Author + information
- Published online March 13, 2019.
- Kensuke Nishimiya, MD, PhD,
- Biwei Yin, PhD,
- Zhonglie Piao, PhD,
- Jiheun Ryu, PhD,
- Hany Osman, MD,
- Hui Min Leung, PhD,
- Gargi Sharma, PhD,
- Chia Pin Liang, PhD,
- Joseph A. Gardecki, PhD,
- Hui Zheng, PhD,
- Hiroaki Shimokawa, MD, PhD and
- Guillermo J. Tearney, MD, PhD∗ ()
- ↵∗Department of Pathology, Harvard Medical School and Massachusetts General Hospital, Wellman Center for Photomedicine, 55 Fruit Street, Boston, Massachusetts 02114
Coronary arteries are covered by a layer of endothelial cells (ECs) that have a thickness of approximately 1 μm. Impairment of ECs is at the origin of coronary atherosclerosis and its clinical manifestations. The current gold standard, scanning electron microscopy (SEM), has demonstrated that ECs form an endoluminal feature referred to as “endothelial pavementing” (1). However, the assessment of ECs in humans remains elusive because a clinical imaging modality with sufficient resolution does not exist. This study investigated the use of a new form of optical coherence tomography (OCT), termed micro-OCT (μOCT) (2), which offers an axial resolution of 1 μm and a lateral resolution of 2 μm, for evaluating EC morphology.
First, we stripped the endothelium from fresh swine coronary segments with cyanoacrylate adhesive. Coronary segments were imaged 3 dimensionally (3D) with μOCT. μOCT images were then 3D-volume rendered using ImageJ (3). 3D µOCT allowed clear visualization of endothelial pavementing (Figure 1A, left top and middle panels) with cells oriented parallel to the coronary flow direction (Figure 1A, left top and middle panels), not seen at the sites where ECs were stripped off (Figure 1A, top right panel). The surface roughness, measured as root mean squared (RMS), diminished significantly at sites of EC stripping compared with intact sites (3.4 ± 0.1 μm vs. 1.5 ± 0.1 μm, p < 0.01). Subsequently, swine coronary segments were processed for SEM and were co-registered to the same area imaged by μOCT. The morphology of ECs visualized by 3D μOCT was similar to that seen by SEM (Figure 1A, middle panels). 3D SEM data were computed from 2-dimensional SEM images using intensity thresholding and Mountains-Map software (Digital Surf, Besançon, France). For both intact and stripped sites, strong positive correlations were noted between the RMS calculated for μOCT and SEM (R2 = 0.95, p < 0.01; R 2= 0.97, p < 0.01, respectively) (Figure 1B, left top and bottom graphs). We also used μOCT to explore EC morphology in human cadaver coronary plaques. Conventional OCT cross sections were obtained before μOCT to characterize human coronary lesion tissue type. After standard OCT pullback, 1-cm-long coronary segments (n = 45) from 8 fresh cadaver hearts were opened and imaged in 3D with μOCT and co-registered with SEM. As per the corresponding standard OCT images, the tissue type of each coronary segment was classified as intimal hyperplasia, fibrous plaque, fibroatheroma, or fibrocalcific plaque. Figure 1A, bottom panels, show typical endothelial morphology of a fibrous plaque seen by 3D μOCT and co-registered SEM. μOCT RMS was significantly lower over fibroatheroma and fibrocalcific plaques compared with intimal hyperplasia and fibrous segments (p < 0.01) (Figure 1B, right).
The major findings of the present study were that: 1) 3D μOCT was capable of clearly visualizing EC morphology that manifested endothelial pavementing in intact swine coronary arteries, as confirmed by surface morphology seen by SEM; 2) 3D μOCT imaging was able to identify and quantify EC morphology overlying various human cadaver coronary lesions. These results suggest that μOCT could be useful for improving our understanding of the role of ECs in the pathogenesis of the diverse manifestations of coronary artery disease.
Importantly, μOCT is a noncontact, 3D imaging technology that can ultimately be implemented in catheters to study ECs in living patients (4). 3D μOCT visualization of ECs may allow a more precise capability to predict plaque progression. Although the extent to which μOCT can visualize ECs beneath thrombus remains an open question, μOCT could also be helpful for making a more precise diagnosis of coronary “endothelial” erosion that has emerged as the second most prevalent histopathological finding in acute coronary syndrome. The use of μOCT technology to assess coronary stent strut endothelial coverage may also help resolve current questions and controversies regarding stent healing and optimal antiplatelet therapy durations.
Please note: Dr. Tearney has reported receiving catheter materials from Terumo Corporation, with which Massachusetts General Hospital has a licensing arrangement and from which he has the rights to receive royalties; has received sponsored research funding from Vivolight and Canon Inc.; has reported a financial or fiduciary interest in SpectraWave, a company developing an OCT-Near Infrared Reflectance Spectroscopy intracoronary imaging system and catheter; and has reported consulting for SpectraWave; his financial or fiduciary interest was reviewed and is managed by the Massachusetts General Hospital and Partners HealthCare in accordance with their conflict of interest policies. Drs. Tearney and Gardecki are named inventors on OCT and µOCT patents. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.