Incidence and significance of the pseudo stent strut in optical coherence tomography analysis for coronary artery stents

Introduction: Quantitative optical coherence tomography (OCT) analysis is about to be relevant for the correct assessment of incomplete stent apposition which can result to late stent thrombosis. Nevertheless, the pseudo stent struts (PS), which show the strong signal same as the true strut, are sometimes seen at odd positions in the lumen and locate at the same distance from the image wire as a true strut. PS may be produced by the distorted beam and interfere accurate analysis. Our aim was to investigate the incidence of PS. Methods: We created a simple phantom model (2.5 mm-coronary artery stent apposed in 2.5-mm silicon tube). OCT pullback images at 1 mm/sec were obtained with an eccentric imagewire position for 5 times with different 5 pieces of imagewire. The strut location was recognized by the strong signal. Of these, PS was defined as: an irregularity of the alignment of strut locations; the difference in the strut-wire distance with one of the adjacent struts is within 20 micron. Strut contour with and without PS were delineated by semi-automated dedicated software with cubic spline interpolation, and symmetry index (= Min/Max diameter) was calculated. Results: In the phantom with Cypher stent and Tsunami stent, a pseudo strut reflection was observed in 71 of 7112 (1%) frames and 43 of 10302 (0.4%) frames, respectively. The PS incidence was the highest at fifth pull-back images. The symmetry index was significantly higher in strut contours without pseudo strut (0.95±0.02 versus 0.83±0.07, p<0.001). Conclusion: PS may mislead to the wrong data of clinical OCT analysis, in spite of the infrequency. When one starts to use the new image modality, one should be careful if there is some artifact which can affect on the data of the clinical investigations.