2.2. IVUS/OCT imaging

IVUS imaging (40-MHz IVUS catheter, Boston Scientific Corp, Natick, Mass; 40-MHz IVUS catheter, Volcano Therapeutics, Inc, California, USA) and OCT imaging (C7-XR system, LightLab Imaging Ic., Westford, Massachusetts) was performed before all interventions and after intracoronary administration of 0.1 mg nitroglycerin. The probe was advanced into the distal reference segment and an imaging run was performed back to coronary ostium using a motorized transducer pullback (0.5 mm/s) system of IVUS.

The OCT catheter was pulled back at a speed of 20 mm/s to guarantee sufficient time to acquire images of a 54–mm long segment (frame density: 10 frames/mm). OCT images were acquired after removing all blood adequately from the imaging site. Non-occlusive flushing was performed using continuously injected contrast medium via an automated power injector. When poor image quality was obtained, the pullback was repeated subsequently for modification of the flushing intensity or probe position. OCT images were analyzed online and offline. Intravascular imaging was recorded continuously into digital media for offline analysis. OCT images were analyzed using Lightlab software (v1.13, Lightlab Imaging Incorporated, USA). IVUS imaging were analyzed using QIvus post-processing software (v3.1, Medis Medical Imaging Bv, the Netherlands). Qualitative and quantitative analysis were performed by independent observers according to current consensus on standards for acquisition, measurement, and reporting of IVUS or OCT studies.^[14] Calcium was brighter than adventitia with acoustic shadowing of the underlying tissue in IVUS imaging. The calcium component was detected on OCT using validated criteria.^[15] We classified calcium according the max calcified arc as arc ≤ 90°, 90° < arc ≤ 180°, 180°< arc ≤ 270°, and > 270° subgroups. Reference segments were defined as the most normal-looking cross sections proximal and distal to the lesion.