Perspectives in vascular ultrasound imaging: tissue characterization, 3D reconstruction and vascular mechanics

Atherosclerosis is a variable morphologic process resulting in heterogeneous plaque components and nonuniform extent and degree of plaque deposition. We and others have developed techniques of arterial imaging, segmental reconstruction and motion analysis to determine regional vascular reactivity in arterial segments having varying and expanding degrees of atherosclerosis. We have developed and validated position registration devices (PRD) for geometric three dimensional reconstruction of coronary and peripheral arteries using intravascular ultrasound. Elaborating upon an algorithm (McKay et al.), we have developed a technique using biplane cine fluoroscopy to identify intravascular ultrasound image catheter coordinates. Initial data demonstrates clinical feasibility for accurate intracoronary three-dimensional ultrasound reconstruction. For intravascular imaging across occlusions, a prototype 20 MHz forward viewing intravascular ultrasound catheter (Cardiovascular Imaging Systems, Sunnyvale, CA) which provides a two dimensional setting distal to the catheter tip, has been developed. Transcutaneous ultrasound has been used for many years to follow atheroma progression. The use of new position registration devices allows for proper orientation such that accurate three dimensional reconstruction of the carotid bifurcation and the ilio-femoral arteries can be performed. Transesophageal echocardiography is used to evaluate different arterial beds and we have shown in familial hyperlipidemic patients undergoing LDL-apheresis, plaque progression, as determined with transesophageal echocardiography, is delayed. The accurate identification of plaque components would allow for better prediction of the effects of lipid modification regimens on plaque progression. We utilized a modified intravascular frequency device for such plaque characterization. Similarly, we are performing Doppler waveform frequency, finite element stress and finite analytic flow analysis. Data obtained from the femoral arteries to determine alterations in shear stress with expanding and eccentric atheroma. Taken together, these techniques should allow for quantitative evaluation of structural and functional characteristics of the arterial wall in different vascular beds.