Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands.
Magn Reson Med. 2024 Jan;91(1):297-311. doi: 10.1002/mrm.29857. Epub 2023 Oct 6.
Respiratory-correlated 4D-MRI may provide motion characteristics for radiotherapy but is susceptible to irregular breathing. This study investigated the effectiveness of visual biofeedback (VBF) guidance for breathing regularization during 4D-MRI acquisitions on an MR-linac.
A simultaneous multislice-accelerated 4D-MRI sequence was interleaved with a one-dimensional respiratory navigator (1D-RNAV) in 10 healthy volunteers on a 1.5T Unity MR-linac (Elekta AB, Stockholm, Sweden). Volunteer-specific breathing amplitudes and periods were derived from the 1D-RNAV signal obtained during unguided 4D-MRI acquisitions. These were used for the guidance waveform, while the 1D-RNAV positions were overlayed as VBF. VBF effectiveness was quantified by calculating the change in coefficient of variation ( ) for the breathing amplitude and period, the position SD of end-exhale, end-inhale and midposition locations, and the agreement between the 1D-RNAV signals and guidance waveforms. The 4D-MRI quality was assessed by quantifying amounts of missing data.
VBF had an average latency of 520 ± 2 ms. VBF reduced median breathing variations by 18% to 35% (amplitude) and 29% to 57% (period). Median position SD reductions ranged from -3% to 35% (end-exhale), 29% to 38% (end-inhale), and 25% to 37% (midposition). Average differences between guidance waveforms and 1D-RNAV signals were 0.0 s (period) and +1.7 mm (amplitude). VBF also decreased the median amount of missing data by 11% and 29%.
A VBF system was successfully implemented, and all volunteers were able to adapt to the guidance waveform. VBF during 4D-MRI acquisitions drastically reduced breathing variability but had limited effect on missing data in respiratory-correlated 4D-MRI.
呼吸相关 4D-MRI 可为放射治疗提供运动特征，但易受不规则呼吸的影响。本研究旨在探讨在 MR 直线加速器上进行 4D-MRI 采集时，使用视觉生物反馈（VBF）指导进行呼吸规律化的效果。
在 1.5T Unity MR 直线加速器（Elekta AB，斯德哥尔摩，瑞典）上，对 10 名健康志愿者进行了同时多切片加速 4D-MRI 序列与一维呼吸导航仪（1D-RNAV）的交错采集。志愿者在未引导的 4D-MRI 采集过程中获得的 1D-RNAV 信号中提取特定于志愿者的呼吸幅度和周期。这些信号被用于指导波形，同时将 1D-RNAV 位置叠加为 VBF。通过计算呼吸幅度和周期的变异系数（ ）、呼气末、吸气末和中位置的位置标准差（SD），以及 1D-RNAV 信号与指导波形的一致性来量化 VBF 的有效性。通过量化缺失数据量来评估 4D-MRI 的质量。
VBF 的平均潜伏期为 520±2ms。VBF 将呼吸变异减少了 18%至 35%（幅度）和 29%至 57%（周期）。位置 SD 减少范围从-3%至 35%（呼气末）、29%至 38%（吸气末）和 25%至 37%（中位置）。指导波形和 1D-RNAV 信号之间的平均差异为 0.0s（周期）和+1.7mm（幅度）。VBF 还使中位缺失数据量减少了 11%和 29%。
成功实施了 VBF 系统，所有志愿者都能够适应指导波形。4D-MRI 采集过程中的 VBF 大大降低了呼吸变异性，但对呼吸相关 4D-MRI 中的缺失数据影响有限。
