Evaluation of Renal Function with Diffusion Weighted MRI of the Kidneys

Introduction: In recent years diffusion weighted MRI (DWI) has begun to be applied outside of the central nervous system, with researchers examining DWI of the abdominal and pelvic organs. Initial studies of DWI in the kidneys [1-3] have shown a relationship between the apparent diffusion coefficient (ADC) in renal parenchyma and renal function, with scan subjects with elevated serum creatinine (Cr) generally having lower renal ADC values than subjects with normal renal function. One significant limitation of these studies has been the lack of gold standard measurements of renal function (inulin or iothalamate clearance) in the subjects. Serum creatinine is affected by factors other than glomerular filtration rate (GFR), such as muscle mass, and predictive equations based on Cr such as the CockroftGault equation or the Modification of Diet in Renal Disease (MDRD) equation are known to correlate somewhat poorly with GFR [4,5]. Additionally, differences in technique among these early studies have limited evaluation of the exact relationship between GFR and renal ADC. In order to accurately assess the relationship between renal function and renal DWI it is necessary to have accurate measurements of GFR in patients getting diffusion weighted MRI, preferably on the same day, as GFR is known to fluctuate up to 10% in normal individuals. We hypothesize that renal cortical ADC provides an accurate measure of the function of renal cortex, so that the product of cortical ADC and renal cortical volume is proportional to GFR. This may provide a simple, rapid, non-invasive method of accurately measuring renal function.