Muslu Yavuz, Tamada Daiki, Roberts Nathan T, Cashen Ty A, Mandava Sagar, Kecskemeti Steven R, Hernando Diego, Reeder Scott B
Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA.
Department of Radiology, University of Wisconsin-Madison, Madison, Wisconsin, USA.
Magn Reson Med. 2024 Nov;92(5):1913-1932. doi: 10.1002/mrm.30182. Epub 2024 Jun 23.
Quantitative T mapping has the potential to replace biopsy for noninvasive diagnosis and quantitative staging of chronic liver disease. Conventional T mapping methods are confounded by fat and inhomogeneities, resulting in unreliable T estimations. Furthermore, these methods trade off spatial resolution and volumetric coverage for shorter acquisitions with only a few images obtained within a breath-hold. This work proposes a novel, volumetric (3D), free-breathing T mapping method to account for multiple confounding factors in a single acquisition.
Free-breathing, confounder-corrected T mapping was achieved through the combination of non-Cartesian imaging, magnetization preparation, chemical shift encoding, and a variable flip angle acquisition. A subspace-constrained, locally low-rank image reconstruction algorithm was employed for image reconstruction. The accuracy of the proposed method was evaluated through numerical simulations and phantom experiments with a T/proton density fat fraction phantom at 3.0 T. Further, the feasibility of the proposed method was investigated through contrast-enhanced imaging in healthy volunteers, also at 3.0 T.
The method showed excellent agreement with reference measurements in phantoms across a wide range of T values (200 to 1000 ms, slope = 0.998 (95% confidence interval (CI) [0.963 to 1.035]), intercept = 27.1 ms (95% CI [0.4 54.6]), r = 0.996), and a high level of repeatability. In vivo imaging studies demonstrated moderate agreement (slope = 1.099 (95% CI [1.067 to 1.132]), intercept = -96.3 ms (95% CI [-82.1 to -110.5]), r = 0.981) compared to saturation recovery-based T maps.
The proposed method produces whole-liver, confounder-corrected T maps through simultaneous estimation of T, proton density fat fraction, and in a single, free-breathing acquisition and has excellent agreement with reference measurements in phantoms.
定量T映射有潜力取代活检，用于慢性肝病的无创诊断和定量分期。传统的T映射方法受脂肪和不均匀性影响，导致T估计不可靠。此外，这些方法为了缩短采集时间，以牺牲空间分辨率和容积覆盖范围为代价，在一次屏气中仅获得少数图像。本研究提出一种新颖的容积（3D）自由呼吸T映射方法，可在单次采集中考虑多个混杂因素。
通过非笛卡尔成像、磁化准备、化学位移编码和可变翻转角采集的组合，实现自由呼吸、混杂因素校正的T映射。采用子空间约束、局部低秩图像重建算法进行图像重建。通过数值模拟和在3.0 T下使用T/质子密度脂肪分数体模进行的体模实验，评估所提方法的准确性。此外，同样在3.0 T下，通过对健康志愿者进行对比增强成像，研究所提方法的可行性。
该方法在广泛的T值范围（200至1000 ms）内，与体模中的参考测量结果显示出极佳的一致性（斜率 = 0.998（95%置信区间（CI）[0.963至1.035]），截距 = 27.1 ms（95% CI [0.4至54.6]），r = 0.996），并且具有高度的可重复性。与基于饱和恢复的T图相比，体内成像研究显示出中等程度的一致性（斜率 = 1.099（95% CI [1.067至1.132]），截距 = -96.3 ms（95% CI [-82.1至-110.5]），r = 0.981）。
所提方法通过在单次自由呼吸采集中同时估计T、质子密度脂肪分数和，生成全肝、混杂因素校正的T图，并且与体模中的参考测量结果具有极佳的一致性。
