CAD-RADS

Coronary Artery Disease-Reporting and Data System

Csilla Celeng, Richard Takx, Robin Smithuis and Tim Leiner

Radiology Department University Medical Center Utrecht and the Alrijne hospital in Leiderdorp, The Netherlands

CAD-RADS is the Coronary Artery Disease-Reporting and Data System.

It was published in 2016 by the Society of Cardiovascular Computed Tomography (SCCT), the American College of Radiology (ACR) and the North American Society for Cardiovascular Imaging (NASCI) (1) and it has been endorsed by the American College of Cardiology (ACC).

CAD-RADS is developed to standardize reporting of coronary CTA, to improve communication and to guide therapy. 

Understanding Chest pain

Cardiac chest pain can be categorized into stable angina, unstable angina, non-ST-elevation myocardial infarction (NSTEMI) and ST-elevation myocardial infarction (STEMI) (2,3).

The latter three are called acute coronary syndromes.

Stable angina

Stable angina is characterized by exertional chest pain induced by exercise, stress or emotion.
It is a mismatch between myocardial oxygen demand and supply due to the presence of atherosclerosis, microvascular dysfunction or spasm.
This type of angina is relieved by rest or administration of nitroglycerin.
The troponin-levels are normal.

Unstable angina

Unstable angina (UAP) is defined as chest pain which occurs at rest or minimal exertion and is characterized by the absence of cardiomyocyte necrosis and normal troponin-levels (3).
UAP is  caused by plaque rupture with thrombus formation causing partial occlusion of the affected vessel. 

NSTEMI

NSTEMI or non-ST-elevation myocardial infarction is the result of plaque rupture and thrombus formation which causes partial occlusion and subendocardial infarction with elevated troponin-levels.
The ECG can be normal, or abnormal with inverted-T or ST-depression.

STEMI

STEMI or ST-elevation myocardial infarction is characterized by complete occlusion of the lumen leading to transmural infarction with elevated troponin-levels.
The ECG is abnormal with ST-elevation or a hyperacute T-wave.

Target population for coronary CTA

Click to enlarge

According to the new guidelines of the European Society of Cardiology non invasive imaging (including CTA) can be used in all patients with pre-test probability of >15% (4). The pre-test probability is based on the age and gender of the patient combined with the type of complaints: typical angina, atypical angina or non-specific chest pain (Table). 

  • Typical angina is: 
    • substernal chest discomfort of characteristic quality and duration
    • provoked by exertion or emotional stress
    • relieved by nitrates or rest within minutes. 
  • Atypical angina meets two of the before mentioned criteria.
  • Non-specific angina lacks these criteria or meets only one.


CAD-RADS

Quantitative assessment of stenosis degree

CAD-RADS categories of the different coronary segments are based on the SCCT stenosis grading and coronary segmentation diagram  (15).
All coronary arteries >1.5 mm diameter are graded for stenosis severity and the clinically most relevant stenosis has to be documented.  

The degree of stenosis is determined by eyeballing.

CAD-RADS 1 category also includes the presence of positive remodeling and no stenosis.

CAD-RADS 4 category is divided into two subcategories: 

  • 4A = single or two-vessels with severe (70-99%) stenosis
  • 4B = in the left main > 50% stenosis or three-vessel > 70% stenosis. 

In patients with CADRADS 4A the next step can be ICA or functional assessment.
In patients with CADRADS 4B  ICA is recommended. 

Click here to go to case 1 for an example of quantitative assessment of stenosis degree.

Society of Cardiovascular Computed Tomography (SCCT) coronary segmentation diagram (15). Click to enlarge.

This diagram of the Society of Cardiovascular Computed Tomography is used to indicate where the stenoses are located.

 LM: left main

LAD: left anterior descending artery 
D1: diagonal 1 
D2: diagonal 2 

LCX: circumflex artery
OM1: obtuse marginal 1
OM2: obtuse marginal 2
L-PDA: PDA from LCX
PLB: posterolateral branch; L-PLB: PLB from LCX. 

RCA: right coronary artery;
PDA: posterior descending artery
R-PDA: PDA from RCA 
PLB: posterolateral branch; R-PLB: PLB from RCA; L-PLB: PLB from LCX.

Dashed lines represent the division between LM, LAD and LCX as well as the proximal, mid and distal segments of LAD, LCX and RCA.

CAD-RADS Modifiers

There are 4 modifiers that can be added to the CAD-RADS category:

  • N: indicates that a study is non-diagnostic
  • S: presence of stents
  • G: coronary artery bypass grafts
  • V: vulnerable plaque

A modifier is named after the highest stenosis degree with the use of symbol  “/” (slash).
For instance CAD-RADS 3/S. 

CAD-RADS N: Stair-step artefact (large arrow) in combination with mild stenosis in proximal RCA (small arrows).

Modifier N - nondiagnostic

If not all segments >1.5 mm diameter are diagnostic, then the highest stenosis degree should be listed in addition to modifier N.
For example, a patient with moderate (50-69%) stenosis and one or more non-diagnostic segments should be graded as CAD-RADS 3/N. 

However, a patient with no (0%), minimal (< 25%) or mild (25-49%) stenosis and one or more non-diagnostic segments should be graded as CAD-RADS N (no stenosis grade should be listed), since coronary CTA is not able to guide patient management.
An additional test might be needed to exclude obstructive CAD. 

Study the image.
How would you classify?

There is a mild stenosis (25-49%) in the proximal RCA, classifies as CAD-RADS 2
There is also a stair-step artifact (N). 
Study is classified as CAD-RADS N.

Stent in the mid LAD with minimal in-stent restenosis.

Modifier S - stent

The presence of a stent is indicated by modifier “S”.

Examples:

  • If a patient has a stent, showing no in-stent restenosis and a mild (25-49%) stenosis in the coronaries, this patient is classifies as CAD-RADS 2/S. 
  • Similarly, a patient with no in-stent restenosis but severe (70-99%) stenosis in a coronary other than LM classifies as CAD-RADS 4A/S.
  • If there is a severe (70-99%) in-stent restenosis in a coronary other than LM, this patient would classifies as CAD-RADS 4A/S. 
  • If the stent is non-diagnostic and there is no ≥ 49 % stenosis present in the coronaries, the patient classifies as CAD-RADS N/S. 


Note: the location of the stenosis does not matter, when using CAD-RADS.
What matters is that the patient has a severe stenosis and needs further management.  

Go to case 2 for an example of modifier S.

A. example of LIMA-LAD without stenosis. B.example of SVG to posterior descending artery also with no stenosis in the graft. NB: there is a severe stenosis distal to the SVG, which is the bypassed stenosis and as of that is not considered for CAD-RADS classification.

Modifier G - graft

The presence of coronary artery bypass grafts is indicated by modifier “G”.
A bypassed stenosis is not considered for CAD-RADS classification. 

Examples: 

  • If a patient has a patent LIMA-LAD graft (left internal mammary artery graft to left anterior descending artery) with no stenosis in the graft but there is a mild (25-49%) stenosis in the coronaries- in addition to the “expected” LAD bypassed stenosis - this patient classifies as CAD-RADS 2/G. 
  • If a patient has an occluded LIMA-LAD graft, a patent SVG (saphenous vein graft) to the RCA and a severe (70-99%) stenosis in the coronaries, this patient would classify as CAD-RADS 5/G (the highest stenosis is graded).  

Note: the location of the stenosis does not matter, when using CAD-RADS.
What matters is that the patient has an occlusion and needs further management.  

Modifier V - vulnerable plaque

The presence of vulnerable plaque feature is indicated by modifier “V”.
Vulnerable plaque features include: low-attenuation plaque, positive remodeling, spotty calcification and napkin-ring sign. 

There are three plaque types on coronary CTA: 

  • calcified
  • partially calcified
  • non-calcified

Calcified plaque is an atherosclerotic plaque in which the entire plaque appears as calcium density (>130 HU on non-enhanced CT).
The previous terminology “hard plaque” is not recommended. 

Partially calcified plaque is an atherosclerotic lesion with 2 components of which one is calcification.
The previous term was “mixed plaque”, which is no longer recommended.

Non-calcified plaque is a plaque with no calcium content.
The use of “soft-plaque”, “low-density plaque” and “fibrous plaque” should be avoided (16). 

CTA features of stable and vulnerable plaque

The morphology of vulnerable plaques that lead to acute coronary syndrome differs from stable plaques.

Stable plaques
On histology stable plaques are characterized by large calcifications, fibrotic tissue and smaller lipid pools.

Vulnerable plaques
In contrary vulnerable plaques can contain spotty calcifications, large-lipid pool (necrotic core), which is covered by a thin fibrous cap.
These plaques are sometimes referred to as thin-cap fibroatheroma (TCFA).
Some features of vulnerable plaque can be identified by CTA. 

Low-attenuation plaque (HU=14) with severe (70-99%) stenosis in the LAD.

Low-attenuation plaque

Lesions associated with plaque rupture frequently have a large lipid rich core. Lipid on CT appears as low attenuation. Plaques with <30 HU on CTA were found to be present significantly more often in patients with acute coronary syndrome (17). 

Positive remodeling

Positive remodeling is defined as a compensatory outward enlargement of the vessel wall at the site of the atherosclerotic lesion with the preservation of the coronary lumen (18).
On histology plaques with positive remodeling show a higher lipid content and abundance of macrophages (19).
Patients with positive remodeled plaques can present with an acute coronary syndrome without any prior cardiac history. 

An example of positive remodeling of a non-calcified plaque in the mid RCA.
There is outward growth of the plaque with minimal stenosis of the lumen. 

Another example of positive remodeling of a calcified plaque in the proximal LAD.
Again, the plaque is outward from the lumen causing no stenosis in the LAD. 

Spotty calcification in the LAD and D1.

Spotty calcification

Spotty calcifications are usually defined as calcifications < 3 mm (17).
Another classification further differentiates spotty calcification into small (< 1 mm), intermediate (1-3 mm) and large (> 3 mm) calcifications. 

Small spotty calcifications on CTA are associated with high-risk plaques (20).

A: On the coronal image the so-called napkin-ring sign (dark area adjacent to the lumen, surrounded by a higher “ring-like” attenuation (white arrows). B: Tissue characterization on CT by HU number

Napkin-ring sign

The Napkin-ring sign is a qualitative high-risk plaque feature on CTA.
It is defined as a central low-attenuation area adjacent to the coronary lumen and a higher “ring-like” attenuation tissue surrounding this central area (21).
On histology the area of low-attenuation corresponds to the large necrotic core, while the “ring-like” outer area correlates with fibrous plaque tissue.
The Napkin-ring sign is strongly associated with major adverse cardiovascular events (22). 

Click here to go to case 4.

Coronary CTA protocol

Example of a CTA scan performed on the same scanner in the same patient without (A) and with (B) administration of nitroglycerin, showing the increased diameter of the LAD. Due to the vasodilatory effect nitroglycerine increases the number of assessable (>1.5 mm diameter) segments.

Coronary CTA basics are:

  • Administration of betablockers - if the heart rate > 65 BPM 
  • Administration of nitroglycerine 
  • Prospective ECG-gating (or retrospectively gated helical mode). 
  • Calcium score reported in the form of Agatston score 
  • Post-processing: axial image review, multiplanar reformation and maximum intensity projection. 
  • Optional image review: curved multiplanar reformation and volume rendered reconstruction.  

Extra cardiac findings

Of patients presenting with acute chest pain 5-10% suffer from STEMI, 15-20% from NSTEMI, 10% from UAP, 15% from other cardiac conditions and in the remaining approximately 50% non-cardiac diseases are the underlying cause (23,24).
Non-cardiac conditions include acute aortic syndrome (e.g. dissection, rupture, ulcer), pulmonary embolism, pericarditis, or other intra-thoracic pathologies.
For these conditions the use of double or triple-rule-out CTA could provide an alternative explanation for the symptoms. 

Examples

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case 1 - CAD-RADS 2

First, scroll through the scan.
Not all images are included. Some images without any abnormalities are skipped from the series.

How would you describe the findings on the coronary CTA?


The findings are:

  1. Agatston score of this patient was 14. Please, also note the calcification of the aortic valve.
  2. Some partially calcified and calcified plaques are present in the LAD with mild stenosis (25-49%). 
  3. Calcified-plaque in the LCX causing minimal stenosis (<25%).
  4. Non-calcified plaque in the distal RCA causing minimal stenosis (<25%).
  5. This patient classifies as CAD-RADS 2, which means no further workup is needed.  

Go back to article

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case 2 - CAD-RADS 5S

First, scroll through the CTA images. 
How would you describe the findings on the coronary CTA?

The findings are:

  1. Stent in the mid LAD with low-attenuation within the stent suggestive of minimal in-stent restenosis (<25 %). Notice bridging on a short segment in the distal LAD.
  2. Non-calcified plaque in the LCX causing mild stenosis (25-49%). 
  3. Occlusion of the proximal OM1 branch with distal filling.
  4. Calcified plaque and non-calcified plaques in the RCA causing mild (25-49%) stenosis. 

Due to the occlusion of OM1 branch and presence of the stent, this case reads as CAD-RADS 5S, which means that this patient needs further diagnostic workup. 

Back to the article

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case 3 - Calcium score 0 and severe stenoses.

First, scroll through the CTA images. 
How would you describe the findings on the coronary CTA?


The findings are: 

  1. The total calcium score of 0 indicates the absence of calcified plaque in the coronary tree. 
  2. Severe stenosis (70-99%) in the mid LAD and D2 branch.

Continue with the next images of the same patient.

Same patient. First, study the CTA image. 
How would you describe the findings?

The coronal image shows a central low-attenuation area around the lumen of the LAD. This low-attenuation area is surrounded by a higher attenuation area. This phenomenon is the earlier discussed napkin-ring sign, which is a high-risk plaque feature. This patient classifies as CAD-RADS 4A/V.

Continue with the next images of the same patient.

Same patient.

Double-oblique (A) and volume-rendered (B) images of the LAD showing the location and the length of the plaque.
Also, D2 can be appreciated on the volume rendered reconstruction.
Due to the degree of stenosis and the presence of napkin-ring sign (visible on axial images) this patient underwent ICA where the presence of severe stenosis was confirmed. 

Continue with next images.

A: ICA correlates with CTA and shows an 80% stenosis in the mid LAD (white arrows) and a 60% stenosis in the D2 branch (black arrows). The D2 stenosis was overestimated on CTA. 

B: PCI was performed during which a drug eluting stent (DES) was implanted (white arrows). 

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case 4 - CAD-RADS 3 with thrombus in left ventricle

First, scroll through the CTA images.
How would you describe the findings on the coronary CTA?

The findings are: 

  1. Moderate (50-69%) stenosis in the proximal LAD caused by a non-calcified plaque. 
  2. Variant of sinoatrial (SA) nodal artery. The artery usually arises from the RCA as a second branch after the conus artery, however in this case it arises from the LCX, courses behind the aorta, anastomosing with the right atrium and with a small branch supplies the SA-node of the heart.   
  3. Thrombus in the apex of the left ventricle. 

This patient classifies as CAD-RADS 3, which means this patient requires further investigation. 

Continue with the next images of the same patient.

Same patient.

A: Curved MPR of the LAD with non-calcified plaque causing moderate (50-69%) stenosis. 

B: The so-called “spider-view” (LAO Caudal) of the heart with a 70% stenosis in the proximal LAD. Note the presence of SA nodal artery arising from the proximal LCX and coursing to posterior direction. 

C: A drug eluting stent was implanted into the proximal LAD with good results. 

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case 5 - CTA overestimates stenosis due to calcium

First, scroll through the CTA images. 
How would you describe the findings on the coronary CTA?

Continue with the next images of the same patient.

Curved MPR images of the coronary arteries.

The findings are:

  1. Long, partially calcified plaque in the LM-LAD causing moderate stenosis (50-69%) (white arrows).
    This segment of the LAD is difficult to evaluate because of blooming and step artefacts. 
  2. Calcified plaque in the D1 causing severe stenosis (70-99%) at the origin (white arrows). 
  3. Partially calcified plaque proximal from the LCX stent with moderate (50-69%) stenosis (white arrow).
    LCX stent patent, no stenosis (black arrows). 
  4. Calcified plaques in the proximal RCA with minimal stenosis (<25%) (white arrows).
    RCA stent patent (black arrows).
    Non-calcified plaque distal to the stent causing minimal stenosis (white arrowheads).
    Another non-calcified plaque in the distal RCA causing minimal stenosis (<25%) (white arrows).
    Partially calcified plaque distal RCA with mild stenosis (25-49%) (two white half-arrows).


Due to severe stenosis in D1 and because of some non-diagnostic segments this patient classifies as CAD-RADS 4A/N, which means that this patient needs further workup.

The ICA shows some wall irregularities to a maximum of 30% stenosis in the proximal LAD.
The D1 shows 50% stenosis at the origin (black arrows). The LCX shows some wall irregularities with no stenosis in the stent.
The RCA shows minimal wall irregularities, no in-stent restenosis.
This case also shows that CTA is limited in case of calcium and it can overestimate the actual luminal stenosis. 

Continue with the next images of the same patient.

Myocardial SPECT attenuation corrected (AC) images during stress showing no perfusion defect. A: apex to base; B: septum to lateral wall; C: inferior to anterior

Shortly after the PCI the patient was again admitted with symptoms of atypical angina.
SPECT was performed to exclude the presence of ischemia, which showed no perfusion defect in the left ventricle.
The patient was treated with optimal medical care and no intervention was performed. 

  1. Task Force M, Montalescot G, Sechtem U et al. 2013 ESC guidelines on the management of stable coronary artery disease: the Task Force on the management of stable coronary artery disease of the European Society of Cardiology. Eur Heart J 2013;34:2949-3003

  2. Roffi M, Patrono C, Collet JP et al. 2015 ESC Guidelines for the Management of Acute Coronary Syndromes in Patients Presenting Without Persistent ST-segment Elevation. Rev Esp Cardiol (Engl Ed) 2015;68:1125.

  3. Knuuti J, Wijns W, Saraste A, Capodanno D, Barbato E, Funck-Brentano C, et al. 2019 ESC Guidelines for the diagnosis and management of chronic coronary syndromes. Eur Heart J. 2019.

  4. Leipsic J, Abbara S, Achenbach S, Cury R, Earls JP, Mancini GJ, et al. SCCT guidelines for the interpretation and reporting of coronary CT angiography: a report of the Society of Cardiovascular Computed Tomography Guidelines Committee. J Cardiovasc Comput Tomogr. 2014;8(5):342-58.

  5. Weigold WG, Abbara S, Achenbach S et al. Standardized medical terminology for cardiac computed tomography: a report of the Society of Cardiovascular Computed Tomography. J Cardiovasc Comput Tomogr 2011;5:136-44.

  6. Motoyama S, Kondo T, Sarai M et al. Multislice computed tomographic characteristics of coronary lesions in acute coronary syndromes. J Am Coll Cardiol 2007;50:319-26.

  7. Glagov S, Weisenberg E, Zarins CK, Stankunavicius R, Kolettis GJ. Compensatory enlargement of human atherosclerotic coronary arteries. N Engl J Med 1987;316:1371-5.

  8. Varnava AM, Mills PG, Davies MJ. Relationship between coronary artery remodeling and plaque vulnerability. Circulation 2002;105:939-43.

  9. van Velzen JE, de Graaf FR, de Graaf MA et al. Comprehensive assessment of spotty calcifications on computed tomography angiography: comparison to plaque characteristics on intravascular ultrasound with radiofrequency backscatter analysis. J Nucl Cardiol 2011;18:893-903.

  10. Maurovich-Horvat P, Hoffmann U, Vorpahl M, Nakano M, Virmani R, Alkadhi H. The napkin-ring sign: CT signature of high-risk coronary plaques? JACC Cardiovasc Imaging 2010;3:440-4.

  11. Nerlekar N, Ha FJ, Cheshire C et al. Computed Tomographic Coronary Angiography-Derived Plaque Characteristics Predict Major Adverse Cardiovascular Events: A Systematic Review and Meta-Analysis. Circ Cardiovasc Imaging 2018;11:e006973.