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Diagnosis of Coronary Stenosis with CT Angiography

Posted Feb 28, 2011 Updated Apr 10, 2023
By Ethan J. Halpern MD , David J. Halpern
7 min read

Rationale and Objectives

To compare computer-generated interpretation of coronary computed tomography angiography (cCTA) by commercially available COR Analyzer software with expert human interpretation.

Materials and Methods

This retrospective Health Insurance Portability and Accountability Act‑compliant study was approved by the institutional review board. Among 225 consecutive cCTA examinations, 207 were of adequate quality for automated evaluation. COR Analyzer interpretation was compared to human expert interpretation for detection of stenosis defined as ≥50% vessel diameter reduction in the left main, left anterior descending (LAD), circumflex (LCX), right coronary artery (RCA), or a branch vessel (diagonal, ramus, obtuse marginal, or posterior descending artery).

Results

Among 207 cases evaluated by COR Analyzer, human expert interpretation identified 48 patients with stenosis. COR Analyzer identified 44/48 patients (sensitivity 92%) with a specificity of 70%, a negative predictive value of 97% and a positive predictive value of 48%. COR Analyzer agreed with the expert interpretation in 75% of patients. With respect to individual segments, COR Analyzer detected 9/10 left main lesions, 33/34 LAD lesions, 14/15 LCX lesions, 27/31 RCA lesions, and 8/11 branch lesions. False-positive interpretations were localized to the left main (n = 16), LAD (n = 26), LCX (n = 21), RCA (n = 21), and branch vessels (n = 23), and were related predominantly to calcified vessels, blurred vessels, misidentification of vessels and myocardial bridges.

Conclusions

Automated computer interpretation of cCTA with COR Analyzer provides high negative predictive value for the diagnosis of coronary disease in major coronary arteries as well as first-order arterial branches. False-positive automated interpretations are related to anatomic and image quality considerations.

Although catheter angiography is the accepted “gold standard” for the diagnosis of coronary disease, a negative coronary computed tomography angiography (cCTA) study is sufficient to exclude obstructive coronary artery disease because of the high sensitivity and negative predictive value of cCTA . Several recent studies suggest that cCTA is a cost-effective examination for evaluation of low- to intermediate-risk patients with suspected acute coronary syndrome presenting to the emergency department . The diagnostic accuracy and reproducibility of interpretation for cCTA, however, is directly related to the experience of the interpreting physician . A major limitation of cCTA for evaluation of emergency room chest pain patients is the lack of available experienced readers, especially during night time and weekend hours.

The fundamental task required for the interpretation of coronary angiography is identification and quantification of stenosis within the coronary circulation. This task is facilitated by computer-aided vessel tracking and image reconstruction techniques available on CT workstations that improve visualization of the vascular lumen and assist the interpreting physician to quantify the degree of stenosis. The presence and degree of stenosis must be evaluated in the major coronary arteries—including the left main (LM) artery, left anterior descending (LAD) artery, left circumflex (LCX) artery, right coronary artery (RCA), posterior descending artery (PDA)—as well as the diagonal branches of the LAD (D1 and D2) and obtuse marginal branches of the LCX (OM1 and OM2). Because this task is well defined and quantitative, and because computer-aided techniques are currently used to facilitate human observers, it seems reasonable that this task may be amenable to automated computer diagnosis.

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Methods

Patient Selection

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Vessel Analysis Software

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cCTA Studies

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Figure 1, Moderate to severe stenosis (∼70% narrowing) at the origin of the first marginal branch of the circumflex artery identified by COR Analyzer but overlooked in the final clinical interpretation of the study. (a) Coronary tree created by COR Analyzer demonstrates all of the major coronary arteries. A site of stenosis is identified at the origin of the first obtuse marginal artery ( arrowhead ). (b) Slab maximum intensity projection (MIP) image demonstrates narrowing at the origin of the first obtuse marginal artery ( arrow ). (c) Tracked MIP of the first marginal artery again demonstrates the narrowing at the origin of this vessel ( arrow ).

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Results

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Table 1

Associated Findings in False-negative Cases

Left Main LAD LCX RCA Branch Vessels Stenosis close to 50% 1 1 3 Vessel misidentification 2 Left dominant coronary system (with small RCA <1.5 mm) 1 Small vessel (<1.5 mm) 1

LAD, left anterior descending artery; LCX, circumflex artery; RCA, right coronary artery.

Figure 2, Moderate lesions in the proximal left anterior descending (LAD) artery and at the origin of the first diagonal artery with a false negative COR Analyzer reading in the first diagonal branch. (a) Coronary tree demonstrates >50% stenosis in the proximal LAD ( arrowhead ), but the first diagonal artery was not identified in the coronary model created by COR Analyzer, and therefore the stenosis at the origin of D1 was not detected. (b) Tracked, curved maximum intensity projection (MIP) confirms areas of stenosis in the proximal LAD ( arrowhead ) as well as the origin of the first diagonal artery ( arrow ). (c) Slab MIP demonstrates the LAD ( arrowhead ) and D1 ( arrow ) stenoses in a different projection.

Figure 3, Right coronary artery (RCA) stenosis interpreted as >50% narrowing by the human expert reader, but not identified by COR Analyzer. (a) Coronary tree definition by COR Analyzer demonstrates all the major coronary vessels, including the RCA ( arrow ), but does not define a focal stenosis. (b) Vessel tracking with curved and straightened lumen maximum intensity projection (MIP) views demonstrates a focal area of >50% narrowing in the mid-distal RCA ( arrows ). (c) Slab MIP view demonstrates irregularity with mild narrowing in the mid RCA ( arrowheads ) as well as a focal narrowing in the mid-distal RCA interpreted by the human expert as >50% ( arrow ).

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Table 2

Associated Findings in False-positive Cases

Left Main LAD LCX RCA Branch Vessels Stenosis close to 50% 1 1 1 1 Vessel misidentification 1 1 4 1 10 Anomalous coronary artery 2 Left dominant coronary system (with small RCA <1.5 mm) 2 Small vessel (<1.5 mm) 2 4 Vascular calcification 11 15 7 5 5 Coronary stent 1 2 Blurred vessel 1 8 10 2 Streak from pacemaker wire 1 1 Poor contrast opacification 2 1 3 2 Myocardial bridging 6 1

LAD, left anterior descending artery; LCX, circumflex artery; RCA, right coronary artery.

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Figure 4, Diffusely calcified coronary tree with multivessel disease, but no significant narrowing diagnosed by the human expert reader. (a) Coronary tree demonstrates multiple vessels identified with >50% stenosis by COR Analyzer ( red overlay ). The proximal right coronary artery (RCA) ( arrow ) and proximal first diagonal artery ( arrowhead ) are illustrated in subsequent figure parts. (b) Curved maximum intensity projection (MIP) demonstrates a calcified segment of the proximal to mid-RCA ( between arrows ). The lumen is difficult to visualize under the calcifications. (c) Straightened lumen view suggests that the calcified plaques result in less than 50% diameter narrowing ( arrow ). (d) Tracked curved MIP of the first diagonal artery also demonstrates calcified plaque ( arrowhead ) with less than 50% luminal narrowing.

Figure 5, Patent coronary stents in calcified coronary arteries interpreted as areas of stenosis by COR Analyzer. (a) Areas of stenosis are identified by COR Analyzer in the right coronary artery (RCA) and left anterior descending (LAD) ( red overlays ). Stents in the RCA ( arrowhead ) are illustrated in subsequent figure parts. (b) Slab maximum intensity projection (MIP) in the left anterior oblique projection demonstrates patent RCA stents ( arrowheads ). (c) Orthogonal slab MIP again demonstrates the patent stents with linear beam hardening artifacts extending through the stents ( arrowheads ). (d) Straightened lumen view more clearly demonstrates that the stents ( arrowheads ) are patent.

Figure 6, Myocardial bridging of the left anterior descending (LAD) artery associated with a false positive interpretation of stenosis by COR Analyzer. (a) Coronary tree model created by COR Analyzer demonstrates a focal stenosis in the mid-LAD ( arrowhead ). No additional stenosis is identified. (b) Tracked curved maximum intensity projection (MIP) of the LAD demonstrates a myocardial bridge ( arrowhead ) with a very mild narrowing of the mid-LAD. (c) Coronary tree model created by COR Analyzer in another patient with a shorter segment myocardial bridge, suggesting a focal stenosis as the LAD dives into the bridge ( arrowhead ). MIP imaging demonstrated no stenosis.

Figure 7, Tortuous ramus intermedius branch with subtle myocardial bridge associated with a false positive interpretation of stenosis by COR Analyzer. (a) Coronary tree model created by COR Analyzer demonstrates a trifurcation of the left main coronary artery with a focal stenosis in the ramus intermedius ( arrow ). (b) Slab maximum intensity projection (MIP) again demonstrates the trifurcation of the left main coronary artery with a patent, but tortuous ramus intermedius and a shallow bridged segment ( arrow ). (c) Tracked, curved MIP of the ramus branch confirms patency of this artery without stenosis. The myocardial bridge is not appreciated in this view.

Figure 8, Coronary tree demonstrates an acute marginal branch of the right coronary artery (RCA) identified with >50% stenosis by COR Analyzer ( red overlay and white arrowhead ). This was interpreted as the posterior descending artery (PDA). The true PDA is a more distal branch of the RCA ( arrow ) with no evidence of stenosis.

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Discussion

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Academic Radiology, Volume 18, Issue 3
Journals General Radiology
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