Diffusion-weighted MRI sequences (DW-MRI) of the kidney: normal findings, influence of hydration state and repeatibility of results

PURPOSE: This study was performed to determine the apparent diffusion coefficient (ADC) of the normal kidney using diffusion-weighted magnetic resonance imaging (DW-MRI) sequences and to analyse both the changes due to hydration state and results repeatability. MATERIALS AND METHODS: Ten volunteers underwent DW-MRI imaging of the kidneys with a breath-hold single-shot spin-echo planar imaging (SE-EPI) sequence in the axial and coronal planes with b values of 300, 500, 800 s/mm(2), in different states of hydration. Urine osmolarity (OsmU) and sodium excretion (NaU) were measured at the time of each examination. ADC maps were created for all b values, and ADC values were calculated and compared between different states of hydration. In five subjects, the protocol was conducted twice to test data repeatability. RESULTS: ADC values were lower with higher b values (3.00 vs. 2.47 vs. 1.99 x 10(-3) mm(2)/s with b values of 300, 500, 800 s/mm(2), respectively). ADC values in different hydration states were not statistically different. Measurements were reproducible. OsmU and NaU were statistically different in the different states of hydration (p<0.01). CONCLUSIONS: ADC values significantly decrease with higher b values. Average ADC values in the normal kidney are reproducible. Hydration state does not significantly influence mean ADC values.