Diffusion-weighted imaging in the evaluation of transplanted kidneys: correlation between renal creatinine clearance and apparent diffusion coefficient value

Purpose: To compare value of Apparent Diffusion Coefficient (ADC) with renal creatinine clearance in a population of kidney transplant recipients who underwent MR exam with Diffusion-Weighted Imaging (DWI) of the transplanted graft. Methods and Materials: 35 patients with transplanted kidney were studied by unenhanced MR exam; diffusion single-shot echo-planar sequences were acquired with a b value of 500 mm2/sec. The study population was divided into three groups according creatinine-clearance values: group A= clearance >60 ml/min; group B= clearance >30 and ≤60 ml/min; group C= clearance ≤30 ml/min; ADCs values between groups were compared using a Mann-Whitney test. The correlation between clearance and ADC was investigated by Pearson linear regression. Receiver Operating Characteristic (ROC) curves were used for prediction of normal and low renal function. Results: In the comparison between group A and group C, we observed a significant statistical difference - p=0.0003 - with ADC values higher in patients with normal clearance; comparing group B and group C, we didn’t find a statistical difference (p=0.051); considering group A and group B, we didn’t observe a statistical difference again (p=0.38). Pearson regression showed a coefficient r=0.5138 (95% CI=0.2179-0.7232), with significant level P=0.0016. In the prediction of group A ROC curve showed an AUC (area under curve) of 0.780, with sensitivity of 92.3% and specificity of 68.2% using a threshold ADC value of 2.08x10-3 mm2/sec. Conclusion: The statistical difference between non-contiguous groups seems to suggest DWI as a promising tool for non-invasive assessment of renal function; however, an overlap of ADC values between groups represents a limit.