Settling properties of venous blood demonstrated in the peripheral vasculature using susceptibility‐weighted imaging (SWI)

PURPOSE: To evaluate the settling properties of venous blood in the peripheral vasculature during periods of immobility. MATERIALS AND METHODS: Susceptibility-weighted imaging (SWI) was performed for nine subjects at two time points: within 10 minutes of entering the magnet and after 40 minutes spent stationary in the magnet. Changes in the phase and in the distribution of phase of the veins were used to draw conclusions about the separation of red blood cells from plasma over time. RESULTS: Settling was observed to occur in eight of the nine subjects, the only exception being the youngest subject (18 years old). The bottom half of some veins was seen to darken while the top half showed little change often with a clear dividing line between the two. Phase values measured in the bottom layer were consistent with the layer consisting entirely of red blood cells. Settling was seen to increase with time spent stationary and to correlate with the size of veins in the calf. CONCLUSION: Older subjects tended to have larger veins and consequently more settling of the red blood cells. Our results show that even 40 minutes of rest can easily lead to settling of the blood depending on the position of the leg.