01Principles and purposeThe professional or clinical skill and the decisions it supports.
The best investigation is the one that answers the relevant question in time to improve care. A request for a CT abdomen without a proposed problem provides less useful information than suspected postoperative leak with worsening physiology or possible mesenteric vascular compromise. The clinical question helps radiology select coverage, contrast and acquisition timing. Choice of modality therefore begins with the patient and the decision, rather than an imagined hierarchy in which the most complex scan is always superior.
Imaging also has practical requirements. The patient must be able to reach the scanner safely, lie in the required position and receive monitoring or treatment compatible with that environment. Different techniques have different blind spots, and disease can evolve after a scan. A report should therefore be read as evidence within a continuing assessment. When results and clinical severity conflict, discuss the discrepancy rather than dismissing the patient or mechanically repeating the identical request.
Key points
- Write the clinical question first: localisation, obstruction, perforation, bleeding, vascular compromise or staging require different imaging choices.
- Plain radiography is a selective tool; a normal film does not comprehensively exclude serious intra-abdominal disease.
- Ultrasound is valuable for focused biliary, urinary, pelvic or vascular questions but can be limited by gas, habitus and operator access.
- CT provides rapid cross-sectional anatomy, but contrast choice and acquisition timing must match the suspected pathology.
- MRI can answer selected ductal, pelvic and soft-tissue questions without ionising radiation, but still requires device and patient-safety screening.
- Interpret the report against the clinical picture and ensure significant results lead to a named management decision.
02Situations and prioritiesThe context, relevant information and actions that matter most.
State the action under consideration before ordering. A scan might identify a drainable collection, establish whether obstruction is present, map vascular anatomy or distinguish gallbladder from duct disease. If the result would not alter the immediate response to profound instability, senior clinicians should decide whether imaging is worthwhile now or whether urgent intervention takes priority.
A deteriorating patient requires an explicit transfer plan with suitable staff, monitoring, oxygen and equipment. The radiology department is not a resuscitation team merely because a scan has been accepted. Communicate haemodynamic or respiratory concerns directly and agree who remains responsible during transport and the procedure.
Establish pregnancy possibility where relevant, renal history, previous contrast reactions, implanted devices, claustrophobia and ability to lie flat or cooperate. These factors do not all lead to cancellation; they guide risk reduction and selection of a useful alternative. Specify the actual reaction or implant rather than relying on a vague label such as contrast allergy or metalwork.
An incidental abnormality may not explain the symptoms. For example, gallstones can coexist with an unrelated cause of pain. Ask whether the finding matches the location, time course and physiology, and whether the report identifies the suspected complication. Additional findings may need follow-up even when they are not the reason for the acute admission.
A technically limited study is not equivalent to a confident negative result. In ultrasound, bowel gas or poor visualisation may leave the target unassessed; on CT, a protocol chosen for one question may be less suitable for another. Explain exactly what has been evaluated and what uncertainty remains.
03Assessment and interpretationHow to gather information, assess the situation and recognise uncertainty.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
Plain chest or abdominal radiography - Why
- Answer selected questions quickly when a film is likely to influence the immediate pathway.
- Interpretation and limitations
- Plain films provide a projection rather than complete abdominal anatomy. They may demonstrate useful gas, bowel or thoracic findings, but absence of an abnormality cannot exclude every perforation or obstruction. A preoperative chest radiograph is not routinely recommended by NG45. Choose a film for its specific expected contribution rather than making it an automatic prerequisite for CT.
- 02
Ultrasound with a focused target - Why
- Assess selected fluid-filled organs, ducts, superficial lesions or vascular structures without ionising radiation.
- Interpretation and limitations
- NICE recommends liver tests and ultrasound for suspected gallstone disease. In suspected symptomatic or ruptured AAA, immediate bedside aortic ultrasound is recommended, with immediate vascular discussion for a positive scan or continuing suspicion when imaging is unavailable or non-diagnostic. Seeing an aneurysm and proving the site of rupture are different questions.
- 03
CT with a question-specific protocol - Why
- Define cross-sectional anatomy rapidly and assess complications when the clinical situation warrants it.
- Interpretation and limitations
- Contrast-enhanced CT is recommended in the NG147 pathway for suspected complicated diverticulitis with raised inflammatory markers. By contrast, NG118 recommends low-dose non-contrast CT for adults with suspected renal colic, with ultrasound in pregnancy. Do not assume intravenous contrast is either always needed or always inappropriate; agree the protocol for the particular question.
- 04
MRI and MRCP - Why
- Characterise selected soft-tissue or ductal anatomy when MRI adds useful information.
- Interpretation and limitations
- CG188 supports MRCP when ultrasound has not identified common bile duct stones but the duct is dilated or liver tests are abnormal. MRI involves magnetic-field, device, heating and monitoring considerations despite having no ionising radiation. Implant compatibility depends on the exact device and required conditions; the MRI safety team must assess uncertainty before scanning.
- 05
Contrast-risk assessment and alternatives - Why
- Balance the clinical benefit of the required examination against preventable contrast-related harm.
- Interpretation and limitations
- Review renal status and the previous reaction history, and discuss mitigation or alternatives with radiology. NICE’s updated AKI guidance advises against delaying iodine-based contrast when delay is likely to be clinically significant. The correct comparison includes the harm of missing or delaying a dangerous diagnosis, not just the possibility of kidney injury.
04Worked approachesCases with ordered reasoning, an action and a check of the outcome.
01Worked case: an unresolved duct questionChoose the next useful biliary investigationA stable adult has episodic right upper quadrant pain. Ultrasound identifies gallbladder stones and a dilated common bile duct but no visible duct stone; liver tests are abnormal. There is no current shock or clinical cholangitis.+
- 1Identify the remaining question: whether a common bile duct stone is present, rather than whether gallbladder stones exist. The ultrasound has answered one question and left another unresolved.
- 2Review the symptoms and blood-test pattern and consider MRCP under CG188 because ultrasound has not shown a duct stone despite duct dilatation or abnormal liver tests. Explain the purpose and check MRI screening requirements.
- 3Avoid requesting another identical ultrasound simply to repeat the same limited answer, and avoid assuming a negative visualisation of a stone excludes duct disease. Discuss alternatives if MRI is unsuitable.
- 4The decision is further duct assessment with MRCP, with specialist evaluation of the result and subsequent management. If the clinical state changes to suspected infected obstruction, urgency and the need for drainage assessment change as well.
- 5Verify that the report addresses the duct question, that a responsible clinician reviews it and that the patient has instructions for new fever, jaundice or worsening pain while awaiting the next step.
02Acute abdominal imagingMatch urgency and protocolA surgical patient has a possible intra-abdominal complication and the team is deciding whether and how to obtain CT.+
- 1Assess physiological stability, the leading diagnosis and whether imaging will guide a near-term intervention. Call the appropriate senior and radiology teams rather than entering a vague request and waiting silently.
- 2Provide the operation, symptoms, examination, key laboratory data and precise diagnostic concern. Discuss contrast phase and coverage where these affect the question, including potential vascular pathology.
- 3Arrange a safe transfer, review the report promptly and communicate the management consequence. Escalate if imaging access or transfer safety prevents the intended urgent assessment.
03Unexpected or incomplete resultsResolve the mismatch with the patientA study is normal, equivocal or technically limited but the patient’s symptoms or physiology remain concerning.+
- 1Recheck what the study was designed to evaluate and whether the report describes limitations. Compare the result with the current examination and trajectory rather than an earlier snapshot.
- 2Discuss the case with radiology and the responsible senior clinician to decide whether reassessment, another modality, a different protocol or intervention is appropriate. Avoid both automatic dismissal and indiscriminate repeated scanning.
- 3Document the unresolved question, the agreed next action and who will act if deterioration occurs. Follow up incidental findings separately so they neither distract from nor disappear behind the acute problem.
05Feedback, follow-up and evidenceReview outcomes, seek feedback and identify what to improve.
- If waiting for imaging, specify observation and review arrangements that match the clinical risk; an accepted request does not protect a patient who deteriorates on the ward.
- After contrast administration, respond promptly to an acute reaction and document its actual features so future risk assessment is informed.
- Confirm that actionable reports and verbal radiology findings are communicated to the team making treatment decisions, including after a shift change.
- Check that important incidental findings have a follow-up owner and that the patient is informed in a proportionate, understandable way.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Modality and protocol are separate decisions
Choosing CT is only part of the request. A study optimised for stones differs from a vascular study, and the relevant contrast timing can matter. A clearly stated suspicion lets the radiologist tailor the examination instead of being asked to infer the intended decision from abdominal pain alone.
Diagnostic confidence is conditional
The meaning of a negative result depends on test performance, image quality and the likelihood of disease beforehand. Severe continuing symptoms after a limited study require a different response from a reassuring examination after a high-quality study that addressed the exact question.
MRI safety is active work
No ionising radiation does not mean no risk. An implant may be suitable only under specified scanning conditions, and monitoring equipment must also be appropriate for the environment. Use the established safety process rather than extrapolating from a previous uneventful scan.
A clear examination answer
When asked to select imaging, name the modality, any essential protocol feature, the finding sought and why it changes management. Then state a meaningful limitation. This demonstrates understanding of the investigation rather than recall of a one-word association.
07Common pitfallsFrequent interpretation and management errors.
- 01
Using a routine plain film as a compulsory step before useful cross-sectional imaging may add delay without answering the clinical question.
- 02
Regarding non-visualisation on ultrasound as proof that the target is normal overstates the evidence.
- 03
Cancelling clinically urgent contrast imaging solely because kidney function is impaired ignores the competing harm of delay.
- 04
Choosing MRI because it is perceived as universally safer neglects implants, monitoring requirements, availability and the time needed to answer the question.