Intravascular imaging of angioplasty balloon under-expansion during pre-dilation predicts hyperelastic behavior of coronary artery lesions

FIGURE 1. Diagnostic vs pre-dilation intravascular imaging for comprehensive morphology and material characterization of a representative target lesion. 3D representation of the artery lumen (A) and representative OCT slices at proximal (B), middle (C), and distal (D) locations. The presence of atherosclerosis is traditionally confirmed using diagnostic OCT conducted during diastole. According to the modified AHA criteria, the presence of fibrocalcific plaque is confirmed at slices (B) and (C) with protrusion of calcium into the lumen (arrows). Early stage fibroatheroma is also observed (arrowheads) toward the distal region (D) as characterized by superficial high backscattering bright signal and pronounced signal attenuation of light in the deeper plaque regions, which is probably secondary to the presence of activated macrophages, calcification, or both. After balloon inflation to 8ATM, the same artery segments were imaged, and the effect of local stiffness was quantified using balloon under-expansion relative to the diameter at 8ATM in an associated compliance table for the angioplasty balloon (contour plots).

FIGURE 2. Hyperelastic characterization of coronary plaques in the circumferential (A) and longitudinal (B) directions. Equiaxial extension testing was performed to characterize material properties corresponding to under-expansion levels that are color coded for three range of <15% (aqua), 15%–30% (navy) and >30% (pink). Cauchy stress vs stretch curves were calculated from force/displacement and sample dimension data where non-linear hyperelastic behavior was observed in both directions.

FIGURE 3. Characterization of local lesion material properties via angioplasty balloon under-expansion. Regression model to interpret neo-Hookean (A) and Exponential (B) stress-like parameters (i.e., μ and k1 ) for direct constitutive characterization of the target lesions from angioplasty balloon under-expansion.

FIGURE 4. Spatial distributions of balloon under-expansion (A), stress-like constitutive material parameters (B), and strain energy density (C) for three representative atherosclerotic coronary arteries. Arteries are shown in two orientations and data are visualized on the luminal surface of the artery at pre-dilation. Balloon under-expansion was quantified as percent reduction in expanded radius relative to the expected nominal radius at 8 ATM using an associated compliance table. Stress-like Neo-Hookean and Exponential constitutive parameters are quantified through transfer functions identified empirically using biaxial extension testing results as shown in Figure 3. Strain energy density was calculated according to Eq. 1 and at a virtually applied 1.15 equibiaxial stretch ratio.