Parametric and quantitative analysis of MR renographic curves for assessing the functional behaviour of the kidney

Abstract

The aim of this study was to refine the description of the renal function based on MR images and through transit-time curve analysis on a normal population and on a population with renal failure, using the quantitative model of the up-slope. Thirty patients referred for a kidney MR exam were divided in a first population with well-functioning kidneys and in a second population with renal failure from ischaemic kidney disease. The perfusion sequence consisted of an intravenous injection of Gd-DTPA and of a fast GRE sequence T1-TFE with 90° magnetisation preparation (Intera 1.5 T MR System, Philips Medical System). To convert the signal intensity into 1/T1, which is proportional to the contrast media concentration, a flow-corrected calibration procedure was used. Following segmentation of regions of interest in the cortex and medulla of the kidney and in the abdominal aorta, outflow curves were obtained and filtered to remove the high frequency fluctuations. The model of the up-slope method was then applied. Significant reduction of the cortical perfusion ( Q c=0.057±0.030 ml/(s 100 g) to Q c=0.030±0.017 ml/(s 100 g), P<0.013), of the medullary perfusion ( Q m=0.023±0.018 ml/(s 100 g) to Q m=0.011±0.006 ml/(s 100 g), P<0.046) and of the accumulation of contrast media in the medulla ( Q a=0.005±0.003 ml/(s 100 g) to Q a=0.0009±0.0008 ml/(s 100 g), P<0.001) were found in presence of renal failure. High correlations were found between the creatinine level and the accumulation Q a in the medulla ( r 2=0.72, P<0.05), and between the perfusion ratio Q c/ Q m and the accumulation Q a in the medulla ( r 2=0.81, P<0.05). No significant difference was found in times to peak between both populations despite a trend showing T a the time to the end of the increasing contrast accumulation period in the medulla, arriving later for renal failure. Advances in MR signal calibration with the building of quantitative model such as the up-slope allow to assess kinetic and haemodynamic and functional parameters of the diseased kidney.