Technical feasibility and validation of a coronary artery calcium scoring system using CT coronary angiography images.

OBJECTIVES: We validate a novel CT coronary angiography (CCTA) coronary calcium scoring system. METHODS: Calcium was quantified on CCTA images using a new patient-specific attenuation threshold: mean + 2SD of intra-coronary contrast density (HU). Using 335 patient data sets a conversion factor (CF) for predicting CACS from CCTA scores (CCTAS) was derived and validated in a separate cohort (n = 168). Bland-Altman analysis and weighted kappa for MESA centiles and Agatston risk groupings were calculated. RESULTS: Multivariable linear regression yielded a CF: CACS = (1.185 × CCTAS) + (0.002 × CCTAS × attenuation threshold). When applied to CCTA data sets there was excellent correlation (r = 0.95; p < 0.0001) and agreement (mean difference -10.4 [95% limits of agreement -258.9 to 238.1]) with traditional calcium scores. Agreement was better for calcium scores below 500; however, MESA percentile agreement was better for high risk patients. Risk stratification was excellent (Agatston groups k = 0.88 and MESA centiles k = 0.91). Eliminating the dedicated CACS scan decreased patient radiation exposure by approximately one-third. CONCLUSION: CCTA calcium scores can accurately predict CACS using a simple, individualized, semiautomated approach reducing acquisition time and radiation exposure when evaluating patients for CAD. This method is not affected by the ROI location, imaging protocol, or tube voltage strengthening its clinical applicability. KEY POINTS: • Coronary calcium scores can be reliably determined on contrast-enhanced cardiac CT • This score can accurately risk stratify patients • Elimination of a dedicated calcium scan reduces patient radiation by a third.

Evaluation of High-Pitch Ungated Pediatric Cardiovascular Computed Tomography for the Assessment of Cardiac Structures in Neonates.

PURPOSE: We evaluated a high-pitch, non-electrocardiogram-gated cardiac computed tomographic protocol, designed to image both cardiac and extracardiac structures, including coronary arteries, in a neonatal population (less than 1 year old) that was referred for congenital heart disease assessment and compared it with an optimized standard-pitch protocol in an equivalent cohort. MATERIALS AND METHODS: Twenty-nine high-pitch scans were compared with 31 age-matched, sex-matched, and weight-matched standard-pitch, dosimetrically equivalent scans. The visualization and subjective quality of both cardiac and extracardiac structures were scored by consensus between 2 trained blinded observers. Image noise, signal-to-noise and contrast-to-noise ratios, and radiation doses were also compared. RESULTS: The high-pitch protocol better demonstrated the pulmonary veins (P=0.03) and all coronary segments (all P<0.05), except the distal right coronary artery (P=0.10), with no significant difference in the visualization of the remaining cardiac or extracardiac structures. Both contrast-to-noise and signal-to-noise ratios improved due to greater vessel opacity, with significantly fewer streak (P<0.01) and motion (P<0.01) artifacts. Image noise and computed tomographic dose index were comparable across the 2 techniques; however, the high-pitch acquisition resulted in a small, but statistically significant, increase in dose-length product [13.0 mGy.cm (9.0 to 17.3) vs. 11.0 mGy.cm (9.0 to 13.0), P=0.05] due to greater z-overscanning. CONCLUSIONS: In neonates, a high-pitch protocol improves coronary artery and pulmonary vein delineation compared with the standard-pitch protocol, allowing a more comprehensive assessment of cardiovascular anatomy while obviating the need for either patient sedation or heart rate control.

Deriving coronary artery calcium scores from CT coronary angiography: a proposed algorithm for evaluating stable chest pain.

We validate a method of calcium scoring on CT coronary angiography (CTCA) and propose an algorithm for the assessment of patients with stable chest pain. 503 consecutive patients undergoing coronary artery calcium score (CACS) and CTCA were included. A 0.1 cm2 region of interest was used to determine the mean contrast density on CTCA images either in the left main stem (LM) or right coronary artery. Axial 3 mm CTCA images were scored for calcium using conventional software with a modified threshold: mean LM contrast density (HU) + 2SD. A conversion factor (CF) for predicting CACS from raw CTCA scores (rCTCAS) was determined using a multivariable regression model adjusted for model over-optimism (1,000 bootstrap samples). Accuracy of this method was determined using weighted kappa for NICE recommended CACS groupings (0, 1-400, >400) and Bland-Altman analysis for absolute score. With the CF applied: CACS = (1.183 × rCTCAS) + (0.002 × rCTCAS × threshold), there was excellent agreement between methods for absolute score (mean difference 5.44 [95% limits of agreement -207.0 to 217.8]). The method discriminated between high (>400) and low risk (<400) calcium scores with a sensitivity and specificity of 85 and 99%, and a PPV and NPV of 92 and 98%, respectively, and led to a significant reduction in radiation exposure (6.9 [5.1-10.2] vs. 5.2 [6.3-8.7] mSv; p < 0.0001). Our proposed method allows a comprehensive assessment of coronary artery pathology through the use of an individualised, semi-automated approach. If incorporated into stable chest pain guidelines the need for further functional testing or invasive angiography could be determined from CTCA alone, supporting a change to the current guidelines.