Archives of Cardiovascular Disease (2012) 105, 529—534
Available online at
Optical coherence tomography: From physicalprinciples to
Tomographie par cohérence optique : des principes physiques aux
Righab Hamdan ∗, Ricardo Garcia Gonzalez,Said Ghostine,
Centre chirurgical Marie-Lannelongue, cardiologie, 133, avenue
de la Resistance, 92350 LePlessis Robinson, France
Received 1st January 2012; received in revised form 14 February
2012; accepted 16 February2012Available online 17 July 2012
Summary Optical coherence tomography is a new endocoronary
imaging modality employingnear infrared light, with very high axial
resolution. We will review the physical principles,including the
old time domain and newer Fourier domain generations, clinical
applications,controversies and perspectives of optical coherence
tomography.© 2012 Elsevier Masson SAS. All rights reserved.
Résumé La tomographie par cohérence optique est une modalité
d’imagerie récente endo-coronaire utilisant la lumière infrarouge,
caractérisée par une haute résolution. Dans cet
percutanée ;Athérosclérose ;Tomographie parcohérence optique
article, on discute les principes physiques en discutant
l’ancienne et la nouvelle générationde tomographie par cohérence
optique, time domain et Fourier domain respectivement.© 2012
Elsevier Masson SAS. Tou
Abbreviations: FD-OCT, Fourier domain optical coherence
tomographcoherence tomography; TD-OCT, time domain optical
∗ Corresponding author.E-mail address: firstname.lastname@example.org (R.
1875-2136/$ — see front matter © 2012 Elsevier Masson SAS. All
s droits réservés.
y; IVUS, intravascular ultrasound; OCT, opticalphy.
5 R. Hamdan et al.
Table 1 Physical properties of optical coherencetomography and
Wavelength (�m) 35—80 1.3Energy source Ultrasound
InfraredPenetration (mm) 10 1—2.5Axial resolution (�m) 100—200
15—20Lateral resolution (�m) 200—300 20—40
IVUS: intravascular ultrasound; OCT: optical coherence
ptical coherence tomography (OCT) is a new imagingodality, used
for the first time by Huang et al. in 1991
n vitro on the human peripapillary region of the retina
andoronary arteries . OCT is based on near infrared light;n
optical beam is directed at the tissues, most of the lightcatters
and only the small portion of this light that reflectsrom
subsurface features is collected and forms the imagey yielding
spatial information about tissue microstruc-ure. The critical
advantage of OCT over ultrasonographynd magnetic resonance imaging
is due to its microme-er resolution (about 10—15 �m of tissue axial
hysical principles and acquisition systems
CT uses low coherent near infrared light. The wavelengthsed is
around 1300 nm to minimize energy absorption inhe light beam caused
by protein, water, haemoglobin andipids . The physics principle
that allows the filtering ofcattered light is optical coherence
. A light source emits
low-coherence, laser light wave. The light wave reaches beam
splitter or a partial mirror, which splits the lightave in half.
One part of the light wave travels to a refe-
ence mirror, where it reflects directly back towards theeam
splitter. The second part travels to the sample tis-ue. Depending
on the optical properties of the tissue, somemount of light may be
absorbed, refracted or reflected5—8]. Reflection occurs when there
is a region of sharpefractive index mismatch; therefore the
velocity of lights not considered constant when it passes through
differentedia. Light travels faster in a medium of low
ndex compared to a medium of high refractive index. Themount of
reflection depends on the level of mismatch,he angle and the
polarization of the incident angle. Theeflected portion of the
light travels back towards the beamplitter, where it meets with the
reference light wave. Thenteraction between these two light waves
is the basis onhich OCT produces images . When two light waves
he same wavelength and constant phase difference meet,hey are
combined through superposition; this phenomenons called
interference. If the light waves are in phase, theydd together in
constructive interference; if they are outf phase, they cancel each
other out in destructive inter-erence . When the sample and
reference light waveseet, they either intensify or diminish
depending on how
he sample light interacts with the tissue . A detectorses the
light or dark pattern produced to create a pixelor that specific
region . OCT cross-sectional imaging ischieved by performing
successive axial measurements ofack-reflected light at different
transverse positions. Aftercanning a whole area, a full image of
the tissue may beroduced.
The major limitation of intracoronary OCT is blood atten-ation
due to the backscattering properties of red blood
ells, thus we need to displace blood from the field of view.
There are two OCT systems: the first-generation sys-em or time
domain OCT and the new-generation systemr Fourier domain OCT.
ime domain OCT
ime domain OCT (TD-OCT) uses an occlusive technique thatequires
stopping of the coronary blood flow by soft bal-oon inflation
[3,9,10]. The pullback speed of TD-OCT rangesetween 1 and 5 mm/s
[11—15]. TD-OCT uses a broadbandight source containing a moving
mirror that allows scan-ing of each depth position in the image,
pixel by pixel.his mechanical scanning process limits the rate at
mages can be acquired .TD-OCT is limited by the risk of
balloon injury, a balloon-
essel size mismatch, a long diseased lesion exceeding0 mm, the
inability to visualize ostial or very proximalesions and the
inability to study the left main coronaryrtery.
ourier domain OCT
he development of the new-generation or Fourieromain OCT
(FD-OCT) enables high-speed pullbacks10—25 mm/second) during image
acquisition, allowing theisualization of long coronary segments in
a much reducedcquisition time and without the need for transient
occlu-ion of the coronary artery. The non-occlusive
techniqueequires simultaneous flushing with a viscous
iso-osmolarolution through the guiding catheter . The fluid
infusedequires a viscosity higher than that of blood;
non-occlusiveCT image acquisition using iodixanol 320 is the
standardushing solution [2,11,12,15]. The amount of iodixanol
320sed for OCT pull-back is usually 3-fold greater than thatequired
for standard coronary iodixanol 320.
FD-OCT uses a wavelength-swept laser as the light sourcend the
reference mirror is fixed. This change in technologyesults in a
better signal-to-noise ratio and faster sweeps,llowing a
dramatically faster image acquisition and pull-ack speed than
TD-OCT [3,16,17]. Presently, the maximummaging speed that can be
achieved with FD-OCT is limitedy digital data transfer and storage
CT versus intravascular ultrasound
any trials have compared OCT with intravascular ultra-
ound (IVUS) for tissue characterization of human coronarylaques.
OCT is mainly limited by its penetration depth.ithin its
penetration depth OCT has much higher sensitivity
nd specificity for characterizing calcification, fibrosis,
Optical coherence tomography 531
nsitivity for plaque definition.
following information [21,25,26]: plaque rupture, identifiedby
the presence of fibrous cap discontinuity and a cavityformation
within the plaque (Fig. 4); plaque erosion, cha-racterized by loss
of the endothelial lining with lacerationsof the superficial
intimal layers and without ‘trans-cap’ rup-tures; intracoronary
thrombus (a red thrombus is visualizedas a hypersignal protruding
in the lumen, with a signal-free posterior shadowing due to
attenuation of the opticalbeam by red blood cells; a white thrombus
does not containred blood cells and can be thus fully visualized
with OCT[Fig. 5]).
Percutaneous coronary intervention and stentimplantation
Another domain of interest for endocoronary OCT is percuta-neous
transluminal angioplasty and stent implantation. OCTwas able to
assess in-stent restenosis, in-stent thrombosisand strut coverage
in bioresorbable everolimus stents at 6
Figure 1. Higher optical coherence tomography resolution and
pool intimal hyperplasia [19,20], fibrous cap erosion and
rup-ture, intracoronary thrombus and thin cap fibroatheroma
(Fig. 1), for the detection of stent endothelialization,strut
coverage and stent apposition and expansion, andfor lumen border
visualization and measurement of correctlumen area . As for
IVUS, the critical lumen area forintermediate lesions is 4 mm2 .
Measurements of lumendiameter and lumen area obtained with OCT and
IVUS werehighly correlated, although OCT measurements were foundto
be 7% smaller ; these findings may be more relevant insmall
vessels. Compared with OCT, IVUS tends to underesti-mate stent
tissue coverage . Table 1 shows the physicalproperties of IVUS
Coronary plaque classification
OCT was validated in vitro for atherosclerotic plaque
char-acterization on a large post-mortem specimen in 2002 and
later in vivo human studies confirmed the ability ofOCT to
characterize the plaque : fibrous plaques arecharacterized by a
homogeneous rich signal; fibrocalcificplaques reveal signal-poor
regions with sharply delineatedborders; lipid-rich plaques show
diffusely bordered signal-poor regions (lipid is present in two
quadrants in any of theimages within a plaque); vulnerable plaques
are characte-rized by a thin-capped fibroatheroma, defined as a
fibrouscap thickness < 70 �m (Fig. 1), within a lipid-rich
plaque;microchannels are defined as no-signal tubuloluminal
struc-tures without a connection to the vessel lumen, recognizedon
three consecutive cross-sectional OCT images [2,14], andare seen
with increased neovascularization of atheroscle-rotic plaque (Fig.
2). Fig. 3 shows a typically stable andcalcified coronary plaque
with thick fibrous cap.
Acute coronary syndromes
In the setting of acute coronary syndromes, OCT is feasi-ble and
can yield, in addition to plaque description, the
Figure 2. Neo-channels (black arrow) could be visualized
withinthe plaque in some of our acute coronary syndrome
532 R. Hamdan et al.
Figure 3. A typically stable coronary plaque, calcified with a
Otoaggressive medical therapy as well as percutaneous
angio-plasty and stent implantation. Most interesting is the use
onths and 1 and 3 years [27—29]. The vascular responsestent
apposition and endothelialization) after drug-elutingtent and
bare-metal stent implantation between stablend unstable angina
pectoris patients was also success-ully assessed by OCT [30—33].
OCT analysed the impact oftent strut thickness and the design of
different drug-elutingtents on acute stent strut apposition .
Vessel injury (tis-ue prolapse, luminal protrusion and intrastent
dissection)fter stent implantation can be detected by OCT
[35,36].ig. 6 shows an example of strut malapposition revealed
The reproducibility of quantitative OCT for stent analysisas
been studied and showed excellent inter- and intraob-erver
variability for strut count, strut apposition and strut
issue coverage measurements . O
igure 5. (A) A red thrombus with a signal-free posterior
igure 4. A plaque rupture site (arrow) with cavity
formationithin the plaque.
ndications and clinical implications
efore or after stent implantation?
hen OCT is performed in the setting of percutaneous angio-lasty,
it is to be done as for IVUS, before stent implantation,o
accurately measure the vessel dimensions and cross-ectional areas,
and after stent implantation, to detect goodtent expansion and
apposition short term and good stentndothelialization long
or stable angina patients or during acuteoronary syndrome?
CT is helpful in some stable angina patients for assessinghe
atherosclerotic plaque burden and detecting markersf plaque
instability, which should indicate the need for
CT in the setting of acute coronary syndrome, especially
B) A white thrombus fully visualized.
Optical coherence tomography
Figure 6. Localized malapposition of a drug-eluting stent.
to detect and measure the thrombus burden and analyse
OCT can potentially lead to a change in strategies, especiallyin
the setting of acute myocardial infarction. Regarding therecently
developed minimally invasive strategy for acutemyocardial
infarction, consisting of a conservative strategyafter thrombus
aspiration in Myocardial Infarction and TIMIgrade III flow
restoration, OCT can document and supportthis strategy by showing
the thrombus component of theresidual luminal narrowing and by
studying the underlyingplaque. This can avoid or delay systematic
stent implanta-tion in a prothrombotic context.
Haemorrhagic components appear as signal-poor OCTregions, thus
distinguishing haemorrhage from lipid necroticpools is difficult
. Validation studies of angiogenesisidentification are still
lacking, although there is a generalconsensus that OCT should be
able to identify microvessels[2,14]. OCT is a costly technique that
is not available inall catheterization centres but it appears to be
cost effec-tive, although there are still no international
guidelinesregarding OCT, because the large OCT trials studied its
diag-nostic impact; recently, trials studying therapeutic
decisionsguided by OCT have been published and others are still
ongo-ing. The lack of international guidelines is mainly due
thefact that this is a recently developedimaging modality.
In vivo intracardiac OCT imaging on a swine model
throughpercutaneous access was able to acquire high-quality OCT
images . OCT assessed depolarization-related
artefactsinduced by the birefringence of myocardium and
readilyevaluated catheter-tissue contact. This is a critical
steptoward image-guided radiofrequency ablation in a clinical
etting, indicating that OCT could be a promising techniqueor in
vivo guidance of radiofrequency ablation.
Transplant allograft vascular disease is characterizedy diffuse
concentric fibrointimal proliferation. Coronaryngiography
underestimates the extent of the disease. OCTas the potential to
become an appropriate imaging tool foronitoring the effects of
preventive treatments and diseaserogression .
isclosure of interest
he authors declare that they have no conflicts of
interestoncerning this article.
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Optical coherence tomography: From physical principles to
clinical applicationsIntroductionPhysical principles and
acquisition systemsTime domain OCTFourier domain OCT
OCT versus intravascular ultrasoundClinical applicationsCoronary
plaque classificationAcute coronary syndromesPercutaneous coronary
intervention and stent implantation
Indications and clinical implicationsBefore or after stent
implantation?For stable angina patients or during acute coronary
ControversiesPerspectivesDisclosure of interestReferences