Ilab ultrasound imaging system

IVUS images were acquired with the AtlantisTM SR Pro Imaging Catheter 40 MHz ECG-triggered and connected to an iLabTM Ultrasound Imaging System (Boston Scientific Corporation, Natick, MA, USA). The acquisition was performed with a frame rate of 30FPS and with constant velocity pullback at 0.5mm/s. IVUS images were gated as proposed in^{34 (link)} to retrieve the diastolic cardiac phase. Additionally, two orthogonal (along the cranial-caudal plane) AX films were acquired, also ECG-triggered, spanning 8 heartbeats. A specialist selected the images from the AX films at the full exhalation end-diastolic phase. The integration of the AX images and the IVUS dataset enabled a consistent time-coherent reconstruction of the vessel in 3D space. Then, the lumen area was manually segmented by a specialist using cubic splines. The transducer path was retrieved using both AX images through a biplane snakes method³⁵ . The recovered transducer path served to place the segmented luminal areas consistently with the acquisition time and the pullback velocity. Finally, the segmentation of side branches in the IVUS dataset was also manually performed. At a final stage, all contours were rotated around the axis described by the transducer path in order to minimize the mismatch between the projected luminal area from IVUS and the contrast observed in the AX film^{36 (link)}.

IVUS was conducted as described previously (Cui et al., 2017 (link)). We used a 40-MHz 2.9 Fr sheath-based catheter (Atlantis, SR Pro, Boston Scientific) and IVUS (iLAB^TM Ultrasound Imaging System, Boston Scientific, Natick, MA, United States). The IVUS catheter was positioned 10 mm distal to the stent, and imaging was subsequently performed back to a point 10 mm proximal to the treated section using an automated transducer pullback at 0.5 mm/s. The scaffold area, minimal lumen area, intrascaffold neointimal area, and vessel area (area in the vessel’s EEL) were measured. The stent expansion index and percentage of lumen area stenosis were calculated according to the following formulas: stent expansion index = ([actual lumen area/ideal lumen area] × 100) and percentage of lumen area stenosis = ([mean lumen intrascaffold area ˗ the lumen area]/mean lumen intrascaffold area × 100).

All patients were performed with coronary angiography by standard Judkins technique. IVUS examination was performed using an IVUS system (iLAB™ Ultrasound Imaging System, Boston Scientific, USA) and a 40 MHz intravascular catheter (OptiCross™, Boston Scientific, USA) before any intervention. The IVUS catheter was advanced into the culprit vessel more than 10 mm beyond the culprit lesion and withdrawn at a pullback speed of 0.5 mm/s automatically. In this study, a culprit lesion was defined as the lesion related to the clinical event, as identified by both coronary angiography and electrocardiogram findings. A ruptured plaque was defined as the plaque contained a cavity that communicated with the lumen with an overlying residual fibrous cap fragment. A fragmented and loosely adherent plaque without a distinct cavity and without a fibrous cap fragment was not considered as a plaque rupture [14 (link)]. IVUS quantitative analysis was performed by two independent experienced interventional cardiologists who were blinded to the patients’ clinical information according to the criteria of the American College of Cardiology Clinical Expert Consensus Document on IVUS.