Image-Based Quantification Workflow for Coronary Morphology: A Tool for Use in Next-Generation Bifurcation Stent Design

IMAGE-BASED QUANTIFICATION WORKFLOW FOR CORONARY MORPHOLOGY: A TOOL FOR USE IN NEXT-GENERATION BIFURCATION STENT DESIGN Sara M. Nomeland, B.S. Marquette University, 2010 Coronary artery disease (CAD) occurs in ~200,000 bifurcation lesions annually. Trea tment of CAD near bends and bifurcations is challenging and a preferred strategy for bifurc ation lesions has yet to be established. However, a favorable treatment option may be elucidated by a more thorough understanding of vessel morphology as well as local hemodynamic alterations caused by current stenting approaches. Computational modeling of human arteries offers an attractiv e w y to investigate the relationships between geometry, hemodynamics and vascular disease. Recent de v lopments also make it possible to perform analysis on realistic geometries acquired noninvas ively. The objective of this work was twofold. The first aim was to build on previous work in this area by quantifying hemodynamic alterations introduced by treatment of an ideali ze coronary bifurcation using several approaches that involve multiple stents. Each model w as created using combined computer aided design techniques and computational fluid dynamics (CFD) analys is tools. Resting and hyperemic blood flow conditions were also studied to determine the severit y of local hemodynamic alterations and for comparison to previous results. Indices of time-a veraged wall shear stress (TAWSS) and oscillatory shear index (OSI) were quantified for four ide alized computational models. The luminal surface exposed to low TAWSS was similar in the main vess el (MV) for all models. Greatest differences were noted between un-stented versus s t nted ide branch vessels (ex. rest: 1% vs. 35%). Sites of elevated OSI (>0.1) were minimal, except under hypere mia conditions in the MV (10% surface area). Flow disturbances were quantified for each provis ional technique used, illustrating how stents protruding in main vessels impact flow profiles. Stents wi thout kissing balloon dilation had abnormal flow disturbances, but showed decreased percentage of area exposed to a reas of low WSS. A second aim of this work was to design a robust and unbiased method to quantify vessel morphology and representative trends for three bifurcation sites prone to CAD. Computa tional models of these sites were generated using computed topography images from 22 patients. Models were used to query geometric characteristics from each bifurcation site including area , length, eccentricity, taper, curvature and bifurcation angles. Post-processing was accomplished by a combinati n of statistical methods and clustering analysis. Vessel length and area were significantly di fferent within and between bifurcation sites. The left main coronary artery (LCA) bifurcation w as significantly different from its two daughter bifurcations (left anterior descending and left circumflex ar t ries). Specifically vessel area and length were significantly different both between and within bifurca tion sites. The daughter bifurcation sites were similar for all characteristics. Vesse l area and length proved to be the most useful properties for identifying trends within a particular bifurcation si te. The outcome of this work provides a workflow for characterizing coronary bifurcations and a strong foun datio for elucidating common parameters from normal, healthy coronary arteries. Collectively these results from idealized and patient-specific coronary bifurcations offer additional insight into the impact of current treatment approaches and characteris tics as ociated with current stenting techniques. Flow disturbances and local hemodynamic changes have been quantified for provisional techniques currently used. These methods and results may ultim tely be useful in the design of next-generation bifurcation stents.