Effect of Body Position on Dynamic Apparent Diffusion Coefficient Changes During the Cardiac Cycle in the Human Brain.

BACKGROUND

Dynamic changes in the apparent diffusion coefficient (ΔADC) during the cardiac cycle reflect water molecule fluctuations in the brain and intracranial conditions. While body position strongly affects intracranial conditions, the relationship between ΔADC and body position has been less explored, as conventional MRI is typically performed only in the supine position.

PURPOSE: To investigate ΔADC and mean ADC (ADCmean) of the brain in supine and sitting positions using a multi-posture MRI system.

STUDY TYPE: Prospective.

SUBJECTS: Nine healthy volunteers (all males; mean age, 23.5 years).

FIELD STRENGTH/SEQUENCE: 0.4 T, electrocardiographically synchronized single-shot diffusion echo-planar imaging sequence with b-values of 0 and 500 s/mm2.

ASSESSMENT: ADC maps were generated at multiple cardiac phases in each subject in the sitting and supine positions. For each position, an ADCmean map was then generated as the voxel-wise mean ADC across all phases, and a ΔADC map was generated as the voxel-wise maximum difference in ADC across phases. ΔADC and ADCmean were measured in 2 frontal and 2 occipital lobe regions and averaged. ΔADC, ADCmean, and heart rate (HR) were compared between supine and sitting positions.

STATISTICAL TESTS: Wilcoxon signed-rank test. Significance was set at p < 0.05.

RESULTS

Both ΔADC and ADCmean were significantly higher in the sitting position compared with the supine position (ΔADC: 0.84 ± 0.06 × 10-3 mm2/s vs. 0.68 ± 0.05 × 10-3 mm2/s; ADCmean: 0.87 ± 0.02 × 10-3 mm2/s vs. 0.79 ± 0.06 × 10-3 mm2/s, respectively). These increases were consistent across all participants. In addition, HR was significantly higher in the sitting position compared with the supine position (73.8 ± 8.4 bpm vs. 58.1 ± 3.7 bpm).

DATA

CONCLUSION

ΔADC and ADCmean of the brain are significantly higher in the sitting position than in the supine position.

EVIDENCE LEVEL: 2. Technical Efficacy: Stage 1.