Quantification of renal t2 relaxation rate by use of blood oxygen level–dependent magnetic resonance imaging before and after furosemide administration in healthy beagles

OBJECTIVE To assess the feasibility of blood oxygen level–dependent (BOLD) MRI for measurement of the renal T2* relaxation rate (R2*; proxy for renal oxy-genation) 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* (∆R2*) 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 ∆R2* 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 ∆R2* values had good or excellent reliability and repeatability, except the cortical ∆R2*, which had poor repeatability. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that BOLD MRI, when performed before and after furo-semide administration, was noninvasive and highly reliable and repeatable for dynamic evaluation of renal oxygenation in healthy dogs.