CEST-MRI 无创成像评估肾脏尿素处理
Noninvasive imaging of renal urea handling by CEST-MRI.
机构信息
Department of Bioengineering, University of California, Berkeley, Berkeley, California.
Berkeley Preclinical Imaging Core, University of California, Berkeley, Berkeley, California.
出版信息
Magn Reson Med. 2020 Mar;83(3):1034-1044. doi: 10.1002/mrm.27968. Epub 2019 Sep 4.
PURPOSE
Renal function is characterized by concentration of urea for removal in urine. We tested urea as a CEST-MRI contrast agent for measurement of the concentrating capacity of distinct renal anatomical regions.
METHODS
The CEST contrast of urea was examined using phantoms with different concentrations and pH levels. Ten C57BL/6J mice were scanned twice at 7 T, once following intraperitoneal injection of 2M 150 µL urea and separately following an identical volume of saline. Kidneys were segmented into regions encompassing the cortex, outer medulla, and inner medulla and papilla to monitor spatially varying urea concentration. Z-spectra were acquired before and 20 minutes after injection, with dynamic scanning of urea handling performed in between via serial acquisition of CEST images acquired following saturation at +1 ppm.
RESULTS
Phantom experiments revealed concentration and pH-dependent CEST contrast of urea that was both acid- and base-catalyzed. Z-spectra acquired before injection showed significantly higher CEST contrast in the inner medulla and papilla (2.3% ± 1.9%) compared with the cortex (0.15% ± 0.75%, P = .011) and outer medulla (0.12% ± 0.58%, P = .008). Urea infusion increased CEST contrast in the inner medulla and papilla by 2.1% ± 1.9% (absolute), whereas saline infusion decreased CEST contrast by -0.5% ± 2.0% (absolute, P = .028 versus urea). Dynamic scanning revealed that thermal drift and diuretic status are confounding factors.
CONCLUSION
Urea CEST has a potential of monitoring renal function by capturing the spatially varying urea concentrating ability of the kidneys.
目的
肾功能的特点是通过尿液去除来浓缩尿素。我们测试了尿素作为 CEST-MRI 对比剂，用于测量不同肾脏解剖区域的浓缩能力。
方法
使用不同浓度和 pH 值的体模来检查尿素的 CEST 对比。在 7T 下对 10 只 C57BL/6J 小鼠进行了两次扫描，一次是在腹腔注射 2M 150µL 尿素后，另一次是在相同体积的生理盐水后。将肾脏分割成包含皮质、外髓质和内髓质以及乳头的区域，以监测空间变化的尿素浓度。在注射前和注射后 20 分钟采集 Z 谱，通过在 +1 ppm 处饱和后连续采集 CEST 图像来动态扫描尿素处理。
结果
体模实验显示，尿素的 CEST 对比与浓度和 pH 值有关，既有酸催化又有碱催化。注射前采集的 Z 谱显示，内髓质和乳头的 CEST 对比明显高于皮质（2.3%±1.9% 比 0.15%±0.75%，P=0.011）和外髓质（0.12%±0.58%，P=0.008）。尿素输注使内髓质和乳头的 CEST 对比增加了 2.1%±1.9%（绝对值），而生理盐水输注使 CEST 对比降低了-0.5%±2.0%（绝对值，P=0.028 与尿素相比）。动态扫描显示，热漂移和利尿状态是混杂因素。
结论
通过捕捉肾脏空间变化的尿素浓缩能力，尿素 CEST 具有监测肾功能的潜力。
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