By Dr Christian Winiger, GP & Chief Medical Officer, Dr.Online
One of the most common questions I hear as a GP is:
“What scan do I need?”
Whether you’re experiencing persistent pain, headaches, a new lump or another worrying symptom, it’s natural to think that a scan is the quickest route to an answer.
However, the best scan isn’t necessarily the most advanced one—it’s the one that answers the right clinical question. Choosing the correct investigation can speed up diagnosis, avoid unnecessary tests and ensure you receive the most appropriate treatment without delay.
Not every symptom needs a scan
Modern medical imaging is an invaluable diagnostic tool, but many common conditions can be diagnosed through a careful medical history and examination without requiring imaging.
In fact, most headaches, uncomplicated neck or back pain, minor sports injuries and acute coughs do not need a scan. Many conditions improve with time, medication or physiotherapy, while others are better investigated initially with blood tests or simpler imaging such as an X-ray or ultrasound.
Advanced imaging such as MRI or CT should only be requested when it is clinically indicated and likely to influence diagnosis or treatment.
Ordering the wrong investigation can delay diagnosis, provide false reassurance or identify incidental findings that may lead to unnecessary anxiety and further testing.
For this reason, imaging requests should always be based on a clinical assessment rather than simply choosing a scan yourself.
The main types of imaging
| Scan | Best for | Limitations |
|---|---|---|
|
X-ray |
Broken bones, arthritis and many chest conditions |
Limited assessment of muscles, nerves and internal organs |
|
Ultrasound |
Gallbladder, kidneys, thyroid, pelvis, pregnancy, tendons and soft tissue lumps |
Cannot image well through bone or air-filled lungs and bowel |
|
CT |
Lung disease, major injuries, abdominal emergencies and many cancers |
Uses ionising radiation |
|
MRI |
Brain, spine, joints, muscles, ligaments and detailed soft tissue assessment |
Longer examination time and not suitable for some implanted devices |
|
DEXA |
Bone density and osteoporosis |
Only assesses bone strength |
Important: Symptoms suggestive of a medical emergency—such as sudden severe chest pain, stroke symptoms, major trauma, severe abdominal pain or significant neurological changes—require immediate assessment in A&E and should not be investigated through routine outpatient imaging.
MRI or CT—which is better?
This is one of the most common questions patients ask.
The answer is simple: neither is universally better. They answer different clinical questions.
MRI is often the preferred investigation for:
- Brain disorders
- Spinal conditions
- Persistent neck or back pain with neurological symptoms or red flag features
- Ligament, tendon and cartilage injuries
- Joint disorders
- Prostate disease
- Many pelvic conditions
CT is often the preferred investigation for:
- Chest and lung disease
- Major trauma
- Suspected internal bleeding
- Many emergency conditions
- Investigation and staging of many cancers
The choice of scan depends on what your clinician is trying to diagnose, not simply which machine provides the most detailed images.
Is radiation something to worry about?
One of the biggest differences between imaging tests is whether they use ionising radiation.
Scans that do not use ionising radiation
- MRI
- Ultrasound
Scans that do use ionising radiation
- X-ray
- CT
- Mammography
- DEXA
The radiation dose from a chest X-ray is very small. CT scans involve higher doses, but when they are clinically indicated, the benefits of reaching an accurate diagnosis almost always outweigh the risks.
In the UK, every exposure to ionising radiation must be justified under the Ionising Radiation (Medical Exposure) Regulations (IR(ME)R), ensuring patients receive the most appropriate investigation using the lowest reasonable radiation dose.
Which scan might be appropriate?
The table below provides a general guide only. Imaging should only be arranged following an appropriate clinical assessment and where the result is likely to influence diagnosis or management.
| Symptom or concern | Imaging that may be appropriate following clinical assessment |
|---|---|
|
Persistent or progressive headaches with red flag features or an abnormal neurological examination |
MRI (or CT in emergency setting |
|
Neck or back pain with persistent neurological symptoms, suspected nerve compression or other red flag features |
MRI |
|
Suspected broken bone |
X-ray |
|
Persistent cough where imaging is clinically indicated |
Chest X-ray (sometimes CT) |
|
Suspected gallbladder disease or upper abdominal pathology |
Ultrasound (sometimes MRI/MRCP for further assessment) |
|
Persistent pelvic pain or suspected gynaecological pathology |
Pelvic ultrasound (sometimes MRI pelvis for further characterisation) |
|
Raised PSA following appropriate assessment |
Multiparametric MRI (mpMRI) Prostate |
|
Persistent knee or shoulder pain after appropriate assessment and conservative treatment, or where significant structural injury is suspected |
MRI |
This is only a general guide. Many common conditions—including most headaches, uncomplicated neck or back pain, acute coughs and minor musculoskeletal injuries—do not require imaging.
Before requesting advanced imaging such as MRI or CT, your clinician may recommend conservative treatment, physiotherapy, blood tests or simpler investigations such as an X-ray or ultrasound. The most appropriate investigation depends on your symptoms, examination findings, age, medical history, duration of symptoms and individual risk factors.
Choosing the right scan
At Dr.Online, every imaging request is reviewed by a UK GP before a referral is made.
Our role is to ensure that imaging is clinically appropriate, follows current UK guidance and is likely to answer the clinical question being asked. If further information is required, we may arrange a telephone or video consultation before making a referral.
Occasionally this results in a different investigation—or no scan at all—because good medicine is about choosing the right test at the right time, not simply arranging the most advanced investigation available.
Following your scan, we can review the results with you, explain what they mean and advise on any further investigations, treatment or referral to an appropriate specialist if required.
The bottom line
Medical imaging has transformed the way we diagnose disease, but the best outcomes come from using the right investigation for the right patient at the right time.
If you’re unsure whether you need a scan—or which type of imaging is most appropriate—seek medical advice first. A clinical assessment can often determine whether imaging is needed and, if so, which investigation is most likely to provide the answers while avoiding unnecessary tests.
We offer both a questionnaire and video-based referral service for scan requests – giving you the flexibility to choose what suits you best
Further information
This article reflects current UK imaging practice and evidence-based referral guidance.
For further information, see:
- Royal College of Radiologists – iRefer – Evidence-based referral guidance used by UK clinicians when selecting the most appropriate imaging investigation.
- NHS – MRI scan – What an MRI scan involves, preparation, benefits and potential risks.
- NHS – CT scan – Information about CT scans, radiation exposure and what to expect.
- NHS – Ultrasound scan – Uses of ultrasound, preparation and the scanning process.
- NHS – X-ray – Information on X-rays, indications, safety and radiation.
- NHS – DEXA (Bone density) scan – Information about bone density scanning for osteoporosis assessment.
Dr Christian Winiger is a practising GP and Chief Medical Officer at Dr.Online, a CQC-registered UK digital GP service providing GP consultations, diagnostic imaging referrals and follow-up care.
This article is intended for general information only and should not replace personalised medical advice. If you have symptoms that concern you, please seek assessment from a healthcare professional. In a medical emergency, attend your nearest A&E department or call 999 immediately.