Synopsis
Select and interpret thoracic CT, CT pulmonary angiography and lung ultrasound according to a precise clinical question, recognising each modality's urgent uses, limitations, harms and follow-up responsibilities.
- Start with the question, not the scanner: non-contrast CT, contrast-enhanced CT, thin-section inspiratory and expiratory CT, CTPA and limited follow-up CT are different examinations with different timing and preparation.
- CTPA is justified through clinical assessment of pulmonary-embolism probability and the recommended D-dimer or imaging pathway; it is not a screening test for unexplained breathlessness without risk stratification.
- Confirm current renal information when indicated, previous iodinated-contrast reactions, pregnancy possibility, vascular access and the patient's ability to cooperate before contrast CT, then follow local radiology policy.
Key red flags
A contrast filling defect within an adequately opacified pulmonary artery supports acute embolism; chronic embolic disease may show eccentric organised material, webs, vessel narrowing and mosaic perfusion. Right-heart strain features alter urgency but must be integrated with haemodynamics and formal reporting.
Investigation priorities
Determine whether suspected pulmonary embolism needs CTPA or alternative imaging under the current diagnostic pathway.
Management branches
A patient may need thoracic CT but the optimal protocol is not yet defined.
- State the leading diagnostic question, urgency and the management decision that a positive or negative scan will change.
- Provide relevant history, examination, physiology, previous imaging, cancer or thromboembolic risk, renal and contrast information, and pregnancy possibility where relevant.