CCTA Glossary: coronary CT angiography terms

A–Z index

Absent left main coronary artery absent LM

There is no left main when the LAD and the LCx each leave the left coronary sinus through their own ostium, with no trunk joining them.

Acute marginal branch AM · no number

The acute marginal is the RCA branch you find at the acute margin of the right ventricle.

Agatston score CAC

The Agatston score is the calcium number from the non-contrast, ECG-gated scan, acquired before the angiogram with the standard protocol of 120 kVp and 3 mm slices.

Anomalous origin of a coronary artery AAOCA · ALCAPA · ARCAPA

A coronary artery has an anomalous origin when it arises outside its usual site.

Arterial graft (internal mammary and radial artery) LIMA

An arterial graft uses one of the patient's own arteries as the conduit.

Assignment of disease at segment intersections and bifurcations

A focal lesion sitting right where two segments meet, bifurcations included, goes to the preceding segment: the more proximal one in the direction of flow.

Atherosclerotic plaque

Plaque is tissue in the vessel wall, between the contrast-enhanced lumen and the outer vessel contour, that you can tell apart from both the lumen and the pericoronary fat.

Beam-hardening artifact

Low-attenuation areas or streaks appear next to metal, calcium or dense contrast and can mimic non-calcified plaque or a perfusion defect.

Blooming artifact

Dense calcium and stent struts look bigger than they are, so the lumen looks tighter than it is.

Bypassed native segment

A native segment is bypassed when it lies proximal to the distal anastomosis of a graft.

CAD-RADS 0 versus CAD-RADS 1

CAD-RADS 0 means a clean study: no plaque and no stenosis (0%).

CAD-RADS 2 and CAD-RADS 3

The line between them is 50%.

CAD-RADS 4A versus 4B 4A · 4B

CAD-RADS 4A is severe stenosis (70–99%) in one or two vessels.

CAD-RADS 5 (total occlusion)

CAD-RADS 5 means at least one coronary artery is totally occluded (100%).

CAD-RADS coding order and modifiers P · N · HRP · I · S · G · E

The code reads left to right in a fixed order: stenosis category, plaque burden (P), then the modifiers N, HRP, I, S, G and E, separated by slashes.

CAD-RADS in stable chest pain

No further cardiac testing is suggested for CAD-RADS 0–2; functional testing is considered for 3; invasive angiography is also considered for 4A and recommended for 4B.

Calcified plaque

A plaque is calcified when most of it is brighter than the contrast-filled lumen next to it.

Coronary artery aneurysm and ectasia

Both are an artery that is too wide; what separates them is how much of the vessel is involved.

Coronary artery fistula CAF

A coronary artery fistula connects a coronary artery with a cardiac chamber, the coronary sinus or a great vessel, bypassing the myocardial capillary bed.

Coronary dominance (right, left and codominant)

Dominance answers one question: which artery gives off the posterior descending artery? It is right if the PDA arises from the RCA (70–80%), left if it arises from the LCx (5–10%), and codominant if both contribute (10–20%).

Coronary vasculitis

Coronary vasculitis is inflammation of the wall of the coronary arteries.

Course of an anomalous coronary artery

The course tells you where the anomalous artery crosses the base of the heart on its way to its groove.

Diameter stenosis %DS

Diameter stenosis is how much narrower the lumen is at its tightest point than in a normal reference segment, expressed as a percentage.

Dual left anterior descending artery dual LAD · types I–IV

A dual LAD means two arteries share the LAD territory: a short one and a long one.

Eccentric and concentric

Eccentric plaque involves only part of the wall's circumference, and concentric plaque involves the entire circumference; neither term indicates the degree of stenosis.

Evaluable and nonevaluable stent

A stent is evaluable when you can see its lumen well enough to grade restenosis.

First and second diagonal branches D1 (9) · D2 (10)

D1 and D2 are the two largest diagonal branches crossing the anterolateral wall of the left ventricle.

First and second obtuse marginal branches OM1 (12) · OM2 (14)

The obtuse marginals are the LCx branches that cross the lateral wall of the left ventricle.

Graft stenosis and graft occlusion

Graft stenosis is graded exactly like native-vessel stenosis, and you say where it is: at an anastomosis or in the graft body.

High-risk anatomy of an anomalous coronary artery

These are the features that make an anomalous coronary artery a concern, because they are associated with ischemia: an interarterial course, an intramural segment, a slit-like orifice, an acute take-off angle, proximal narrowing and a high origin.

High-risk plaque HRP

A plaque is high-risk when that one plaque clearly shows at least two of four features: low attenuation, positive remodeling, spotty calcification and the napkin-ring sign.

Image noise

Noise is the grain you get when too few photons reach the detector.

In-stent restenosis ISR

In-stent restenosis is narrowing of the lumen inside a stent or at its edges.

In-stent total occlusion

A stent is totally occluded when a segment of its lumen shows no contrast at all.

Intramural course

The intramural segment is the proximal portion of an anomalous artery that runs within the aortic wall before separating from it.

Ischemia modifier with CT-derived fractional flow reserve I+ · I± · I−

CT-FFR calculates, from CCTA, the ratio between coronary and aortic pressure during simulated hyperemia. Measured 1 to 2 cm distal to the lesion, a value of 0.75 or less in a vessel large enough for PCI is I+, 0.76 to 0.80 is I±, and above 0.80 is I−.

Ischemia modifier with stress CT perfusion CTP

On stress CT perfusion, what counts is the difference between stress and rest.

Left main coronary artery LM · segment 5

The left main is the short trunk between the left coronary ostium and the point where it splits.

Lesion, segment and vessel

A lesion is a specific plaque and can involve more than one segment; a segment is the unit of the SCCT segment model, and a vessel is the artery made up of those segments.

Low-attenuation plaque

Low-attenuation plaque is non-calcified plaque whose inside measures less than 30 HU.

Maximum and minimum intensity projection MIP · MinIP

A maximum intensity projection (MIP) keeps, for each line of sight through a slab of the chosen thickness, only the voxel with the highest attenuation; a minimum intensity projection (MinIP) keeps the voxel with the lowest.

Minimum assessable vessel diameter ≥1.5 mm

You are expected to read every branch of 1.5 mm or more when the scan is of good quality, and every branch of 2.0 mm or more when quality is standard.

Misalignment (stair-step) artifact

It is a step: structures are abruptly offset at the boundary between slabs acquired in different heartbeats.

Modifier E (exceptions) E

Modifier E is how CAD-RADS 2.0 flags a coronary finding that is not atherosclerosis.

Modifier G (graft) G

G says there is at least one coronary artery bypass graft.

Modifier S (stent) S

S says there is at least one coronary stent anywhere in the coronary tree.

Motion artifact

Something moved during acquisition, and the vessel contours came out blurred.

Multiplanar and curved multiplanar reformat MPR · CPR

A multiplanar reformat (MPR) displays the acquired volume in any plane you choose.

Myocardial bridge depth, length and systolic compression

SCCT 2026 calls a bridge deep with 2 mm or more of overlying myocardium, very deep with 5 mm or more and long at 25 mm or more, and grades systolic compression with a 50% cutoff.

Myocardial bridging

A myocardial bridge is a stretch of epicardial artery that dives into the heart muscle and comes back out: the artery runs through a tunnel within the myocardium, and the muscle band covering it is the bridge.

Napkin-ring sign

The napkin-ring sign is a dark center with a brighter ring around it, seen on the cross-section of a non-calcified plaque.

Non-calcified plaque

Non-calcified plaque is plaque that stays darker than the contrast-filled lumen.

Non-interpretable (nondiagnostic) segment

It is a segment you cannot read with confidence because an artifact is in the way.

Nondiagnostic (N) category and modifier N

N means a segment of 1.5 mm or more cannot be interpreted with confidence.

Not assessed, nonevaluable and demonstrated absence

A finding is not assessed when it was not examined, nonevaluable when the images do not allow a confident assessment, and absent when it was looked for with adequate image quality and not found.

Obstructive and nonobstructive stenosis ≥50% · ≥70%

In CAD-RADS 2.0, which this glossary follows, a stenosis of 50% or more is obstructive and one below 50% is nonobstructive.

Ostial and juxta-ostial

“Ostial” means plaque involves the orifice where the vessel arises: that of the RCA or the left main at the aorta, or that of a branch at its parent vessel, such as the LAD ostium at the left main bifurcation.

Overall image quality

It is your one-line verdict on how far the whole study can be trusted.

Partially calcified plaque

A partially calcified plaque has a calcified and a non-calcified component in the same plaque.

Patent, no stenosis and no plaque

“Patent” means that the lumen opacifies; “no stenosis” means that it is not narrowed, although plaque may be present; and “no plaque” means that the wall has no plaque.

Per-patient CAD-RADS category CAD-RADS

CAD-RADS 2.0 gives each patient a single category, not one per vessel.

Plaque burden (P1–P4) P1–P4

Plaque burden answers one question: how much coronary plaque does this patient have overall, regardless of how tight the worst stenosis is? CAD-RADS 2.0 expresses it as P1 (mild), P2 (moderate), P3 (severe) or P4 (extensive), based on the SIS, the Agatston score or visual assessment.

Positive remodeling

Positive remodeling means the vessel has grown outward at the plaque: its outer diameter there is more than 10% larger than the reference diameter.

Proximal and distal anastomoses, and distal runoff

The proximal anastomosis joins the graft to its inflow vessel; the distal anastomosis joins it to the recipient coronary artery.

Proximal and distal left circumflex artery LCx · segments 11 and 13

The LCx has only two segments, and one landmark splits them: the origin of OM1.

Proximal, mid and distal left anterior descending artery LAD · segments 6, 7 and 8

The LAD has three segments, and landmarks set the boundaries, not thirds of length.

Proximal, mid and distal right coronary artery RCA · segments 1, 2 and 3

The RCA has three segments, and the acute margin of the right ventricle is the landmark that organizes them.

Ramus intermedius RI · segment 17

The ramus intermedius is the third vessel you get when the left main trifurcates instead of bifurcating.

Reference luminal diameter RLD

The reference luminal diameter is the lumen of a normal segment near the stenosis: proximal, distal, or the average of both.

Reporting a coronary stenosis

You describe each stenosis with three things: where it is, by anatomical name; what type of plaque causes it; and its grade, as a term with its range.

Right and left posterior descending arteries; right and left posterolateral branches R-PDA (4) · L-PDA (15) · R-PLB (16) · L-PLB (18)

These are the four posterior branches, and the vessel of origin gives each its name.

Saphenous vein graft SVG

A saphenous vein graft is a segment of the great saphenous vein used as a free graft from the ascending aorta to a coronary artery.

SCCT coronary artery segmentation model (18 segments)

It is the shared map for saying where a coronary lesion sits: 18 named segments.

Segment involvement score SIS

The SIS is a head count of coronary segments that have plaque: one point per segment, whatever the plaque’s composition or stenosis grade.

Serial stenoses and diffuse disease

Serial stenoses are two or more stenoses in the same vessel separated by normal lumen; in diffuse disease, plaque extends over a long length with no normal segment nearby.

Single coronary artery SCA · Lipton: R or L · I, II or III · A, B or P

In a single coronary artery, the entire coronary tree arises from a single aortic ostium and there is no second coronary ostium.

Spontaneous coronary artery dissection and intramural hematoma SCAD

Spontaneous coronary artery dissection is the acute formation of a false lumen within the wall of an epicardial coronary artery that is not caused by atherosclerosis, trauma or a coronary procedure.

Spotty calcification

Spotty calcification is a small fleck of calcium, less than 3 mm in diameter, inside a plaque.

Stenosis grading scale 0–5

SCCT 2026 and CAD-RADS 2.0 sort diameter stenosis into six grades: no visible stenosis (0%), minimal (1–24%), mild (25–49%), moderate (50–69%), severe (70–99%) and total occlusion (100%).

Suboptimal contrast enhancement

The contrast did not opacify the lumen well, so the artery shows low or uneven attenuation.

Total occlusion 100%

A total occlusion is a coronary segment with no luminal opacification at all, equivalent to 100% stenosis.

Visual estimation and quantitative measurement

In visual estimation, you assign the stenosis range by eye, comparing the lumen with the reference; quantitative measurement calculates the percentage from diameters or areas traced by software.