The CAD-RADS classification is based on the degree of stenosis, as determined by the Society of Cardiovascular Computed Tomography (SCCT) system,⁸ having five categories, ranging from absence of atherosclerosis (CAD-RADS 0) to the presence of at least one total occlusion (CAD-RADS 5) for vessels larger than 1.5 mm in diameter. The 2022 update added the grading of plaque burden through P categories (Table 1), depending on the coronary calcium score, or the degree and number of segments affected by atherosclerosis.⁶ There was also the inclusion of ischemia findings by FFR (fractional flow reserve) or myocardial perfusion tomography, which is scored as positive, negative, or indeterminate. Another update of the 2022 version was the inclusion of coronary abnormalities unrelated to atherosclerosis, considered in the “E” (Exceptions) modifier.⁶

Table 1

	Overall Coronary Plaque Burden	Calcium Score	Involved Segment Score	Visual
P1	Mild	1-100	≤ 2	1-2 vessels with low plaque burden
P2	Moderate	101-300	3-4	1-2 vessels with moderate involvement or 3 vessels with low plaque burden
P3	Severe	301-999	5-7	3 vessels with moderate plaque burden or 1 vessel with high plaque burden
P4	Extensive	> 1000	≥ 8	2 or 3 vessels with high plaque burden

Source: Modified from Radiology: Cardiothoracic Imaging 2022; 4(5):e220183

Tables 2 and 3 show the evaluation of findings by the CAD-RADS classification in scenarios of stable (Table 2) or acute (Table 3) chest pain, with their specific management suggestions, which involve the need for complementary methods or specific treatments. Thus, the CAD-RADS category, along with its modifiers (as shown in Figures 1 to 8), can be included at the end of the report as complementary information to the diagnostic impression, which remains essential, as it includes critical details for clinical decision-making, such as vessel caliber, the location and extent of stenosis, and other relevant data not covered by the CAD-RADS system.

Table 2

Category	Degree of Stenosis	Interpretation	Further Investigation	Management Considerations
CAD-RADS 0	0% (absence of plaque or stenosis)	Absence of CAD	None	Reassure. Consider non-atherosclerotic causes for symptom
CAD-RADS 1	1-24% (minimal stenosis or stenosis-free plaque)	Minor non-obstructive CAD	None	Consider the non-atherosclerotic cause of symptom P1: Consider risk factor modification and preventive drug therapy P2: Risk factor modification and preventive drug therapy P3 or P4: Risk factor modification and aggressive preventive drug therapy
CAD-RADS 2	25-49% (Mild stenosis)	Mild non-obstructive CAD	None	Consider non-atherosclerotic causes for symptom P1 or P2: Risk factor modification and preventive drug therapy P3 or P4: Risk factor modification and aggressive preventive drug therapy
CAD-RADS 3	50-69% (Moderate stenosis)	Moderate stenosis	Consider functional testing	P1, P2, P3 or P4: Risk factor modification and aggressive preventive drug therapy Other treatments should be considered according to specific guidelines (including antianginals) I+: consider coronary angiography, especially if optimized therapy
CAD-RADS 4	A: 70-99% or B: LMCA ≥ 50% or 3 vessels ≥ 70%	Significant stenosis	A: Consider coronary angiography or functional testing B: Coronary angiography recommended	P1, P2, P3 or P4: Risk factor modification and aggressive preventive drug therapy Other treatments should be considered according to specific guidelines (including antianginals and revascularization options)
CAD-RADS 5	100% (total occlusion)	Total or subtotal occlusion	Consider coronary angiography, functional testing, or viability assessment	P1, P2, P3 or P4: Risk factor modification and aggressive preventive drug therapy Other treatments should be considered according to specific guidelines (including antianginals)
CAD-RADS N	Nondiagnostic	Obstructive CAD cannot be excluded	Additional evaluation may be necessary

CAD: coronary artery disease; CAD-RADS: Coronary Artery Disease-Reporting and Data System. Source: Modified from Radiology: Cardiothoracic Imaging 2022; 4(5):e220183

Table 3

Category	Degree of Stenosis	Interpretation	Additional Cardiac Investigation	Management Considerations
CAD-RADS 0	0%	ACS very unlikely	None If troponin (+), consider other causes	Reassure
CAD-RADS 1	1-24%	ACS unlikely	None If troponin (+), consider other causes	P1 or P2: refer for risk factor follow-up and preventive drug therapy P3 or P4: refer for risk factor follow-up and aggressive preventive drug therapy
CAD-RADS 2	25-49%	ACS somewhat unlikely	None If troponin (+), high suspicion or risk factors, consider hospital admission and cardiologist evaluation	P1 or P2: refer for risk factor follow-up and preventive drug therapy P3 or P4: refer for risk factor follow-up and aggressive preventive drug therapy
CAD-RADS 3	50-69%	ACS possible	Consider hospital admission and cardiologist evaluation Consider functional testing	P1, P2, P3 or P4: Preventive treatment, including aggressive preventive drug therapy. Other treatments should be considered, including anti-anginal drugs according to specific guidelines. I+: Consider coronary angiography
	A: 70-99%		Hospital admission with cardiologist evaluation	P1, P2, P3 or P4: Preventive treatment, including aggressive preventive drug therapy. Other treatments should be considered, including anti-anginal drugs and revascularization options according to specific guidelines.
	or
CAD-RADS 4	B: LMCA ≥ 50%	ACS likely	A: Consider coronary angiography or functional testing
	or
	3 vessels ≥ 70%		A: Consider coronary angiography or functional testing
CAD-RADS 5	100% (total occlusion)	ACS very likely	Hospital admission with cardiologist evaluation Urgent coronary angiography and revascularization if acute occlusion is suspected	P1, P2, P3 or P4: Preventive treatment, including aggressive preventive drug therapy. Other treatments should be considered, including anti-anginal drugs and revascularization options according to specific guidelines.
CAD-RADS N	Nondiagnostic	ACS cannot be excluded	Additional evaluation may be necessary

ACS: acute coronary syndrome; CAD-RADS: Coronary Artery Disease-Reporting and Data System; LMCA: left main coronary artery. Source: Modified from Radiology: Cardiothoracic Imaging 2022; 4(5):e220183

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modifiers can supplement the CAD-RADS categories for cases in which technical limitations make the study non-diagnostic (N), in the presence of a stent (S), a graft (G), signs of plaque vulnerability (HRP - high-risk plaque), ischemia (I), and exceptions (E). When there is more than one modifier, a slash (“/”) is used between the letters, in the following order:

To be used when at least one segment (with a caliber equal to or greater than 1.5 mm) cannot be reliably evaluated. It can be applied as a category or as a modifier depending on the degree of stenosis in the other segments. In the context of at least moderate stenosis (≥50%) in some other segment, the “N” flag should be used as a modifier (e.g., CAD-RADS 3/P2/N), since the recommendations for anti-ischemic therapy and prevention apply, regardless of any additional studies that may be necessary. In the scenario where other segments have at most mild stenosis, it should be included as a category and precede the P category (e.g., CAD-RADS N).

In addition to the degree of stenosis, some imaging characteristics are associated with a higher risk of plaque instability and progression to acute coronary syndrome. The positive remodeling, presence of plaque with attenuation below 30 HU, eccentric spotty calcification and the napkin ring sign stands out in Figure 9.^9,10 Therefore, the HRP modifier should be included in the report when two or more high-risk characteristics are present, and these features should be detailed within the report body. Additionally, the presence of this modifier should lead to more aggressive risk factor management in cases of stable chest pain, or hospital admission and extended observation in cases of acute chest pain, as it is linked to a higher incidence of serious cardiovascular events.

Figure 9

Initially, CCTA only provided anatomical information with the assessment of luminal stenosis and atherosclerotic burden. With a growing understanding of the importance of coronary disease physiology and the development of techniques enabling functional assessment through tomography, CAD-RADS was expanded to include the categorization of ischemia in cases involving FFR-CT and stress perfusion. In cases in which FFR-CT and myocardial perfusion tomography are nondiagnostic, modifier N can also be applied.

FFR-CT was introduced as a non-invasive method to assess pressure in the coronary tree using machine learning techniques and fluid dynamics analysis, with similar accuracy to invasive FFR (via catheterization).¹¹ It is recommended in cases of stenosis between 50-90%, particularly in CAD-RADS 3 and 4A, or in cases of CAD-RADS 2 with proximal lesions and the presence of high-risk features (HRP), being considered positive with values ≤ 0.75, when complementation with coronary angiography is considered in the appropriate clinical context. FFR-CT > 0.8 is considered negative (Figure 10), with no need for complementation with coronary catheterization. Values between 0.76 and 0.80 are considered indeterminate and require additional assessment of the lesion site, symptoms and the translesional gradient between 1-2 cm proximal and 1-2 cm distal to the stenosis (significant when ≥ 0.12), when invasive coronary angiography is suggested.^6,12,13

Figure 10

In the context of acute, stable chest pain, several studies have validated myocardial perfusion computed tomography compared with myocardial scintigraphy, cardiac perfusion magnetic resonance imaging, invasive coronary angiography, invasive FFR, and cardiac biomarkers. Its complementary use to CCTA has better diagnostic accuracy in patients at intermediate to high risk. It allows the detection of hemodynamically significant lesions by identifying areas of reversible myocardial ischemia. It also allows ischemia to be ruled out in stenotic lesions between 50-69% and lesions above 70% densely calcified, eliminating the need for additional complementary exams.^6,14,15 It may also identify a fixed perfusion defect, suggesting a previous myocardial infarction; however, this finding should be described within the body of the report, rather than labeled as modifier I. Positive ischemia (I+) refers to cases where there is a reversible perfusion alteration between stress and rest (figure 11) or in cases of peri-infarction ischemia, where the perfusion defect during the stress phase is larger compared to the at rest phase. Negative ischemia (I-) is defined by either the absence of perfusion changes or a fixed/non-reversible perfusion defect, which may indicate myocardial infarction and/or fibrosis without evidence of ischemia. Doubtful cases are classified as indeterminate (I+/-).

Figure 11

Indicates the presence of at least one stent, as an independent indicator. In this context, the modifier does not specify whether the stenosis is related to the same vessel as the stent (Figure 12). For instance, significant stenosis in the left main coronary artery (LMCA), along with a stent in the right coronary artery that shows no signs of restenosis, is classified as CAD-RADS 4B/P3/S. If the evaluation of the stent’s lumen is compromised but there are no stenoses greater than 50%, the suggested CAD-RADS classification is N/S.

Figure 12

Indicates the presence of at least one myocardial revascularization graft. In this scenario, it is worth noting that any stenoses in the segment transposed by the bypass should be excluded from the CAD-RADS analysis (Figure 13), considering the lumen of the graft for interpretation purposes. For example, in the case of a graft in the left anterior descending artery (LAD) with no evidence of stenosis greater than 50% — whether in the graft itself, the anastomosis, the distal native bed, or other coronary segments — the classification would be CAD-RADS 2/P2/G, even if there is significant stenosis in the crossed LAD segment. The evaluation of the graft lumen follows the same rationale as for the other segments.

Figure 13

The CAD-RADS classification is not typically applied to non-atherosclerotic coronary abnormalities, such as origin or course anomalies, aneurysms or pseudoaneurysms, vasculitis, dissections, fistulas, extrinsic compression, and others (Figure 14). Although these causes of coronary obstruction are much less common, they remain important differential diagnoses that require specific approaches. Modifier E is designated for these cases, indicating that the CAD-RADS classification and its usual clinical recommendations do not encompass all coronary abnormalities.

Figure 14

Example 1: Absence of obstructive lesions, moderate plaque burden, stent with limited luminal assessment. Classification: CAD-RADS N / P2 / S.

Example 2: Diffuse moderate stenoses, severe plaque burden, high-risk features and presence of stent. Classification: CAD-RADS 3 / P3 / HRP / S.

Example 3: Limited luminal assessment, severe plaque burden, presence of stent and myocardial graft. Classification: CAD-RADS N / P3 / S / G.

Example 4: Significant stenosis in proximal LAD, mild stenoses in RCA and Cx, extensive plaque burden, left internal mammary graft for LAD. Classification: CAD-RADS 2 / P4 / G.

Example 5: Significant stenosis in proximal LAD and limited luminal assessment of mid-RCA, severe plaque burden. Classification: CAD-RADS 4A / P3 / N.

Example 6: Moderate stenosis in mid-LAD, severe plaque burden, FFR-CT < 0.75. Classification: CAD-RADS 3 / P3 / I+.

Example 7: Significant stenosis in distal LAD, moderate plaque burden, absence of reversible ischemia on myocardial perfusion CT. Classification: CAD-RADS 4A / P2 / I-.