Wallimann Philipp, Piccirelli Marco, Nowakowska Sylwia, Armstrong Tess, Mayinger Michael, Boss Andreas, Bink Andrea, Guckenberger Matthias, Tanadini-Lang Stephanie, Andratschke Nicolaus, Pouymayou Bertrand
Department of Radiation Oncology, University Hospital Zurich and University of Zurich, Zurich, Switzerland.
Department of Neuroradiology, Clinical Neuroscience Center, University Hospital Zurich and University of Zurich, Zurich, Switzerland.
Phys Imaging Radiat Oncol. 2024 Apr 20;30:100579. doi: 10.1016/j.phro.2024.100579. eCollection 2024 Apr.
The feasibility of acquiring diffusion-weighted imaging (DWI) images on an MR-Linac for quantitative response assessment during radiotherapy was explored. DWI data obtained with a Spin Echo Echo Planar Imaging sequence adapted for a 0.35 T MR-Linac were examined and compared with DWI data from a conventional 3 T scanner.
Apparent diffusion coefficient (ADC) measurements and a distortion correction technique were investigated using DWI-calibrated phantoms and in the brains of seven volunteers. All DWI utilized two phase-encoding directions for distortion correction and off-resonance field estimation. ADC maps in the brain were analyzed for automatically segmented normal tissues.
Phantom ADC measurements on the MR-Linac were within a 3 % margin of those recorded by the 3 T scanner. The maximum distortion observed in the phantom was 2.0 mm prior to correction and 1.1 mm post-correction on the MR-Linac, compared to 6.0 mm before correction and 3.6 mm after correction at 3 T. In vivo, the average ADC values for gray and white matter exhibited variations of 14 % and 4 %, respectively, for different selections of b-values on the MR-Linac. Distortions in brain images before correction, estimated through the off-resonance field, reached 2.7 mm on the MR-Linac and 12 mm at 3 T.
Accurate ADC measurements are achievable on a 0.35 T MR-Linac, both in phantom and in vivo. The selection of b-values significantly influences ADC values in vivo. DWI on the MR-Linac demonstrated lower distortion levels, with a maximum distortion reduced to 1.1 mm after correction.
探讨在磁共振直线加速器（MR-Linac）上获取扩散加权成像（DWI）图像用于放疗期间定量反应评估的可行性。对采用适用于0.35 T MR-Linac的自旋回波平面回波成像序列获得的DWI数据进行了检查，并与来自传统3 T扫描仪的DWI数据进行了比较。
使用DWI校准体模和7名志愿者的脑部研究表观扩散系数（ADC）测量和失真校正技术。所有DWI均利用两个相位编码方向进行失真校正和失谐场估计。对脑内自动分割的正常组织的ADC图进行分析。
MR-Linac上体模的ADC测量值与3 T扫描仪记录的值相差在3%以内。在MR-Linac上，体模中校正前观察到的最大失真为2.0 mm，校正后为1.1 mm，而在3 T时，校正前为6.0 mm，校正后为3.6 mm。在体实验中，对于MR-Linac上不同b值的选择，灰质和白质的平均ADC值分别有14%和4%的变化。通过失谐场估计，MR-Linac上脑图像校正前的失真达到2.7 mm，3 T时为12 mm。
在0.35 T MR-Linac上，无论是在体模还是在体内，都能实现准确的ADC测量。b值的选择对体内ADC值有显著影响。MR-Linac上的DWI显示出较低的失真水平，校正后最大失真降至1.1 mm。
