Intravascular hematocrit layering in equilibrium phase contrast-enhanced MR angiography of the peripheral vasculature

To evaluate intravenous hematocrit (HCT) layering detected in patent calf veins that potentially simulate filling defects seen in deep venous thrombosis (DVT).

Flow characteristics, vessel size, and enhancement patterns of veins with HCT layering were examined and compared with those of normal veins in vivo. Ex vivo studies were conducted with conventional and blood pool contrast agents to study the effects of MRI parameters and intrinsic variables on detecting HCT layering.

HCT layering was detected in high resolution equilibrium phase images in one of six healthy subjects, and five of five patients with peripheral vascular occlusive disease (PVOD). Layering occurred only in deep veins that had significantly slower flow and larger diameter (P < 0.001) compared to normal veins. Enhancement patterns observed in vivo were similar to those found in the ex vivo study.

The HCT layering effect in MR venography has not been previously reported, likely because delayed equilibrium phase venous imaging is not frequently performed. The use of blood pool contrast agents and high resolution equilibrium phase imaging allows intravascular HCT layering to be observed within a 30-60-minute time frame. Several imaging characteristics that distinguish HCT layering from DVT are discussed.