Kristen O. Cardinal

An automatic algorithm for detecting stent endothelialization from volumetric optical coherence tomography datasets

Recent research has suggested that endothelialization of vascular stents is crucial to reducing the risk of late stent thrombosis. With a resolution of approximately 10 microm, optical coherence tomography (OCT) may be an appropriate imaging modality for visualizing the vascular response to a stent and measuring the percentage of struts covered with an anti-thrombogenic cellular lining. We developed an image analysis program to locate covered and uncovered stent struts in OCT images of tissue-engineered blood vessels. The struts were found by exploiting the highly reflective and shadowing characteristics of the metallic stent material. Coverage was evaluated by comparing the luminal surface with the depth of the strut reflection. Strut coverage calculations were compared to manual assessment of OCT images and epi-fluorescence analysis of the stented grafts. Based on the manual assessment, the strut identification algorithm operated with a sensitivity of 93% and a specificity of 99%. The strut coverage algorithm was 81% sensitive and 96% specific. The present study indicates that the program can automatically determine percent cellular coverage from volumetric OCT datasets of blood vessel mimics. The program could potentially be extended to assessments of stent endothelialization in native stented arteries.

Assessment of blood vessel mimics with optical coherence tomography

Optical coherence tomography (OCT) is an imaging modality that enables assessment of tissue structural characteristics. Studies have indicated that OCT is a useful method to assess both blood vessel morphology and the response of a vessel to a deployed stent. We evaluated the ability of OCT to visualize the cellular lining of a tissue-engineered blood vessel mimic (BVM) and the response of this lining to a bare metal stent. We develop a side-firing endoscope that obtains intraluminal, longitudinal scans within the sterile bioreactor environment, enabling time-serial assessment. Seventeen BVMs are imaged with the endoscopic OCT system. The BVMs are then evaluated via fluorescence microscopy and/or standard histologic techniques. We determine that (1) the OCT endoscope can be repeatedly inserted without visible damage to the BVM cellular lining, (2) OCT provides a precise measure of cellular lining thickness with good correlation to measurements obtained from histological sections, and (3) OCT is capable of monitoring the accumulation of cellular material in response to a metallic stent. Our studies indicate that OCT is a useful technique for monitoring the BVM cellular lining, and that OCT may facilitate the use of BVMs for early stage device assessment.

A Concentric Three Element Radial Scanning Optical Coherence Tomography Endoscope

We have developed a 2.1 mm outer diameter optical coherence tomography endoscope that provides radial scans of luminal structures. The endoscope consists of three elements: (1) a stationary central core containing the fibers and focusing elements, (2) a rotating intermediate tube with a distal rod prism, and (3) a stationary sterilized glass cover. This design enables radial and spiral scanning and allows adjustment of the axial focal distance. Additionally, this design is capable of focusing light from multiple fibers into tissue. The performance of the endoscope was demonstrated in a study of tissue engineered blood vessels imaged at various time points during development.

Imaging stented tissue engineered blood vessel mimics

An ideal vascular stent design promotes a thin anti-thrombogenic cellular lining while avoiding restenosis. To assess the utility of their designs, stent manufactures often use destructive techniques such as scanning electron microscopy to measure the percentage of the stent covered with a cellular lining. In this study, we use a custom-built longitudinal/rotational scanning endoscope and determine the ability of optical coherence tomography (OCT) to quantify the percent cellular coverage of stented tissue engineered blood vessel mimics. Stents were deployed within twelve mimics after 14-days of development in bioreactors. OCT images were acquired within the bioreactor at several time points after the stent deployment. At 20-days post deployment, the mimics were fixed and imaged volumetrically with OCT. Matlab software was developed to automatically calculate the percent cellular coverage from the OCT images. Algorithm results were compared to similar measurements performed with bis-benzimide (BBI) fluorescence imaging and manually calculated percent coverage from three different observers of the OCT images. Progressive accumulation of cellular material on the stents could be visualized with OCT. For the volumetric images, the algorithm calculated percent cellular coverages ranging from 11 to 76%. Good agreement was found between the OCT-based measurements and the other techniques. On average, the algorithm differed less than 5% from the manual percent coverage calculations. OCT together with automated software can provide an accurate, non-destructive measurement of the percent cellular coverage of vascular stents.

Evaluation of Blood Vessel Mimic Development with Optical Coherence Tomography

An endoscope for optical coherence tomography was developed to acquire cross-sectional images of tissue engineered blood vessels. This device was used to examine how the scaffold material affects the development of the cellular lining.