patients with the least and most distortion, respectively. Maximum absolute distortion under 0.5 mm required bandwidths from 120 to 390 Hz px.The method for B0 mapping was shown to be valid and may be applied to assess distortion clinically. Future work will adapt the readout bandwidth to prospectively mitigate distortion with the goal to improve radiosurgery treatment outcomes by reducing healthy tissue exposure.
在基于 MRI 的放射治疗计划中，使用标准高带宽扫描来减轻患者特定的失真可能会导致不必要的信噪比牺牲。本研究探讨了一种基于患者个体的失真检测和缓解技术。使用先前开发的用于高分辨率、大动态范围场映射的技术进行快速 B0 映射，无需相位解缠算法。进行了一项体模研究来验证该方法。通过增加采集带宽来减少几何失真来验证失真缓解，并通过 B0 映射技术和手动测量来确认。对 25 例脑立体定向放射外科患者和 95 个靶区的图像和轮廓进行分析，以估计脑内预期的几何失真范围，并估计保持所有治疗靶区在±0.5mm 等失真轮廓内所需的带宽。体模研究表明，在 3T 下，该技术可以以 0.12mm（0.18ppm）的平均绝对误差测量失真，最大误差为 0.37mm（0.6ppm）。对于在 3T 和 1.0mm 分辨率下进行图像采集，患者的平均绝对失真低于 0.5mm，分别需要 109 到 200Hz px的带宽，而失真最小和最大的患者需要的带宽分别为 120 到 390Hz px。在最大绝对失真低于 0.5mm 时，需要的带宽分别为 120 到 390Hz px。B0 映射的方法被证明是有效的，并且可以应用于临床评估失真。未来的工作将适应读出带宽，以便前瞻性地缓解失真，目标是通过减少健康组织的暴露来改善放射外科治疗效果。
