Normal and transplanted rat kidneys: diffusion MR imaging at 7 T.
OBJECTIVE
To investigate the feasibility of obtaining reproducible apparent diffusion coefficient (ADC) maps of normal rat kidneys by using respiratory-triggered spin-echo diffusion-weighted magnetic resonance (MR) imaging, to investigate the sensitivity of ADC maps in the evaluation of renal blood flow, and to use this technique to monitor acute graft rejection in transplanted rat kidneys.


METHODS
Spin-echo diffusion-weighted MR imaging measurements were performed in 20 normal rats and nine rats that had undergone transplantation (six rats had received allografts; three had received isografts) at 7 T. To evaluate the effect of alteration in blood flow and water transport function, angiotensin II was infused in six normal rats and a series of spin-echo diffusion-weighted MR images was obtained at five time points. Transplanted kidneys were monitored by obtaining spin-echo diffusion-weighted MR images and gradient-echo MR images every 2 hours for 8 hours on postoperative day 4. Statistical analysis was performed with repeated-measures multivariate analysis of variance and the paired t test.


RESULTS
No significant differences in ADC values were observed between right and left kidneys in all three orthogonal directions; however, a small difference was observed between the cortex and medulla. ADC values in the cephalocaudal and mediolateral directions were higher than those in the anteroposterior direction (P <.01 for all). ADC values in the cortex and medulla decreased significantly (by >35%, P <.01) during angiotensin II-induced reduction in renal blood flow. No significant signal intensity change was observed between native and transplanted kidneys on gradient-echo MR images. Allografts exhibited decreased ADC values (P <.01) and isografts exhibited similar ADC values compared with native kidneys.


CONCLUSIONS
These findings suggest that reproducible renal ADC maps can be obtained in rats by using spin-echo diffusion-weighted MR imaging at 7 T. Spin-echo diffusion-weighted MR imaging may have potential as a noninvasive tool for monitoring early graft rejection after kidney transplantation.
Yang
Dewen
D
Department of Biological Sciences, Pittsburgh NMR Center for Biomedical Research, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213, USA.
Ye
Qing
Q
Williams
Donald S
DS
Hitchens
T Kevin
TK
Ho
Chien
C
D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D038524:Diffusion Magnetic Resonance Imaging; D005240:Feasibility Studies; D006084:Graft Rejection / Q000175:diagnosis; D007672:Kidney Cortex / Q000098:blood supply; D007679:Kidney Medulla / Q000098:blood supply; D016030:Kidney Transplantation / Q000502:physiology*; D008297:Male; D051381:Rats; D011914:Rats, Inbred BN; D011919:Rats, Inbred Strains; D012079:Renal Circulation / Q000187:drug effects; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D014662:Vasoconstrictor Agents; D000804:Angiotensin II