Intravascular imaging has provided new understanding of mechanisms associated with SB compromise following bifurcation PCI. Plaque shift has been traditionally considered as the principal mechanism for side-branch compromise after main vessel intervention. Rotational atherectomy(RA) has been advocated for the treatment of bifurcation lesions, since it can effectively remove plaque with minimal injury to adjacent normal arterial segments and potentially reduce plaque shifting, the "snow plow" effect. Intravascular ultrasound (IVUS) has been used for guidance in bifurcation lesions, aiding the visualization of plaque morphology at the main vessel and the side-branches and helping the selection of stent size and length as well as the selection of stenting strategy. However, due to the low spatial resolution of IVUS, all attempts for three-dimensional visualization have only focused on visualization of the luminal contour and not on the vessel morphology or the vessel-stent interaction. Optical coherence tomography (OCT) has ~10 times higher resolution than IVUS, which allows precise evaluation of the microstructure of the vessel wall including lipid pool, fibrous cap, calcification, and thrombus. OCT has been shown to constitute a valuable tool for PCI guidance and also the utility of three-dimensional (3D) renderings for assessing the mechanism of side-branch compromise following intervention in bifurcation lesions. The recent development of OCT with online 3D reconstruction allows the operator to obtain a 3D visualization of the lesion and may provide a unique tool for guidance during complex bifurcation PCI and potentially improve stenting results. 3D OCT has been used to visualize jailed side branches after implantation of bioresorbable scaffolds in the main branch and develop a new classification system based on the number of SB compartments. In addition, its potential clinical application in guiding the rewiring of the distal compartment of the SB ostium (jailed with stent struts after MB stenting) to minimize the risk of floating struts was demonstrated It is important to note that while OCT, 3D-OCT, and 3D-QCA (such as that used in the ORBID trial) are imaging modalities that can be used to answer important research questions, their wide-spread adoption in daily clinical practice has been very limited. Intravascular ultrasound (IVUS) is used more frequently as part of a PCI guidance strategy in daily clinical practice.