Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts.
F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland.
Magn Reson Med. 2018 Dec;80(6):2449-2463. doi: 10.1002/mrm.27221. Epub 2018 May 13.
To develop a fast magnetic resonance fingerprinting (MRF) method for quantitative chemical exchange saturation transfer (CEST) imaging.
We implemented a CEST-MRF method to quantify the chemical exchange rate and volume fraction of the N -amine protons of L-arginine (L-Arg) phantoms and the amide and semi-solid exchangeable protons of in vivo rat brain tissue. L-Arg phantoms were made with different concentrations (25-100 mM) and pH (pH 4-6). The MRF acquisition schedule varied the saturation power randomly for 30 iterations (phantom: 0-6 μT; in vivo: 0-4 μT) with a total acquisition time of ≤2 min. The signal trajectories were pattern-matched to a large dictionary of signal trajectories simulated using the Bloch-McConnell equations for different combinations of exchange rate, exchangeable proton volume fraction, and water T and T relaxation times.
The chemical exchange rates of the N -amine protons of L-Arg were significantly (P < 0.0001) correlated with the rates measured with the quantitation of exchange using saturation power method. Similarly, the L-Arg concentrations determined using MRF were significantly (P < 0.0001) correlated with the known concentrations. The pH dependence of the exchange rate was well fit (R = 0.9186) by a base catalyzed exchange model. The amide proton exchange rate measured in rat brain cortex (34.8 ± 11.7 Hz) was in good agreement with that measured previously with the water exchange spectroscopy method (28.6 ± 7.4 Hz). The semi-solid proton volume fraction was elevated in white (12.2 ± 1.7%) compared to gray (8.1 ± 1.1%) matter brain regions in agreement with previous magnetization transfer studies.
CEST-MRF provides a method for fast, quantitative CEST imaging.
开发一种快速磁共振指纹（MRF）方法用于定量化学交换饱和转移（CEST）成像。
我们实现了一种 CEST-MRF 方法来量化 L-精氨酸（L-Arg）幻影中的 N-胺质子的化学交换率和体积分数以及体内大鼠脑组织中的酰胺和半固体可交换质子。L-Arg 幻影的浓度（25-100 mM）和 pH（pH 4-6）不同。MRF 采集方案在 30 次迭代中随机改变饱和功率（幻影：0-6 μT；体内：0-4 μT），总采集时间≤2 分钟。信号轨迹与使用不同交换率、可交换质子体积分数以及水 T 和 T 弛豫时间的 Bloch-McConnell 方程模拟的大信号轨迹字典进行模式匹配。
L-Arg 的 N-胺质子的化学交换率与使用饱和功率法测量的交换率显著相关（P < 0.0001）。同样，使用 MRF 确定的 L-Arg 浓度与已知浓度显著相关（P < 0.0001）。交换率的 pH 依赖性很好地符合碱催化交换模型（R ² = 0.9186）。大鼠大脑皮层测量的酰胺质子交换率（34.8 ± 11.7 Hz）与先前用水交换光谱法测量的交换率（28.6 ± 7.4 Hz）非常吻合。白质（12.2 ± 1.7%）的半固体质子体积分数高于灰质（8.1 ± 1.1%），这与先前的磁化转移研究一致。
CEST-MRF 提供了一种快速、定量 CEST 成像的方法。
