McCullum Lucas, van Rijssel Michael J, Hwang Ken-Pin, Ding Yao, Tang Chad, Hassanzadeh Comron, Yang Jinzhong, Balter Peter A, Wang Jihong, Fuller Clifton D, Subashi Ergys D
Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
UT MD Anderson Cancer Center UTHealth Houston Graduate School of Biomedical Sciences, Houston, TX, USA.
medRxiv. 2025 Jul 29:2025.07.28.25332213. doi: 10.1101/2025.07.28.25332213.
Quantitative mapping of the longitudinal relaxation rate (R1=1/T1) is a major building block for several multiparametric MRI protocols intended for adaptive radiation therapy planning. The implementation of these protocols is challenging in anatomical sites that experience large physiological motion.
To implement and validate a motion-resolved quantitative T1 mapping method on a 1.5T MR-Linac that combines non-Cartesian k-space sampling trajectories with compressed sensing (CS) reconstruction techniques.
Four 3D non-Cartesian k-space trajectories were evaluated: radial and stack-of-stars sampling using half- and full-spoke coverage. A variable flip angle acquisition was performed using the spoiled gradient-echo sequence, and T1 mapping was validated using two standard phantoms. Gradient delay timing was optimized empirically to minimize trajectory-induced artifacts. Eight compressed sensing reconstruction strategies were tested using spatial and spatiotemporal regularization operators. Reconstructions were evaluated across multiple implementation parameters and ranked based on spatial resolution, bias, and variability. In vivo studies included one healthy volunteer and one patient undergoing radiotherapy to a target in the kidney. Motion-resolved imaging was performed using respiratory self-gating and phase-sorted reconstruction.
All non-Cartesian trajectories demonstrated high repeatability and low longitudinal bias in phantom studies, with coefficients of variation below 3.3%. Radial half-spoke sampling achieved the shortest scan times and highest agreement with Cartesian benchmarks. Reconstruction methods incorporating spatiotemporal regularization maintained spatial resolution and quantitative accuracy across undersampling factors up to 20-fold. In human subjects, non-Cartesian T1 mapping provided improved accuracy and reduced variability in mobile abdominal tissues compared to Cartesian acquisitions, particularly in the kidney cortex and medulla, where motion artifacts led to overestimation and higher variance in the reference method.
T1 mapping using non-Cartesian trajectories and compressed sensing reconstruction is feasible on a 1.5T MR-Linac. The proposed approach enables accurate, motion-resolved quantitative imaging within clinically practical acquisition times. These results support integration of quantitative T1 mapping into adaptive MR-guided radiotherapy workflows and establish a foundation for future development of multiparametric imaging and response-adaptive treatment strategies.
纵向弛豫率（R1 = 1/T1）的定量映射是几种用于自适应放射治疗计划的多参数MRI协议的主要组成部分。在经历较大生理运动的解剖部位实施这些协议具有挑战性。
在1.5T MR直线加速器上实现并验证一种运动分辨定量T1映射方法，该方法将非笛卡尔k空间采样轨迹与压缩感知（CS）重建技术相结合。
评估了四种3D非笛卡尔k空间轨迹：使用半辐条和全辐条覆盖的径向采样和星状堆叠采样。使用扰相梯度回波序列进行可变翻转角采集，并使用两个标准体模验证T1映射。通过经验优化梯度延迟定时，以最小化轨迹诱导的伪影。使用空间和时空正则化算子测试了八种压缩感知重建策略。对多种实现参数的重建进行了评估，并根据空间分辨率、偏差和变异性进行排名。体内研究包括一名健康志愿者和一名接受肾脏靶区放射治疗的患者。使用呼吸自门控和相位排序重建进行运动分辨成像。
在体模研究中所有非笛卡尔轨迹均显示出高重复性和低纵向偏差，变异系数低于3.3%。径向半辐条采样实现了最短扫描时间，并与笛卡尔基准具有最高一致性。纳入时空正则化的重建方法在欠采样因子高达20倍的情况下保持了空间分辨率和定量准确性。在人体受试者中，与笛卡尔采集相比，非笛卡尔T1映射在移动腹部组织中提供了更高的准确性并降低了变异性，特别是在肾皮质和髓质中；在这些部位，运动伪影导致参考方法出现高估和更高的方差。
在1.5T MR直线加速器上使用非笛卡尔轨迹和压缩感知重建进行T1映射是可行的。所提出的方法能够在临床实际采集时间内实现准确的、运动分辨定量成像。这些结果支持将定量T1映射整合到自适应MR引导放射治疗工作流程中，并为多参数成像和反应自适应治疗策略的未来发展奠定基础。
