Choice of Intracoronary Imaging: When to Use Intravascular Ultrasound or Optical Coherence Tomography

Login or register to view PDF.
Abstract

Intracoronary imaging has the capability of accurately measuring vessel and stenosis dimensions, assessing vessel integrity, characterising lesion morphology and guiding optimal percutaneous coronary intervention (PCI). Coronary angiography used to detect and assess coronary stenosis severity has limitations. The 2D nature of fluoroscopic imaging provides lumen profile only and the assessment of coronary stenosis by visual estimation is subjective and prone to error. Performing PCI based on coronary angiography alone is inadequate for determining key metrics of the vessel such as dimension, extent of disease, and plaque distribution and composition. The advent of intracoronary imaging has offset the limitations of angiography and has shifted the paradigm to allow a detailed, objective appreciation of disease extent and morphology, vessel diameter, stent size and deployment and healing after PCI. It has become an essential tool in complex PCI, including rotational atherectomy, in follow-up of novel drug-eluting stent platforms and understanding the pathophysiology of stent failure after PCI (e.g. following stent thrombosis or in-stent restenosis). In this review we look at the two currently available and commonly used intracoronary imaging tools – intravascular ultrasound and optical coherence tomography – and the merits of each.

Disclosure
The authors have no conflicts of interest to declare
Correspondence
Roby Rakhit, Consultant Interventional Cardiologist, Department of Cardiology, Royal Free Hospital, Pond Street, London, NW3 2QG, UK. E: roby.rakhit@nhs.net
Received date
13 January 2016
Accepted date
08 February 2016
DOI
http://dx.doi.org/10.15420/icr.2016:6:1

Intracoronary imaging is able to aid the interventional cardiologist in the characterisation of atherosclerotic plaque morphology, in optimising stent sizing, and in minimising the complications associated with percutaneous coronary intervention (PCI). Intravascular ultrasound (IVUS) and optical coherence tomography (OCT) are commonly used methods, while newer spectroscopic methods are under development.

Intravascular Ultrasound Versus Optical Coherence Tomography: Technology

Table 1 displays a technical comparison of the IVUS and OCT imaging methods. The principle of IVUS imaging is based on the ultrasound waves produced by the oscillatory movement of a transducer.1 Commercially available IVUS systems have transducers mounted on catheters that are compatible with guiding catheters in sizes of 5Fr or larger. These catheters can be inserted into the coronary artery over a 0.014 inch conventional guide wire and imaging can be obtained by manual or motorised pullback. Motorised pullbacks are carried out at a speed of 0.5 mm/s, thus a 50 mm coronary artery can be imaged in approximately 90s. Integrated IVUS consoles add to the rapidity of imaging, but mobile IVUS carts are also available. When co-registration of IVUS with angiography becomes available, this will be a useful adjunct in locating the anatomical lesion precisely. Once the pullback is recorded, measurements of the lumen can be carried out either manually or using automated software. Greyscale IVUS has an axial resolution of 100–150 μm, lateral resolution of 200 μm1 and penetration depth of 4–8 mm. Post-processing of greyscale IVUS images is possible with radiofrequency-based technology such as IVUS virtual histology.2 IVUS virtual histology may assist in characterisation of plaque morphology by differentiating between various types of plaque using colour coding. As a result of limited resolution, IVUS cannot reliably identify the separation between intima and media and the relation between adventitia and peri-adventitial structures (see Figure 1).3

In contrast to IVUS, intracoronary imaging by OCT is obtained using near-infrared light. The first generation of OCT imaging was based on occlusive balloon technology called time domain (TD) imaging. Use of frequency domain (FD) imaging, also referred to as Fourier domain spectral imaging, has now surpassed TD imaging.4 FD imaging does not require occlusion of the proximal artery with a balloon as high viscosity liquids such as contrast media can be used to purge blood from the vessel, while imaging is completed rapidly. Current commercially available OCT catheters consist of a single-mode optical fibre in a hollow metal wire torque that rotates at a speed of 100 rps. The axial and lateral resolutions of OCT are 10–20 μm and 20 μm, respectively – which is superior to that of IVUS. However, better resolution comes at a drawback of limited penetration – a maximum of 2 mm.5 With acquisition speeds of up to 25 mm/s, rapid imaging of coronary artery can be achieved within a few seconds. Commercially available OCT catheters can be inserted into coronary artery on a 0.014 inch guide wire and are compatible with guiding catheters sized 5Fr or larger. For optimal imaging quality, a bloodless field is required, which can be achieved with injection of 12–15 ml of highly viscous medium such as contrast, either by hand or by use of a power injector. Blood clearance can be challenging through a 5Fr catheter, therefore 6Fr or larger is generally recommended. Caution needs to be exercised in people with renal impairment where multiple pullbacks are contemplated due to the risk of contrast nephropathy.

Table 1: Technical Comparison of IVUS and OCT

Open in new tab
Open ppt

Figure 1: IVUS (A) and OCT (B) Showing a Normal Segment of Coronary Artery

Open in new tab
Open ppt

Figure 2: IVUS Showing a Circumferential Calcified Lesion (A) and Eccentric Mixed Plaque (B)

Open in new tab
Open ppt

Current commercially available OCT software automatically detects the lumen, allows marking of every frame and gives user-defined proximal and distal reference frames with dimensions. Furthermore, every pullback of the coronary artery can be viewed in cross-sectional frames (see Figure 1), longitudinal view and lumen profile view. Cross-sectional views are helpful in detailed study of plaque where as longitudinal and lumen profile views can be used for longitudinal measurements such as stent length. 3D reconstruction is possible and may assist in detailed assessment of bifurcation lesions and in optimising PCI results. Co-registration of OCT with angiography can be a useful adjunct in locating anatomical lesions precisely, reducing the chances of geographical miss.

Intravascular Ultrasound Versus Optical Coherence Tomography: Safety and Feasibility

One of the limitations of earlier TD-OCT imaging was the requirement to have a bloodless field for adequate imaging. This was achieved by proximal occlusion of the coronary artery with a semi-compliant balloon followed by flushing of the artery with ringer’s lactate solution. Although this method was not associated with any serious complications, minor complications such as transient ST elevation with associated chest pain were common.6 Furthermore, the acquisition time was longer with a pullback speed of only 0.5–3.0 mm/s. In comparison, current FD-OCT imaging does not require balloon occlusion of coronary artery and, with higher pullback speeds, a bloodless field can be achieved by contrast injection.

Both IVUS and current-generation FD-OCT have been shown to have a favourable safety profile. An integrated biomarker and imaging substudy (IBIS-4) assessed the feasibility and the procedural and longterm safety of OCT and IVUS in patients with ST-elevation MI (STEMI) undergoing primary PCI.7 In this prospective cohort study, 103 patients with STEMI who underwent serial three-vessel coronary imaging during primary PCI were compared with 485 patients with STEMI undergoing primary PCI without additional imaging after 13 months. Feasibility (defined as the number of pullbacks suitable for analysis) and safety (defined as the frequency of peri-procedural complications and major adverse cardiac events [MACE, a composite of cardiac death, MI and any clinically indicated revascularisation at 2 years]) outcomes were recorded. Successful imaging was achieved in <90 % of patients at baseline and follow-up using IVUS and OCT. Although peri-procedural complications occurred with OCT imaging (<2.0 % versus 0 % with IVUS), long-term safety was favourable with both modalities, with no significant difference in MACE rates at 2 years.7 Of note, the majority of OCT-related complications were transient ST elevation due to coronary spasm, which in clinical practice can be mitigated by administering intracoronary nitrates prior to imaging.

In another registry-based study, OCT and IVUS were shown to have comparable safety and feasibility profiles.8 Analysis of 3,045 OCT pullbacks from 1,142 patients and 5,148 IVUS pullbacks from 2,476 patients revealed seven complications related to OCT and 12 to IVUS imaging. Transient ST-elevation requiring withdrawal of the imaging catheter was noted with OCT, whereas IVUS appears to have been associated with coronary spasm, thrombus formation, dissection of the imaged vessel and stent deformation.8

Is One Choice of Intracoronary Imaging Superior to the Other and What are the Clinical Scenarios Where They Should be Used?

Intravascular Ultrasound

Over the past two decades, IVUS has become the reference tool for intracoronary imaging. Advances in IVUS technology have resulted in better resolution and penetration: IVUS can now be used to assess plaque characteristics, volume and constituents (see Figure 2; Table 2).9 Coronary arterial and lumen dimensions, particularly minimal luminal area (MLA), can be measured accurately by IVUS algorithms, which can assist in the decision-making process for revascularisation.10 One of the most important roles of IVUS is in optimising PCI, particularly in complex lesions subsets such as left main stem (LMS), calcific and bifurcation lesions.11 IVUS can be used to optimise PCI as it has a role in stent sizing and in detecting adequate stent expansion and strut malapposition (see Figure 3).12 IVUS, with its better penetration, is superior to OCT in assessing the remodelling patterns of the vessel wall. IVUS-detected positive vessel remodelling of the coronary artery is associated with late stent thrombosis following drug-eluting stent (DES) implantation.13

Table 2: Clinical Situations in Which IVUS and OCT Can be Useful

Open in new tab
Open ppt

Optical Coherence Tomography

OCT, with even better resolution when compared with IVUS, can be used in assessing plaque characteristics14 and constituents15 and in optimising PCI.16 However, with limited penetration, assessment of plaques with thickness of >1.0–1.5 mm is not possible with OCT.4,17 Up to 25 % of acute coronary syndrome events are secondary to thrombus present on a non-ruptured plaque, also called an erosion.15,18 OCT helps in accurately identifying eroded plaques, where if no lumen narrowing is present stenting may not be needed. The presence of thin-cap fibroatheroma (TCFA), defined as lipid plaque thickness of <65 μm, is predictive of future adverse cardiac events.18 However, interpretation of TCFA on OCT requires caution as artefacts due to tangential dropout can lead to misinterpretation.19 The superior resolution of OCT means it can detect TCFA with adequate sensitivity/ specificity,20 and also detects the presence of macrophages21 and neovessels, and lipid volume – the features of so-called vulnerable plaque (see Figure 4). Furthermore, OCT not only identifies the presence of thrombus, but can also distinguish between red and white thrombus often seen in STEMI (see Figure 5; Table 2).20 Injury to the vessel wall post-PCI reflected by the presence of intimal tears, edge dissections, tissue prolapse, presence of thrombus and incomplete stent apposition can be readily assessed by OCT, which allows for optimisation, as required.16 Two further areas where imaging with OCT is useful are capability of detecting thin neo-intima in follow-up imaging after DES implantation22 and in delineating tissue characteristics of in-stent restenosis (see Figure 4).23 OCT is superior to IVUS in identifying uncovered stent struts. Sub-analysis of the Optical Coherence Tomography for Drug Eluting Stent Safety (ODESSA) trial showed 8 % of the stented segments with no detectable neointima by IVUS were found to have neo-intimal coverage by OCT.24

Figure 3: OCT Showing a Well-opposed Stent (A) and Malapposed Stent (B); IVUS Showing a Well-opposed Stent (C) and Malapposed Stent (D)

Open in new tab
Open ppt

Is There Evidence Supportive of One Modality Over the Other?

In the field of interventional cardiology, any new diagnostic tool or treatment modality needs to be associated with better clinical outcomes before being incorporated into guidelines and adapted widely in the clinical environment. Here, we review the data supporting the use of these imaging techniques in contemporary clinical practice.

Intravascular Ultrasound

A meta-analysis of IVUS-guided PCI by Zhang et al. showed improved clinical outcomes.25 In their analysis, over 19,000 patients across eleven studies (one randomized controlled trial and 10 registries) were included. Compared with angiography alone, IVUS-guided DES implantation was associated with reduced rates of death, MACE and stent thrombosis. No difference was found in the rates of MI, target lesion and target vessel revascularisation.

Figure 4: OCT Showing a Thin-walled Plaque (A), Ruptured Plaque (B) and In-stent Restenosis (C)

Open in new tab
Open ppt

Figure 5: OCT Showing Red Thrombus Resulting in Image Dropout (A) and White Thrombus Within a Previously Implanted Stent With no Image Dropout (B)

Open in new tab
Open ppt

The non-randomised Assessment of Dual Antiplatelet Therapy With Drug-Eluting Stents (ADAPT-DES) study analysed 3,349 patients in whom IVUS was used to guide PCI.26 IVUS guidance changed the PCI strategy in 74 % of cases. IVUS guidance compared with angiography alone was associated with reduced 1-year rates of stent thrombosis, MI and MACE following DES implantation.

IVUS can be a useful adjunct in the assessment of LMS disease. IVUS generated MLA correlates with fractional flow reserve (FFR) in the absence of proximal left anterior descending and circumflex artery disease. IVUS MLA of <5.9 mm2 correlates well with FFR of <0.75.27 However, caution need to be exercised in Asian patients who have smaller coronary arteries. Kang et al. showed that an MLA cut-off of <4.1 mm2 correlated with FFR <0.7528 in a Korean population. In non- LMS lesions, the correlation of IVUS derived MLA with FFR is weak with limited accuracy.29 The reasons for this are lesion location in the coronary tree, lesion length, eccentricity, entrance and exit angles, shear forces, reference vessel dimensions, and the amount of viable myocardium subtended by the lesion.30 Although it is safe to defer PCI in non-LMS lesions with MLA >4 mm2, lesions with MLA <4 mm2 may need to be physiologically tested before intervention.31

Optical Coherence Tomography

Currently trial data looking at OCT use and clinical outcomes are limited. The Centro per la Lotta contro l’Infarto-Optimisation of Percutaneous Coronary Intervention (CLI-OPCI) study compared outcomes between patients undergoing PCI under angiography guidance alone versus angiography plus OCT guidance.32 The group that underwent PCI with angiography and OCT guidance had overall significantly lower rates of cardiac death, MI and repeat revascularisation. Furthermore, OCT revealed adverse features following PCI in almost 35 % of patients who needed further intervention.

The Observational Study of Optical Coherence Tomography in Patients Undergoing Fractional Flow Reserve and Percutaneous Coronary Intervention (ILUMIEN) I study assessed how the clinical decisionmaking process is influenced when OCT is added to angiography and FFR.33 This study enrolled 418 patients scheduled for PCI from 35 international centres, including patients with stable and unstable coronary syndromes, prospectively in a non-randomised fashion. Once recruited, the majority of patients underwent pre-PCI FFR and OCT imaging. OCT imaging influenced physician decision-making processes pre-PCI in 57 % and post-PCI in 27 % of cases. Additional in-stent post-dilatation was carried out in 81 % and additional stent placement in 12 % of the cases. Device-oriented MACE (cardiac death, MI and target lesion revascularisation) and patient-oriented MACE (all-cause death, MI and any repeat revascularisation) were rare in hospital and at 30 days. The rates of other events such as stent thrombosis were also extremely low.33 The ILUMIEN II study showed the degree of stent expansion achieved after OCT versus IVUS guidance to be comparable.34 In this retrospective study, propensitymatched analysis of 354 patients who underwent OCT in the ILUMIEN I trial and 586 patients from the IVUS substudy of the ADAPT-DES trial based on reference vessel diameter, lesion length, calcification, and reference segment availability was comparable between OCT and IVUS guidance, as were the rates of major stent malapposition, tissue protrusion, and stent-edge dissection.34 The ongoing Optical Frequency Domain Imaging Versus Intravascular Ultrasound In Percutaneous Coronary Intervention (OPINION – OFDI) and ILUMIEN III randomised trials will further help in elucidating the potential of OCT versus IVUS in optimising PCI outcomes. The OPINION – OFDI study has completed recruitment with 800 patients divided equally between OCT and IVUS arms.35 The preliminary results showed comparable safety profiles and stent expansion with OCT and IVUS guidance immediately after PCI. The follow-up results at 1 year, including outcome data, are awaited.

As with IVUS, the OCT-derived MLA of 1.9 mm2 correlates well with an FFR of <0.75.36 Another study of 56 stable patients reported OCTderived MLA of 1.95 mm2 correlating well with an FFR of <0.80, with a sensitivity of 82 % and specificity of 63 %. However, 5 of the 26 patients with MLA >1.95 mm2 had an FFR of <0.80, suggesting that OCT cannot be a surrogate for FFR.37

Guidelines

The American College of Cardiology Foundation/American Heart Association/Society for Cardiac Angiography (ACC/AHA/SCAI)31 and European Society of Cardiology/European Association for Cardio-Thoracic Surgery (ESC/EACTS)38 guidelines on myocardial revascularisation have issued a class II recommendation for IVUS with varying levels of evidence depending on the indication (see Table 3). OCT, Owing to a lack of clinical data, OCT is not included in the US guidelines, whereas the European guidelines have given a class II recommendation for OCT (see Table 3).

Table 3: Current Guidelines for Use of IVUS and OCT

Open in new tab
Open ppt

Future Directions

It is evident that both technologies have advantages and limitations. More technological adaptions are under way to enhance the use of IVUS and OCT. For example, OCT equipment that can complete pullback of entire coronary artery with in one heartbeat to minimise artefacts is undergoing experiments.39 Micro-OCT that has the ability to study endothelium and macrophages in vivo in detail is also under development.40 Experiments looking into feasibility of photo acoustic imaging in humans one are also underway.41

Conclusion

Intracoronary imaging has given a new dimension to the field of interventional cardiology. When choosing the modality of intracoronary imaging, the anatomic location in the coronary tree appears to be a good discriminator. IVUS has better data when it comes to LMS-related lesions, whereas OCT seems to be superior in arteries with an MLA of <3 mm2. When it comes to establishing diagnosis and optimising stent deployment, OCT has the advantage of better resolution. However, when it comes to assessing the significance of intermediate coronary stenosis, physiological assessment with FFR should remain the first choice as IVUS- and OCT-derived MLA cut-off values have at best moderate correlation and accuracy.

IVUS and OCT are safe and feasible to use in modern cardiac catheter laboratory practice. In the hands of an experienced operator, imaging can be done rapidly with minimal or no complications. With advantages and limitations of one modality over the other, intracoronary imaging with IVUS and or OCT have the potential to complement each other. Future data justifying their routine use based on improved clinical endpoint data is forthcoming. The future of intracoronary imaging is likely to incorporate co-registration with angiography as standard, hybrid and molecular imaging. Future technological advances in intracoronary imaging provide further exciting opportunities for a better understanding of the coronary disease process and response to revascularisation.

References
  1. Garcia-Garcia HM, Gogas BD, Serruys PW, Bruining N. IVUS-based imaging modalities for tissue characterization: similarities and differences. Int J Cardiovasc Imaging 2011;27:215–24.
    Crossref | PubMed
  2. Gogas BD, Farooq V, Serruys PW, Garcia-Garcia HM. Assessment of coronary atherosclerosis by IVUS and IVUSbased imaging modalities: progression and regression studies, tissue composition and beyond. Int J Cardiovasc Imaging 2011;27:225–37.
    Crossref | PubMed
  3. Mintz GS, Nissen SE, Anderson WD, et al. American College of Cardiology Clinical Expert Consensus Document on Standards for Acquisition, Measurement and Reporting of Intravascular Ultrasound Studies (IVUS). A report of the American College of Cardiology Task Force on Clinical Expert Consensus Documents. J Am Coll Cardiol 2001;37:1478–92.
    Crossref | PubMed
  4. Prati F, Guagliumi G, Mintz GS, et al. Expert review document part 2: methodology, terminology and clinical applications of optical coherence tomography for the assessment of interventional procedures. Eur Heart J 2012;33:2513–20.
    Crossref | PubMed
  5. Terashima M, Kaneda H, Suzuki T. The role of optical coherence tomography in coronary intervention. Korean J Intern Med 2012;27:1–12. epub ahead of press.
    Crossref | PubMed
  6. Takarada S, Imanishi T, Liu Y, et al. Advantage of nextgeneration frequency-domain optical coherence tomography compared with conventional time-domain system in the assessment of coronary lesion. Catheter Cardiovasc Interv 2010;75:202–6.
    Crossref | PubMed
  7. Taniwaki M, Radu MD, Garcia-Garcia HM, et al. Longterm safety and feasibility of three-vessel multimodality intravascular imaging in patients with ST-elevation myocardial infarction: the IBIS-4 (integrated biomarker and imaging study) substudy. Int J Cardiovasc Imaging 2015;31:915–26.
    Crossref | PubMed
  8. Van der Sijde JKA, van Geuns R-J, Valgimigli M, et al. Safety of optical coherence tomography in daily practice: how does it compare to intravascular ultrasound? EuroIntervention 2015;Abstracts EuroPCR 2015.
  9. Nissen SE, Yock P. Intravascular ultrasound: novel pathophysiological insights and current clinical applications. Circulation 2001;103:604–16.
    Crossref | PubMed
  10. Waksman R, Kitabata H, Prati F, et al. Intravascular ultrasound versus optical coherence tomography guidance. J Am Coll Cardiol 2013;62:S32–40.
    Crossref | PubMed
  11. Kim JS, Hong MK, Ko YG, et al. Impact of intravascular ultrasound guidance on long-term clinical outcomes in patients treated with drug-eluting stent for bifurcation lesions: data from a Korean multicenter bifurcation registry. Am Heart J 2011;161:1:80–7.
    Crossref | PubMed
  12. Parise H, Maehara A, Stone GW, et al. Meta-analysis of randomized studies comparing intravascular ultrasound versus angiographic guidance of percutaneous coronary intervention in pre-drug-eluting stent era. Am J Cardiol 2011;107:374–82.
    Crossref | PubMed
  13. Guagliumi G, Sirbu V, Musumeci G, et al. Examination of the in vivo mechanisms of late drug-eluting stent thrombosis: findings from optical coherence tomography and intravascular ultrasound imaging. JACC Cardiovasc Interv 2012;5:12–20.
    Crossref | PubMed
  14. Jang IK, Bouma BE, Kang DH, et al. Visualization of coronary atherosclerotic plaques in patients using optical coherence tomography: comparison with intravascular ultrasound. J Am Coll Cardiol 2002;39:604–9.
    Crossref | PubMed
  15. Yabushita H, Bouma BE, Houser SL, et al. Characterization of human atherosclerosis by optical coherence tomography. Circulation 2002;106:1640–5.
    Crossref | PubMed
  16. 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;95:1913–9.
    Crossref | PubMed
  17. Manfrini O, Mont E, Leone O, et al. Sources of error and interpretation of plaque morphology by optical coherence tomography. Am J Cardiol 2006;98:156–9.
    Crossref | PubMed
  18. Virmani R, Kolodgie FD, Burke AP, et al. Lessons from sudden coronary death: a comprehensive morphological classification scheme for atherosclerotic lesions. Arterioscler Thromb Vasc Biol 2000;20:1262–75.
    Crossref | PubMed
  19. van Soest G, Regar E, Goderie TP, et al. Pitfalls in plaque characterization by OCT: image artifacts in native coronary arteries. JACC Cardiovasc Imaging 2011;4:810–3.
    Crossref | PubMed
  20. Kume T, Akasaka T, Kawamoto T, et al. Measurement of the thickness of the fibrous cap by optical coherence tomography. Am Heart J 2006;152:755 e751–4.
    Crossref | PubMed
  21. 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;44:972–9.
    Crossref | PubMed
  22. Matsumoto D, Shite J, Shinke T, et al. Neointimal coverage of sirolimus-eluting stents at 6-month follow-up: evaluated by optical coherence tomography. Eur Heart J 2007;28:961–7.
    Crossref | PubMed
  23. Habara M, Terashima M, Nasu K, et al. Difference of tissue characteristics between early and very late restenosis lesions after bare-metal stent implantation: an optical coherence tomography study. Circ Cardiovasc Interv 2011;4:232–8.
    Crossref | PubMed
  24. 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;3:531–9.
    Crossref | PubMed
  25. Zhang Y, Farooq V, Garcia-Garcia HM, et al. Comparison of intravascular ultrasound versus angiography-guided drug-eluting stent implantation: a meta-analysis of one randomised trial and ten observational studies involving 19,619 patients. EuroIntervention 2012;8:855–65.
    Crossref | PubMed
  26. Witzenbichler B, Maehara A, Weisz G, et al. Relationship between intravascular ultrasound guidance and clinical outcomes after drug-eluting stents: the assessment of dual antiplatelet therapy with drug-eluting stents (ADAPTDES) study. Circulation 2014;129:463–70.
    Crossref | PubMed
  27. Jasti V, Ivan E, Yalamanchili V, et al. Correlations between fractional flow reserve and intravascular ultrasound in patients with an ambiguous left main coronary artery stenosis. Circulation 2004;110:2831–6.
    Crossref | PubMed
  28. Kang SJ, Lee JY, Ahn JM, et al. Intravascular ultrasoundderived predictors for fractional flow reserve in intermediate left main disease. JACC Cardiovasc Interv 2011;4:1168–74.
    Crossref | PubMed
  29. Abizaid A, Mintz GS, Pichard AD, et al. Clinical, intravascular ultrasound, and quantitative angiographic determinants of the coronary flow reserve before and after percutaneous transluminal coronary angioplasty. Am J Cardiol 1998;82:423–8.
    Crossref | PubMed
  30. Pijls NH, Sels JW. Functional measurement of coronary stenosis. J Am Coll Cardiol 2012;59:1045–57.
    Crossref | PubMed
  31. Lotfi A, Jeremias A, Fearon WF, et al. Expert consensus statement on the use of fractional flow reserve, intravascular ultrasound, and optical coherence tomography: a consensus statement of the Society of Cardiovascular Angiography and Interventions. Catheter Cardiovasc Interv 2014;83:509–18.
    Crossref | PubMed
  32. Prati F, Di Vito L, Biondi-Zoccai G, et al. Angiography alone versus angiography plus optical coherence tomography to guide decision-making during percutaneous coronary intervention: the Centro per la Lotta contro l’Infarto- Optimisation of Percutaneous Coronary Intervention (CLIOPCI) study. EuroIntervention 2012;8:823–9.
    Crossref | PubMed
  33. Wijns W, Shite J, Jones MR, et al. Optical coherence tomography imaging during percutaneous coronary intervention impacts physician decision-making: ILUMIEN I study. Eur Heart J 2015;36:3346–55.
    Crossref | PubMed
  34. Maehara A, Ben-Yehuda O, Ali Z, et al. Comparison of Stent Expansion Guided by Optical Coherence Tomography Versus Intravascular Ultrasound: The ILUMIEN II Study (Observational Study of Optical Coherence Tomography [OCT] in Patients Undergoing Fractional Flow Reserve [FFR] and Percutaneous Coronary Intervention). JACC Cardiovasc Interv 2015;8:1704–14.
    Crossref | PubMed
  35. Akasaka T. OPINION: OPtical frequency domain imaging versus INtravascular ultrasound in percutaneous coronary InterventiON. Presented at: EuroPCR, Paris, France, 20 May 2015.
  36. Shiono Y, Kitabata H, Kubo T, et al. Optical coherence tomography-derived anatomical criteria for functionally significant coronary stenosis assessed by fractional flow reserve. Circ J 2012;76:2218–25.
    Crossref | PubMed
  37. Gonzalo N, Escaned J, Alfonso F, et al. Morphometric assessment of coronary stenosis relevance with optical coherence tomography: a comparison with fractional flow reserve and intravascular ultrasound. J Am Coll Cardiol 2012;59:1080–9.
    Crossref | PubMed
  38. Kolh P, Windecker S. ESC/EACTS myocardial revascularization guidelines 2014. Eur Heart J 2014;35:3235–6.
    Crossref | PubMed
  39. Wang T, Pfeiffer T, Regar E, et al. Heartbeat OCT: in vivo intravascular megahertz-optical coherence tomography. Biomed Opt Express 2015;6:5021–32.
    Crossref | PubMed
  40. Liu L, Gardecki JA, Nadkarni SK, et al. Imaging the subcellular structure of human coronary atherosclerosis using microoptical coherence tomography. Nat Med 2011;17:1010–4.
    Crossref | PubMed
  41. Desjardins AE, van der Voort M, Roggeveen S, et al. Needle stylet with integrated optical fibers for spectroscopic contrast during peripheral nerve blocks. J Biomed Opt 2011;16:077004.
    Crossref | PubMed