Assessment of time-resolved renal diffusion parameters over the entire cardiac cycle.

Object: To assess changes diffusion properties of renal cortex over the entire cardiac cycle using electrocardiogram-gated respiratory-triggered dynamic diffusion-weighted imaging (DWI).

Materials And Methods: 20 healthy volunteers were investigated on a 1.5 T MR scanner. Blood flow velocity within the renal arteries was determined by electrocardiogram-gated phase-contrast measurements. For dynamic renal DWI, an electrocardiogram-gated respiratory-triggered coronal single-slice EPI sequence was acquired at 14 times at 20, 70, 120, 170, …, 570, 620, 720 ms after the R-wave over the cardiac cycle. ROI measurements were performed by two authors in the renal cortex on apparent diffusion coefficient (ADC) maps. A pulsatility index was calculated for ADC as maximal percentage change. Five subjects were measured twice to assess scan-rescan reproducibility.

Results: Flow measurements exhibited a minimum velocity of 15.7 ± 4.3 cm/s during the R-wave and a maximum of 43.2 ± 10.4 cm/s at 182.5 ± 48.3 ms after the R-wave. A minimal mean ADC of 2.19 ± 0.09 × 10 mm/s was observed during the R-wave. A maximum mean ADC of 2.85 ± 0.20 × 10 mm/s was measured 193 ± 57 ms after the R-wave. The mean ADC pulsatility index in the renal cortex was 29.9 ± 5.8%. ADC variation exhibited a significant correlation with pulsatile blood flow velocity. The scan-rescan reproducibility in this study had a low deviation of 0.3 ± 0.1%. The inter-reader reproducibility was 2.9 ± 0.6%.

Conclusion: Renal ADCs exhibit pulsatile characteristics. Due to the significant difference of systolic and diastolic ADCs, the pulsatility index can be calculated.