Radiology Fundamentals

Radiography (X-ray)

Excellent for rapid triage and diagnosis

The classic radiology examination, the plain radiograph, has historically been the mainstay of most radiology departments, but in recent years lower-dose CT scanners and increasingly detailed MRI have gradually begun to supplant this old, reliable workhorse. However, plain radiographs remain extremely useful and are readily available in almost every healthcare setting. For some examinations, a plain radiograph provides all the necessary information in a single image, allowing a faster and easier diagnosis that is no less accurate. In some situations, however, a plain radiograph is much less accurate than CT or MRI. Despite their relatively low radiation dose, plain radiographs will remain a vital part of any radiology department for many years to come.

Computed tomography (CT)

Excellent for most acute and cross-sectional questions

Computed tomography is the modern workhorse of acute and cross-sectional imaging, with high spatial resolution, short acquisition times and near-universal availability in secondary care. Multi-detector scanners can image the whole chest and abdomen in seconds, which is why CT is first line for acute presentations, trauma, most suspected malignancies and vascular disease. Its main weakness is that it uses ionising radiation at doses higher than those of plain radiography, and it often requires iodinated contrast (an iodine-based agent injected to make structures easier to see), which carries risks of allergy and renal injury. Other technical issues, such as beam-hardening and metal artefact, can also obscure detail -- an issue less prevalent with plain radiographs. Regardless, every exposure must be justified under IR(ME)R.

Magnetic resonance imaging (MRI)

Excellent for soft tissues

MRI delivers high soft-tissue contrast without ionising radiation and is the modality of choice for soft-tissue, marrow, joint and neurological questions. Multiplanar acquisition and a range of contrast weightings make it central to musculoskeletal, neurological, hepatobiliary and pelvic imaging, and it will demonstrate pathology that CT resolves poorly or not at all. Its constraints are physical rather than dosimetric. The static field is permanently energised, so implant, device and foreign-body screening is mandatory before entry to the controlled area, and ferromagnetic projectile injury remains the principal safety hazard. Acquisition times are long, motion degrades the study, and a proportion of patients cannot tolerate the examination. Gadolinium (an intravenous contrast agent) requires a documented renal function assessment, and there are ongoing concerns about tissue deposition in the brain. MRI capacity and cost continue to limit access compared with CT. Its principal advantage is that it carries no ionising radiation and therefore no IR(ME)R justification requirement, but the request must still identify a clinical question that MRI answers better than a faster or lower-cost alternative.

Ultrasound

Excellent for superficial structures and blood flow

Ultrasound provides real-time imaging without ionising radiation. It is a dynamic examination rather than a set of static images, so it can assess flow and superficial structures that projection and cross-sectional imaging demonstrate poorly. It is widely used in abdominal, obstetric, musculoskeletal and soft-tissue imaging, and it is the guidance method for many interventional procedures. Its principal weakness is operator dependence: image quality and interpretation vary with the practitioner, and the examination is the least reproducible of the modalities. Penetration is limited, and bowel gas obscures deeper structures. Ultrasound uses no ionising radiation, so no IR(ME)R justification requirement arises.

Justification and optimisation keywords explained

• Justification: The benefit of the exposure to the patient must outweigh any potential harm. The referrer must provide sufficient clinical information to allow the practitioner to justify the examination and authorise the exposure.
• Optimisation: Radiation doses are kept as low as reasonably practicable (ALARP) while achieving the required diagnostic purpose. The 2024 amendments to IR(ME)R strengthened duties to have regard for diagnostic reference levels and to audit practice.
• Diagnostic reference levels (DRLs): National values derived from wide-scale surveys, typically set at the third quartile of the dose distribution for standard practice. Local DRLs should sit below national values, and departments consistently exceeding them must review their practice and take corrective action.
• Protocol choice: Ensuring the chosen study is capable of answering the specific clinical question asked. A technically adequate scan that fails to address the clinical query does not constitute optimised care.

Who are the duty holders under IR(ME)R?

• Employer: Establishes the organisational framework, including written procedures, protocols, training, staff entitlements, and compliance.
• Referrer: Provides sufficient and accurate clinical information to enable the justification of an exposure.
• Practitioner: Justifies and authorises the individual exposure by weighing clinical benefits against potential risks.
• Operator: Carries out the practical aspects of the procedure and ensures optimisation in practice.

What needs recording and reporting

• Significant accidental or unintended exposures are reportable incidents and must be investigated, with the findings recorded.
• Occupational exposure is controlled through designated areas, monitoring and dose limits. Under IRR17 a controlled area is required where a person is likely to receive more than 6 mSv per year, and a supervised area above 1 mSv per year.
• Dose limits under IRR17 are 20 mSv per year (100 mSv over five years), 150 mSv for the lens of the eye and 500 mSv for the extremities.
• Equipment must be commissioned, tested and withdrawn from use when faulty.
• QA records and dose records are evidence. They are routinely sought years after the event, and their absence is itself a finding.

Report content

A report must answer the clinical question asked, describe the findings, state the limitations of the study and give a clear conclusion. A structured format is expected where one has been agreed for that investigation. The conclusion should provide a radiological diagnosis or a reasoned differential, acknowledge limitations and make recommendations aligned with recognised guidelines.

Named author and accountability

Every report must be attributable to a named reporting author, including where reporting is remote or assisted by software. The author's name, position and profession should be identifiable. The content must not imply a level of scrutiny that has not in fact been applied.

Remote and offsite reporting

Remote reporting is acceptable only where the reporter has the images, the prior studies, the clinical information and the means to communicate an urgent finding. The same expectations of quality, turnaround and escalation apply as for onsite work. The RCR standards for teleradiology set out the governance, data-transfer and indemnity requirements.

AI-assisted and speech-recognition output

Where software generates or transcribes content, the named human author remains responsible for its accuracy. Every automated contribution must be reviewed and approved before the report is released. The use of AI does not transfer accountability to the software provider.

Turnaround and communication of critical findings

Providers must have procedures for turnaround times, communication of unexpected or time-critical findings, imaging classification for reporting priority, and acknowledgement of reports. A critical finding must be communicated directly and the communication documented, not left to the patient or referrer to discover.

Addenda and corrections

An addendum supplements the original report; it does not replace it. It must be attributable, dated and linked to the original study. Where a discrepancy or error is identified, the addendum should be non-judgemental and should trigger the local discrepancy and candour processes.