Strain imaging of coronary arteries with intraluminal ultrasound: experiments on an inhomogeneous phantom.

In coronary arteries, knowing the relative stiffness of atherosclerotic lesions can help physicians select the most appropriate therapeutic modality. Because soft material supports larger strains than hard, measurements of this quantity can distinguish tissue of differing stiffness. In a previous paper, we described techniques for computing displacements and strains in coronary arteries using an integrated angioplasty and imaging catheter. Here, we demonstrate that hard and soft materials in a tissue-mimicking phantom can be differentiated with this device. Because tissue motion cannot be distinguished from catheter motion a priori, we perform all computations in the coordinate system centered at the balloon's geometric center. This reference frame depends only on balloon shape and is independent of catheter motion. A specialized correlation-based, phase-sensitive speckle tracking algorithm has been developed to compute strain. Maximum phantom displacement was about 25 microns, and the maximum radial, normal strain was about 1.5 percent.