OCT.pptx

Optical Coherence Tomography
Dr. Yogesh Shilimkar

Optical Coherence Tomography Principles
• Optical coherence tomography (OCT) uses near-infrared light to
generate high-resolution images of coronary arteries in vivo.
• The near-infrared light with a wavelength of about 1.3 μm is invisible
to the human eye.
• To generate cross-sectional images, OCT uses low-coherence
interferometry by measuring
• the echo time delay and
• intensity of the light reflected from internal structures in tissue.

• The light beam from
an OCT system is
split by an
interferometer into
two arms,
• a sample arm and
• a reference arm.
• The sample arm
light travels to the
sample tissue, then
is being reflected,
refracted, or
absorbed by the
tissue and finally
travels back to the
interferometer.

• The reference arm is
directed to a mirror,
which reflects it back
to the interferometer.
• Light from the
specimen consisting of
multiple echoes and
light from reference
mirror consisting of
single echo, at a known
delay, are combined
and detected by
detector.

OCT image formation
• The OCT image is built based on the interaction between these two light waves,
depending on whether there is constructive or destructive interference between
the waves.
• Cross-sectional images are generated by measuring the delay time and intensity
of light reflected or backscattered from internal structures in biologic tissue.
• Depth information:
• Determined by time of flight – i.e. time taken by light wave to go to interface and coming
back
• Intensity of reflection determines brightness
• Higher intensity – brighter structure
• Lower intensity – darker structure

Imaging System
• The intravascular OCT imaging system consists of
• an optical engine emitting and receiving infrared light signals;
• a catheter interface unit including a motor drive;
• a fiberoptic imaging catheter; and
• a computer processor and display console for system control, image
reconstruction, and digital recording.
• The optical engine includes a super-luminescent diode as a source of
low-coherence, infrared light, with a wavelength of approximately
1,300 nm to minimize light absorption by vessel wall and blood cell
components (protein, water, hemoglobin, and lipids) .

Types
• There are two types of OCT systems:
• first generation time domain (TD-OCT) and
• second generation frequency domain (FD-OCT).
• A reference arm and an interferometer are used by both
systems to detect echo time delays of light.

• The first generation of OCT -
time domain (TD) system
• light from a broadband source
with wavelengths centered on
1300 nm was directed at the
tissue of interest.
• The reference arm in TD-OCT
is mechanically scanned (by a
moving mirror) in order to
produce a time-varying time
delay.
• Determination of imaged
tissue depth requires a
reference mirror to be moved
back and forth, significantly
limiting the speed of image
acquisition.

• The FD-OCT platforms
• uses a technology called Fourier or
frequency domain (FD) detection
• a monochromatic source emits light
sweeping across a range of
wavelengths between 1250 and 1350
nm.
• Reflected light from various tissue
depths can therefore be detected
simultaneously, facilitating significantly
faster image acquisition
• The backscattered (reflected)
interference signals of different
wavelengths and amplitude from
both the mirror and the tissue are
detected and amplified.

• The Fourier transformation converts it into an amplitude versus depth
for display as an axial image (A-line image).
• As the catheter rotates, there are 500 A-line scan images generated
per frame to combine and display as a B-mode cross-sectional
tomographic view of the structure.
• The motor drive unit of the current system rotates the probe and
automatically pulls back spirally at a speed of 30 mm/sec generating
180 frames/sec and this is displayed as the longitudinal view (L-view).

Comparison Between TD-OCT and Prototype FD-OCT

Equipment
• At present, FD-OCT imaging is most commonly performed using the C7XR system.

• Newer FD-OCT systems such as the ILUMIEN and ILUMIEN
OPTIS OCT Intravascular Imaging Systems have recently
become commercially available and are replacing the C7XR
system, because they offer additional features to facilitate
improved image acquisition and real-time interpretation,
including
• faster pullback speed,
• longer pullback length,
• automated measurements,
• three-dimensional image reconstruction, and
• combined wireless fractional flow reserve measurement capability.

OCT catheters
• Intravascular OCT catheters consist of a fiberoptic core encapsulated in an
optically transparent imaging sheath.
• The Dragonfly OPTIS catheter is a rapid exchange, dual lumen imaging catheter
with a tip that tapers to a 2.7-F diameter.
• It is compatible with a 6-F or larger guiding catheter and offers fast acquisition,
with automated pullback 2 sedonds to 3 seconds in duration.
• There are 3 radiopaque markers on the imaging catheter:
• The distal marker located 4 mm from the tip of the catheter,
• the lens marker located 2 mm proximal to the lens, and
• third marker located 50 mm proximal to the lens marker (length marker) that can be used to
approximate the imaging segment.

• (A) The Dragonfly OPTIS catheter;
• (B) depiction of the longitudinal cross-section of the catheter

• (C) dimensions of catheter components; and (D) angiogram with the Dragonfly imaging catheter
with 3 radiopaque markers:
1. Distal marker: a fixed marker located 4 mm from the tip of the catheter;
2. Lens marker: located 2 mm proximal to the lens;
3. Optical lens: located 2 mm distal to the lens marker;
4. Proximal length marker: located 50 mm proximal to the lens and can be used to approximate
the imaging segment.

• The length marker and lens markers are affixed to the imaging core
and move proximally during the pullback, with the tip marker
remaining stationary.
• The Dragonfly OPTIS imaging catheter connects to the OPTIS or the
ILUMIEN OCT imaging system through the drive motor and optical
controller.
• The newest generation of the technology, the OPTIS integrated
system, allows for OCT-angiography coregistration

Image Acquisition Procedures
• An important consideration in the use of OCT as an
intravascular imaging modality is that blood must be cleared
or flushed from the vessel lumen,
• because the backscatter of light by red blood cells precludes OCT
imaging through a blood field.
• Two techniques:
• Occlusion technique
• Non-occlusion technique

Occlusion Technique:
• In the this technique, the occlusion balloon catheter is first advanced beyond the target
site over a standard angioplasty guide wire .
• After replacing the guide wire with the OCT imaging probe through the over-the-wire
lumen, the balloon is repositioned proximal to the target and inflated at a low pressure
(0.3 to 0 . 5 atm) to avoid unnecessary vessel stretching.
• While flushing from its distal exit ports typically via a power injector at a flow rate of 0.5
to 1 ml/second, the length of the target site is imaged with an automatic pullback device
(0.5 to 2.0 mm/second) .
• Limitations:
• ischemia during balloon occlusion,
• potential damage to the vessel at the site of balloon occlusion,
• the need for multiple catheter exchanges, and
• the inability to image ostial lesions.
• In addition, vessel dimensions measured on OCT images obtained with the occlusion
technique may be artificially small because of reduced intracoronary pressure
downstream from the occlusion balloon.

Nonocclusion / Continuous Flushing Technique
• Image acquisition is performed during continuous flushing through
the guide catheter typically using a power injector at a flow rate of 3
to 6 ml/second.
• FD-OCT utilizes this technique, since its high-speed image acquisition
enables rapid pullback (20 to 40 mm/second) to scan a long coronary
segment during short flushing for <5 seconds.

• The pullback length can be selected as either 54 mm (high-resolution mode, 10
frames/mm) or 75 mm (survey mode, 5 frames/mm).
• The survey mode allows for a greater length of imaging of the artery while using
less contrast with a shorter pullback time; thus, this should be preferentially
selected as the default mode for initial lesion assessment.
• The OCT catheter should be advanced to the area of interest on standby mode
under fluoroscopic guidance.
• “Live image” should be enabled several millimeters distal to the edge of the
angiographic lesion.

• Pullback can be triggered manually or automatically, with automatic set as the
default.
• Automatic pullback is triggered when the lens detects a significant change in
luminal pixilation in the peri-catheter zone.
• Flush medium is necessary to clear the lumen of blood to allow imaging
acquisition by the OCT near infrared light, which is conventionally achieved with
radiocontrast medium.
• Prior to initial flush clearance, intracoronary nitroglycerin should be administered
to minimize catheter related spasm.
• Flush clearance allows for clear differentiation between the lumen and vessel
structure, allowing for automatic detection of the lumen contour and its
dimensions.

IVUS vs OCT
• The main difference between OCT and IVUS is a ten-fold better resolution
with worse penetration.
• In studies in which OCT and IVUS were compared in vivo, the mean
differences in lumen area varied from 0.19 mm2 to 1.15 mm2; lumen area
was consistently larger with IVUS than OCT, especially in smaller lumens
and in nonstented segments.
• The tissue protrusion, incomplete stent apposition, stent edge dissection,
and intrastent thrombus are better detected by OCT compared with IVUS.

IVUS vs OCT
• Because the clearance of blood by flushing with contrast or dextran is
required for OCT imaging, the border between the lumen and vessel
structure is clearer than with IVUS, resulting in
• less variability of diagnosis, and
• acceptable automatic contouring of the lumen border in most cases.
• However, a major drawback of OCT is less image penetration, and one
often cannot evaluate vessel size according to media-to-media
diameter; nor can one quantitate plaque burden,

Optical Coherence Tomography Vs. Angiography
• The utility of OCT in clinical practice, has been established through
several important studies.
• In CLI-OPCI and CLI-OPCI II studies, OCT was associated with improved
outcomes compared with angiography alone.
• The OPUS-CLASS study demonstrated the superior accuracy and
reproducibility of dimension measurements using OCT compared with
IVUS.

• ILUMIEN I study defined PCI optimization parameters with OCT and
determined the impact of OCT guidance on decision making by physicians
and on clinical events.
• This study demonstrated that pre-PCI OCT led to a change in treatment strategy in
57% of lesions and
• post-PCI OCT led to further stent optimization in 27% of lesions.
• In the randomized DOCTORS trial including 240 patients with non-ST-
segment elevation ACS, OCT-guided PCI was associated with a small but
significant improvement in the primary endpoint, post-procedural
fractional flow reserve (FFR) compared with angiography-guided PCI.
• This benefit was mainly driven by improved stent expansion.

• ILUMIEN III was a landmark randomized controlled trial comparing OCT-
guided, IVUS-guided, and angiography-guided PCI.
• The ILUMIEN III study demonstrated that
• stent diameter sizing decisions based on the use of the external elastic lamina (EEL)
diameter measurement (rather than historical use of the lumen) was feasible and
resulted in similar stent expansion compared with IVUS-guided stenting.
• Prior to ILUMIEN III, OCT-guided diameter measurements and stent sizing had been
based on lumen measurements, resulting in smaller final minimum stent areas
(MSAs) achieved compared with EEL-based measurements on IVUS.
• In ILUMIEN III, OCT was substantially more sensitive than IVUS and angiography in
detecting and preventing major dissections and areas of stent malapposition.

Correlation Of OCT With FFR
• Although OCT is an excellent tool to assess atherosclerosis, it is limited in
its inability to assess the functional significance of moderate coronary
atherosclerotic lesions.
• Although, minimal luminal area (MLA) or minimal luminal diameter (MLD)
by OCT has limited correlation with fractional flow reserve (FFR), OCT-
derived MLA thresholds have reasonably high-positive predictive value
(80–92%) but lower negative predictive value for physiological significance
of coronary artery stenosis (66–89%).
• Therefore, PCI based on OCT derived MLA alone is not routinely
recommended.

Advantages of OCT
• 10 times higher resolution compared with IVUS -> OCT can detect fine details which are
missed by IVUS (edge dissections, tissue coverage of stent struts, and malapposition that
is below the resolution of IVUS)
• Better tissue characterization (calcium)
• Better suited for thrombus detection
• Images are clearer and easier to interpret
• OCT predictors of restenosis and stent thrombosis are well established
• More user friendly due to rapid availability of reliable automatic analyses (i.e. accurate
lumen profile)

Disadvantages of OCT
• Additional contrast
• Flushing is necessary to clear the lumen of blood to visualize the vessel wall
• Pre-dilation may be necessary pre-intervention to allow blood to be
flushed from the lumen
• Limited penetration of OCT
• Compared with IVUS, there is limited research evidence on OCT-guided vs.
angiography-guided PCI with respect to surrogate endpoints and no RCT
powered for clinical outcomes

Normal Coronary Artery
• Normal coronary arterial wall
appears on OCT as a 3-layered
structure composed of an
intima, media, and adventitia.
• The intima and adventitia
appear as bright signal-rich
(high-reflectivity) layers,
whereas the intervening media
appears as a darker signal-poor
(low-reflectivity) layer.

OCT Image Interpretation Terminology
• Backscatter:
• Reflection of light waves off the tissue and back to the catheter (Brightness)
• High backscattering by a tissue gives it a high pixel intensity, bright picture,(Internal and external
elastic lamina (EEL), fibrous tissue)
• Low backscattering will be seen as a darker, low pixel intensity region (media layer and calcium).
• Attenuation:
• Reduction in intensity of the light waves as they pass through the tissue, due to absorption or
scattering (penetration depth)
• High attenuation means the light can not penetrate to deeper tissue (lipids and red thrombus)
• Low attenuation means light passes through the tissue to deeper layers that can be seen in images
(calcium, fibrous tissue).
• Composition: Homogenous vs Heterogenous (similar/dissimilar)
• Texture: Coarse vs Fine
• Edge/Border: Sharp/diffuse

Plaque Characterization
Homogeneous area
High backscatter
Low signal
attenuation
Homogeneous area
Low backscatter
High signal attenuation
Diffuse border
(signal-poor regions (lipid pools) with
overlying signal-rich bands, corresponding to
fibrous caps)
Heterogeneous area
Low backscatter
Low signal attenuation
Sharp demarcating
border

(A)Fibrotic plaque: characterized by high
signal (high backscattering) and low
attenuation (deep penetration).
(B) Predominantly calcified plaque:
calcified regions have a sharp border,
low signal, and low attenuation
permitting deeper penetration.
(C) Lipid-rich plaque: the lipid core has a
diffuse border. High light attenuation
results in poor tissue penetration (in
contrast to calcified regions).

Intraluminal abnormalities
High backscatter
High attenuation
Low backscatter
Low attenuation
Mass with channels
Intact media
Blood in media

Algorithm for Identification of plaque composition

OCT Artifacts
• Artifacts related to imaging technique
• Artifacts related to image processing
• Artifacts related to imaging catheter or guidewire
• Artifacts related to stent struts
• Artifacts related to eccentric wire position

Artifacts Related to Imaging Technique
• Obliquity artifact:
• Occurs when the imaging catheter is not parallel to the
longitudinal axis of the vessel wall,
• Creating an elliptically distorted off axis image;
• This artifact can occur because of vessel curvature or
tortuosity and can make measurements less accurate.
• Residual blood:
• Caused by suboptimal flushing
• Appears as a signal-rich swirling pattern within the
lumen and can sometimes be falsely identified as red
thrombus.
• Because red blood cells cause high OCT signal
attenuation, residual blood in the vessel lumen may also
limit characterization of the underlying tissue.

Artifacts Related to Image Processing
• Sew-up artifact
• Results from the rapid movement of
the artery or imaging wire.
• Appears as a single radius of
misalignment in the circumferential
image.

• Nonuniform rotation distortion
• Variation in the rotational speed of the
imaging catheter along the circumference
• Appears as smearing within an arc of the
circumferential OCT image;
• Most commonly occurs in the setting of
vessel tortuosity, tight stenosis, heavy
calcification, or equipment imperfections
that perturb the smooth rotation of the
optical components.

• Fold-over artifact:
• Occurs when reflected
signals from structures
beyond the system’s field
of view produce aliasing
along the fourier
transformation,
• Causing a portion of the
vessel to appear to fold
over in the image;
• This artifact occurs most
commonly at side
branches or with large
vessels.

Artifacts Related to the Imaging Catheter or
Guidewire
• Shadow artifact:
• Appears as a reduction in
signal intensity beyond a
structure such as a
guidewire or metallic stent
strut, or small bubbles in
the imaging catheter.
• limits the evaluation of
underlying structures.

Artifacts Related to the Imaging Catheter or
Guidewire
• Multiple reflections
• Multiple reflections appear as 1
or more circles centered on the
imaging catheter
• Result from reflections from
multiple facets of the catheter.

Artifacts Related to Stent Struts
• Reverberation artifact
• Reverberation artifact is similar to
the multiple reflections artifact
• describes reflections produced by
stent struts that are centered on
the imaging catheter.

• Saturation artifact
• Occurs when stent struts or other
highly reflective structures produce a
high-amplitude backscattered signal
that is beyond the range that can be
accurately detected by the data
acquisition system;
• This artifact appears as spokes of high
and low intensity signal emanating
from the center of the imaging
catheter and passing through the
highly reflective structure.

• Blooming artifact:
• Blooming artifact occurs when
stent struts or other highly
reflective structures appear
slightly smeared or thickened in
the axial direction.

Artifacts Related to Eccentric Wire Position
• Proximity artifact
• Proximity artifact can occur when the
imaging catheter is near or touching the
artery wall,
• causing the adjacent tissue to appear
brighter or more signal rich.
• Tangential signal dropout
• Tangential signal dropout also occurs
when the imaging catheter is near or
touching the artery wall and
• appears as attenuated signal tangential
to the luminal surface.

• Merry-go-round effect
• The reduced lateral resolution at
increased distances or depths
from the imaging catheter.
• Stent struts that are farther from
the imaging catheter encompass a
wider arc, appearing wider than
struts closer to the imaging
catheter.

• Sunflower effect
• Sunflower effect (also called strut orientation
artifact) describes the artificial alignment of
reflections from stent struts toward the
imaging catheter, mimicking the way
sunflowers align toward the sun.
• At its extreme, this type of artifact can cause
stent struts to appear almost perpendicular
to the lumen surface in order to align
towards the eccentrically positioned
catheter.

Quantitative Assessment By OCT
• For accurate measurements , the OCT image should be correctly calibrated
for refractive index and z-offset.
• Refractive index is a property of a material that governs the speed of light
through the material.
• Because the speed of light is slower in flushing media and tissue than in air,
the distances in the images need to be corrected for this delay.
• OCT manufacturers provide a correction for refractive index by dividing the
distances in the axial direction in the OCT image by the estimated refractive
index of the flushing media and tissue.

Quantitative Assessment
• Z-offset refers to slight variations in optical path length of the optical fiber
within the catheter.
• Calibration can be achieved by adjusting the optical path length in the
sample and/or reference arm, which can be performed automatically or
manually before each O CT examination.
• Since the fiber length can also change during a single pullback, resulting in
a varying z-offset across the OCT dataset, OCT images should be evaluated
to verify the z-offset and adjust it, if necessary, before quantitative analysis.

Quantitative Assessment
• Whereas measurements by OCT are
generally performed at the leading edge
of boundaries, stent measurements may
require using the axial center (or the
highest intensity point) of the strut image.
• This is because a blooming artifact can
often occur at the surface of a high
reflector (such as metallic stent struts) ,
creating an enlarged or smeared
appearance of the bright reflector along
the axial direction.
Due to a blooming effect of metal
struts (arrow), the highest
intensity point within the strut
image should be used for the
measurement.

Recommendations on the adjunctive use of intravascular imaging
• Diagnostic assessment of coronary
lesions
• Angiographically unclear/ambiguous
findings (e.g. dissection, thrombus,
calcified nodule)
• Assessment of left main stenosis
• Complex bifurcation lesions
• Suspected culprit lesion of ACS
• Identification of mechanism of
stent failure
• Restenosis
• Stent thrombosis
• PCI guidance and optimization
• Long lesions
• Chronic total occlusions
• Patients with acute coronary
syndromes
• Left main coronary artery lesions
• Two stents bifurcation
• Implantation of bioresorbable
scaffolds
Expert consensus document of the European Association of Percutaneous Cardiovascular Interventions L. Raber et al. EHJ(2018)39, 3281–3300

Plaque Assessment
• Preinterventional OCT can offer unique information on lesion
characteristics, such as
• the thickness of superficial calcification,
• TCFA,
• plaque rupture , or
• presence and type of thrombus.
• Thinner fibrous caps and larger lipid arcs are particularly associated with
unfavorable events, and thus may benefit from adjunctive pharmacologic
or device therapies to protect distal microvasculature during PCI.
• For largely fibrous and lipidic lesions without calcification, predilatation
may be unnecessary, and direct stenting may be considered.

• OCT can predict no-reflow and impaired microcirculation after PCI in the setting of
NSTEACS.
• Lipid content from a culprit plaque may play a key role in damage to the
microcirculation following PCI for NSTEACS.
Tanaka, et al. European Heart Journal,
Volume 30, 2009, 1348–1355

Plaque Assessment
• OCT allows operators to access the thickness of superficial calcification,
suggesting the need for plaque modification with rotational atherectomy
prior to stenting.
• Moderate/severe calcification is strongly predictive of target lesion
revascularization and is an independent predictor of stent thrombosis.
• Evidence of calcium fractures following lesion preparation is associated
with improved stent expansion.
• OCT is the imaging modality of choice to detect the presence and severity
of calcification, because, unlike angiography or IVUS, OCT can
• differentiate deep from superficial calcium
• measure the thickness of calcium, a critical predictor of stent underexpansion.

• An OCT-based calcium scoring system can help to identify lesions that would
benefit from plaque modification prior to stent implantation.
• A calcium score of 4 had a particularly high risk of stent underexpansion
• Lesions with calcium deposit with maximum angle >180°, maximum thickness
>0.5 mm, and length >5 mm may be at risk of stent underexpansion.
Fujino,
etal.
EuroIntervention
2018;13:
e
2182-
e
2189

Healed Coronary Plaques
• Intracoronary thrombosis following plaque rupture or erosion is the major
pathogenic mechanism for acute coronary events.
• Some of thrombotic lesions lead to the evolution of life-threatening
luminal thrombosis, whereas the others heal with a residual non-occlusive
thrombus material without clinical manifestations.
• Some plaques have a healed thrombus overlying fibroatheroma indicating
healed plaque ruptures, and others have a multilayered organized
thrombus on eroded plaques indicating healed plaque erosion.
• Intracoronary imaging techniques have the potential to identify healed
coronary plaques (HCPs).

Healed Coronary Plaques
• (A) Histopathological cross-section
shows fibroatheromatous plaque
with thick fibrous tissue close to
the lumen and underlying necrotic
core (asterisk).
• (B1 & B2) Corresponding cross-
section under polarizing microscopy
shows multiple layers overlying the
necrotic core (asterisk), indicating
histologically-defined HCP.
• (C1,C2) The corresponding OCT image
shows multiple layers of different
optical signal density located close to
the luminal surface with clear
demarcation, overlying the lipid
content (L), indicating OCT-derived
HCP.

OCT Features Associated with Vulnerability for
Plaque Rupture
• Thin-cap fibroatheromas (TCFAs) –
• precursor lesions for plaque rupture.
• TCFA are lipid-rich plaque with an
overlying fibrous cap measuring less than
65 um.
• On OCT imaging, fibrous tissue appears as
a signal-rich area with low signal
attenuation, and lipid pools appear as
homogeneous signal-poor areas.
• This sharp contrast in signal intensity
between a fibrous cap and underlying
lipid makes OCT particularly useful in
accurately measuring fibrous cap
thickness.

• Lipid-rich plaques
• are defined as lipid occupying greater
than or equal to 2 quadrants of the
cross-sectional image.
• Lipid occupies > 1800 of
circumference.
• Oct-identified lipid-rich plaques have
been shown to be more prevalent in
patients presenting with acute
coronary syndrome compared with
patients with stable angina

• Microchannels
• have been defined as small black (signal
absent) holes within a plaque that measure
50 to 300 um in diameter and span at least 3
consecutive frames on pullback OCT imaging.
• presence of microchannels in culprit lesions
is associated with a higher incidence of other
features associated with plaque vulnerability,
such as TCFA and large lipid pools.
• In nonculprit lesions, the presence of
microchannels is associated with subsequent
plaque progression.
• presence of microchannels in nonculprit
lesions may portend a resistance to statin
therapy.
OCT Features Associated with Vulnerability for Plaque Rupture

• Macrophage accumulations
identified as linear series of
signal rich spots with high signal
attenuation.
• Cholesterol crystals described as thin,
linear, signal-rich structures with low
signal attenuation.

• Spotty calcium
• describes calcium deposits with an arc
less than 900 (occupying only 1
quadrant of the cross-sectional
image).
• The depth of calcium deposits, defined
as the minimum distance between the
inner edge of the calcium deposit and
the luminal surface, can be measured
by OCT and may influence plaque
vulnerability.
• Colocalization of spotty calcium
deposits and TCFA has been shown to
predict procedure related myocardial
injury following elective stent
implantation.

Stent Sizing By OCT
• Reference vessel – normal appearing vessel proximal and distal to the
lesion.
• Diameter selection with intravascular OCT is dictated by the smallest
reference vessel diameter, which is usually the distal reference.
• Depending on the "quality" of the landing zone, different degrees of
diameter oversizing can be applied.

Stent Sizing By OCT
2.6
2.8
3
3.25

Stent length
• Stent length selection on intravascular OCT is determined mostly by
volumetric assessment of the lumen area profile and adding a minimum of
3 mm to the total length.
• The quality of the landing zone may influence length selection.
• Avoidance of the landing zone within an area of residual plaque burden
(e.g. >50%) and particularly lipid-rich plaque is clinically important, as this
has been linked to subsequent stent edge restenosis following new-
generation DES implantation.
• Co-registration of intracoronary imaging and angiography is an important
tool to facilitate stent length selection and precise implantation.

Current Consensus
• From a practical standpoint, a distal lumen reference based sizing may represent a safe
and straightforward approach with subsequent optimization of the mid and proximal
stent segments.
• Specifically, the mean distal lumen diameter with up rounding stent (0–0.25mm) may be
used (e.g. 3.76 -> 4.0mm), or the mean EEM (2 orthogonal measurements) with down
rounding to the nearest 0.25mm stent size (e.g. 3.76 -> 3.5mm).
• When using OCT, an EEM reference based sizing strategy appears feasible, although more
challenging than a lumen based approach for routine clinical practice.
• Appropriate selection of the landing zone is crucial as residual plaque burden (>50%) and
particularly lipid rich tissue at the stent edge is associated with subsequent restenosis.
• Co-registration of angiography and IVUS or OCT is a useful tool to determine stent length
and allows for precise stent placement.
L. Raber et al. European Heart Journal (2018) 39, 3281–

OCT Imaging Post Stenting
• Stent expansion
• Stent apposition
• Geographic miss
• Dissection
• Hematoma
• Prolapse

Stent expansion
• Stent expansion:
• absolute stent expansion: the minimum cross-sectional area (CSA) of a stent
as an absolute measurement or
• relative stent expansion: the minimum cross-sectional area (CSA) of a stent
as compared to a predetermined reference site that can be the proximal,
distal, largest, or average reference site.
• A greater absolute stent expansion is associated with better stent-
related clinical outcomes and a lower risk of stent failure.
• Compared to the relative stent expansion, the absolute stent
expansion appeared to be able to better predict the stent patency.

IVUS- or OCT-Detected Morphological
Parameters Associated With Clinical Outcomes

Absolute Stent Expansion
• Intravascular ultrasound studies have been relatively consistent in showing
that a stent cross-sectional area of 5.5 mm2 best discriminates subsequent
events in non-left main lesions.
• Consistently, in the DOCTORS trial the optimal cut-off to predict post-
procedural FFR >0.90, was >5.44 mm2 by OCT.
• Data from the CLI-OPCI registries identified an MLA of 4.5 mm2 as a
threshold for discriminating patients with MACEs.
• For LM lesions, cut-offs values are higher (e.g. >7 mm2 for distal LM and >8
mm2 for proximal left main by IVUS).

Limitations Of Absolute Area Criteria
• This cutoff may not be achievable in small vessels or may result in
stent undersizing in large vessels.
• There is a step-wise decrease in event rates with larger MSAs.
• Evidence exists that cut-offs of absolute stent expansion that predict
future events differ between BMS and DES.
• Different criteria apply in the case of left main lesions (larger cut-offs).

Relative stent expansion
• MSA measures 3.43 mm2, and the proximal and distal lumen areas at the most normal-
looking slice measure 4.17 and 2.99 mm2, respectively, for an average reference lumen
area of (4.17 1 2.99)/2 5 3.58 mm2.
• Therefore, stent expansion for this stent is calculated as MSA/(average of reference
lumen area) x 100 = 3.43/3.58 x 100 = 95.8%.

Relative stent expansion
• Different targets for stent optimization
include either MSA greater than the distal
reference lumen area; or >80% or >90% of
the average (proximal and distal)
reference area.
• Considering that the requirement for
achieving >90% expansion was frequently
out of reach, European Association of
Percutaneous Cardiovascular
Interventions states that
• the cut-off >80% for the MSA (relative to
average reference lumen area) appears to be a
reasonable approach to adopt in clinical
practice.

Volumetric Analysis Method for Stent Expansion
• Conventional methods, whether using IVUS or OCT, may have
important limitations because it does not take into account vessel
tapering, thus not accurately reflecting areas of underexpansion.
• Volumetric analysis to assess lumen expansion that takes into account
vessel tapering may be more functionally accurate and therefore
more predictive of outcomes.
• There is a mathematical relationship between the distal and proximal
reference and the intermediate side-branch.

Volumetric Analysis Method for Stent Expansion
• This method is based on a minimum expansion index (MEI), obtained by
creating an ideal lumen profile along the stented region, considering vessel
tapering.
• Each frame was assigned a normalized expansion index value, calculated
as: ([actual lumen area / ideal lumen area] x 100).
• MEI was defined as the cross section with lowest expansion index along the
entire stented segment.
• Cases with low expansion index were defined as cases with at least 1 cross-
section with an MEI <80%.
Nakamura, et al. JACC : CARDIOVASC INTERVENTIONS 2018 : 1467 – 78

Malapposition
• Stent malapposition (SM), also referred to as incomplete stent apposition,
is defined by the separation of at least one stent strut from the intimal
surface of the arterial wall with evidence of blood behind the strut,
without involvement of side branches.
• Stent malapposition refers to the lack of contact of the stent struts with the
vessel wall of ≥200 μm as viewed by OCT.
• Malapposition can be quantified by measuring
• the number of malapposed struts,
• the arc subtended by the malapposed struts,
• the distance between the malapposed struts and the vessel wall, &
• the area, length and volume of the gap between the stent and the vessel wall.

Measurement of stent strut malapposition
• A, distance from stent surface to the surface of plaque; B, malapposition distance; C,
strut thickness; D, polymer thickness.
• Because of attenuation behind stent struts, the actual thickness of the stent (sum of strut
thickness and polymer thickness) is not visualized by optical coherence tomography.
• Therefore, A is measured; B is calculated by subtracting C + D from A; and if B >0, the
strut is diagnosed as malapposed.

Measurement of stent strut malapposition
• Percent maximum malapposed area, defined as maximum malapposed area
([lumen area – stent area]/lumen area x 100), and total malapposed length (the
length having consecutive visible malapposed struts) can be determined.
• In this case, malapposition area (0.66 mm2) was calculated as lumen area (8.72
mm2, shown in gray) subtracted from the stent area (8.06 mm2 shown in the
dotted area).

Malapposition
• Malapposition can occur either in
• the acute, post-procedural period, or
• it may develop later, possibly as a
result of an underlying vascular
process of inflammation and positive
(outwards) remodelling of the vessel
wall.
• When malapposition is identified at
follow-up, it may represent either
persistent (i.e. ongoing since the
time of implantation), or late
acquired malapposition.
• A differentiation of these two
entities is not possible in the
absence of imaging immediately
post stenting.

Malapposition
• While stent underexpansion is a major predictor of early stent thrombosis
or restenosis, no clear link exists between acute malapposition (in the
absence of underexpansion) and subsequent stent failure, as acute
malapposition may subsequently resolve.
• Prospective studies with imaging immediately after stent placement have
shown that acute malapposition is not an independent predictor of stent
thrombosis.
• In contrast, studies of stents presenting with thrombosis have consistently
identified malapposition as a frequent underlying stent abnormality and
showed a higher incidence and extent of malapposition in stent segments
with vs. without thrombus.

Malapposition
• Three recent registries performed OCT in patients with definite stent (BMS or
DES) thrombosis.
• In two studies (PRESTIGE and PESTO) malapposition emerged as a frequent
finding:
• 27% and 60%, respectively, in acute stent thrombosis (within 24 h of implantation),
• 6% and 44%, respectively in subacute stent thrombosis (1–30 days,) and
• 10% and 44%, respectively in late stent thrombosis (between 30 days and 1 year post-PCI).
• Moreover, malapposition was among the three leading mechanisms in studies
investigating patients with very late stent thrombosis (>1 year following stent
implantation).
• In line with these observations, malapposition has been associated with
increased thrombogenicity in in vitro studies.

Current Consensus
• The clinical relevance of acute malapposition is uncertain.
Nonetheless, extensive malapposition after stent implantation should
be avoided and corrected, if anatomically feasible.
• Acute malapposition of <0.4mm with longitudinal extension <1mm
should not be corrected as spontaneous neointimal integration is
anticipated. This cut-off requires prospective validation.
• Late acquired malapposition represents an established cause of late
and very late stent thrombosis.

Geographic Miss
• Longitudinal GM - length of
angiographic injured or diseased
segment not covered by a stent.
• Axial GM - balloon/artery size
ratio <0.9 or >1.3.
Costa, et al. STLLR trial, Am J Cardiol 2008;101:1704–11.

Geographic Miss and Inflow/Outflow Disease
• After post-PCI OCT, the rendered stent selection should be activated. Visual
inspection of the proximal and distal outflow (5 mm from the stent edges) allows
for rapid determination of reference segment disease.
• If untreated reference segment disease is detected, the reference markers should
be used to bound the respective reference segment and determine the MLA.
• If the MLA is less than or equal to 4.5 mm2, an additional stent should be placed
to correct the inflow or outflow unless there are anatomic reasons that the
disease should not be covered (eg, diffuse distal disease or significant vessel
tapering).
• Both inflow and outflow MLA less than 4.5 mm2 have been shown to be strong
predictors of poor PCI outcome.

Stent Edge Dissections
• In CLIP-OPCI study, edge dissection is defined as a linear rim of tissue
adjacent to a stent edge (<5 mm) with a width of ≥200 μm.
• In ILUMIEN III, edge dissections were defined as being major by OCT
when they extend in an arc of >60° and were >3 mm in length.
• Dissections are frequently associated with remaining plaques at the
landing zone and with the technique of implantation, suggesting
some geographic mismatch as the main causative factor.

Classification of edge dissections
Flap Cavity Double-lumen
dissections
Fissures
Intimal Medial Adventitial
Radu, et al. EuroIntervention 2014;9:1085-

Morphometric Assessment of Stent Edges
• Flap morphometric parameters:
a) Depth - distance from the luminal
surface to the joint point with the
vessel wall at the base of the flap;
b) Opening - distance from the tip of the
flap to the lumen contour along a line
projected through the gravitational
center of the lumen;
c) Length - measured from the tip of the
flap to the joint point of the flap with
the vessel wall; and
d) Area (white region) planimetry of the
region outlined by the lumen contours
incorporating (solid blue tracing) and
interpolating (black dotted tracing) the
flap.

• For cavities:
• The cavity depth - measured from the deepest
point in the cavity to a virtual line extrapolated
between the luminal vessel contours on each
side of the cavity.
• The cavity width - quantified at its widest point
as parallel to the virtual line as possible.
• The cavity area - assessed as the area bounded
by the luminal contour of the cavity and the
help line extrapolated between the luminal
vessel contour on each side of the cavity.

OCT Predictors For Stent Edge Dissection
• Mechanical factors, such as vessel overstretching by an oversized stent.
• Atherosclerotic disease at stent margins
• Morphometric aspects of FC overlying lipid/necrotic core
• TCFA
• FC thickness ≤ 80 mm is considered as an independent predictor for the occurrence
of edge dissections
• Angle of calcification ≥ 72o
• Stent eccentricity
Chamié et al. JACC : CARDIOVASCULAR INTERVENTIONS , 6 ,
2013:800 – 13

Outcomes Of Edge Dissection
• Dissections having favorable outcomes that can be left untreated include
dissections with
• longitudinal length <1.75 mm,
• fewer than two concomitant flaps,
• flap depth of less than 0.52 mm, and
• flap opening of less than 0.33 mm and not extending into the media.
• Dissections a/w adverse outcomes:
• Presence of residual plaque burden,
• extensive lateral (>60 degrees) and longitudinal dissection (>2 mm),
• involvement of deeper vessel layers (tunicae media and adventitia), and
• Localization distal to the stent
• dissection with angiographic evidence of flow limitation
• dissection associated with an inadequate MLA (<4.5 mm2)

Intramural Hematoma
• Accumulation of blood within the medial space displacing the internal
elastic membrane inward and the external elastic membrane outward, with
or without identifiable entry and exit points.
• Detection of intra-and extramural haematomas by IVUS or OCT may be
relevant, as these findings usually appear as edge stenosis by angiography
and can be misdiagnosed as stent vessel mismatch or spasm.
• The progression of uncovered haematoma may lead to early stent
thrombosis.
• Stent edge haematoma may be detected by IVUS or OCT in case of
angiographic appearance of a residual stent edge stenosis.

Tissue Prolapse
Smooth protrusion: bowing
of the plaque is seen between
stent struts, without intimal
disruption (arrowheads).
Disrupted fibrous tissue
protrusion: fragments of
disrupted fibrous tissue can
be seen protruding into the
lumen (arrowheads).
Irregular protrusion: material
of irregular shape is observed
protruding between stent
struts (arrowheads).
Soeda, et al. Circulation. 2015;132:1020–1029

Tissue prolapse/Thrombus
• Tissue protrusion due either to thrombus or nonthrombotic plaque can be
of varying importance based on its characteristics and morphology.
• Thrombus is defined as intraluminal tissue greater than 0.25 mm in
diameter and either high backscattering with high attenuation (red-cell–
rich thrombus), less backscattering with homogeneous low attenuation
(platelet-rich thrombus), or a mixture of both.
• Typically, tissue protrusion can be left untreated; however, in the situation
of major tissue protrusion (effective MLA <5.5 mm2 or reduction in flow
area >10%) present, further postdilation, aspiration (in the case of
thrombus), or additional short DES placement should be considered.

Tissue prolapse
• In particular, irregular protrusion, defined as protrusion of material
with an irregular surface into the lumen between stent struts, has
been identified as an independent predictor of 1-year device-oriented
clinical end points and thus should be considered for treatment.
• Tissue protrusion may have a greater detrimental effect in cases of
acute coronary syndrome.
• The volume of the protruding tissue as viewed by OCT is associated
with an unstable plaque feature and peri-procedural MIs.

Tissue prolapse
To evaluate the significance of tissue protrusion, percent
tissue protrusion area (tissue protrusion area/stent area
x 100) is calculated. Tissue protrusion area (0.58 mm2,
green area) is calculated as stent area (5.82 mm2, dotted
line) minus lumen area (5.24 mm2, gray area).

Summary of post-PCI optimization targets

Assessment of mechanisms of stent failure

• Use of OCT is particularly important in cases of stent failure
(thrombosis or restenosis) to determine the etiology and determine
the best treatment strategy.
• OCT demonstrates whether stent thrombosis is due to mechanical
(eg, underexpansion) or other causes (eg, unrecognized edge
dissection or major inflow/outflow obstruction).
• If the cause is not mechanical, optimal antiplatelet therapy may be
readdressed using platelet reactivity assays.

• OCT can provide insight into the mechanism of ISR, guiding the best
treatment approach.
• OCT morphologic characteristics of ISR with second-generation DES differ
for early and late presentation.
• Early ISR is associated with underexpansion, whereas neoatherosclerosis
contributes more commonly to late ISR.
• Stent underexpansion when diagnosed by OCT can be treated with high
pressure balloon inflation, cutting or scoring balloons, laser, or
atherectomy.

Strut coverage
• Struts are stratified into four main categories:
• Covered embedded (covered by tissue and not otherwise interrupting the
smooth lumen contour),
• Covered protruding (covered by tissue but extending into the lumen),
• Uncovered apposed (not covered by tissue but abutting the vessel wall), and
• Uncovered malapposed (not covered by tissue and not abutting the vessel
wall),

Neointimal Hyperplasia
• Pathological studies have demonstrated that neointima within a stent
comprises various tissue components including collagen, proteoglycan,
smooth muscle, fibrin, and thrombus.
• Intravascular optical coherence tomography (OCT) has higher resolution
and is useful for the qualitative as well as quantitative evaluation of
neointimal tissue.
• Recent OCT studies have reported differential morphological characteristics
of neointimal tissue, which correlated well with histological findings.

Neointimal Hyperplasia
A. Homogeneous neointima, a uniform signal-rich band without focal variation or attenuation;
correlates with smooth muscle cells within collagenous/proteoglycan matrix
B. Heterogeneous neointima, focally changing optical properties and various backscattering
patterns; and
C. Layered neointima, layers with different optical properties (i.e , an adluminal high-scattering
layer and an abluminal low-scattering layer) correlates with healed neointimal rupture or
erosion

Long-Term Outcomes of Neointimal Hyperplasia Without
Neoatherosclerosis After Drug-Eluting Stent Implantation
Kim,
et
al.
J
Am
Coll
Cardiol
Cardiovasc
Imaging.
2014
Jul,
7
(8)
788–795

Neoatherosclerosis
OCT spectrum of in-stent neoatherosclerosis
A. Intimal rupture (red arrow);
B. TCFA-containing neointima
surrounded by signal-poor
lipidic area (red arrow);
C. Fibrotic neointima with
microvessels (red arrow).
D. Intraluminal red thrombus
with fast attenuation (red
arrow);
E. TCFA-containing neointima
(red arrow) with lipidic
tissue;
F. Intimal rupture (red arrow)
surrounded by tcfa-
containing neointima.

Stent thrombosis
• Stent thrombosis has multiple underlying mechanisms and most of
these are recognizable by intracoronary imaging.
• Optical coherence tomography, as opposed to IVUS, can distinguish
thrombus from other tissue components, and is therefore, considered
the preferred imaging technique for stent thrombosis.

Frequency Of Presumable Causes Of Early And Very Late Metallic DES
Thrombosis As Assessed In Three OCT Registries

Acute Coronary Syndrome Lesion Classification By OCT
Jia
H,
et
al.
J
Am
Coll
Cardiol
2013;62(19):1750

Plaque rupture is defined as a
lipid plaque with fibrous cap
discontinuity and cavity
formation inside the plaque.
Calcified nodules are defined by fibrous cap
disruption (solid arrow) with underlying calcified
plaque (dotted arrow) characterized by protruding
calcification, superficial calcium, or the presence of
significant calcium adjacent to the lesion.

Algorithm For Acute Coronary Syndrome Lesion
Classification By OCT
Jia
H,
et
al.
J
Am
Coll
Cardiol
2013;62(19):1750
• Definite plaque erosion is defined by the presence of
attached thrombus (arrow) overlying an intact and visualized
plaque.
• Probable plaque erosion is identified
• in the absence of attached thrombus by luminal surface
irregularity at the culprit site or
• in the presence of attached thrombus without underlying
plaque by a lack of superficial lipid or calcification in sites

Treatment Algorithm To Guide The Use Of Intravascular
Imaging In Patients Presenting With ACS

2018 ESC/EACTS Guidelines on myocardial
revascularization
• Recommendations on Restenosis
• Recommendations on intravascular imaging for procedural
optimization

Future Directions
• Integration of the OCT technology into catheter-
based therapeutic devices is being pursued actively.
• One example is a combined OCT/atherectomy
catheter recently approved in Europe for the
treatment of peripheral artery disease.
• This device has an OCT probe mounted near a
corkscrew cutter at the distal tip , offering real-time
imaging guidance for the CTO revascularization
procedure.

• The baseline CAG revealed significant stenosis in the proximal right coronary artery (A).
• A longitudinal OCT image revealed a lesion length of 23.4 mm (B) and the cross-sectional OCT image
revealed a 1.66 mm2 lumen area with a red thrombus (C).
• Because the EEL contours were identifiable in both the proximal (C) and distal (D) reference segments, the
mean EEL to EEL diameter was calculated. Of these, the lowest EEL to EEL diameter was 3.86 mm in the
proximal reference segment (E).
• Thus a 3.5×28 mm Xience stent was chosen based on downsizing to the nearest stent diameter (3.5 mm)
from the lowest EEL to EEL diameter (3.86 mm) and was implanted with a 12 atmospheric pressure.
Lee,
et
al.
Korean
Circ
J.
2019
Sep;49(9):771-793

• CAG after stent implantation - mild residual stenosis
at proximal portion within stented segments (F) &
longitudinal OCT image showed that MSA was 4.24
mm2 and was located proximal one-third portion
within stented segments (G).
• Reference bar was moved to each distal & proximal
stented segment for an evaluation of optimal
relative stent expansion. Then, residual AS was
manually calculated by OPTIS system: [[{1−(proximal
(or distal) MSA/proximal (or distal) reference lumen
area)}×100]=residual proximal (or distal) AS (%)].
• Longitudinal & cross-sectional OCT images showed
that MSA in distal half of stented segments was 5.21
mm2, which calculated that the residual distal AS
value was 17.4% relative to distal reference lumen
area: [{1−(5.21/6.31)×100}=17.4% of AS] (I).
• MSA in the proximal half of stented segments was
4.24 mm2, which calculated that residual proximal
AS value was 39.1% relative to proximal reference
lumen area [{1−(4.24/6.96)×100}=39.1% of AS] (K).
• The post-dilatation balloon size was determined by
the EEL to EEL diameter of the proximal reference
segment.
Lee, et al. Korean Circ J. 2019 Sep;49(9):771-793

• After additional balloon dilatation, a
CAG showed no residual stenosis within
the stented segments (L).
• The longitudinal and cross-sectional
OCT images showed that MSA in the
distal half of the stented segments
improved from 5.21 mm2 to 6.48 mm2,
which calculated that the residual distal
AS value had reduced from 17.4% to
1.2% relative to the distal reference
lumen area [{1−(6.48/6.56)×100}=1.2%
of AS] (O).
• Similarly, the MSA in the proximal half
of the stented segments improved from
4.24 mm2 to 6.65 mm2, suggesting that
the residual proximal AS value had
decreased from 39.1% to 2.7% relative
to the proximal reference lumen area
[{1−(6.65/6.83)×100}=2.6% of AS] (Q).
• Based on the AS results post-dilatation,
the stent optimization was confirmed
without any complications.
Lee, et al. Korean Circ J. 2019 Sep;49(9):771-793

• Double lumen dissections - those having a false
lumen separated from the true lumen by a cap.
• The cap thickness - quantified semi-automatically
from the joint point with the vessel wall to the
luminal vessel contour along a line projected
through the gravitational centre of the lumen, and
the largest of the two cap thicknesses was used.
• The cap length - measured as the distance
between the two joint points connected by a
straight line.
• The cap area - defined as the area bounded
luminally by the vessel surface to the sides by the
cap thickness

Criteria for Defining Vulnerable Plaque, Based
on the Autopsy Study
• Major criteria
• Active inflammation (monocyte/macrophage and T-cell infiltration)
• Thin cap with large lipid core
• Endothelial denudation with superficial platelet aggregation
• Fissured plaque
• Stenosis 90%
• Minor criteria
• Superficial calcified nodule
• Glistening yellow
• Intraplaque hemorrhage
• Endothelial dysfunction
• Outward (positive) remodeling
 Circulation. 2003;108:1664-1672

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