01Core principlesThe concepts and mechanisms needed to understand the subject.
Imaging is a diagnostic intervention rather than a search for every abnormality. A complete request describes the problem, relevant history, examination findings, previous tests, pregnancy status where relevant, and the decision that depends on the result.
Selection weighs diagnostic accuracy, radiation or procedure risk, contrast risk, speed, availability, portability, patient tolerance, and whether the proposed study covers the required anatomy at the required time.
Appropriateness guidance supports rather than replaces judgement. Age, comorbidity, changing physiology, local capability, and specialist expertise can justify a different route when the reasoning is recorded.
Key points
- Begin with one explicit clinical question and the management decision the result could change.
- Review relevant previous imaging and reports before exposing the patient or duplicating an examination.
- Match modality, anatomical coverage, contrast phase, urgency, and patient factors to that question.
- Prefer a non-ionising test when it answers the question adequately, but do not accept harmful delay or inadequate performance.
- A normal result only reduces probability according to test sensitivity, image quality, timing, and pre-test probability.
- Discuss uncertainty, protocol choice, and discordant results with radiology; document the agreed plan and safety information.
02Mechanisms and patternsImportant relationships and how to distinguish them.
A precise suspected process, location, severity, or complication allows imaging staff to select the relevant technique and protocol.
The examination is valuable when a positive, negative, or indeterminate result will lead to a defined change in treatment or disposition.
History, examination and bedside tests determine how much a result should shift probability and whether a negative study can reassure.
Pregnancy, renal function, previous contrast reaction, body habitus, ability to cooperate, and implanted devices may change feasibility or risk.
Motion, poor timing, incomplete coverage, artefact, or an insensitive modality can make an apparently normal study non-exclusionary.
A clinically correct test scheduled too late may be the wrong test for the current decision and should trigger direct discussion.
03Interpreting evidenceInformation, measurements and their limitations.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
Clinical question and examination - Why
- Define the diagnosis or complication being tested.
- Interpretation and limitations
- A vague request produces a poorly targeted study; include the decision the result will change.
- 02
Previous imaging and reports - Why
- Avoid duplication and identify interval change.
- Interpretation and limitations
- Comparison may answer the question without repeat exposure or determine the appropriate follow-up technique.
- 03
Ultrasound - Why
- Provide real-time non-ionising assessment of selected superficial, abdominal, pelvic, obstetric and vascular questions.
- Interpretation and limitations
- Performance is operator- and patient-dependent; limited windows or non-visualisation may require another modality.
- 04
Plain radiography - Why
- Rapidly assess selected chest, bone, joint and device questions.
- Interpretation and limitations
- Projectional imaging may miss subtle or early disease, so interpret a negative film against the clinical probability.
- 05
Computed tomography - Why
- Provide rapid cross-sectional anatomical assessment with tailored contrast phases.
- Interpretation and limitations
- High diagnostic value in many emergencies must be balanced against ionising radiation and iodinated-contrast considerations.
- 06
Magnetic resonance imaging - Why
- Characterise soft tissue and many neurological or musculoskeletal processes without ionising radiation.
- Interpretation and limitations
- Longer acquisition, motion sensitivity, access, device conditions and gadolinium questions may limit immediate use.
04Applied reasoningWorked examples connecting principles to decisions.
01Worked caseStable focal abdominal painA stable adult has recurrent focal pain without shock or peritonism.+
- 1Context: define whether the working question concerns gallstones, inflammation, obstruction, a mass, or another process.
- 2Reasoning: review examination, laboratory results and prior imaging, then compare ultrasound and CT performance for that question.
- 3Outcome: agree the study and protocol that can change management while avoiding redundant or poorly targeted phases.
- 4Verification: read the report, check whether it answered the question, and reassess if symptoms and imaging remain discordant.
02Emergency routeEscalate a time-critical requestThe diagnosis will alter immediate treatment and routine scheduling creates unsafe delay.+
- 1Resuscitate and obtain the essential bedside information without postponing contact with imaging.
- 2State the suspected emergency, current physiology, required anatomy, and latest useful decision time.
- 3Agree modality, contrast and transfer requirements with the responsible radiology team.
- 4Ensure the result is actively received, acknowledged, documented and acted upon without relying on passive release.
03Discordant resultResolve persistent suspicionThe reported result does not explain the clinical picture or carries a material limitation.+
- 1Recheck the examination, timing, pre-test probability and exact wording of the report.
- 2Identify whether the limitation is modality sensitivity, protocol, artefact, anatomical coverage, or disease evolution.
- 3Discuss re-review, alternative imaging, repeat timing, or non-imaging investigation with radiology and the clinical team.
- 4Give safety-net advice and assign ownership for obtaining and acting on the next result.
04Protocol refinementPrepare a useful referralImaging is indicated but the optimal technique or contrast phase is uncertain.+
- 1Provide concise symptoms, examination findings, relevant laboratory data, prior diagnoses and treatment history.
- 2Disclose pregnancy possibility, renal impairment, previous contrast reaction and any implanted device before attendance.
- 3Ask the single question whose answer will determine the next clinical action.
- 4Record advice received and update the request if the clinical state changes before imaging.
05Checking understandingVerify the reasoning, revisit uncertainties and apply feedback.
- Track whether the examination was performed within the urgency required by the clinical decision.
- Review the entire report, including limitations, comparison studies, incidental findings and recommendations.
- Confirm that a named clinical team owns every further investigation or review requested in the report.
- Reassess the patient when imaging is negative but symptoms persist, evolve, or remain unexplained.
- Document communicated critical findings, the recipient, acknowledgment, planned action and escalation if no response occurs.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Probability not certainty
A result shifts probability according to sensitivity, specificity and pre-test likelihood; the post-test conclusion must still fit the patient.
Protocol determines performance
An anatomical label such as CT abdomen is incomplete without considering contrast, phase, coverage, reconstruction and timing for the clinical question.
Incidental cost
Broader or repeated imaging increases incidental findings, anxiety and downstream procedures, so more imaging may reduce rather than increase net benefit.
Portable trade-off
Bedside imaging can be faster and safer for transfer but may sacrifice views, resolution or diagnostic completeness compared with departmental acquisition.
Child-specific optimisation
Paediatric anatomy, disease prevalence and radiation sensitivity require child-sized protocols and an examination matched to the specific question.
Dialogue changes value
Early discussion can convert an unsuitable request into a targeted study, reveal a prior answer, or identify a faster non-imaging route.
07Common pitfallsFrequent interpretation and management errors.
- 01
Requesting a scan without stating what diagnosis, complication, or management decision is being tested.
- 02
Treating availability or image detail as sufficient justification for a modality.
- 03
Ignoring previous imaging and causing duplicate exposure, cost, delay, or confusing interval comparisons.
- 04
Reading a negative result as absolute exclusion despite poor sensitivity, wrong timing, artefact, or incomplete coverage.
- 05
Assuming that electronic report release guarantees clinical review, action, or patient communication.