\textit{In vivo} spin spin relaxation time (T2) heterogeneity of hyperpolarized \textsuperscript{13}C urea in the rat kidney was investigated. Selective quenching of the vascular hyperpolarized \textsuperscript{13}C signal with a macromolecular relaxation agent revealed that a long-T2 component of the \textsuperscript{13}C urea signal originated from the renal extravascular space, thus allowing the vascular and renal filtrate contrast agent pools of the \textsuperscript{13}C urea to be distinguished via multi-exponential analysis. The T2 response to induced diuresis and antidiuresis was performed with two imaging agents: hyperpolarized \textsuperscript{13}C urea and a control agent hyperpolarized bis-1,1-(hydroxymethyl)-1-\textsuperscript{13}C-cyclopropane-2H8. Large T2 increases in the inner-medullar and papilla were observed with the former agent and not the latter during antidiuresis suggesting that T2 relaxometry may be used to monitor the inner-medullary urea transporter (UT)-A1 and UT-A3 mediated urea concentrating process. Two high resolution imaging techniques - multiple echo time averaging and ultra-long echo time sub-2 mm3 resolution 3D imaging - were developed to exploit the particularly long relaxation times observed.
@article{arxiv.1511.00200,
title = {Imaging Renal Urea Handling in Rats at Millimeter Resolution using Hyperpolarized Magnetic Resonance Relaxometry},
author = {Galen D. Reed and Cornelius von Morze and Alan S. Verkman and Bertram L. Koelsch and Myriam M. Chaumeil and Michael Lustig and Sabrina M. Ronen and Jeff M. Sands and Peder E. Z. Larson and Zhen J. Wang and Jan Henrik Ardenkjær Larsen and John Kurhanewicz and Daniel B. Vigneron},
journal= {arXiv preprint arXiv:1511.00200},
year = {2015}
}