Excessive z-axis scan coverage in body CT: frequency and causes

Objectives The aim of this study was to determine the frequency and causing factors of excessive z-axis coverage in body CT examinations. Methods A total of 2032 body CT examinations performed between 1 March and 1 April 2018 in 1531 patients were included in this study. The over-scanned length values in the z-axis for each CT examination on each patient were determined by calculating the difference between the actual scanned length and optimal scan length in the z-axis. Over-scanning and over-scanning ratios were interrogated in terms of potential underlying factors that can be affected by patient demography, time, the throughput of CT, and the experience of technologists. Results Over-scanned CTs in z-axis were 66% of all CTs performed. CT scans were over-scanned in the cranial side in 18.4% and caudal side in 48.5% of patients. Over-scanning was found to be more frequent in 55–64-year-old age group (74%), thorax CTs (89.2%), patients with consciousness change (88.9%), patients with misleading findings related to lung apex or diaphragm on the scout images (76.6%), CTs performed in day shift (66.8 %), in CT with low daily scan (72.4%), and CT scans performed by less-experienced technologists (75.9%). Conclusions Over-scanning in z-axis in body CT examinations is not infrequently encountered in routine practice. Awareness of causes of over-scanning in z-axis can be helpful to prevent over-scanning in CT and unnecessary ionizing radiation exposure in patients. Key Points • Over-scanning in z-axis frequently occurs in body CT. • The frequency of over-scanning in caudal side is higher than cranial side. • Chest CT and any CT performed in following situation were more prone to over-scanning: older patients, patients with consciousness change, presence of misleading findings on the scout images related to lung apex or diaphragm, day shift, CT with low daily scan, less-experienced technologist.