Ultrasonic measurement of differential displacement and strain in a vascular model

The potential in intravascular ultrasound imaging for characterizing regional arterial elasticity was examined in an experimental tissue-equivalent vessel model. Differential intrawall displacement measurement, the first step in regional elasticity determination, was investigated using a crosscorrelation tracking algorithm. Calibration studies showed that tracking accuracy varied significantly with tracking direction (axial versus lateral) and position in the field of the transducer. Midfield geometric error in the axial direction for a nominal displacement of 100 microns was 5.5 microns whereas the corresponding error in the lateral direction was 31.7 microns. Displacement was tracked in serial intravascular images of vessel phantoms acquired during stepwise pressurization experiments from 0-250 mmHg. Two-dimensional grey scale maps of axial, lateral and net intrawall displacement components over the full pressurization range were generated. Displacement profiles demonstrated successful detection of differential radial displacement and good correlation with theoretical profiles (root mean square difference 3%). The corresponding experimental strain profiles were significantly noisier (root mean square difference 76%) due to small fluctuations in the displacement data. This work demonstrates that, with further refinement, regional strain mapping in vessel walls with intravascular ultrasound imaging is feasible. Mechanical characterization of arteries may provide a new tool to aid and treating atherosclerotic lesions.