Rationale and objectives: The purpose of the study was to quantitatively assess the percentage of total lung parenchyma visualized on cardiac computed tomographic angiography (CTA) using standard and tight-coned fields of view (FOVs).
Materials and methods: The authors evaluated lung volumes in 43 electrocardiogram-gated cardiac CTAs performed as part of triple rule-out/chest pain protocol CTAs over a 9-month period. Using a commercially available software package, a quantitative tissue differentiation analysis was performed using a threshold of -750 Hounsfield units to segment air in the lungs. Using each triple rule-out data set as a starting point, measurements of lung volume were performed with 2 cardiac CTA FOV scenarios, obtained by excluding the periphery of the triple rule-out volume: (1) standard cardiac CTA FOV typically used and recommended by the manufacturer and (2) tight cardiac CTA FOV maximally coned to the heart. For each scenario, the volume of the lung within the restricted FOV was compared with the overall volume of the lungs derived from the triple rule-out study, expressed as a percentage.
Results: On the standard cardiac CTA FOV typically used at our institution, a mean of 58% of the lung parenchyma is included with wide variability (range, 26%-86%). On the severely limited FOV, a mean of 14% (range, 7.5%-22%) of the lung parenchyma is included.
Conclusions: The percentage of lung parenchyma included in a standard FOV is considerable, although this can be mitigated by using a tight FOV, with potential exclusion of part of the cardiac anatomy. Interpreters of cardiac CTA images should have adequate training and skill in evaluating structures outside the heart.