Spatial distribution and temporal evolution of scattering centers by optical coherence tomography in the poly(L-lactide) backbone of a bioresorbable vascular scaffold.

BACKGROUND: Scattering centers (SC) are often observed with optical coherence tomography (OCT) in some struts of bioresorbable vascular scaffolds (BVS). These SC might be caused by crazes in the polymer during crimp-deployment (more frequent at inflection points) or by other processes, such as physiological loading or hydrolysis (eventually increasing with time). The spatial distribution and temporal evolution of SC in BVS might help to understand their meaning. METHODS AND RESULTS: Three patients were randomly selected from 12 imaged with Fourier-domain OCT at both baseline and 6 months in the ABSORB cohort B study (NCT00856856). Frame-by-frame analysis of the SC distribution was performed using spread-out vessel charts, and the results from baseline and 6 months were compared. A total of 4,328 struts were analyzed. At baseline and follow-up all SC appeared at inflection points. No significant difference was observed between baseline and 6 months in the number of SC struts (14.9 vs. 14.5%, P=0.754) or in the distribution of SC. The proportion and distribution of SC did not vary substantially among the patients analyzed. CONCLUSIONS: The SC observed in OCT imaging of the BVS are located exclusively at inflection points and do not increase with time. These findings strongly suggest that SC are caused by crazes in the polymer during crimp-deployment, ruling out any major role of hydrolysis or other time-dependent processes.

In vivo characterisation of bioresorbable vascular scaffold strut interfaces using optical coherence tomography with Gaussian line spread function analysis.

AIMS: Optical coherence tomography (OCT) of a bioresorbable vascular scaffold (BVS) produces a highly reflective signal outlining struts. This signal interferes with the measurement of strut thickness, as the boundaries cannot be accurately identified, and with the assessment of coverage, because the neointimal backscattering convolutes that of the polymer, frequently making them indistinguishable from one another. We hypothesise that Gaussian line spread functions (LSFs) can facilitate identification of strut boundaries, improving the accuracy of strut thickness measurements and coverage assessment. METHODS AND RESULTS: Forty-eight randomly selected BVS struts from 12 patients in the ABSORB Cohort B clinical study and four Yucatan minipigs were analysed at baseline and follow-up (six months in humans, 28 days in pigs). Signal intensities from the raw OCT backscattering were fit to Gaussian LSFs for each interface, from which peak intensity and full-width-at-half-maximum (FWHM) were calculated. Neointimal coverage resulted in significantly different LSFs and higher FWHM values relative to uncovered struts at baseline (p<0.0001). Abluminal polymer-tissue interfaces were also significantly different between baseline and follow-up (p=0.0004 in humans, p<0.0001 in pigs). Using the location of the half-max of the LSF as the polymer-tissue boundary, the average strut thickness was 158±11 µm at baseline and 152±20 µm at six months (p=0.886), not significantly different from nominal strut thickness. CONCLUSIONS: Fitting the raw OCT backscattering signal to a Gaussian LSF facilitates identification of the interfaces between BVS polymer and lumen or tissue. Such analysis enables more precise measurement of the strut thickness and an objective assessment of coverage.