Diffusion tensor imaging and tractography of the kidney in children: feasibility and preliminary experience.

BACKGROUND: Functional magnetic resonance urography (fMRU) provides morphological and functional information based on perfusion. Diffusion tensor imaging (DTI) complements fMRU by measuring renal microstructure and provides insight into the relationship between renal structure and function.

OBJECTIVE: To evaluate the feasibility and utility of renal DTI and tractography in the setting of fMRU in children.

MATERIALS AND METHODS: We prospectively enrolled 9 children (6 boys, 3 girls) with a mean age of 4.3 years (range 6 months to 14.8 years). All children were examined with MRI at 3.0 tesla. DTI was acquired with an echo-planar sequence (TR/TE = 2,300/69 ms, b = 300 s/mm2) with 12 non-collinear directions and 3 signal averages. Functional MRU results were used to group the moieties as normal or abnormal. Regions of interest were placed in the medulla and cortex to measure DTI parameters of microstructure. DTI tractography measures of parenchymal volume were compared to fMRU-derived volumes.

RESULTS: We analyzed 19 moieties (13 normal; 6 abnormal). Tractography of normal moieties showed numerous tracks with a radial arrangement and convergence into pyramids. Abnormal moieties did not show the radial arrangement or converging architecture and had tracks that were loosely arranged and left hollow spaces. Tractography volume correlated with MRU parenchymal volume (r 2 = 0.93, P < 0.005) and abnormal moieties exhibited greater tractography volume than normal moieties (P < 0.005). Tractography volume also correlated with age of the child (P < 0.001). In normal moieties, the medulla had higher fractional anisotropy (0.401 +/−0.05) than the cortex (0.183 +/− 0.03) (P < 0.001); fractional anisotropy in these regions did not change with age (P > 0.1). There were no differences in apparent diffusion coefficient values between the cortex and medulla (P > 0.5). We observed a trend of increasing apparent diffusion coefficient values with age in the cortex and medulla, which did not reach statistical significance (cortex: r2 = 0.21, P > 0.1; medulla: r2 = 0.135, P > 0.1).

CONCLUSION: DTI with tractography is feasible in children and can complement the functional information obtained from fMRU.