Linking To And Excerpting From “Standards for quantitative assessments by coronary computed tomography angiography (CCTA): An expert consensus document of the society of cardiovascular computed tomography (SCCT)”

Posted on May 5, 2026 by Tom Wade MD

Today, I review, link to, and excerpt from “Standards for quantitative assessments by coronary computed tomography angiography (CCTA): An expert consensus document of the society of cardiovascular computed tomography (SCCT)”. [PubMed Abstract] [Full-Text HTML] [Full-Text PDF]. J Cardiovasc Comput Tomogr. 2024 Sep-Oct;18(5):429-443. doi: 10.1016/j.jcct.2024.05.232. Epub 2024 Jun 6.

All that follows is from the above resource.

Abstract

In current clinical practice, qualitative or semi-quantitative measures are primarily used to report coronary artery disease on cardiac CT. With advancements in cardiac CT technology and automated post-processing tools, quantitative measures of coronary disease severity have become more broadly available. Quantitative coronary CT angiography has great potential value for clinical management of patients, but also for research. This document aims to provide definitions and standards for the performance and reporting of quantitative measures of coronary artery disease by cardiac CT.

Keywords: Coronary plaque, Atherosclerosis, Computed coronary tomography angiography, Definitions

1. Introduction

The present document is an Expert Consensus Document on standards for quantitative assessments by coronary computed tomography angiography (CCTA). The document is intended to inform practitioners, researchers, and other interested parties of the opinion of the Society of Cardiovascular Computed Tomography (SCCT) concerning quantitative CCTA methods. Thus, the reader should view the Expert Consensus Document as the best attempt of the SCCT to inform and guide clinical/research practice in this area where rigorous evidence may not yet be available or the evidence to date is not widely accepted.

During the past decade, CCTA has become increasingly important in both clinical care and research. For the clinical management of patients semiquantitative measures of coronary artery disease (CAD) are often sufficient. Existing guidelines recommend reporting of coronary stenoses by categories of obstructive severity rather than an exact percentage stenosis measurements. Coronary plaque can be visually classified as predominantly calcified, non-calcified and partially calcified. The amount of coronary calcium can be measured on non-enhanced CT scans in absolute terms such as volume or calcium hydroxyapatite mass, although semi-quantitative Agatston scores are more commonly reported. Semi-quantitative scores, for instance the Segment Involvement Score, have been developed to report the global quantity of both calcified and non-calcified atherosclerotic plaque on CCTA. The Coronary Artery Disease Reporting and Data System (CAD-RADS) was introduced to “improve communication between interpreting and referring physicians, facilitate research, and offer mechanisms to contribute to peer review and quality assurance, ultimately resulting in improvements to quality of care”. The recently released CAD-RADS™ 2.0 includes semi-quantitative assessment of stenosis and plaque, as well as functional parameters. Other disease classification scores may predict the response to revascularization, such as the CT SYNTAX score for coronary revascularization, and the CT-RECTOR score for chronic total occlusions (CTO)., These well-described semiquantitative scores and classifications, which are valuable for guidance of clinical management of patients with CAD, are primarily based on visual interpretation without the need for quantification.

The prognostic value of coronary plaque on CT, by qualitative and (semi-)quantitative techniques, has been demonstrated in numerous cohorts and has been comprehensively discussed in prior SCCT consensus documents. In addition to well-known measures of global plaque burden (e.g. calcium score, segment-involvement-score), more recently the napkin-ring sign was identified as a specific CT marker of plaques with a large necrotic core associated with adverse clinical events. In the SCOT-HEART cohort, Williams et al., recently showed that low-attenuation plaque burden is the strongest predictor of fatal or non-fatal myocardial infarction, irrespective of cardiovascular risk score, coronary artery calcium burden or area stenosis.

With expanding availability of tools for comprehensive coronary analyses used both in research clinical care, the field currently lacks standards for the quantitative image interpretation of and reporting of results. The lack of standards has affected the ability of clinicians/researchers to communicate findings using a common language. Similarly, the literature has been confounded by ambiguous terminology and various alternative synonyms for similar structures and measurements. CCTA has been recognized as a promising noninvasive tool to monitor CAD progression and assess the effects of medical therapy or mechanical interventions in clinical trials. Specific and clear definitions and as well as standardization of methodology are essential for CCTA to mature as an accurate and reproducible endpoint in clinical research. Therefore, this document aims to provide a framework for standardization of nomenclature, methodology and reporting of quantitative CCTA analyses.

In accordance with SCCT policy, writing group members and reviewers are required to disclose relationships with industry; see Appendix B, Appendix C for detailed information. The document was approved by the Society of Cardiovascular Computed Tomography’s Board of Directors on May 13, 2024.

2. Image acquisition, quality, and analysis

2.1. Image acquisition

2.1.1. Scanner technology

2.1.2. Spatial resolution

2.1.3. Temporal resolution

2.1.4. Image contrast and noise

2.2. Artifacts and image degradation

2.3. Vessel and lumen segmentation

2.4. Deep learning based vessel segmentation

3. Nomenclature and definitions

CCTA images depict the enhanced lumen as well as atherosclerotic plaque in the wall of the coronary artery. Compared to invasive angiography it displays more completely the extent of CAD, even if the disease does not impact the lumen dimensions substantially. Separation of individual “lesions”, traditionally defined by invasive angiography as lumen narrowing where atherosclerosis is present, may not be as straightforward on CT images if diffuse CAD is present. Given the fact that atherosclerotic plaque expands outward and many plaques go undetected by invasive angiography, “lesion” by traditional definition has become a misnomer. Nowadays, and particularly in CCTA studies, the term atherosclerotic lesion often includes both stenotic and non-stenotic atherosclerotic plaques. To avoid confusion, in this document we will avoid the term lesion entirely. In the intravascular imaging literature, atherosclerotic disease is typically termed atheroma, while in CCTA publications the term plaque is more widely used. Therefore, total atheroma volume (TAV) as introduced by IVUS, is termed total plaque volume (TPV) in this document.

In Tables 1 and 2 are outlined the definitions of key variables to quantify lumen, vessel and plaque dimensions, typically by diameter, area or volume. Cross-sectional variables are reported as a unique value (either a diameter or an area) at a given point in the vessel (Fig. 1, panels A and B). These variables are also used for the calculation of internally normalized variables such as the area stenosis. In general, 2-dimensional (i.e., area) and 3-dimensional (i.e., volume) parameters are preferred over 1-dimensional parameters (i.e., diameters or perimeters) because of higher overall reproducibility.

Table 1.

Relative performance of quantitative coronary CT parameters.

Ease of scan performance Diagnostic accuracy Acquisition reproducibility Analysis reproducibility Clinical relevance Target for intervention
Lumen parameters
Minimal lumen area (mm2) +++ +++ ++++ +++ +++* ++
Diameter stenosis (%) +++ +++ ++++ ++ +++++ ++
Area stenosis (%) +++ +++ ++++ +++ ++++ ++
Plaque parameters
Calcium score (Agatston score) +++++ ++ +++ +++++ +++ +
Total plaque volume (mm3) ++ ++ +++ +++ ++ +++
Percent plaque volume (%) ++ ++ ++** +++ ++ +++
Normalized proximal plaque size (mm3) ++ +++ +++ ++++ +++ +++
Total non-calcified plaque volume (mm3) ++ ++ ++ ++ +++ ++++
Total low-attenuation plaque volume (mm3) + + + ++ ++++ ++++

Ease of scan performance: ranging from dedicated scan protocols on state-of-the-art equipment by a highly skilled team (+) to routine protocols that can be performed on most cardiac CT systems by less experienced teams (+++++). Diagnostic accuracy: degree of technical validation of the CT parameter against reference standards (histology, intra-coronary imaging). Acquisition reproducibility: degree of variation in outcome between scans and different scanners. Analysis reproducibility: degree of variation in outcome between analysis ranging from poorly reproducible or only by identical analysis software and same reader (+), to highly reproducible between software packages and readers (+++++). Clinical relevance: degree the CT parameter is important for clinical outcome and patient management. Target for intervention: degree the CT parameter can serve as a surrogate endpoint and is amenable to pharmaceutical or mechanical interventions. Percent plaque volume: total plaque volume divided by the total vessel volume. Normalized proximal plaque size: total plaque in a proximal coronary segment normalized for the length of the vessel segment. This table is based on working group consensus and reflects the current state of the field, which may change with the introduction of higher-resolution CT technology (photon-counting CT) or further-advanced, validated analysis software (including AI-based techniques).

* Relevant for left main disease.
** The %PV is affected by changes in vessel size and the use of nitroglycerine.

Table 2.

Quantitative plaque variables.

Lumen
Reported as diameter (mm), area (mm2) & volume (mm3)		 The space within the intimal boundary that is filled by (contrast-enhanced) blood, excluding thrombus or other protruding tissue (Fig. 1).
Vessel
Reported as diameter (mm), area (mm2) & volume (mm3)		 The space within the outer vessel boundary, generally defined by the interface with the low-attenuation epicardial fat (Fig. 1).
Plaque
Reported as Thickness (mm), area (mm2) & volume (mm3)		 The space between the outer vessel boundary and the lumen that is occupied by atherosclerotic tissue.

Plaque = vessel– lumen

* This is applicable to the analysis of a coronary segment/vessel rather than the characterization of an individual and isolated plaque
Length (mm) Distance parallel to the longitudinal axis of the vessel, often based on the coronary center-lumen line. Examples are plaque, coronary segment or stent length.
Short-axis cross-sectional variables and internally normalized variables
Minimum lumen diameter (mm) and area (MLA, mm2) Smallest lumen diameter and area within the diseased vessel section. These variables are used to calculate the diameter and area stenosis (Fig. 1).
Maximum lumen diameter (mm) and area (mm2) Largest lumen diameter and area within a lesion, segment or vessel, including in abnormally dilated arteries.
Maximum vessel diameter and area (mm2) The largest vessel diameter and area within a vessel or section, used for instance in abnormally dilated arteries.
Reference lumen/vessel dimensions
Reference lumen diameter (RLD, mm), area (RLA, mm2)
Reference vessel diameter (RVD, mm), area (RVA, mm2)		 Cross-sectional dimensions as previously described, obtained at a normal part of the vessel as close to the vessel section of interest to perform relative measurements, i.e. stenosis, outward remodeling. Deciding on the proximal or distal reference site is subjective and often a compromise between proximity and normalcy, and the balance will be affected by the specific study objectives. In case of both a proximal and a distal reference dimension, the reference vessel dimension will be an average of both. Reference sites beyond large side branches should be avoided. A practical approach to classify a side branch as non-significant is a relative diameter cut-off of <50%, which would correspond to a lumen area size of <25%.
Interpolated reference vessel dimensions take into account the distance of the reference samples to the narrowest section, and potentially other features along the vessel, to improve estimation of the nominal dimensions at the site of interest.
Average RLA = (Proximal RLA + Distal RLA) / 2
Area stenosis (%AS) Stenosis severity at the narrowest section (MLA) relative to the (averaged/interpolated) reference lumen area.
%AS = [(RLA – MLA) / RLA] x 100%
Diameter stenosis (%DS) Stenosis severity at the narrowest section (MLD) relative to the (average/interpolated) reference lumen diameter.
%DS = [(RLD – MLD) / RLD] x 100%
Plaque burden (PB, %) Plaque burden indicates the amount of plaque as a proportion of overall vessel size
Cross-sectional plaque burden = [plaque area / vessel area]*100%
Volumetric plaque burden = [plaque volume / vessel volume]*100%
Remodeling index (RI) Enlargement of vessel dimensions to accommodate plaque development compared to normal vessel sections.
Remodeling index (RI) = (maximum vessel area / reference vessel area)
Positive or outward remodeling: RI ≥1.10.
Negative or constrictive remodeling: RI < 0.90.
Lumen, vessel and plaque volume (mm3) Volumetric dimensions are typically calculated by integrating 2D segmentations on serial cross-sections that are equally spaced along the center-lumen line. Automated software may derive these parameters directly through volumetric segmentation of the lumen or vessel boundaries. Typically, volumetric dimensions are limited to specific vessel segments. To compare between individuals/cohorts or temporal changes of volumetric parameters it is important to account for the length and location of the interrogated vessel section (Fig. 1).
Total plaque volume (TPV, mm3) The difference between vessel and lumen volume for the studied region
TPV per vessel = total vessel volume – total lumen volume
Averaged cross-sectional dimensions Mean lumen, vessel and plaque area (mm2) From an equidistant range of cross-sections along the center-lumen line, or a volumetrically segmented vessel section, average cross-sectional dimensions can be calculated.
Mean vessel area = vessel volume / segment length
Mean vessel area = VA1 + VA2 + VA3 … + VAn) / n
Percent plaque volume (%PV) Total plaque volume divided by the total vessel volume encompassing each coronary artery in the coronary artery tree (>2mm diameter).
%PV per vessel = [TPV per vessel / total vessel volume] x 100
Subclassified plaque volume (mm3) and percentage (%):
Calcified plaque volume and percentage
Non-calcified plaque volume and percentage
Low-attenuation plaque volume and percentage		 Volume of calcified, non-calcified or low-attenuation plaque, typically based on attenuation values, as an absolute measure (mm3) or as a proportion of the total plaque (%). Normalization as described previously.

Percent calcified plaque = calcified volume / plaque volume x 100%

Percent noncalcified plaque = noncalcified volume / plaque volume x 100%

Fig. 1.

Fig. 1.

Graphic representation of commonly reported variables by computed tomography angiography.

4. Coronary plaque assessment

The traditional definition of plaque on CCTA is the presence of tissue structures ≥1 mm2 within or adjacent to the coronary artery lumen, identified in at least two independent planes, that can be distinguished from the surrounding tissues (epicardial fat) and the lumen. This definition, which was developed before (automated) segmentation tools became available, is still valid for qualitative plaque characterization and semiquantitative plaque burden scores. For analyses using (semi-)automated segmentation and quantification tools, plaque is defined as the space between the inner lumen and outer vessel boundaries, occupied by atherosclerotic tissue.

Using conventional post-processing tools, plaques can be qualitatively classified as predominantly calcified, i.e. containing mostly high-density tissue; predominantly non-calcified, i.e. no discernible calcification; or partially calcified plaque, i.e. both calcified and non-calcified tissue is present. The adjective “predominantly” is added because histopathological studies have shown that exclusively calcified plaques are rare, while non-calcified plaques may contain very small calcifications beyond the resolution of CT. Calcified tissue is typically defined by attenuation values higher than the lumen (brighter). Tissue with attenuation values distinctively higher than non-calcified tissue, but lower than the contrast-enhanced lumen, may still be classified as calcium if it is embedded in non-calcified plaque. It is recommended to avoid plaque classifications that inappropriately suggest mechanical or histological characteristics that cannot be reliably assessed by CCTA, including soft, hard, mixed, vulnerable, lipid-rich and fibrous plaque.

Among the many semi-quantitative plaque characteristics that have been investigated, a few features with demonstrated prognostic value are referred to as high-risk plaque features. These include positive vessel remodeling, low-attenuation plaque, spotty calcification, and the napkin-ring sign.– Positive or outward vessel remodeling is defined as an outer vessel area that is >10% larger than a representative reference site. Spotty calcifications are small scattered calcified lesions. A definition based on a maximum diameter of 3 mm in any direction has been proposed, although measured dimensions highly depend on acquisition and reconstruction parameters, as well as window display settings.

Low attenuation plaque components are considered as the surrogate for the lipid-rich parts of atherosclerotic plaques and thin-cap fibroatheromas. For manual sampling of plaque attenuation values, it is recommended to obtain the average attenuation values from a sufficiently large region-of-interest. Small or single-voxel samples should be avoided because these can produce non-representative attenuation measurements due to the inherent presence of image noise. Table 3. Indeed, measured attenuation values in non-calcified plaque vary across a wide range and are affected by the contrast enhancement of the coronary lumen and reconstruction kernels. Although a range of thresholds have been reported, an upper threshold of 30 HU has typically been used for low attenuation plaque, based on prognostic studies that examined both low attenuation plaque as a visually assessed plaque feature and quantitative volume or burden. This threshold has also been verified against lipid-rich plaque identified by IVUS.,,,,

Table 3.

Effect of selected CT parameter modifications on quantitative plaque assessment.

CT parameter modification Effect on image quality Effect on plaque quantification
↓ Tube voltage ↑ Lumen attenuation
↑ Attenuation values for all plaque components		 ↑ Calcified plaque volume
↓ Low-attenuation plaque volume
↑ Tube current ↓ Image noise
↑ Overall image quality		 ↑ Homogeneity of plaque attenuation values
↑ Reproducibility
↑ Intra-coronary iodine concentration ↑ Lumen attenuation
↑ Attenuation values for all plaque components		 ↑ Calcified plaque volume
↓ Low-attenuation plaque volume
↑ Reconstruction kernel sharpness ↑ Lumen contour sharpness
↑ Image noise		 ↓ Homogeneity of plaque attenuation values
↑ Iterative reconstruction strength ↓ Image noise Small effects on attenuation values and plaque size in some studies

Effect of isolated modifications and assumption of fixed HU-thresholds for segmentation of inner and outer vessel boundaries and plaque components.

The napkin-ring sign is a qualitative plaque feature, defined as a non-calcified plaque with two features when viewed in short-axis cross-section: a central area of lower CT attenuation that is apparently in contact with the lumen; and a ring-like higher attenuation plaque tissue surrounding this central area., Important to note that no attenuation measurements are needed to describe the napkin-ring sign. Histopathological studies have shown that the napkin-ring sign is a specific CT marker of plaques with a large necrotic core, and outcome studies have demonstrated this feature is associated with future adverse clinical events.

The CAD-RADS™ 2.0 reporting system recommends noting plaques that clearly demonstrate two or more high-risk features. It is important to note that the prevalence of these plaque features on CCTA is relatively high and thus their positive predictive value to identify plaques that will cause future events is modest.

4.2. Quantitative CCTA plaque analysis

Applications with (semi-)automated segmentation of the inner and outer vessel wall can produce numerous measures of lumen narrowing and plaque burden (Fig. 2). It is recommended to measure the length of the plaque from the proximal to the distal normal edge. Within the segmented plaque, tissue types can be subclassified based on attenuation values. The default thresholds and terminology for the tissue subclassifications vary between software applications (Fig. 3). Most software define the threshold for (dense) calcification as >350HU. Calcified plaque with a very high CT density of >1000 HU (so-called 1K plaques), associated with lower risk of acute coronary syndrome, may be classified separately. For plaque within the lowest attenuation category the upper threshold varies between 30 and 75HU. As mentioned, the intensity of contrast enhancement of the coronary lumen affects the measured attenuation values in coronary plaques, thereby affecting how plaque tissue components are classified. For this reason, this guideline does not recommend a specific absolute threshold for low-attenuation plaque. Scan-specific thresholds based on attenuation values sampled in the proximal coronary arteries have been proposed to compensate for variations in lumen opacification.

Fig. 2.

Fig. 2.

Semi-automated plaque segmentation by commercially available software.

Extensive atherosclerosis in the left anterior descending coronary artery (LAD, panels A and B), analyzed using (semi-)automated, quantitative software by 7 different vendors: Aquarius Intuition by TeraRecon (Durham, NC; panels C and D), Qangio CT by Medis (Leiden, The Netherlands; panels E and F) Autoplaque V3.0 from Cedars-Sinai Medical Center (Los Angeles, CA; panels G and H), SyngoVia/Frontier CT Coronary Plaque Analysis by Siemens Healthineers (Forchheim, Germany; I and J). Cleerly LABS version 2.0 (Cleerly Healthcare, Denver CO; panels K and L) and HeartFlow Plaque Analysis (Mountain View, CA; panels M and N), CtaPlus by Shanghai Pulse Medial Technology, Inc. (Shanghai, China; panels O and P). The inner and outer vessel wall boundaries are segmented and the plaque in between is categorized and color-coded based on software-specific Hounsfield-unit thresholds. The location of the cross-section (left side) is indicated by an arrow on the curved (D, F, H, O) or straightened (J, L, N) longitudinal cross-section (right side).

The measured minimal lumen area ranged between 1.2 mm2 and 2.3 mm2 and the area stenosis between 65% and 88%. The total plaque volume ranged between 76 mm3 and 486 mm3, in part reflecting differences in interrogated vessel length, as the plaque burden (total plaque/total vessel volume) had a much a narrower range between 58% and 70%, and a single outlier at 88%. The percentage non-calcified plaque volume ranged from 75% to 99%. The proportion of plaque within the lowest attenuation category varied substantially: 0.3%–35% of the total plaque volume. . (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 3.

Fig. 3.

Classification of plaque components on CCTA based on Hounsfield Units

Summary of Hounsfield-unit thresholds for classification of plaque components on CCTA from selected studies. Low-density plaque (LD), non-calcified plaque (NCP), calcified plaque (CP), necrotic core (NC), fibro-fatty plaque (FFP), fibrous plaque (FP), low-attenuation plaque (LAP), dense calcification plaque (DCP), lipid-rich plaque (LRP), fatty plaque (FaP), intermediate-attenuation plaque (IAP), low-density plaque (LDP), as defined by the original publications. Evaluation of calcific plaques.–,–

5. Additional recommendations for specific situations

Considerations and recommendations for quantitative CCTA after percutaneous or surgical revascularization and the assessment of are bifurcation lesions and total coronary occlusions are listed in Table 4 and Fig. 4. Restenosis may develop following coronary interventions using metallic stents, resorbable scaffolds or drug eluting balloons. For the evaluation of in-stent restenosis (ISR), CCTA has a high negative predictive value but moderate positive predictive value.,*[emphasis added]

*negative predictive value vs positive predictive value

Although CCTA is not widely recommended for clinical assessment of in-stent restenosis, quantitative CCTA has been used for longitudinal follow-up of radiolucent bio-resorbable scaffolds without a metal platform (Figs. 4 and 5)., The accuracy of CCTA for detecting bypass graft disease is very good, and excellent for complete graft occlusion.– Clinical trials that applied CCTA to assess interventions to prevent graft failure generally considered complete graft occlusion as the primary endpoint, and reported excellent diagnostic utility of CCTA.– CCTA can evaluate coronary bifurcations in terms of plaque, stenosis and the angles between the bifurcation branches (Fig. 4).– CCTA can identify characteristics of (chronic) total coronary occlusions (CTO), defined by the complete absence of lumen opacification, with modest to excellent reproducibility (Fig. 4)., Apart from single CTO features derived from CCTA, combined CT scoring systems (e.g. CT-RECTOR and KCCT scores) have been developed to predict time-efficiency of CTO percutaneous recanalization and thus to grade the CTO difficulty level prior to percutaneous coronary intervention.–

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