Dynamic contrast-enhanced quantitative susceptibility mapping with ultrashort echo time MRI for evaluating renal function
Luke Xie1,5, Anita T. Layton2, Nian Wang3, Peder E.Z. Larson4, Jeff L. Zhang5, Vivian S. Lee5, Chunlei Liu1,3, G. Allan Johnson1
1Center for In Vivo Microscopy, Department of Radiology, Duke University Medical Center
2Department of Mathematics, Duke University
3Brain Imaging and Analysis Center, Duke University Medical Center
4Department of Radiology and Biomedical Engineering, University of California, San Francisco
5Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah-Salt Lake City
American Journal of Physiology - Renal Physiology, 2015 Oct 7:ajprenal.00351.2015. doi: 10.1152/ajprenal.00351.2015. [Epub ahead of print]
Dynamic contrast-enhanced (DCE) MRI can provide key insight into renal function. DCE MRI is typically achieved through an injection of a gadolinium (Gd)-based contrast agent, which has desirable T1 quenching and tracer kinetics. However, significant T2* blooming effects and signal voids can arise when Gd becomes very concentrated, especially in the renal medulla and pelvis. One MRI sequence designed to alleviate T2* effects is the ultrashort echo time (UTE) sequence. In the present study, we observed a T2* blooming effect in the inner medulla of the mouse kidney, despite using UTE at an echo time of 20 microseconds and a low dose of 0.03 mmol/kg Gd. We applied quantitative susceptibility mapping (QSM) and resolved the signal void into a positive susceptibility signal. The susceptibility values (in ppm) were converted into molar concentrations of Gd using a calibration curve. We determined the concentrating mechanism (referred as concentrating index) as a ratio of maximum Gd concentration in the inner medulla to the renal artery. The concentrating index was assessed longitudinally over a 17-week course (3, 5, 7, 9, 13, 17 weeks of age). We conclude that a UTE-based DCE method is limited in resolving extreme T2* content caused by the kidney’s strong concentrating mechanism. QSM was able to resolve and confirm the source of the blooming effect to be the large positive susceptibility of concentrated Gd. UTE with QSM can complement traditional magnitude UTE and offer a powerful tool to study renal pathophysiology.
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Acknowledgements:
All imaging was performed at the Duke Center for In Vivo Microscopy, an NIH/NIBIB National Biomedical Technology Resource Center supported by (P41 EB015897 to G.A.J.) and NIH/Office of the Director (S10 OD010683 to G.A.J.). This work was also supported in part by NIH/MIMH (R01 MH096979 to C.L.), NIH/NIDDK (R01 DK089066 to A.T.L.), and National Science Foundation (DMS-1263995 to A.T.L.).
