Department of Diagnostic and Interventional Radiology, Medical Faculty, Heinrich Heine University Düsseldorf, Dusseldorf, Germany.
Institute of Physical Biology, Heinrich Heine University Düsseldorf, Dusseldorf, Germany.
Magn Reson Med. 2019 Sep;82(3):935-947. doi: 10.1002/mrm.27778. Epub 2019 Apr 19.
To characterize the proton exchange in aqueous urea solutions using a modified version of the WEX II filter at high magnetic field, and to assess the feasibility of performing quantitative urea CEST MRI on a 3T clinical MR system.
In order to study the dependence of the exchange-rate constant of urea as a function of pH and T, the WEX-spectra were acquired at 600 MHz from urea solutions in a pH range from 6.4 to 8.0 and a temperature range from to . The CEST experiments were performed on a 3T MRI scanner by applying a train of 50 Gaussian-shaped pulses, each 100-millisecond long with a spacing of 100 milliseconds, for saturation. Exchange rates of urea were calculated using the (extended) AREX metric.
The results showed that proton exchange in aqueous urea solutions is acid and base catalyzed with the rate constants: l/(mol·s) and l/(mol·s), respectively. Since the urea protons undergo a slow exchange with water protons, the CEST effect of urea can be observed efficiently at 3T. However, in neutral solutions the exchange rate of urea is minimal and cannot be estimated using the quantitative CEST approach.
By means of the WEX-spectroscopy, the kinetic parameters of the proton exchange in urea solutions have been determined. It was also possible to estimate the exchange rates of urea in a broad range of pH values using the CEST method at a clinical scanner.
在高磁场下使用经过改进的 WEX II 滤波器对水合尿素溶液中的质子交换进行特征描述，并评估在 3T 临床磁共振系统上进行定量尿素 CEST MRI 的可行性。
为了研究 pH 值和温度对尿素交换率常数 的依赖性，在 pH 值范围从 6.4 到 8.0 和温度范围从 到 的条件下，在 600 MHz 下从尿素溶液中获取 WEX 谱。CEST 实验是在 3T MRI 扫描仪上进行的，通过施加 50 个高斯形脉冲序列进行饱和，每个脉冲持续 100 毫秒，脉冲间隔为 100 毫秒。使用（扩展）AREX 度量来计算尿素的交换率。
结果表明，水合尿素溶液中的质子交换受酸和碱催化，其速率常数分别为 l/(mol·s)和 l/(mol·s)。由于尿素质子与水质子进行缓慢交换，因此可以在 3T 下有效地观察到尿素的 CEST 效应。然而，在中性溶液中，尿素的交换率最小，无法使用定量 CEST 方法进行估计。
通过 WEX 光谱法，已经确定了尿素溶液中质子交换的动力学参数。还可以使用 CEST 方法在临床扫描仪上在较宽的 pH 值范围内估计尿素的交换率。
