Integrated IVUS-OCT for real-time imaging of coronary atherosclerosis.

Accurate assessment of atherosclerotic plaque characteristics and the subsequent tailoring of optimal therapy holds great promise for preventing acute coronary syndromes (ACS) and life-threatening sequelae (1). Combined use of optical coherence tomography (OCT) and intravascular ultrasound (IVUS) was proposed as a potential method for accurate assessment of plaque characteristics and vulnerability (2,3). However, significant challenges remain in trying to adapt an integrated OCT-IVUS system for clinical applications. We report here a fully integrated intracoronary OCT-IVUS imaging technique to visualize atherosclerotic plaque in living animals and human coronary arteries from cadavers with high resolution and deep penetration capability simultaneously. First, we created lesions, similar to human atherosclerotic plaques, inmaleNewZealandwhite rabbits by feeding themahighcholesterol diet and subjecting them to de-endothelization procedures (4). We imaged plaques in rabbit aortas using the OCT-IVUS system with a 3.4-F integrated catheter (5) and a 10-ml Omnipaque (iohexol, 350 mgI/ml, GE Healthcare, Princeton,New Jersey) injection flushing into the artery atw3ml/s for blood clearance. A total of 10 volumetric datasets were obtained from 5 rabbits. Ten 2to 20-mm long aorta segments were imaged at 5 mm/s pull-back speed. A representative OCT-IVUS image pair and corresponding histology of a rabbit abdominal aorta with a thick-cap fibroatheroma is shown in Fig. 1 (row I). IVUS enables the visualization of the layer structure of the artery wall. Intimal thickening and a low-density acoustic signal region (denoted by the arrow inFig.1Ia)demonstrate plaque in the IVUSimage.However, this image also illustrates the inability of IVUS to determinate the plaque type and the plaque cap boundary. At the same site in the OCT image (Fig. 1Ib), a homogenous boundary and weak signal region under a high signal region indicates that this plaque is a necrotic/lipid plaque with an overlying fibrous cap. In addition, the minimum thickness of the cap can be easily measured to be w200 mm by using OCT, which is indicative of a thick-cap fibroatheroma. The classification of plaque type is validated by the corresponding histology photo (Fig. 1Ic), which shows loose necrotic material. This area is covered by smooth muscle and fibrous proliferations at the luminal surface, which is consistent with a fibrous cap. All IVUS-OCT images of rabbit aortas were matched with histology for correlation of accuracy. Linear regression showed a high correlation between plaque circumference percent (PCP) (defined as the circumference of lumen in which there is plaque divided by the entire lumen circumference) determined from histological analysis and the estimated PCP of OCT and IVUS (R 1⁄4 0.955, p < 0.001 between OCT and histology; R 1⁄4 0.970, p < 0.001 between IVUS and histology). Second, a female Yorkshire white swine was imaged by conventional femoral access and angiography guidance under