Quantification of renal T2 relaxation rate by use of blood oxygen level-dependent magnetic resonance imaging before and after furosemide administration in healthy Beagles

Abstract

Objective: To assess the feasibility of blood oxygen level-dependent (BOLD) MRI for measurement of the renal T2* relaxation rate (R2*; proxy for renal oxygenation) before and after furosemide administration and to evaluate the reliability and repeatability of those measurements in healthy dogs. Animals: 8 healthy adult Beagles (4 males and 4 females). Procedures: Each dog was anesthetized and underwent BOLD MRI before (baseline) and 3 minutes after administration of furosemide (1 mg/kg, IV) twice, with a 1-week interval between scanning sessions. Mapping software was used to process MRI images and measure R2* and the difference in R2* (ΔR2*) before and after furosemide administration. The intraclass correlation coefficient was calculated to assess measurement reliability, and the coefficient of variation and Bland-Altman method were used to assess measurement repeatability. Results: Mean ± SD baseline R2* in the renal medulla (24.5 ± 3.8 seconds-1) was significantly greater than that in the renal cortex (20.6 ± 2.7 seconds-1). Mean R2* in the renal cortex (18.6 ± 2.6 seconds-1) and medulla (17.8 ± 1.5 seconds-1) decreased significantly after furosemide administration. Mean ΔR2* in the medulla (6.7 ± 2.4 seconds-1) was significantly greater than that in the renal cortex (2.1 ± 0.7 seconds-1). All R2* and ΔR2* values had good or excellent reliability and repeatability, except the cortical ΔR2*, which had poor repeatability. Conclusions and clinical relevance: Results suggested that BOLD MRI, when performed before and after furosemide administration, was noninvasive and highly reliable and repeatable for dynamic evaluation of renal oxygenation in healthy dogs.