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

Abstract

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 (ADC_mean) 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 ADC_mean 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 ADC_mean were measured in 2 frontal and 2 occipital lobe regions and averaged. ΔADC, ADC_mean, 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 ADC_mean 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; ADC_mean: 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 ADC_mean of the brain are significantly higher in the sitting position than in the supine position.

Evidence Level: 2.

Technical Efficacy: Stage 1.