Diffusion MR Imaging of the Rat Kidney at 7T

Feasibility of obtaining reliable and reproducible ADC maps in rat kidneys at 7 Tesla, and the effect of renal blood flow on ADC is investigated. A spin echo DWI sequence with respiratoly gating gave reproducible ADC maps with no significant differences between right and left kidneys. ADC of cortex and medulla in readout and phase direction were higher than that in slice direction (P35% during angiotensin 11-induced reduction in renal blood flow (P<O.Ol, n=6). The study suggests that ADC in the kidneys may be a good measure of renal blood perfusion and function. Introduction: Renal perfusion imaging may provide imponant information with regard to the pathophysiology of kidneys. Diffusion-weighted imaging (DWI) of the kidneys could provide a measure of perfusion according to the intravoxel incoherent motion (IVIM) model (1,Z). DWI of kidneys, in vivo, has been challenging because of respiration-induced motion. In some studies, echo planar imaging (EPI) bas helped in overcoming abdominal motion in renal MRI, but strong susceptibility artifacts present at high-field strengths typically used in animal scanners preclude the use of EPI for abdominal imaging in animals. In this study, we investigate the feasibility of obtaining reliable and reproducible apparent diffusion coefficient (ADC) maps in rat kidneys at 7 Tesla with a conventional spin echo (SE) sequence with respiratory gating. Because of the highly anisotropic nature of the renal vasculature, the dependence of ADC values on the direction of diffusion sensitizing gradient is also examined to ascertain if the diffusion sensitizing gradient in any particular direction causes ADC to be more flow sensitive. Finally, as a way of testing the sensitivity of ADC to flow, changes in ADC maps are monitored during pharmacologicallyinduced reduction in renal blood flow. To our knowledge, this is the fin1 study where ADCs of kidneys have been monitored during flow alterations.