01Purpose and principlesWhat the assessment is for and the core concepts behind it.
CT excels when cross-sectional anatomy or tissue pattern will change a decision. Standard contrast-enhanced thoracic CT evaluates masses, nodes, mediastinum, pleura and many complications; non-contrast imaging may suit selected nodule, calcification or follow-up questions; thin-section volumetric techniques characterise diffuse parenchymal disease and may include expiratory or prone acquisitions; CTPA times iodinated contrast to the pulmonary arteries. Writing only 'CT chest' transfers the clinical decision to radiology without supplying the information needed to optimise it. A useful request states the suspected condition, tempo, relevant previous imaging, important risk factors, renal or contrast information and the decision the result will determine.
For suspected pulmonary embolism, imaging follows probability rather than preceding it. Apply the current NICE diagnostic pathway, using clinical assessment, the two-level PE Wells score and D-dimer where indicated, while recognising circumstances in which immediate imaging or interim therapeutic anticoagulation is advised. Pregnancy has a separate multidisciplinary pathway because maternal risk, fetal and breast radiation, alternative imaging and local expertise must be weighed. CTPA quality depends on contrast timing, breath-hold, motion and cardiac output; inadequate arterial opacification can make a scan non-diagnostic. A negative result is most reassuring when the study is technically adequate and the pre-test pathway was appropriate.
Lung ultrasound answers focused bedside questions dynamically and without ionising radiation. Pleural fluid appears as an anechoic or complex space above the diaphragm; septations may indicate complexity but do not alone determine aetiology. Pleural sliding, B-lines, consolidation with air bronchograms and the lung point can support particular diagnoses, yet each sign has mimics. Ultrasound cannot survey the whole lung through aerated tissue and cannot rule out pulmonary embolism, central tumour or deep parenchymal disease. Operators need training, saved images and governance. As with CT, a result is only safe when its limitation, reporting status, downstream action and incidental findings are made explicit.
Key points
- 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.
02Indications, selection and cautionsWhen it is useful, when urgency changes and important limitations.
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.
Reticulation, traction bronchiectasis, honeycombing, ground-glass change, nodules and air trapping have meaning through their distribution and combination. A pattern can narrow a multidisciplinary differential but should not be translated into idiopathic pulmonary fibrosis without clinical exclusion of exposures, drugs and connective-tissue disease.
A fluid space bounded by chest wall, diaphragm and collapsed or floating lung confirms effusion and permits depth assessment. Echogenic debris or septation suggests complexity, while solid tissue, liver or spleen must be identified before any needle path is chosen.
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.
Subpleural tissue-like echotexture with dynamic air bronchograms supports peripheral air-space consolidation. Small infarcts, atelectasis and tumour can appear tissue-like; central disease hidden behind aerated lung may be invisible to ultrasound.
03Method and interpretationA systematic approach to the test and its findings.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Clinical probability and D-dimerFirst step - Why
- Determine whether suspected pulmonary embolism needs CTPA or alternative imaging under the current diagnostic pathway.
- Interpretation and limitations
- Use the validated pathway specified by NICE, including age-adjusted threshold considerations where adopted. A positive D-dimer is non-specific and leads to imaging; a negative result excludes PE only in the appropriate probability group and assay pathway.
- 02
CT pulmonary angiography - Why
- Identify pulmonary arterial thrombus, assess burden and right-heart effects, and reveal alternative thoracic diagnoses when pulmonary embolism is suspected.
- Interpretation and limitations
- First confirm technical adequacy and formal report. A positive scan must be integrated with haemodynamic risk and bleeding risk; a limited or apparently negative scan that conflicts strongly with the clinical picture requires discussion rather than automatic exclusion.
- 03
Contrast-enhanced thoracic CT - Why
- Characterise lung masses, lymph nodes, mediastinal structures, pleural disease, infection complications and vascular or chest-wall involvement.
- Interpretation and limitations
- Enhancement and anatomical staging can direct biopsy or referral, but histology may still be required. Protocol, venous phase and scanned extent must fit the question; a routine contrast study is not interchangeable with CTPA or thin-section interstitial imaging.
- 04
Thin-section inspiratory and expiratory CT - Why
- Define interstitial pattern, bronchiectasis, emphysema and air trapping when chest radiography or physiology suggests diffuse lung disease.
- Interpretation and limitations
- Distribution, chronicity and clinical context inform multidisciplinary diagnosis. Ground-glass change is a density description rather than one disease, and expiratory air trapping may expose small-airway pathology missed on inspiratory images.
- 05
Point-of-care lung ultrasound - Why
- Answer a focused bedside question about pleural fluid, peripheral consolidation, interstitial fluid pattern or pneumothorax and support urgent reassessment.
- Interpretation and limitations
- Record the question, zones, probe, findings, saved images and limitations. A bilateral diffuse B-line pattern can support interstitial syndrome but cannot alone distinguish oedema from inflammation or fibrosis; absence of a visible abnormality does not constitute a complete thoracic scan.
- 06
Thoracic ultrasound for pleural intervention - Why
- Confirm fluid, identify diaphragm and solid organs, measure a safe window and mark or continuously guide aspiration or drain placement.
- Interpretation and limitations
- The scan must be contemporaneous and performed by a trained operator. Patient movement can invalidate a static mark, and a shallow or loculated collection may require expert image-guided intervention rather than bedside aspiration.
- 07
Renal and contrast-risk assessment - Why
- Identify factors that affect iodinated-contrast preparation, protocol and post-scan care without delaying necessary emergency imaging inappropriately.
- Interpretation and limitations
- Apply current radiology policy to kidney function, previous reaction, thyroid context and interacting medicines. Distinguish previous allergic-like contrast reaction from unrelated food allergy, and discuss risk mitigation or alternative imaging with radiology.
04Clinical next stepsHow the result changes management or prompts escalation.
01Protocol selectionConvert concern into a questionFirst stepA patient may need thoracic CT but the optimal protocol is not yet defined.+
- 1State the leading diagnostic question, urgency and the management decision that a positive or negative scan will change.
- 2Provide relevant history, examination, physiology, previous imaging, cancer or thromboembolic risk, renal and contrast information, and pregnancy possibility where relevant.
- 3Discuss 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.
- 4Confirm who will review the authorised report, communicate urgent findings and action incidental or follow-up recommendations.
02Suspected embolismUse a probability-led CTPA pathwayPulmonary embolism is a plausible cause of acute symptoms.+
- 1AlternativeAssess ABCDE and haemodynamic stability, identify alternative emergencies, take a focused thromboembolic and bleeding history, and apply the current NICE probability pathway.
- 2Use D-dimer when the probability group calls for it; arrange immediate CTPA when indicated and follow current guidance on interim anticoagulation if imaging is delayed, unless contraindicated.
- 3Review technical adequacy and the complete report, not only the PE line, then stratify confirmed embolism and seek urgent specialist input for shock or deterioration.
- 4AlternativeIf the scan is non-diagnostic or remains discordant with high concern, discuss repeat or alternative imaging and management with radiology and a senior clinician.
03Bedside ultrasoundAcquire focused, governed imagesPleural fluid, peripheral consolidation, interstitial syndrome or pneumothorax is the immediate bedside question.+
- 1Define the binary or limited question, position the patient safely and scan a reproducible set of bilateral zones using an appropriate probe and preset.
- 2Identify pleural line, lung sliding, artefacts, diaphragm, solid organs and any fluid or tissue-like abnormality; use dynamic signs and more than one view.
- 3DefinitiveSave labelled images, document zones and limitations, and integrate the result with observations and other imaging rather than converting one sign into a definitive diagnosis.
- 4EscalationEscalate uncertain or high-risk findings to an accredited operator or radiology, and obtain CT or radiography when the residual question lies outside ultrasound's field.
04After imagingOwn every resultCT or ultrasound has been performed or an authorised report becomes available.+
- 1Reassess clinical status and review the complete findings, technical limitations, comparisons and radiologist recommendations.
- 2Act on the primary diagnosis, reconcile alternatives and arrange pathology or multidisciplinary review where imaging alone cannot establish aetiology.
- 3List incidental and follow-up findings separately, allocate each to a named clinician and communicate material information to the patient and primary care.
- 4Document completion or planned surveillance under the correct regional pathway, because nodule and cancer arrangements may differ between devolved nations and organisations.
05Risks, monitoring and follow-upComplications, safety checks and further assessment.
- During urgent imaging pathways, trend respiratory rate, SpO2 and oxygen requirement, pulse, blood pressure, consciousness and signs of right-heart or ventilatory failure.
- After iodinated contrast, observe and manage any immediate reaction under the radiology emergency protocol and arrange kidney-function follow-up only where current policy indicates.
- For a non-diagnostic scan, record the unresolved probability, interim management, planned alternative test and responsible reviewer rather than treating ambiguity as a negative result.
- Audit point-of-care ultrasound image storage, operator competence, report wording and discrepancy review within local governance.
- Track nodules, suspected cancer, interstitial abnormalities and recommended interval imaging through a closed-loop system with patient communication and documented completion.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Protocol is part of diagnosis
A beautifully acquired wrong-phase scan may not answer the clinical question. Contrast timing, slice reconstruction, inspiration and expiratory manoeuvres are diagnostic choices, which is why concise radiologist discussion can prevent both delay and repeat radiation.
B-lines describe an artefact
Vertical ring-down artefacts arise when subpleural aeration is reduced. Their number and distribution can support an interstitial syndrome, but oedema, fibrosis, contusion and inflammation can all generate them.
Lung sliding has mimics
Pleural adhesion, apnoea, very shallow ventilation and mainstem intubation can remove visible sliding without pleural air. A lung point strengthens pneumothorax diagnosis, while haemodynamic instability determines urgency.
Negative depends on adequacy
The evidential value of a negative CTPA depends on suitable pre-test selection and sufficient arterial opacification without prohibitive motion. The technical-quality statement is therefore part of the result, not an optional footnote.
Breastfeeding rarely blocks contrast
Current RCR and Society of Radiographers advice does not require routine interruption of breastfeeding after iodinated CT or gadolinium MRI contrast. Address individual concern through radiology policy instead of withholding necessary imaging.
07Common pitfallsFrequent interpretation and management errors.
- 01
Requesting generic CT chest without stating whether the question is embolism, malignancy, pleural disease or diffuse parenchymal disease.
- 02
Ordering CTPA because D-dimer is raised without first using the intended clinical-probability pathway.
- 03
Treating a technically limited CTPA as confidently negative despite persistent high clinical concern.
- 04
Diagnosing cardiogenic oedema from B-lines alone or pneumothorax from absent sliding alone.
- 05
Attempting pleural aspiration from an old skin mark after the patient has moved instead of repeating ultrasound at the procedure.
- 06
Focusing only on the acute CT indication and losing an incidental nodule or formal follow-up recommendation.