%0 Journal Article
%T Imaging Renal Urea Handling in Rats at Millimeter Resolution using Hyperpolarized Magnetic Resonance Relaxometry
%A Galen D. Reed
%A Cornelius von Morze
%A Alan S. Verkman
%A Bertram L. Koelsch
%A Myriam M. Chaumeil
%A Michael Lustig
%A Sabrina M. Ronen
%A Jeff M. Sands
%A Peder E. Z. Larson
%A Zhen J. Wang
%A Jan Henrik Ardenkj£¿r Larsen
%A John Kurhanewicz
%A Daniel B. Vigneron
%J Quantitative Biology
%D 2015
%I arXiv
%X \textit{In vivo} spin spin relaxation time ($T_2$) 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-$T_2$ 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 $T_2$ 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-$^2\textrm{H}_8$. Large $T_2$ increases in the inner-medullar and papilla were observed with the former agent and not the latter during antidiuresis suggesting that $T_2$ 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 mm$^3$ resolution 3D imaging - were developed to exploit the particularly long relaxation times observed.
%U http://arxiv.org/abs/1511.00200v2