Optical coherence tomography (OCT) is a novel, catheter-based, invasive imaging modality based on near-infrared light rather than ultrasound, generating high-resolution images of the arterial wall. This system allows for unparalleled imaging resolution of the coronary artery wall, including plaque characterization, assessment of coronary stent strut apposition, neointimal coverage, vascular proliferative response, complications related to percutaneous coronary intervention (PCI) (ie, focal dissection or thrombus formation), and information regarding the time course of stent dissolution for bioabsorbable stents. We discuss the advantages and limitations of this new imaging modality, with specific emphasis on its current clinical and research applications in intracoronary image generation, as well as future directions of the technology.

INTRAVASCULAR OCT SYSTEMS

OCT was initially applied in clinical settings for highresolution scanning of the retina.1 This technique was later adopted for intravascular OCT with a fiber optic wire that both emits light and records the reflection while simultaneously rotating and being pulled back along the length of the artery.2 Because of the shorter wavelength of infrared light compared to ultrasound, OCT has a 10-fold higher axial and lateral image resolution (10–20 μm) than conventional intravascular ultrasound (IVUS) (150–200 μm) and is therefore able to provide superior arterial wall image quality (Table 1).3 Thus, OCT has recently been approved by the US Food and Drug Administration for human intracoronary imaging and provides a new perspective for intravascular imaging and lesion assessment for interventional cardiologists.

The intravascular OCT laser light source uses a bandwidth in the near-infrared with wavelengths ranging from 1,250 to 1,350 nm.2 Using these wavelengths, tissue penetration is limited to 1 to 3 mm as compared to 4 to 8 mm achieved by IVUS, with the exception of calcified lesions in which sound has a limited penetration depth.3 Although longer wavelengths provide better deep tissue penetration, the optimal wavelength used in an arterial vessel is also defined by minimizing tissue absorption of light to allow more photons in the returning signal. The light reflection is also maximal at regions in the arterial wall with the greatest differences in the refractive index—mechanisms that are not relevant during IVUS. The axial resolution, determined by the light wavelength, usually ranges from 12 to 18 μm compared with 150 to 200 µm for IVUS, and the lateral resolution in catheter-based OCT is typically 20 to 90 μm as compared with 150 to 300 µm for IVUS.3

Light is spilt, and half is aimed at the arterial wall while the other half is aimed at a mirror at an equal distance as the arterial wall. The returning light from both the arterial wall and the mirror interfere with each other, hence the term “interferometer,” resulting in the creation of an image or A scan. Multiple A scans are acquired as the image wire rotates, and a full revolution creates a complete cross-section of the vessel wall. A second factor affecting image formation, which is similar with IVUS, is the time it takes for emitted light to travel back from the target tissue to the lens, producing an “echo time delay.” Further discussion of the physics of OCT is beyond the scope of this article. However, it is important to mention that compared to the initial time-domain (TD) OCT systems, newer generations of intravascular OCT systems, termed “frequency-domain” or “Fourier-domain” (FD) OCT, allow the simultaneous detection of reflections from all echo time delays, resulting in a much faster system for image acquisition.4 It is this last advance that has allowed widespread application of OCT to the catheterization laboratory, where an entire coronary artery can be interrogated with a single flush. There are two types of FD OCT systems, which differ in their method of data generation: optical frequency domain imaging, also known as “swept OCT,” and spectral-domain OCT.

OCT DEVICE DESCRIPTION, IMAGE ACQUISITION, AND SAFETY

Even though the earlier-generation TD OCT systems have been available for quite some time, the FD OCT C7-XR system with its C7 Dragonfly catheter (LightLab Imaging, Inc., a St. Jude Medical, St. Paul, MN) has recently been approved by the US Food and Drug Administration as the first OCT system in North America. The C7-XR system consists of an intravascular OCT catheter, an imaging engine, and a computer. This system is equipped with a tunable laser light source with a sweep range of 1,250 to 1,350 nm. The C7-XR is used with the Dragonfly imaging catheter, a monorail 2.7-F catheter system that is compatible with standard curve 6-F guide catheters and has a light source in an optical fiber that is encased in a rotating torque wire. The imaging catheter can be delivered over a conventional 0.014-inch coronary guidewire. The OCT catheter is withdrawn proximal to the analyzed segment using an automated pullback system during simultaneous contrast infusion at a rate of approximately 4 mL/s.

The infrared light is unable to penetrate red blood cells and, in fact, scatters off the red cells. Thus, OCT imaging must be performed in a blood-free environment. Although proximal balloon occlusion of the coronary artery was required to create a blood-free environment during image acquisition with the earlier TD systems, accelerated pullback speeds of newer FD OCT systems permit the use of a single, high-rate bolus injection of contrast (approximately 4 mL/s) to produce a bloodfree environment, thus eliminating the need for balloon occlusion.5,6 Contrast is preferred over saline because its greater viscosity more effectively clears blood from the vessel being imaged and delays the return of blood as well. The C7-XR system acquires images at a rate of 100 frames/s at a pullback speed of up to 10 to 20 mm/s. Thus, a 5-cm length of a coronary artery can be scanned in less than 3 seconds. Once activated, the C7-XR console will automatically sense the clearance of blood from the vessel lumen and initiate an automated pullback at 10 mm/s.7 The images will be displayed on the console unit for interpretation by the operator.

Besides the C7-RX system, Terumo Interventional Systems (Somerset, NJ) is developing an FD OCT system with a 2.4-F shaft. Volcano Corporation (San Diego, CA) has a third-generation FD OCT system under development with a rapid-exchange nitinol-hybrid drive shaft.8 The goal of all these devices is to scan the proximal two-thirds of the coronary artery in as little as 1 second using the Low Volume OCT imaging system (Volcano Corporation). Developing the Low Volume OCT imaging system will be the key to allowing interventional cardiologists to acquire OCT images during a routine coronary angiographic injection. This extremely low flush volume is expected to allow for optimal imaging while maximizing patient safety, clinical utility, and ease of use for the physician and staff.

The potential procedural risks that are associated with use of OCT have been shown to be comparable to IVUS in clinical evaluations thus far.9-13 Transient events, such as chest discomfort and ST changes, were observed without hemodynamic instability in some patients. The advantages of the new FD OCT as compared to TD OCT have been further supported by studies showing lower mean procedure time, less ischemic changes, and fewer ischemic symptoms.7

IMAGE INTERPRETATION AND ARTIFACTS

Operator-adjustable manual calibration, so-called Zoffset, carries critical importance for accurate measurements. For the C7-XR system, four crescent-shaped marks in the OCT image delineate the outer boundary of the OCT catheter. The proper alignment of these markers with the catheter image is important for manual image calibration.3 This is important because even a small difference in Z-offset calibration can result in significant differences in vascular measurements.14

There are some imaging artifacts that every operator using OCT needs to be familiar with. Some of these artifacts, which are also common with IVUS use, are shown in Figure 1:

  • Residual blood can obscure imaging of the wall and can mistakenly be labeled as red thrombus.
  • Nonuniform rotational distortion similar to IVUS occurs as a result of variation in the rotational speed of the spinning optical fiber, although there is evidence that it is less significant with OCT.
  • Sew-up artifact occurs as a result of misalignment of the lumen border from subsequent images during pullback.
  • Saturation artifact is the result of light reflection from a highly specular surface, such as stent struts, that produce signal amplitudes exceeding the dynamic range of the data acquisition system.
  • Fold-over artifact occurs when the structural signals are reflected outside the system's field of view as dropouts and typically occur in large vessels or distant side branches.
  • Bubble artifact from small bubbles inside the imaging catheter can produce attenuated images.
  • Sunflower effect occurs as a result of eccentric OCT catheter positions and can artifactually turn stent struts toward the light source, creating the mistaken impression of poor strut apposition to the vessel wall.

Most of the vascular measurements with OCT are very similar to IVUS (minimal lumen diameter, minimal lumen area, reference lumen diameter, reference lumen area lesion length, etc.).

OCT IN ATHEROSCLEROSIS IMAGING

Despite the lack of prospective studies, it is generally accepted that acute coronary syndromes are primarily caused by rupture of an inflamed thin-capped fibroatheroma (TCFA).15-18 TCFA is characterized by three key components: a large lipid core, inflammatory cell infiltration, and a thin fibrous cap (Figure 2).19 The criterion for TCFA on OCT is a lipid-rich plaque (lipid core occupying > 40% of the vessel wall) with fibrous cap thickness < 65 µm.15-18 Although TCFAs tend to localize within the proximal segment of the left anterior descending artery, they are evenly distributed throughout the entire left circumflex and right coronary arteries. 20 Multiple OCT-derived TCFAs have been observed in up to 38% of patients with acute myocardial infarction in infarct- and noninfarct-related lesions.21 In patients taking statins, fibrous cap thickness has been shown to increase compared to controls using OCT as the imaging tool.22

The interface between the fibrous cap and the lipid pool produces a bright OCT reflection. However, because of both the imaging depth limitation of OCT and light being absorbed by the arterial wall components, OCT has difficulty defining the full extent of the lipid pool and vascular remodeling. On the other hand, in contrast to ultrasound, light can penetrate calcium, and OCT studies reported a sensitivity of 96% and specificity of 97% to detect calcified nodules and probably microcalcifications, which are also key markers for plaque vulnerability and lesion complexity for PCI.23,24

Vascular inflammation with macrophage-rich infiltrates has previously been identified with OCT by our group and others; however, it remains unclear if quantitative assessment of an inflammatory cell density may be determined using OCT images.25-27 Previous studies also suggested that it is possible to identify thrombus by OCT and even discriminate between red and white thrombus, as confirmed by histopathologic correlation.28 The clinical implications of these findings will have to be determined in prospective clinical trials.

OCT IN CORONARY INTERVENTION

OCT image guidance during PCI can be helpful in both lesion assessment (plaque rupture, stent malapposition, etc.) as well as in optimal sizing of the stent (reference vessel diameter, lesion length). Additional measurements, such as minimal lumen area (Figure 3), percent lumen stenosis, stent apposition, stent expansion, minimal stent cross-section area, lumen gain, late lumen loss, and residual stenosis are all based on the proper evaluation of the lumen/vessel/ stent interface and thus are available to OCT.29-32 OCT images with sharp depiction of the boundaries between lumen and vessel wall has practical advantages over IVUS. The OCT images are easier to interpret, and fully automated lumen segmentation reduces the guesswork in lesion determination. This should facilitate correct selection of stent diameter and length in PCI (Figure 4). Although real-world validation has not yet been performed, typically, a minimal luminal area of 4 mm2 found in an epicardial coronary artery, excluding the left main, is thought to represent a significant lesion when OCT imaging is undertaken, as it would be with IVUS.33 However, there is concern that (1) OCT generates smaller lumen measurements than IVUS, in part due to balloon occlusion with TD OCT systems, and (2) more recent IVUS studies are showing that a 4-mm2 cutoff may be too liberal.

The ability of OCT to penetrate and delineate calcium in the vessel wall also makes it well suited to guide complex interventional strategies in vessels with superficial calcification. Incomplete stent apposition (ISA) has been implicated as a potential factor in the development of late stent thrombosis.34 Compared to IVUS, OCT has been shown to have a higher sensitivity for imaging individual stent struts and malapposed strut assessment.35,36 ISA may occur either acutely at the time of stent deployment or later as a consequence of vessel remodeling. In fact, in current clinical stent trials, OCT imaging has increasingly been used to assess stent apposition and individual strut coverage with intimal hyperplasia as a safety endpoint.37-41 Histological studies have revealed that IVUS does not have adequate resolution to detect the thinnest layer of tissue coverage, and the perception that lack of neointimal hyperplasia by IVUS is synonymous to an uncovered strut needs to be reconsidered.42 Some studies have shown that up to 40% of struts may remain malapposed despite optimal high-pressure postdilation.43 Late ISA and uncovered struts are more common in patients with ST-elevation myocardial infarction.44 The entrapment of thrombus within the stented segment during primary PCI, which later resolves, has been proposed as the mechanism underlying this important observation. The impact of these observations on patient care has not yet been determined.

Despite its high resolution, OCT is limited in detecting strut coverage that may only be composed of single endothelial cells because a normal endothelial coverage is beyond the resolution of OCT. OCT has also enabled the detection of procedural complications, such as edge dissection, that are not detectable with conventional IVUS or coronary angiography (Figure 5).45,46 OCT also has a higher sensitivity than IVUS for detecting tissue prolapse after stenting, although clinical significance of this observation remains to be determined.47,48

FUTURE IMPLICATIONS

Although OCT has emerged as a new intracoronary imaging modality with high resolution, no large-scale prospective studies have shown a relationship between OCT findings and clinical outcomes to date. At present, OCT is the only imaging technology with a resolution high enough for detection of TCFA and studying its progression and regression in patients with coronary atherosclerosis. On the other hand, OCT is certainly becoming an integral tool to study emerging stent technologies, such as bioabsorbable stents and polymers, and intimal thickness of other experimental stents. IVUS does not have the resolution or capability of imaging polymeric stent struts dissolution or strut intimal thickness. Also, neointima thickness covering drug-eluting stents has important clinical implications for predicting late stent thrombosis and for determining the optimal duration of dual-antiplatelet therapy.

CONCLUSION

OCT is a new imaging modality that allows for high-resolution assessment of the coronary artery lumen, coronary stent strut apposition, neointimal coverage thickness, vascular proliferative response, and PCI-related complications, such as focal dissection or thrombus formation. Imaging with OCT appears to have several advantages over IVUS in the assessment of atherosclerotic plaque morphology and outcomes of poor stent apposition. However, similar to the earlier days with IVUS, we will continue to learn more about this technique, which will require further studies to reliably obtain and interpret OCT images, leading to a better understanding of vulnerable plaque and the optimization of treatment algorithms for our patients.

Mehmet Cilingiroglu, MD, FACC, FSCAI, is Director of Structural Heart Interventions, and Director of Interventional Cardiology Research at the University of Maryland Medical Center in Baltimore, Maryland. He has disclosed that he holds patents in the United States, Canada, and the European Union in regard to OCT and the use of nanoparticles for tissue macrophage imaging. He also receives royalties for his work on OCT from the University of Texas Health Sciences Center at San Antonio. Dr. Cilingiroglu may be reached at (410) 328-7716; mcilingiroglu@ yahoo.com.

Marc D. Feldman, MD, FACC, FSCAI, is Professor of Medicine & Engineering, and Director of Cardiac Catheterization Laboratories at the University of Texas Health Science Center at San Antonio in San Antonio, Texas. He has disclosed that he receives grant/research funding from Volcano Corporation.

  1. Hee MR, Izatt JA, Swanson EA, et al. Optical coherence tomography of human retina. Arch Opthalmol. 1995;113:325-332.
  2. Fujimoto JG, Boppart SA, Tearney GJ, et al. High-resolution in vivo intra-arterial imaging with optical coherence tomography. Heart. 1999;82:128-133.
  3. Bezerra HG, Costa MA, Guagliumi G, et al. Intracoronary optical coherence tomography: a comprehensive review clinical and research applications. JACC Cardiovasc Interv. 2009;2:1035-1046.
  4. Chinn SR, Swanson EA, Fujimoto JG. Optical coherence tomography using a frequency-tunable optical source. Opt Lett. 1997;22:340-342.
  5. Tearney GJ, Waxman S, Shishkov M, et al. Three-dimensional coronary artery microscopy by intracoronary optical frequency domain imaging. JACC Cardiovac Imaging. 2008;1:752-761.
  6. Barlis P, Schmitt JM. Current and future developments in intracoronary optical coherence
  7. Takarada S, Imanishi T, Liu Y, et al. Advantage of next-generation frequency-domain optical coherence tomography compared with conventional time-domain system in the assessment of coronary lesion. Catheter Cardiovasc Interv. 2010;75:202-206.
  8. Guagliumi G, Sirbu V. Optical coherence tomography: high-resolution intravascular imaging to evaluate vascular healing after coronary stenting. Catheter Cardiovasc Interv. 2008;72:237-247.
  9. Serruys PW, Ormiston JA, Onuma Y, et al. A bioabsorbable everolimus-eluting stent system (ABSORB): 2-year outcomes and results from multiple imaging methods. Lancet. 2009;373:897- 910.
  10. Yamaguchi T, Terashima M, Akasaka T, et al. Safety and feasibility of an intravascular optical coherence tomography image wire system in the clinical setting. Am J Cardiol. 2008;101:562-567.
  11. Kubo T, Imanishi T, Kitabata H, et al. Comparison of vascular response after sirolimus-eluting stent implantation between patients with unstable and stable angina pectoris: a serial optical coherence tomography study. JACC Cardiovasc Imaging. 2008;1:475-484.
  12. Barlis P, Gonzalo N, Di Mario C, et al. A multicenter evaluation of the safety of intracoronary optical coherence tomography. EuroIntervention. 2009;5:90-95.
  13. Prati F, Cera M, Ramazzotti V, et al. Safety and feasibility of a new non-occlusive technique for facilitated intracoronary optical coherence tomography (OCT) acquisition in various clinical and anatomical scenarios. EuroIntervention. 2007;3:365-370.
  14. Prati F, Regar E, Mintz GS, et al. Expert review document on methodology, terminology, and clinical applications of optical coherence tomography: physical principles, methodology of image acquisition, and clinical application for assessment of coronary arteries and atherosclerosis. Eur Heart J. 2010;31:401-415.
  15. Burke AP, Farb A, Malcom GT et al. Coronary risk factors and plaque morphology in men with coronary disease who die suddenly. N Engl J Med. 1997;336:1276-1282.
  16. Virmani R, Kolodgie FD, Burke AP, et al. Lessons from sudden coronary death: a comprehensive morphological classification scheme for atherosclerotic lesions. Atherioscler Thromb Vasc Biol. 2000;20:1262-1275.
  17. Burke AP, Kolodgie FD, Farb A. Healed plaque ruptures and sudden coronary death: evidence that subclinical rupture has a role in plaque progression. Circulation. 2001;103:934-940.
  18. Virmani R, Burke AP, Farb A, Kolodgie FD. Pathology of the vulnerable plaque. J Am Coll Cardiol. 2006;47(8 Suppl):C13-8.
  19. Finn AV, Nakano M, Narula J, et al. Concept of vulnerable/unstable plaque. Arterioscler Thromb Vasc Biol. 2010;31:401-415.
  20. Fujii K, Kawasaki D, Masutani M, et al. OCT assessment of thin-cap fibroatheroma distribution in native coronary arteries. JACC Cardiovasc Imaging. 2010;3:168-175.
  21. Kubo T, Imanishi T, Kashiwagi M, et al. Multiple coronary lesion instability in patients with acute myocardial infarction as determined by optical coherence tomography. Am J Cardiol. 2010;105:318-322.
  22. Takarada S, Imanishi T, Kubo T, et al. Effect of statin therapy on coronary fibrous-cap thickness in patients with acute coronary syndrome: assessment by optical coherence tomography study. Atherosclerosis. 2009;202:491-497.
  23. Yabushita H, Bouma BE, Houser SL, et al. Characterization of human atherosclerosis by optical coherence tomography. Circulation. 2002;106:1640-1645.
  24. Cilingiroglu M, Oh JH, Sugunan B, et al. Detection of vulnerable plaque in a murine model of atherosclerosis with optical coherence tomography. Catheter Cardiovasc Interv. 2006;67:915-23.
  25. Oh J, Feldman MD, Kim J, et al. Detection of macrophages in atherosclerotic tissue using magnetic nanoparticles and differential phase optical coherence tomography. J Biomed Opt. 2008;13:054006.
  26. Raffel OC, Tearney GJ, Gauthier DD, et al. Relationship between a systemic inflammatory marker, plaque inflammation, and plaque characteristics determined by intravascular optical coherence tomography. Arterioscler Thromb Vasc Biol. 2007;27:1820-1827.
  27. MacNeill BD, Jang IK, Bouma BE, et al. Focal and multi-focal plaque macrophage distributions in patients with acute and stable presentations of coronary artery disease. J Am Coll Cardiol. 2004;44:972-979.
  28. Kume T, Akasaka T, Kawamoto T, et al. Assessment of coronary arterial thrombus by optical coherence tomography. Am J Cardiol. 2006;97:1713-1717.
  29. Schiele F, Meneveau N, Vuillemenot A, et al. Impact of intravascular ultrasound guidance in stent deployment on 6-month restenosis rate: a multicenter, randomized study comparing two strategies—with and without intravascular ultrasound guidance. RESIST Study Group. Restenosis after IVUS Guided Stenting. J Am Coll Cardiol. 1998;32:320-328.
  30. Mudra H, di Mario C, de Jaegere P, et al. Randomized comparison of coronary stent implantation under ultrasound or angiographic guidance to reduce stent restenosis (OPTICUS study). Circulation. 2001;104:1343-1349.
  31. Oemrawsingh PV, Mintz GS, Schalij MJ, et al. Intravascular ultrasound guidance improves angiographic and clinical outcomes of stent implantation for long coronary artery stenosis: final results of a randomized comparison with angiographic guidance (TULIP study). Circulation. 2003;107:62-67.
  32. Serruys PW, Degertekin M, Tanabe K, et al. Intravascular ultrasound findings in the multicenter, randomized, double-blind RAVEL (Randomized Study With the Sirolimus-Eluting Velocity Balloon- Expandable Stent in the Treatment of Patients with De Novo Native Coronary Artery Lesions) trial. Circulation. 2002;106:798-803.
  33. Briguori C, Anzuini A, Airoldi F, et al. Intravascular ultrasound criteria for the assessment of the functional significance of intermediate coronary artery stenoses and comparison with fractional flow reserve. Am J Cardiol. 2001;87:136-141.
  34. Cook S, Wenaweser P, Togni M, et al. Incomplete stent apposition and very late stent thrombosis after drug-eluting stent implantation. Circulation. 2007;115:2426-2434.
  35. Bouma BE, Tearney GJ, Yabushita H, et al. Evaluation of intracoronary stenting by intravascular optical coherence tomography. Heart. 2003;89:317-320.
  36. Rosenthal N, Guagliumi G, Sirbu V, et al. Comparison of intravascular ultrasound and optical coherence tomography for the evaluation of stent segment malapposition (abstract). J Am Coll Cardiol. 2009;53(Suppl A):A22.
  37. Guagliumi G, Sirbu V, Bezerra H, et al. Strut coverage and vessel response to zotarolimus-eluting and bare-metal stents implanted in patients with ST-segment elevation myocardial infarction: the OCTAMI (Optical Coherence Tomography in Acute Myocardial Infarction) study. JACC Cardiovasc Interv. 2010;3:680-687.
  38. Kyono H, Guagliumi G, Sirbu V, et al. Optical coherence tomography (OCT) strut-level analysis of drug-eluting stents (DES) in human coronary bifurcations. EuroIntervention. 2010;6:69-77.
  39. Abizaid A, Costa JR Jr, Feres F. First nine-month complete invasive assessment (angiography, IVUS, and OCT) of the novel NEVO sirolimus-eluting stent with biodegradable polymer. Catheter Cardiovasc Interv. 2011;77:49-51.
  40. Guagliumi G, Musumeci G, Sirbu V, et al. Optical coherence tomography assessment of in vivo vascular response after implantation of overlapping bare-metal and drug-eluting stents. JACC Cardiovasc Interv. 2010;3:531-539.
  41. Guagliumi G, Musumeci G, Sirbu V, et al. A prospective, randomized, controlled study using optical coherence tomography to evaluate strut coverage of sirolimus-, paclitaxel-, and zotarolimus-eluting coronary stents in long lesions requiring overlapping. Paper presented at: Transcatheter Cardiovascular Therapeutics 2008; October 14, 2008; Washington, DC.
  42. Sousa JE, Costa MA, Sousa AG, et al. Two-year angiographic and intravascular ultrasound follow- up after implantation of sirolimus-eluting stents in human coronary arteries. Circulation. 2003;107:381-383.
  43. Tanigawa J, Barlis P, Dimopoulos K, et al. Optical coherence tomography to assess malapposition in overlapping drug-eluting stents. EuroIntervention. 2008;3:580-583.
  44. Gonzalo N, Barlis P, Serruys PW, et al. Incomplete stent apposition and delayed tissue coverage are more frequent in drug-eluting stents implanted during primary percutaneous coronary intervention for ST-elevation myocardial infarction than in drug-eluting stents implanted for stable/unstable angina: insights from optical coherence tomography. JACC Cardiovasc Interv. 2009;2:445-452.
  45. Gonzalo N, Serruys PW, Okamura T, et al. Optical coherence tomography assessment of the acute effects of stent implantation on the vessel wall: a systematic quantitative approach. Heart. 2009;95:1913-1919.
  46. Gonzalo N, Serruys PW, Okamura T, et al. Relation between plaque type and dissections at the edges after stent implantation on the vessel wall: an optical coherence tomography study. Int J Cardiol. In press.
  47. Jang IK, Tearney G, Bouma B, et al. Visualization of tissue prolapse between coronary stent struts by optical coherence tomography: comparison with intravascular ultrasound. Circulation. 2001;104:2754.
  48. Sheris SJ, Canos MR, Weismann NJ. Natural history of intravascular ultrasound-detected edge dissections from coronary stent deployment. Am Heart J. 2000;139:59-63.