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Introduction: Pipeline flow diversion stent is often placed in a tortuous anatomy. Nevertheless, effect of parent artery curvature on the flow diversion effect from Pipeline stent is poorly understood. The flow diversion effect could be enhanced or diminished depending on the curvature of Pipeline or the angle at which blood flow strikes the Pipeline (angle of incidence). These variations may explain why not all aneurysms are obliterated after Pipeline treatment despite its high efficacy. We evaluated the flow diversion effect of Pipeline in various parent artery curvatures and angle of incidence in in-vitro models. Methods: Four acrylic prototypes of curved tube with a side branch were constructed with circular cross section with the inner diameter of 3.8mm. The variation among the prototypes was made in terms of the radius of curvature R (R=25mm & 50mm), and the relative angle θ of the side branch (θ=60, 90, & 120). The angle θ of the side branch determines the angle of incidence. The identical Pipeline of diameter 4.75mm were placed to each prototype and the pressure loss (K) occurring in the flow through the Pipeline mesh was measured for the Reynolds numbers ranging from 100 to 800. Careful error analysis on the measured data made it possible to quantify weak change of the flow resistance due to the geometrical variations.Results: The parent artery curvature and angle of incidence of the blood flow clearly affect the flow diversion effect (K) of Pipeline (Fig.1). Flow diversion effect diminishes in tighter curvature. Also noted is higher angle of incidence reduces flow diversion effect.Conclusion: The parent artery curvature and angle of incidence are important parameters that may affect the efficacy of Pipeline.