Evaluation of renal oxygenation in rat by using R2′ at 3-T magnetic resonance:: Initial observation

Rationale and Objectives. We sought to initially evaluate the feasibility of R2' on a 3-T magnetic resonance (MR) scanner for assessment of renal oxygenation changes following administration of furosemide in rats. Materials and Methods. Eight intact male Wistar rats were involved in experimental group. The experiment was performed at a 3-T MR scanner using a multiple gradient-echo (mGRE) sequence for R2* map and a multiecho fast spinecho (FSE) sequence for R2 map. R2' values of cortex and medulla were calculated using the equation R2* = R2 + R2'. The values of R2 and R2* were measured and R2' was calculated before and after administration of furosemide, and the changes (delta values) were calculated. Results. Both R2* and R2 values decreased significantly after administration of furosemide (P < .001) in both the cortex and medulla. Delta R2* in the medulla was significantly higher than in the cortex (P < .05). Delta R2 was not significantly different between the cortex and medulla (P > .05). The baseline R2' value was 12.13 +/- 0.59 1/s in the cortex and 19.52 +/- 3.44 1/s in the medulla. R2' value decreased significantly in the medulla after administration of furosemide (P < .05), but there was no significant difference in the cortex before and after administration of furosemide (P > .05). Conclusion. R2' may be more appropriate than R2* to indicate the change of oxygenation after administration of furosemide in intact rats at 3-T MR. Further studies are needed for both intact animals and experimental models in comparison with non-MR imaging methods to validate this initial observation.