SP745INFLUENCE OF HIP POSITION ON OXYGENATION OF RENAL TRANSPLANTS AS MEASURED BY FUNCTIONAL MRI METHODS-THE BENT KNEE STUDY

Abstract

INTRODUCTION AND AIMS: Interstitial fibrosis and tubular atrophy (IFTA) is considered multifactorial and determines long-term kidney graft survival. Iliac flow restriction with kinking is described in cyclists secondary to fibrous fixation of the iliac bifurcation. In renal transplants, a fibrous perigraft reaction develops postoperatively. Functional kinking due to tethering of iliac arteries by adjacent fibrotic tissue may occur during sitting position leading to repetitive graft hypoperfusion. The purpose of this study was to assess perfusion and oxygenation of renal grafts during hip flexion and extension using functional magnetic resonance imaging (fMRI) techniques. METHODS: This prospective single center controlled intervention study enrolled 19 consecutive renal transplant recipients (age 48+/-13years) with GFR>=30ml/min/ 1.73m 2. fMRI on a 3T-MR scanner including diffusion weighted (DWI), blood oxygenation level-dependent (BOLD) and ASL (arterial spin labelling) sequences was performed in hip position 0degree and >90degree. The protocol was performed before and after intravenous administration of 20 mg furosemide (FUR) to account for potential magnetic field inhomogeneities. Position order was changed randomly. All subjects previously underwent standardized hydration and determination of eGFR. 16 regions of interest were placed manually in cortical and medullary regions in a blinded fashion. DWI yielded ADC D (pure diffusion coefficient) and perfusion fraction (FP), BOLDMRI the relaxation rate R2* and ASL perfusion-values. RESULTS: DWI and BOLD-MRI were successfully completed in 19, ASL in 17 subjects. Mean values and standard deviations corresponded to published values. FUR reduced medullary R2* significantly in neutral hip position (p<0.0001). R2*-values were not significantly different between hip extension or flexion. However, the medullary R2* ratio without/with FUR was lower during hip flexion (p<0.0005) corresponding to a reduced response to FUR. No significant difference between positions was shown for FP and ADC D, except for medullary ADC D which was higher during hip flexion after FUR. With hip extension, medullary FP increased after FUR administration (p<0.005). Renal perfusion-values were significantly higher (p<0.03) in flexed compared to neutral hip position, except for cortical perfusion before FUR (p=0.051). Correlation coefficients between fMRI and clinical parameters including eGFR were generally low. CONCLUSIONS: The study demonstrates the feasibility and reliability of fMRI in renal grafts investigating two different body positions. Significant correlations between parameters obtained in different hip positions as well as before and after FUR administration confirmed measurement stability. In contrast to our hypothesis, perfusion increased during hip flexion as compared to neutral hip position. This may be due to precluded blood outflow rather than reduced inflow during hip flexion. However, response of R2* to FUR was significantly reduced in flexed position. In conclusion, the results demonstrate an acute impact of hip flexion on functional parameters in the kidney graft.