An Automatic Alogorithm 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 μm, 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. (Some figures in this article are in colour only in the electronic version

Application of siso and mimo Modal Analysis Techniques on a Membrane Mirror Satellite

ABSTRACT The future of space satellite technology lies in the development of ultra-large, ultra-lightweight space structures orders of magnitude greater in size than current satellite technology. Such large craft will increase current communication and imaging capabilities from orbit. To get ultra-large structures in space, they will have to be stored within the Space Shuttle cargo bay and then inflated on-orbit. However, the highly flexible and pressurized nature of these ultra-large spacecraft poses several daunting vibration and control problems. Disturbances (i.e. on-orbit maneuvering, guidance and attitude control, and the harsh environment of space) wreck havoc with the on-orbit stability, pointing accuracy, and surface resolution capability of the inflated satellite. However, recent advances in integrated smart material systems promise to provide solutions to these problems. Recent research into the use of Macro-Fiber Composite (MFC ® ) devices integrated into the dynamic measurement and vibration control of inflated structures has had promising results. These piezoelectric-based devices possess a superior electromechanical coupling coefficient making them superb sensors and actuators in dynamic analysis applications. Initially, research was performed on an inflated torus using single-input, single-output (SISO) testing techniques. Since then, steps have been taken to outline a new, multiple-input, multiple-output (MIMO) testing technique for these ultralarge structures. Based on the matrix formulation and postprocessing techniques recently developed, the current work applies these results to an inflated torus with bonded membrane mirror to extract modal parameters, such as the damped natural frequencies, associated damping, and mode shapes within the frequency bandwidth of interest for these structures (5 -200 Hz). MIMO modal testing techniques are ideal for large, inflated structure applications. The nature of the structure requires the use of multiple sensors and actuators for worthwhile dynamic analysis and control. Therefore, in the future, the results of this work will form the premise for an autonomous, self-contained system that can both identify the vibratory characteristics of an ultra-large, inflated space craft and apply an appropriate control algorithm to suppress any unwanted vibration-all while on-orbit

Assessment of Blood Vessel Mimics with Optical Coherence Tomography

Optical coherence tomography (OCT) is an imaging mo-dality 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