Vein grafts are placed to bypass diseased arteries in the lower limb when symptoms such as pain during walking, rest pain, and tissue necrosis occur. Frequent surveillance of these grafts is recommended since early detection and revision of lumenal narrowing (stenoses) improves the likelihood of long-term patency. We are using three-dimensional (3D) ultrasound imaging to measure progressive changes in vein graft geometry. Quantitative monitoring of vein graft morphology may provide a means to distinguish normal remodeling from pathologic changes that lead to re-stenosis.

Power Doppler images of a vessel are collected while a magnetic tracking system records the location and orientation of the ultrasound scanhead. Contours of the vessel lumen are extracted by manual outlining or automatic segmentation of the 2D images and a surface is reconstructed in 3D space. Cross-sectional area measurements in planes normal to the vessel center axis are calculated from the 3D surface. Data sets from serial studies are registered in a common coordinate system using anatomical reference points and cross-sectional area measurements are compared at matched sites.

Cross-sectional area measurements from repeated scans of 10 normal grafts were compared to provide an estimate of the variability of the 3D imaging method. Repeat scans were performed during a single patient visit. The difference in measured cross-sectional area for the 10 paired scans was 2% ± 12% (mean ± std dev).

Extended studies are underway on patients requiring surgical revision to enlarge the lumen in stenotic regions of their grafts. Follow-up periods on 4 patients range from 13 to 38 weeks to date. Each revised graft segment demonstrated a decrease in cross-sectional area over time. Cross-sectional area reduction ranged from 23% to 60%, averaged over the length of the revision. One repaired segment developed a focal stenosis in which the minimum cross-sectional area decreased from 30 mm² at 2 weeks post operative to 3 mm² after 38 weeks. The sequential area measurements, combined with 3D surface displays, provide a record of remodeling patterns and rates at specific sites within the grafts.