Investigation of diffusion time dependence of apparent diffusion coefficient and intravoxel incoherent motion parameters in the human kidney
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Purpose
To characterize the diffusion time (Δ eff ) dependence of apparent diffusion coefficient (ADC) and intravoxel incoherent motion–related parameters in the human kidney at 3 T.
Methods
Sixteen healthy volunteers underwent an MRI examination at 3 T including diffusion‐weighted imaging at different Δ eff ranging from 24.1 to 104.1 ms. The extended mono‐exponential ADC and intravoxel incoherent motion models were fitted to the data for each Δ eff and the medullary and cortical ADC, (pseudo‐)diffusion coefficients ( D * and D ) and flow‐related signal fraction ( f ) were calculated.
Results
When all the data were used for fitting, a significant trend toward higher ADC with increasing Δ eff was observed between 24.1 and 104.1 ms (median and interquartile range: 2.38 [2.19, 2.47] to 2.84 [2.36, 2.90] × 10 −3 mm 2 /s for cortex, and 2.28 [2.18, 2.37] to 2.82 [2.58, 3.11] × 10 −3 mm 2 /s for medulla). In contrast, no significant differences in ADC were found when only the data acquired at b‐values higher than 200 s/mm 2 were used for fitting. When the intravoxel incoherent motion model was applied, cortical and medullary f increased significantly (cortex: 0.21 [0.15 0.27] to 0.37 [0.32, 0.49] × 10 −3 mm 2 /s; medulla: 0.15 [0.13 0.29] to 0.41 [0.36 0.51] × 10 −3 mm 2 /s). No significant changes in cortical and medullary D and D * were observed as diffusion time increased.
Conclusion
Renal perfusion and tubular flow substantially contribute to the observed increase in ADC over a wide range of Δ eff between 24 and 104 ms.
