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

TL;DR

This study shows that brain diffusion measurements change significantly depending on whether a person is sitting or lying down.

Contribution

The study is the first to investigate ADC changes in different body positions using a multi-posture MRI system.

Findings

ΔADC and ADCmean were significantly higher in the sitting position compared to the supine position.

Heart rate was also significantly higher in the sitting position.

Results were consistent across all participants and brain regions tested.

Abstract

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.

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

Prospective.

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

0.4 T, electrocardiographically synchronized single‐shot diffusion echo‐planar imaging sequence with b‐values of 0 and 500 s/mm2.

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.

Wilcoxon signed‐rank test. Significance was set at p < 0.05.

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).

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.

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