Invasive Cardiac Imaging
Intracoronary Imaging
Cameras placed inside the coronary artery reveal anatomy invisible to X-ray: the thickness and composition of plaque, the depth of calcification, and whether a stent has been deployed precisely and completely. Dr Nijjer uses intravascular imaging routinely to guide complex coronary interventions and achieve the best possible results.
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Beyond the Angiogram
Why X-Ray Alone Is Not Enough
A coronary angiogram is an X-ray silhouette of the lumen — the hollow channel through which blood flows. It shows the outline of the artery but reveals almost nothing about the vessel wall itself: the plaque within it, how deep or calcified that plaque is, or precisely how the artery has responded to a stent. Two arteries can look identical on angiography yet have completely different internal structures and require completely different treatment strategies.
Intracoronary imaging resolves this. A miniaturised catheter — smaller than 1mm in diameter — is advanced into the coronary artery over a standard guidewire and pulled back automatically while capturing thousands of cross-sectional images per second. The result is a detailed, high-resolution map of the vessel wall along its entire length: plaque composition, calcification pattern, vessel diameter, and — after stent deployment — stent expansion, strut contact with the vessel wall, and edge integrity.
Evidence from multiple large randomised trials demonstrates that imaging-guided coronary intervention reduces stent failure, periprocedural myocardial infarction, and the need for repeat procedures compared with angiography-guided treatment alone. The ILUMIEN IV trial, published in 2023, confirmed that OCT-guided stenting significantly improves outcomes at one year versus angiography guidance.
Dr Nijjer's approach. Dr Nijjer uses intracoronary imaging routinely in complex coronary intervention — including calcified lesions, left main disease, chronic total occlusions, and bifurcation stenting. He integrates imaging findings with coronary physiology (iFR, FFR) to achieve precise, physiologically-optimised stent results with the lowest possible risk of future stent-related complications.
The Two Technologies
IVUS & OCT Explained
Both technologies capture cross-sectional images from inside the artery but use fundamentally different physics — sound waves versus light — giving each distinct advantages. They are complementary rather than competing tools, and Dr Nijjer selects between them based on the clinical question being asked.
IVUS
Intravascular Ultrasound
~100
microns
axial resolution
axial resolution
TechnologyHigh-frequency ultrasound (40–60 MHz), emitted from a rotating transducer within the catheter
Penetration~10 mm — visualises the full vessel wall including the external elastic membrane and periadventitial tissue
Blood clearanceNot required — ultrasound passes through blood without artefact
Key evidenceMUSIC criteria · ULTIMATE trial (2019) · PROSPECT plaque study
- No contrast injection required — ideal in renal impairment
- Sees behind superficial calcium to measure total plaque burden
- Gold standard for left main coronary assessment
- Measures true vessel diameter (EEM) for accurate stent sizing in large vessels
- Virtual Histology (VH-IVUS) characterises plaque composition — fibrous, lipid, calcium, necrotic core
Lower resolution limits visualisation of thin fibrous caps and fine stent strut detail
OCT
Optical Coherence Tomography
~15
microns
axial resolution — 10× finer than IVUS
axial resolution — 10× finer than IVUS
TechnologyNear-infrared light (1300 nm wavelength), reflected from tissue interfaces to generate ultra-high-resolution images
Penetration~2–3 mm — sufficient for the vessel wall in most clinical contexts; limited behind dense calcium
Blood clearanceRequired — a brief contrast flush clears blood from the imaging field during automated pullback
Key evidenceILUMIEN I–III · ILUMIEN IV (NEJM 2023) · OPINION trial
- Measures individual stent strut apposition with sub-millimetre precision
- Identifies thin-cap fibroatheroma (fibrous cap <65 microns) — the vulnerable plaque most likely to rupture
- Distinguishes plaque rupture from plaque erosion in acute coronary syndromes — changes treatment strategy
- Detects edge dissections and tissue prolapse through stent struts
- Quantifies neointimal coverage of stent struts at follow-up
Cannot image behind heavy superficial calcification; requires contrast flush (small volume)
When to use each
IVUS is preferred for large-vessel or left main assessment, for patients with renal impairment where contrast must be minimised, and when full plaque burden characterisation is required. OCT is preferred for precision stent optimisation, for identifying the mechanism of an acute coronary syndrome, and for assessing stent failure. In complex multi-vessel disease, both modalities may be used in a single procedure.
The Clinical Value of Imaging
What Imaging Reveals That Angiography Cannot
Each of these findings is clinically significant and invisible to standard X-ray coronary angiography. Identifying them changes the treatment decision.
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True Vessel Diameter
Angiography shows only the lumen — the hollow channel through which blood flows. Intracoronary imaging measures the outer boundary of the vessel wall (the external elastic membrane), revealing the true vessel size. Stents sized to this measurement achieve better expansion and lower rates of restenosis than those sized to the angiographic lumen alone.
Best assessed with: IVUS (full wall penetration)
Ca
Calcification Pattern
Calcium within a coronary plaque appears as a bright arc on OCT or dense echo on IVUS. Its depth (superficial vs deep) and arc (degrees of circumference affected) determine whether a stent can be adequately expanded. Superficial calcium covering more than 180–270° of the vessel arc predicts stent underexpansion and often requires modification — rotational atherectomy, orbital atherectomy, or intravascular lithotripsy — before stenting.
Best assessed with: OCT (calcium arc) + IVUS (plaque burden)
MSA
Minimum Stent Area
The minimum cross-sectional lumen area inside a deployed stent (MSA) is the single strongest predictor of future stent failure. A stent that looks well-deployed on angiography may have a critically underexpanded segment invisible to X-ray. Imaging defines the MSA at every cross-section, allowing post-dilatation with larger balloons until the target is met — reducing restenosis and thrombosis rates substantially.
Best assessed with: both IVUS and OCT
M
Stent Malapposition
Individual stent struts that are not in direct contact with the vessel wall — a finding known as malapposition — are identified only by imaging. Acutely malapposed struts are associated with delayed endothelialisation and late stent thrombosis, one of the most serious and potentially fatal complications of coronary stenting. Additional balloon dilatation corrects most acute malapposition.
Best assessed with: OCT (strut-level precision)
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Edge Dissection
Tears in the vessel wall immediately beyond the proximal or distal edge of a stent are a recognised complication of stent deployment. Small edge dissections are extremely common and usually benign, but large or flow-limiting dissections — invisible on angiography — require additional stenting. Imaging identifies their presence, length, and depth, allowing a precise and targeted response.
Best assessed with: OCT (superior near-field resolution)
ACS
Plaque Rupture vs Erosion
In an acute coronary syndrome, the culprit event is either a ruptured plaque — where the fibrous cap has fractured and the lipid core is exposed — or a plaque erosion, where the surface is intact but thrombus has formed on top. OCT distinguishes these mechanisms reliably. Erosion without a large underlying plaque may be managed with aspiration and potent antiplatelet therapy alone, avoiding a stent entirely in selected younger patients.
Best assessed with: OCT (fibrous cap resolution ≥65 microns)
When Imaging Is Used
Clinical Applications
Intracoronary imaging is used at two key moments in a coronary procedure: before stenting, to characterise the lesion and plan the intervention optimally; and after stenting, to confirm that the result meets the criteria for optimal deployment.
Pre-intervention planning. Imaging defines the true vessel diameter and lesion length for accurate stent selection, identifies the pattern and severity of calcification to guide whether plaque modification is needed before stenting, and reveals whether a lesion that looks intermediate on angiography is truly significant or can be managed medically — complementing iFR assessment.
Complex lesion types. Intracoronary imaging is particularly valuable in calcified lesions (to guide rotablation, orbital atherectomy, or shockwave lithotripsy), left main coronary disease (where correct stent sizing is critical), bifurcation stenting (to confirm side-branch ostial coverage and stent geometry), and chronic total occlusions (to assess the landing zone and confirm wire position).
Stent failure. When a patient presents with in-stent restenosis or late stent thrombosis, imaging identifies the underlying mechanism — underexpansion, neoatherosclerosis, mechanical fracture, or malapposition — and directly guides the treatment strategy for that specific cause.
Acute coronary syndromes. In STEMI and NSTEMI, OCT identifies the culprit plaque mechanism, guides precise stent sizing in the vessel affected by acute thrombosis and spasm, and confirms complete strut apposition after deployment — reducing the risk of late stent thrombosis in a group already at elevated risk.
Post-intervention optimisation criteria. Dr Nijjer targets specific imaging endpoints at the end of every stented case — including minimum stent area relative to the reference vessel, full strut apposition, absence of significant edge dissection, and smooth proximal and distal transitions. These criteria, derived from the MUSIC, ILUMIEN, and ULTIMATE trial data, are associated with substantially better long-term outcomes than those guided by angiography alone.
Combining imaging with physiology. After stenting, iFR can be remeasured to confirm that the physiological result matches the anatomical result — a combined imaging and physiology approach that provides the highest level of procedural certainty. Dr Nijjer routinely integrates both assessments in complex cases.
What to Expect
The Imaging Procedure
01
Arterial Access
A fine sheath is placed in the radial artery at the wrist (preferred) or femoral artery at the groin under local anaesthetic. A guiding catheter is advanced to the mouth of the coronary artery. Intracoronary imaging is always performed as part of a coronary angiography and intervention procedure — it is not performed in isolation.
02
Wire & Catheter Placement
A standard coronary guidewire is placed across the target lesion. The imaging catheter — 0.9 mm in diameter for OCT, slightly larger for IVUS — is advanced over the wire to the distal end of the segment to be imaged. The catheter is connected to an automated motorised pullback device that withdraws it at a constant, controlled speed.
03
Image Acquisition
For IVUS, the pullback begins immediately — no preparation is required. For OCT, a brief injection of contrast dye through the guiding catheter flushes blood from the imaging field; automated pullback then captures up to 200 cross-sectional frames per second across the full length of the artery. The procedure adds approximately 5–10 minutes to the overall procedure time.
04
Analysis & Planning
Dr Nijjer reviews the images immediately on-screen, measuring vessel diameter, plaque arc, lesion length, and — if a stent has been placed — minimum stent area, strut apposition, and edge integrity. Software tools allow automated measurements and three-dimensional reconstruction. Findings directly determine the next step: stent selection, calcium modification, additional dilatation, or confirmation that the result is optimal.
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Post-Procedure
Intracoronary imaging carries no additional risk beyond that of the coronary angiography procedure itself. After the procedure, you are monitored on the ward for a few hours; most patients are discharged the same day or the following morning depending on the complexity of the intervention performed. Dr Nijjer discusses the imaging findings and the overall result with you before discharge.
Precision Stenting, Precisely Guided
Dr Nijjer uses intracoronary imaging routinely in complex coronary intervention — achieving stent results that angiography guidance alone cannot reliably deliver.