Medical Physics Graduate Program, Duke University, 2424 Erwin Road Suite 101, Durham, NC 27705, United States of America.
Phys Med Biol. 2017 Dec 14;63(1):01NT01. doi: 10.1088/1361-6560/aa9746.
To accelerate volumetric cine MRI (VC-MRI) using undersampled 2D-cine MRI to provide real-time 3D guidance for gating/target tracking in radiotherapy.
4D-MRI is acquired during patient simulation. One phase of the prior 4D-MRI is selected as the prior images, designated as MRI. The on-board VC-MRI at each time-step is considered a deformation of the MRI. The deformation field map is represented as a linear combination of the motion components extracted by principal component analysis from the prior 4D-MRI. The weighting coefficients of the motion components are solved by matching the corresponding 2D-slice of the VC-MRI with the on-board undersampled 2D-cine MRI acquired. Undersampled Cartesian and radial k-space acquisition strategies were investigated. The effects of k-space sampling percentage (SP) and distribution, tumor sizes and noise on the VC-MRI estimation were studied. The VC-MRI estimation was evaluated using XCAT simulation of lung cancer patients and data from liver cancer patients. Volume percent difference (VPD) and Center of Mass Shift (COMS) of the tumor volumes and tumor tracking errors were calculated.
For XCAT, VPD/COMS were 11.93 ± 2.37%/0.90 ± 0.27 mm and 11.53 ± 1.47%/0.85 ± 0.20 mm among all scenarios with Cartesian sampling (SP = 10%) and radial sampling (21 spokes, SP = 5.2%), respectively. When tumor size decreased, higher sampling rate achieved more accurate VC-MRI than lower sampling rate. VC-MRI was robust against noise levels up to SNR = 20. For patient data, the tumor tracking errors in superior-inferior, anterior-posterior and lateral (LAT) directions were 0.46 ± 0.20 mm, 0.56 ± 0.17 mm and 0.23 ± 0.16 mm, respectively, for Cartesian-based sampling with SP = 20% and 0.60 ± 0.19 mm, 0.56 ± 0.22 mm and 0.42 ± 0.15 mm, respectively, for radial-based sampling with SP = 8% (32 spokes).
It is feasible to estimate VC-MRI from a single undersampled on-board 2D cine MRI. Phantom and patient studies showed that the temporal resolution of VC-MRI can potentially be improved by 5-10 times using a 2D cine image acquired with 10-20% k-space sampling.
利用欠采样的 2D 电影 MRI 加速容积电影 MRI（VC-MRI），以便在放射治疗中为门控/目标跟踪提供实时 3D 引导。
在患者模拟期间采集 4D-MRI。前 4D-MRI 的一个相位被选为先验图像，指定为 MRI。每个时间步的机载 VC-MRI 被视为 MRI 的变形。变形场图表示为由前 4D-MRI 中通过主成分分析提取的运动分量的线性组合。通过将相应的 VC-MRI 的 2D 切片与采集到的机载欠采样 2D 电影 MRI 匹配来求解运动分量的加权系数。研究了欠采样笛卡尔和径向 k 空间采集策略。研究了 k 空间采样百分比（SP）和分布、肿瘤大小和噪声对 VC-MRI 估计的影响。使用肺癌 XCAT 模拟和肝癌患者数据评估 VC-MRI 估计。计算肿瘤体积的体积百分比差异（VPD）和质心移位（COMS）以及肿瘤跟踪误差。
对于 XCAT，使用笛卡尔采样（SP=10%）和径向采样（21 个辐条，SP=5.2%）时，所有情况下的 VPD/COMS 分别为 11.93±2.37%/0.90±0.27mm 和 11.53±1.47%/0.85±0.20mm。当肿瘤尺寸减小时，较高的采样率比较低的采样率实现更准确的 VC-MRI。VC-MRI 对噪声水平高达 SNR=20 具有鲁棒性。对于患者数据，笛卡尔采样的 superior-inferior、anterior-posterior 和 lateral（LAT）方向的肿瘤跟踪误差分别为 0.46±0.20mm、0.56±0.17mm 和 0.23±0.16mm，SP=20%，径向采样的误差分别为 0.60±0.19mm、0.56±0.22mm 和 0.42±0.15mm，SP=8%（32 个辐条）。
从单个欠采样机载 2D 电影 MRI 中估计 VC-MRI 是可行的。体模和患者研究表明，使用 10-20%k 空间采样采集的 2D 电影 MRI 可以将 VC-MRI 的时间分辨率提高 5-10 倍。
