Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany.
Medical Radiation Physics, Clinical Sciences Lund, Lund University, Lund, Sweden.
PLoS One. 2023 Oct 5;18(10):e0291273. doi: 10.1371/journal.pone.0291273. eCollection 2023.
The study aims to develop easy-to-implement concomitant field-compensated gradient waveforms with varying velocity-weighting (M1) and acceleration-weighting (M2) levels and to evaluate their efficacy in correcting signal dropouts and preserving the black-blood state in liver diffusion-weighted imaging. Additionally, we seek to determine an optimal degree of compensation that minimizes signal dropouts while maintaining blood signal suppression.
Numerically optimized gradient waveforms were adapted using a novel method that allows for the simultaneous tuning of M1- and M2-weighting by changing only one timing variable. Seven healthy volunteers underwent diffusion-weighted magnetic resonance imaging (DWI) with five diffusion encoding schemes (monopolar, velocity-compensated (M1 = 0), acceleration-compensated (M1 = M2 = 0), 84%-M1-M2-compensated, 67%-M1-M2-compensated) at b-values of 50 and 800 s/mm2 at a constant echo time of 70 ms. Signal dropout correction and apparent diffusion coefficients (ADCs) were quantified using regions of interest in the left and right liver lobe. The blood appearance was evaluated using two five-point Likert scales.
Signal dropout was more pronounced in the left lobe (19%-42% less signal than in the right lobe with monopolar scheme) and best corrected by acceleration-compensation (8%-10% less signal than in the right lobe). The black-blood state was best with monopolar encodings and decreased significantly (p < 0.001) with velocity- and/or acceleration-compensation. The partially M1-M2-compensated encoding schemes could restore the black-blood state again. Strongest ADC bias occurred for monopolar encodings (difference between left/right lobe of 0.41 μm2/ms for monopolar vs. < 0.12 μm2/ms for the other encodings).
All of the diffusion encodings used in this study demonstrated suitability for routine DWI application. The results indicate that a perfect value for the level of M1-M2-compensation does not exist. However, among the examined encodings, the 84%-M1-M2-compensated encodings provided a suitable tradeoff.
本研究旨在开发易于实施的同时具有可变速度加权（M1）和加速度加权（M2）水平的伴随场补偿梯度波形，并评估其在纠正信号缺失和保持肝脏扩散加权成像中的黑血状态方面的效果。此外，我们旨在确定最佳补偿程度，在保持血液信号抑制的同时最小化信号缺失。
使用一种新方法适应数值优化的梯度波形，该方法通过仅改变一个时间变量即可同时调整 M1 和 M2 加权。七名健康志愿者在恒定回波时间为 70ms 时，在 b 值为 50 和 800s/mm2 下进行扩散加权磁共振成像（DWI），使用五种扩散编码方案（单极，速度补偿（M1=0），加速度补偿（M1=M2=0），84%-M1-M2 补偿，67%-M1-M2 补偿）。使用左、右肝叶的感兴趣区域量化信号缺失校正和表观扩散系数（ADC）。使用两个五分制 Likert 量表评估血液外观。
在左叶中信号缺失更为明显（与单极方案相比，信号减少 19%-42%），通过加速度补偿可得到最佳校正（与右叶相比，信号减少 8%-10%）。黑血状态在单极编码时最佳，随着速度和/或加速度补偿，黑血状态显著下降（p<0.001）。部分 M1-M2 补偿编码方案可以再次恢复黑血状态。对于单极编码，出现最强的 ADC 偏差（单极编码时左/右叶之间的差异为 0.41μm2/ms，而其他编码时的差异小于 0.12μm2/ms）。
本研究中使用的所有扩散编码均适用于常规 DWI 应用。结果表明，不存在 M1-M2 补偿水平的完美值。然而，在所检查的编码中，84%-M1-M2 补偿编码提供了一个合适的折衷方案。
