Akdag Osman, Mandija Stefano, van Lier Astrid L H M W, Borman Pim T S, Schakel Tim, Alberts Eveline, van der Heide Oscar, Hassink Rutger J, Verhoeff Joost J C, Mohamed Hoesein Firdaus A A, Raaymakers Bas W, Fast Martin F
Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands.
Computational Imaging Group for MR Diagnostics and Therapy, Center for Image Sciences, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands.
Phys Imaging Radiat Oncol. 2022 Mar 9;21:153-159. doi: 10.1016/j.phro.2022.02.017. eCollection 2022 Jan.
The heart is important in radiotherapy either as target or organ at risk. Quantitative T and T cardiac magnetic resonance imaging (qMRI) may aid in target definition for cardiac radioablation, and imaging biomarker for cardiotoxicity assessment. Hybrid MR-linac devices could facilitate daily cardiac qMRI of the heart in radiotherapy. The aim of this work was therefore to enable cardiac-synchronized T and T mapping on a 1.5 T MR-linac and test the reproducibility of these sequences on phantoms and between the MR-linac and a diagnostic 1.5 T MRI scanner.
Cardiac-synchronized MRI was performed on the MR-linac using a wireless peripheral pulse-oximeter unit. Diagnostically used T and T mapping sequences were acquired twice on the MR-linac and on a 1.5 T MR-simulator for a gel phantom and 5 healthy volunteers in breath-hold. Phantom T and T values were compared to gold-standard measurements and percentage errors (PE) were computed, where negative/positive PE indicate underestimations/overestimations. Manually selected regions-of-interest were used for intra/inter scanner evaluation.
Cardiac-synchronized T and T qMRI was enabled after successful hardware installation on the MR-linac. From the phantom experiments, the measured T/T relaxation times had a maximum percentage error (PE) of -4.4%/-8.8% on the MR-simulator and a maximum PE of -3.2%/+8.6% on the MR-linac. Mean T/T of the myocardium were 1012 34/51 2 ms on the MR-simulator and 1034 42/51 1 ms on the MR-linac.
Accurate cardiac-synchronized T and T mapping is feasible on a 1.5 T MR-linac and might enable novel plan adaptation workflows and cardiotoxicity assessments.
心脏在放射治疗中无论是作为靶区还是危及器官都很重要。定量T1和T2心脏磁共振成像（qMRI）有助于心脏射频消融的靶区定义以及心脏毒性评估的成像生物标志物。混合MR直线加速器设备可便于在放射治疗中对心脏进行每日定量心脏qMRI检查。因此，本研究的目的是在1.5T MR直线加速器上实现心脏同步T1和T2映射，并在体模以及MR直线加速器与诊断性1.5T MRI扫描仪之间测试这些序列的可重复性。
使用无线外周脉搏血氧仪在MR直线加速器上进行心脏同步MRI检查。在MR直线加速器和1.5T MR模拟仪上，对凝胶体模和5名屏气状态下的健康志愿者两次采集诊断用的T1和T2映射序列。将体模的T1和T2值与金标准测量值进行比较，并计算百分比误差（PE），负/正PE表示低估/高估。手动选择感兴趣区域用于扫描仪内/间评估。
在MR直线加速器上成功安装硬件后，实现了心脏同步T1和T2 qMRI。在体模实验中，在MR模拟仪上测得的T1/T2弛豫时间的最大百分比误差（PE）为-4.4%/-8.8%，在MR直线加速器上的最大PE为-3.2%/+8.6%。在MR模拟仪上心肌的平均T1/T2为1012±34/51±2ms，在MR直线加速器上为1034±42/51±1ms。
在1.5T MR直线加速器上进行准确的心脏同步T1和T2映射是可行的，这可能会实现新的计划调整工作流程和心脏毒性评估。
