OCT

Optical coherence tomography
(OCT)
DR. SIVA SUBRAMANIYAN
PRIMER AND DR. RML HOSPITAL
NEW DELHI.

INTRODCUTION
OPTICAL 
LIGHT
COHERENCE 
SPECEFIC PROPERTY
OF LIGHT
(MONOCHROMATC
LIGHT )
TOMOGRAPHY 
LOOKING THE TISSUE IN
SLICES
(CROSS SECTIONS )

An optical imaging modality that uses near-infrared light for high resolution
imaging of vessel anatomy, tissue microstructure and stents.
Uses light, not sound
 Does not use X-ray
 Image acquisition is fast
Images acquired are sharp, detailed and easy to interpret

INTRODUCTION
• Coronary angiography is currently the standard modality for the assessment of
coronary artery disease.
• However, this technique is restricted to a two-dimensional representation of the
lumen without providing information about the vessel wall which is the substrate
of atherosclerosis.
• This limitation led to the development of new intracoronary techniques which are
able to image directly the atherosclerotic plaque.
• The introduction of intravascular ultrasound (IVUS) allowed a much more detailed
evaluation of coronary atherosclerosis, but its limited resolution (axial 150–200
μm) precluded the visualization of certain microstructures.

• Optical Coherence Tomography (OCT) is a light-based imaging modality that can
provide in vivo high-resolution images of the coronary artery with a level of
resolution (axial 10-20 μm) ten times higher than IVUS but with a penetration
depth limited to 1.5-2 mm.
• The technique uses low-coherent near infrared light to create high-resolution
cross sectional images of the vessel. OCT, originally described in the early 1990s,
was first applied in the field of ophthalmology.
• The vascular application, initiated in the mid 90s demonstrated the potential of
the technique to identify clinically relevant coronary artery morphology with a
level of resolution never reached before in vivo

PRINCIPLE
• The fundamental principles of optical coherence tomography (OCT) evolved from
optical 1-dimensional low-coherence reflectometry, which uses a Michelson
interferometer and a broadband light source.
• Intravascular OCT requires a single fiberoptic wire that both emits light and
records the reflection while simultaneously rotating and being pulled back along
the artery.
• The coronary OCT light source uses a bandwidth in the near-infrared spectrum
with central wavelengths ranging from 1,250 to 1,350 nm.

• Current intravascular OCT systems use a central wavelength of approximately
1,300 nm. Using this wavelength the tissue penetration is limited to 1 to 3 mm as
compared with 4 to 8 mm achieved by intravascular ultrasound (IVUS)

• It is important to note that the speed of light (3108 m/s) is much faster than that
of sound (1,500 m/s), and, therefore, interferometry techniques are necessary to
measure the backscattered signal since a direct quantification cannot be achieved
on such a time scale.
• The interferometer uses a fiberoptic coupler similar to a beam splitter, which
directs one-half of the beam to the tissue and the other one-half to the reference
arm

TYPES
• Time Domain OCT
• Frequency Domain OCT

Time Domain OCT
• Light is too fast for direct echo measurement  interferometry
• Compare path length between known “reference arm” and sample
• Mechanical reference arm motion limits imaging speed
11
intensity
axial distance
Demod Amp
Broadband
Source
D
Tissue
Mirror
Reflections

Frequency Domain OCT • Measurement of interference
pattern spectrum + Fourier
transform
• Signal generated from all depths
simultaneously
• Faster image acquisition without
loss of quality
Swept Laser
`
D
λ
intensity
intensity
distance
FFT
Amp

TD-OCT
• first-generation time domainOCT system required sequential measurement of
optical echoes from different depths by moving the reference mirror .
• This initially required the use of a balloon to occlude coronary blood flow, and the
slow pullback speed of 1 to 5 mm/s led to image acquisition times of 3 to 45 s .
• Subsequently, a blood-free imaging field was obtained by controlled
intracoronary infusion of isoosmolar contrast, negating the need for an occlusive
balloon

• Second-generation frequency domain OCT systems use a light source that is
rapidly swept in time across wavelengths from 1.25 to 1.35 mm, allowing
simultaneous recording of reflections from different depths without movement
of the reference mirror .
• Depth profiles are then reconstructed by Fourier transformation. This speeds up
image acquisition 10-fold, with achievable pullback speeds of up to 40 mm/s and
imaging runs of up to 150 mm in length with a 3- to 5-s flush of saline or contrast,
without the need for prolonged vessel occlusion.

C7XR System /FD-OCT
• Balloon occlusion not required
• Fast flush, spiral pullback
acquisition
• 5 cm arterial segment in 2.5
sec
• Rapid exchange (Rx) imaging
catheter
100 frames/s,
15 mm axial resolution
10 mm scan diameter

19
OCT Technology from St. Jude Medical
• Console
• Rapid exchange (Rx) imaging catheter
• Contrast flush; balloon occlusion not required
• Fast image acquisition: 7.5cm pullback in 2.5 sec

20
Prior to Starting a Case
Required Materials
• Dragonfly™ Duo imaging catheter
• 3 ml purge syringe
• Contrast media indicated for coronary use
• 0.014" guidewire
• Guide catheter (6-7 F, with no sideholes)
PROCEDURE OF OCT

21
DRAGON-FLY DUO CATHETER
• Fiber optic
• Three radioparque marker
• Compatible with G.C 6 or 7
Fr without holes
• G.W 0.14”

IMAGE DISPLAY
“L-Mode”
longitudinal view
“B-Mode”
cross-sectional view

OCT Image Interpretation Terminology
• Backscatter
• The reflection of light waves off the tissue and back to the Dragonfly catheter
• High backscatter means a brighter pixel  Also described as a “signal rich” region
• Low backscatter means a darker pixel Also described as a “signal poor” region
• Attenuation
• The reduction in intensity of the light waves as they pass through tissue due to absorption or
scattering
• High attenuation means the light cannot penetrate very deep
• Low attenuation means the light can pass through to allow visualization of deeper tissue

• Composition
• Homogeneous
• Uniform in structure
• Heterogeneous
• Structure consists of dissimilar elements
• Texture
• Coarse
• Fine

Vessel wall comprising of
Intima - a highly backscattering or signal-rich intima (thin),
Media - that frequently has low backscattering or is signal
poor.
Adventitia - a heterogeneous and frequently highly
backscattering
The periadventitial tissues may contain IVOCT data consistent
with adipocytes, characterized by large clear structures
resembling cells and/or vessels

ASSESSMENT OF ATHEROSCLEROSIS
Atherosclerotic plaque or atheroma
• An atherosclerotic plaque is defined as a mass lesion (focal thickening) or loss of a
layered structure of the vessel wall.
Fibrous plaque.
• A fibrous plaque has high backscattering and a relatively homogeneous IVOCT
signal. Fibrous plaques by IVOCT may be composed of collagen or smooth muscle
cells
Fibrocalcific plaque.
• A fibrocalcific plaque contains IVOCT evidence of fibrous tissue (defined
previously), along with calcium that appears as a signal-poor or heterogeneous
region with a sharply delineated border

Fibrous plaque VS calcium
Homogeneous
• signal rich
• brighter pixel
High
backscatter
Finely textured
• deeper tissue can be
visualized
Low
attenuation
Sharp edges
Heterogeneous
• signal poorLow backscatter
• deeper tissue can be
visualized
Low
attenuation

Necrotic core.
• A necrotic core by IVOCT is a signal-poor region within an atherosclerotic plaque,
with poorly delineated borders, a fast IVOCT signal drop-off, and little or no OCT
signal backscattering, within a lesion that is covered by a fibrous cap

IMPORTANCE OF FIBROUS CAP
FIBROUS CAP.
• While post-mortem investigations have suggested that a cap thickness 65 micro
M is associated with plaque rupture, OCT has demonstrated that patterns of
plaque rupture and fibrous cap thickness vary widely.
• OCT showed 93% of the culprit plaques in patients presenting with acute
myocardial infarction triggered by exertion had rupture at the shoulder, where
the average cap thickness was 90 micro m.
• In contrast, 57% of acute myocardial infarction patients who experienced
symptoms at rest had plaque rupture in the shoulder with an average cap
thickness of 50 micro m

Characterization of fibrous cap thickness
• Thin capped fibroatheromas (TCFA) - defined pathologically by the triad of:
 Lipid core.
 Fibrous cap with a thickness < 65 micron m.
 Cell infiltration of the fibrous cap.
• OCT for in vivo assessment of fibrous cap thickness ---- Unique ability to image
superficial detail

• In the ACS patients, TCFA was observed in 72 % STEMI and 50 % NSTEMI culprit
lesions as compared with 20 % SAP lesions (p =0.01)
• The same groups exhibited mean fibrous cap thicknesses of 47, 54, and 103
micron m , respectively.
Jang I-K, Tearney GJ, MacNeill BD, et al. Circulation 2005;111:1551–5

• Potential for using OCT measurements of fibrous cap thickness as a possible
marker of plaque vulnerability.
• In a single-center prospective study, cap thickness has been shown to increase in
a statin-treated group
Takarada S,, 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;202:491–7].

INFLAMMATION
• Intense infiltration of the fibrous cap is another of the features of vulnerable
plaques.
• Study by Tearney et al ---- OCT was able to quantify macrophages within the
fibrous cap.
• In vivo---- unstable patients present a significantly higher macrophage density
detected by OCT in the culprit lesion than stable patients.
• The sites of plaque rupture demonstrated a greater macrophage density than
non-ruptured sites.

THROMBUS
• Many studies have suggested that it is possible to identify thrombus by OCT and
even discriminate between red and white thrombus, as confirmed by
histopathologic correlation .
• The sensitivity of OCT to detect thrombus appears to possibly be higher than that
of ultrasound

RED THROMBUS (ACUTE)
Thrombus – red
• Absorbs near-infrared light
• High backscatter on surface due
to signal attenuation
• Appears as a bright mass
• Shadow (cannot see behind it)

WHITE THROMBUS
Thrombus – white
• High backscatter
• Low attenuation
• Able to see behind it

Plaque rupture and intracoronary thrombus
identification
• Plaque rupture/ Subsequent thrombosis ----- ACS.
• OCT can identify intracoronary thrombus and plaque rupture with high accuracy.
• Kubo et al evaluated the ability of OCT to assess the culprit lesion morphology in
acute myocardial infarction in comparison with IVUS and angioscopy.
• Incidence of plaque rupture by OCT of 73%, significantly higher than that
detected by both angioscopy (47%, p = 0.035) and IVUS (40%, p = 0.009).
• Intracoronary thrombus was observed in all cases by OCT and angioscopy, but
was identified in only 33% of patients by IVUS.

OCT and Percutaneous Coronary
Intervention

OCT Applications in PCI
Pre-Intervention
Plaque characterization
(lipid, calcium, fiberous, cap
thickness, thrombus)
Intervention planning and
stent sizing
(lesion diameter, length)
Post-
Intervention
Stent strut
malapposition
Intimal dissection
Follow-Up
Assessment
Neointimal growth (no coverage,
thin coverage, restenosis)
In-stent
thrombosis

• Dissection - Arterial disruption within or adjacent to the stent where
a flap of tissue could be clearly differentiated from the underlying
plaque.
• Prolapse- Protrusion of tissue between stent struts extending inside a
circular arc connecting adjacent struts.
• Incomplete apposition- Clear separation between at least one stent
strut and the vessel wall

• INCOMPLETE STENT APPOSITION- the contact of the stent struts with
the vessel wall or ISA is then defined as a strut–vessel distance
greater than the strut thickness (metal and polymer) with the
addition of a correction factor.

Classiﬁcation of strut apposition by OCT
Totally embedded strut
Embedded subintimally
without disruption of
lumen contour
Completely embedded
with disruption of
lumen contour
Partially embedded
with extension of
strut into lumen
Complete strut
malapposition
(blood able to exist
between strut and
lumen wall)
Type I
Type II
Type IIIa
Type IIIb
Type IV
Giulio. CCI, 2008, 72:237–247

• Strut–vessel distances ≤270 mm are spontaneously corrected by the
neointimal reaction in 100% of the cases (distances ≤400 mm, in 93%
of the cases).
Gutierrez-Chico J et al. Vascular tissue reaction to acute malapposition in human coronary
arteries: sequential assessment with optical coherence tomography. Circ Cardiovasc Interv
2012.

• DESs significantly suppress neointimal hyperplasia. A study of OCT and IVUS
demonstrated that two-thirds of sirolimus-eluting stent (SES) struts are covered
by neointima < 100 μm in thickness, which is beyond the resolution of IVUS .
• Thus, OCT is most useful for examining patients at follow-up after DES
implantation, and is capable of detecting a thin neointima due to its high
resolution .
• In recent years, late stent thrombosis in patients treated with DES has become a
major concern. Delayed coverage or failure to cover an exposed stent with
neointima/ regenerated endothelium has been suggested as a cause of
thrombosis.
• Second generation DES demonstrated more favorable vascular healing following
stent implantation, better neointimal coverage, and less ISA than did first-
generation DESs

Restenotic tissue characteristics
• A typical restenotic tissue of BMS at early follow-up (to 1 year), recognized as
neointimal hyperplasia primarily composed of smooth muscle cells, is visualized
as a homogeneous structure by OCT.
• The restenotic tissue of DESs, even in an early phase, also demonstrates
polymorphic patterns in structure, backscatter, and composition .
• This variation in OCT images could be caused by diverse components, including
mature/ immature smooth muscle cells and persistent fibrin or extracellular
matrix, such as proteoglycans

• Thus, OCT provides important information about the tissue covering the stent
struts. However, few studies have sought to validate OCT findings in comparison
with pathological findings, and further investigations should be conducted until
the impact of these findings on clinical outcomes is known.

Original position
of artery
Shifted position
of artery
Radial scan
lines
Image
Cause: Rapid movement of
the artery or Dragonfly during
a single frame
Effect: Slight elliptical
distortion with visible ‘stitch’.
Sew Up Artifact
Data on file at LLI

Blood in Dragonfly Imaging catheter lumen
68
Data on file at LLI
Blood in catheter lumen Catheter lumen purged of blood.

Non-uniform rotational distortion (NURD)
• Non-uniform rotational distortion (NURD) is a consequence of
mechanical catheter systems that arises from binding of the drive
cable or rotating optical components during image acquisition

Saturation
When a high reflector is encountered by IVOCT light, it may be backscattered at too
high an intensity to be accurately detected by the detector, thereby causing artifacts in
the affected A-lines. Structures that exhibit high backscattering commonly
include the guide wire, the tissue surface, and metallic stent struts. Saturation artifacts
appear as linear streaks of high and low intensities within the image along the axial
direction.

SAFETY
• 468 Patients studied-
COMPLICATION FREQUENCY(%)
QRS WIDENING / ST CHANGES 47.6% OCCL & 45.5% NON
OCCL
VF 1.1%
AIR EMBOLISM 0.6%
VESSEL DISSECTION 0.2%

FIBROUS
PLAQUE
FIBROCALCIFIC
PLAQUE
LIPID RICH
PLAQUE
SENSITIVITY 71–79% 95–96% 90–94%
SPECIFICITY 97–98% 97% 90–92%
comparison with histology

FUTURE
• The future of OCT will include advancements in anatomical and functional
assessment of lesions for the interventional cardiologist.
• Anatomical assessment:
• An advanced edge detection algorithm that enables automated stent strut identification
• Texture analysis of OCT images may also help facilitate tissue characterization,
• Functional assessment.
• Detection of Doppler-like signals may permit integration of physiology and anatomical
assessment using a single device

• Fusion of IVUS and OCT would provide ideal imaging of luminal and vessel wall
pathology.
• IVUS ---Increased penetration allow assessment of plaque burden and identification of
positive or negative remodeling.
• High-resolution OCT ---- Permits assessment of luminal morphology, accurate estimation
of fibrous cap thickness, identification of thrombus, and detection of plaque erosion and
rupture.
• The combined information provided by both modalities would permit a more precise
characterization of the type of plaque.
Combination of IVUS and OCT

• Sawada et al reported how the combined use of IVUS-VH analysis and OCT improved the
accuracy for TCFA detection.
• 56 patients with angina (126 plaques) were included in the study.
• Of the 61 plaques diagnosed initially as TCFA by IVUS-VH analysis criteria, only 28 had a
thin fibrous cap as measured by OCT, so they were considered as definite TCFAs.
• 8 OCT derived TCFAs did not have necrotic core in the IVUS-VH analysis, mainly due to the
misreading in OCT caused by dense calcium.
• combination of the information provided by different methods could be essential for
better identification of high risk coronary lesions

• A catheter combining an IVUS with an OCT probe would also be useful in planning and
assessing the outcome of percutaneous coronary intervention.
• IVUS would provide information about the correct stent diameter (on the basis of the
media-adventitia dimensions) ----- OCT would permit a detailed evaluation of the final
result and detection of dissections, stent malapposition, or the presence of thrombus.
• There is currently no such catheter for clinical applications.

• 3D reconstruction of OCT images---- Automatically detect and quantify features of
interest as
- Shape of lumen
- MLA
- Stent strut malapposition and Thrombus volume.
• Combination of FD-OCT and Spectroscopic technique—allow for detailed analysis of
the cellular and biochemical composition of Vulnerable plaque.

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