# Computed tomography pulmonary angiography in around-the-clock clinical care with individualised scan protocols: a 5-year observational study on incidence and causes of repeat scanning

## TL;DR

This study finds that individualized CT scan protocols reduce repeat scans, with most repeat reasons linked to patient factors like age and gender.

## Contribution

The study evaluates repeat CT pulmonary angiography scans in real-world clinical care using individualized protocols, identifying patient-related factors as key contributors.

## Key findings

- Repeat CT pulmonary angiography rate was 3.1% over 5 years.
- Repeat scans were more common in younger patients and females.
- Expert evaluation suggests repeat rates as low as 1.2% may be achievable.

## Abstract

Elevated repeat-scanning rates are reported for CT pulmonary angiography (CTPA). Individualised protocols optimise contrast- and radiation-doses, but whether this affects repeat scanning is unknown. The current study evaluates repeat-CTPA in a 24/7, state-of-the-art clinical-care setting.

This is a retrospective observational single-centre study of consecutive CTPA acquired over a 5-year period during standard clinical care. The primary outcome is the repeat-scan rate. Repeat- and single-scan groups were compared for initial-scan characteristics (patient-related, CT-scanner, contrast-administration, kV-settings, regular hours/shifts, radiation-dose), and cumulative contrast- and radiation-doses. An expert radiologist panel retrospectively evaluated probable reasons for repeat scanning through visual, subjective assessment of initial-scan images.

CTPA repeat rate was 3.1% (139/4467). Repeat- and single-scan groups significantly differed: age (55 ± 18 vs. 63 ± 17 years; p < 0.001), Body Mass Index (27 kg/m2 (IQR 7) vs. 25 kg/m2 (IQR 6); p = 0.022), radiation-dose (141 mGy∙cm (IQR 73) vs. 121 mGy∙cm (IQR 70); p < 0.001). Cumulative contrast- and radiation-doses were: 96 mL (IQR 31) vs. 48 mL (IQR 22) (p < 0.001); 0.36 gI/kg (IQR 0.11) vs. 0.18 gI/kg (IQR 0.51) (p < 0.001); 272 mGy∙cm (IQR 69) vs. 121 mGy∙cm (IQR 70) (p < 0.001).

Retrospective expert-consensus reasons for repeat scanning were: 31/133 patient-related; 28/133 multifactorial; 12/133 contrast/scan-protocol; 4/133 operator-error; 2/133 unidentified. 56/133 (42%) initial scans were retrospectively deemed diagnostic-quality, and these significantly differed from other repeat-categories in patient characteristics age (51 ± 15 vs. 57 ± 19 years; p = 0.045) and sex (64.3% vs. 50.6% female; p = 0.045), and in contrast volume (48 mL (IQR 17) vs. 46 mL (IQR 24); p = 0.031).

Individualised scan protocols yielded diagnostic images around the clock, with repeat scanning well within ranges published in the literature. Retrospective expert evaluation suggests repeat rates as low as 1.2% may be possible. Repeat- and single-scan groups significantly differed in patient characteristics, and repeat-scanning reasons were mostly patient-related. These results suggest further tailoring protocols to (younger, female) patients might be beneficial in helping to further reduce CTPA-repeats.

Question
CT pulmonary angiography (CTPA) is subject to relatively high repeat-scanning rates, but it is not known how state-of-the-art CTPA and individualised protocols perform in clinical practice today.

Findings
During 5 years of clinical practice the repeat rate was 3%; retrospective expert image-evaluation suggests a repeat rate as low as 1.2% may be possible.

Clinical relevance
Repeat- and single-scan groups significantly differed in patient characteristics, and reasons for repeat scanning were mostly patient-related. Further tailoring protocols to (younger, female) patients may be the best focus to help reduce CTPA-repeats, improve safety, and reduce logistic burden.