Impact of Pitch Selection on Coronary Artery Calcium Scores In Lung Cancer Screening CT
Abstract
Purpose
Opportunistic coronary artery calcium (CAC) assessment from lung cancer screening (LCS) CT can broaden cardiovascular risk stratification, but cardiac motion and acquisition settings may impact the calcium score. This study quantifies the impact of helical pitch on CAC score accuracy and reproducibility from non-gated LCS.
Methods
A CIRS dynamic cardiac phantom with nine calcification inserts (diameter 1.2–5 mm; density 100–400 mg/cc) was scanned on a Siemens Force CT. Heart rates of 60 and 90 beats-per-minute (BPM) were used. Non-gated LCS CT (CTDIvol = 2.0 mGy) was acquired at 0.25 second rotation at pitches 0.9, 1.2, 1.5, and 3 (dual-source Turbo-Flash). All images were reconstructed at 3 mm slice thickness and 20 cm field-of-view. Additionally, ECG-gated CAC scans were performed (CTDIvol = 1.7 mGy) for ground-truth calcium scores. Siemens Syngo.Via was used to score discernible calcium inserts.
Results
Over the five repeated ECG-gated scans, four discernible inserts had a total score of 356 ± 9.7 (coefficient of variation [CV] = 0.03) at 60 BPM and 352 ± 27.8 (CV = 0.08) at 90 BPM. Non-gated LCS scans showed pitch-dependent underestimation and higher variability. At 60 bpm, a pitch of 0.9 scored 173.5 ± 55.7, with the highest CV (0.32); whereas a pitch of 1.5 improved agreement (300.2 ± 30.3) and reduced variability (CV = 0.10). At 90 bpm, a pitch of 1.2 scored 194.6 ± 48.8, with the highest CV (0.25); pitch 1.5 improved agreement (259.0 ± 29.1). The lowest CV at 90 bpm was 0.06 with Turbo-Flash mode.
Conclusion
In lung cancer screening CT, lower pitch (0.9) increases scan time relative to cardiac motion, causing calcium score underestimation and variability. Higher pitches (1.5) improve reproducibility and accuracy. With Turbo-Flash mode, the reproducibility is better with a high heart rate. Careful pitch selection can better benefit opportunistic CAC assessments.