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Noninvasive imaging of renal urea handling by CEST‐MRI
Author(s) -
Shin Soo Hyun,
Wendland Michael F.,
Zhang Brandon,
Tran An,
Tang Albert,
Vandsburger Moriel H.
Publication year - 2020
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.27968
Subject(s) - urea , chemistry , medulla , renal papilla , renal cortex , major duodenal papilla , kidney , endocrinology , anatomy , medicine , biochemistry
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.