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.
- A technically limited or negative CTPA should be interpreted against pre-test probability and alternative diagnoses; persistent discordance requires radiology and senior clinical review rather than reflex reassurance.
- Lung ultrasound is strong for pleural fluid, procedure guidance, peripheral consolidation and rapid pneumothorax assessment, but aerated lung and bone prevent complete visualisation of central thoracic pathology.
- Absent lung sliding is not specific for pneumothorax, and B-lines are not specific for cardiogenic oedema; combine multiple signs, scan distribution, physiology and clinical context.
- Incidental nodules, coronary calcification, emphysema, fibrosis and adrenal or upper-abdominal findings require explicit review and a named follow-up owner; the acute indication does not erase incidental responsibility.
- Use the lowest justified radiation burden and avoid repeat imaging that cannot change management. Pregnancy and breastfeeding require informed protocol discussion, not automatic denial of necessary imaging.
- Protocol names, contrast checks, point-of-care ultrasound credentialling and reporting escalation differ between UK services, so clinicians must follow local radiology governance.
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.
Poor pulmonary-artery enhancement, respiratory motion, streak artefact or suboptimal coverage can prevent reliable exclusion of embolism. The report should state the limitation; subsequent imaging or management depends on clinical probability, bleeding risk and available alternatives.
Loss of pleural sliding and B-lines with a barcode pattern on M-mode can support pneumothorax, and a lung point is more specific when present. Apnoea, pleurodesis, severe emphysema, mainstem intubation and adhesions can also abolish sliding, so physiology and expertise matter.
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.
- Discuss protocol with radiology when the request could require CTPA, arterial phase, thin-section, expiratory, prone or image-guided techniques rather than selecting a generic label.
- Confirm who will review the authorised report, communicate urgent findings and action incidental or follow-up recommendations.