Visual Ordinal Scoring of Coronary Artery Calcium on Contrast-Enhanced and Noncontrast Chest CT: A Retrospective Study of Diagnostic Performance and Prognostic Utility

BACKGROUND. Current guidelines recommend visual evaluation of coronary artery calcium (CAC) on all nongated noncontrast chest CT examinations. However, chest CT examinations are often performed with contrast material administration. OBJECTIVE. The purpose of our study was to evaluate diagnostic performance, prognostic utility, and interobserver agreement of visual CAC assessment on chest CT performed for other indications. METHODS. This retrospective study included 260 patients (158 men, 102 women; mean age, 60 +/- 11 [SD] years) who underwent both nongated chest CT (contrast-enhanced in 116 patients; noncontrast in 144 patients) and cardiac calcium score CT within a 12-month interval. A cardiothoracic radiologist visually assessed CAC on chest CT using an ordinal scale (absent, mild, moderate, or severe). Cardiac CT Agatston calcium scores were quantified according to established guidelines and were categorized as CAC absent (0), mild CAC (1-99), moderate CAC (100-299), or severe CAC (= 300). The diagnostic performance of chest CT for the presence of CAC was assessed using cardiac CT as the reference standard. Major adverse cardiac events (MACE) were assessed as a composite of cardiovascular death and myocardial infarction and were evaluated using Cox proportional hazards models. A second cardiothoracic radiologist performed visual CAC assessments in a random subset of 50 chest CT examinations to assess interobserver agreement. RESULTS. For the presence of any CAC on cardiac CT, contrast-enhanced and non-contrast chest CT had sensitivity of 83% (62/75) and 89% (85/95) (p =.20) and specificity of 100% (41/41) and 100% (49/49) (p =.99). CAC present on cardiac CT was misclassified as absent on 13 contrast-enhanced and 10 noncontrast chest CT examinations; Agatston score was less than 30 in all such patients, and none experienced any MACE. The visual ordinal CAC score was associated with MACE for contrast-enhanced chest CT (hazard ratio [HR] = 4.5 [95% CI, 1.2-16.4], p =.02) and noncontrast chest CT (HR = 3.4 [95% CI, 1.57.8], p =.003). Interobserver agreement was excellent for contrast-enhanced (kappa = 0.89) and noncontrast (kappa = 0.95) chest CT. CONCLUSION. Visual ordinal CAC assessment on both contrast-enhanced and noncontrast chest CT has high diagnostic performance, prognostic utility, and interobserver agreement. CLINICAL IMPACT. Routine reporting of CAC on all chest CT examinations regardless of clinical indication and contrast material administration could identify a large number of patients with previously unknown CAC who might benefit from preventive treatment.