Role of blood oxygen level-dependent magnetic resonance imaging in studying renal oxygenation changes in renal artery stenosis.

Aim: Primary objective of this study was to compare R2* value of the post-stenotic kidney with contralateral kidney, kidneys of essential hypertensive patients, and healthy subjects using blood oxygen level-dependent magnetic resonance imaging (BOLD MRI) technique. The secondary objective was to study the effect of severity of stenosis and viability of kidneys on R2* value.

Methods: We compared 4 groups of kidneys including 92 with renal artery stenosis, 37 normal contralateral kidneys of unilateral renal artery stenosis patients, 62 kidneys of essential hypertensive patients, and 40 kidneys of healthy controls using BOLD MRI. Deoxyhemoglobin level represented by R2* was calculated before and after giving furosemide and was compared among different groups.

Results: Baseline means cortical R2* value did not differ between groups. Response to furosemide was reduced in stenotic kidneys as compared to essential hypertensive and healthy control groups (p < 0.001). The mean R2* value of the contralateral normal kidney group was not significantly different from the stenotic group. Baseline R2* value and delta R2* values did not differ between different degrees of stenosis. Higher mean cortical R2* was seen in stenotic kidneys which were small (< 7 cm) in size (24.27 ± 5.65 vs 21.7 ± 3.88; p value 0.02) or with poor corticomedullary differentiation (24.64 ± 5.8 vs 20.74 ± 3.34; p value 0.006) as compared to other stenotic kidneys. Similarly, the delta R2* value was also blunted in these small shrunken kidneys (p value < 0.001).

Conclusion: R2* values on BOLD MRI are significantly different between kidneys with and without renal artery stenosis and can potentially also predict the utility of revascularization.