When a doctor says you need a scan, the first question is usually: which scan, and why that one? The different types are not interchangeable — each one sees something different, which is why your doctor chooses the scan that answers the specific clinical question in your case. This article explains the differences simply.
Plain X-Ray
The fastest and simplest type, done in minutes. It shows bone clearly and is mostly used for fractures, monitoring bone healing, and some chest and lung conditions. It is not suited to detail in soft tissue such as muscles, ligaments or the brain.
CT scan
A CT takes successive cross-sectional images and assembles them into a detailed picture, and it does so very quickly — which makes it important in emergencies such as head injuries, bleeding and accidents. It is also useful for assessing the abdomen, chest and some vascular conditions.
Some scans require contrast to make vessels or organs clearer. Your doctor assesses whether that is appropriate for you, particularly if you have kidney problems or a history of allergy.
MRI
MRI uses a magnetic field and radio waves — no ionising radiation — and gives the finest detail in soft tissue: the brain, spinal cord and nerves, cartilage, ligaments and joints, among others. That is why it is the primary choice in conditions such as disc herniation, cruciate ligament injuries, and assessment of neurological disease.
The scan takes longer than a CT, the machine is loud (headphones are provided), and you need to stay still so the images come out clear.
Ultrasound
Ultrasound uses sound waves with no radiation at all, works in real time and produces a live moving image. It is widely used in pregnancy monitoring, examining the abdomen, liver, gallbladder and kidneys, the thyroid, and assessing blood flow in vessels (Doppler). It is safe and repeatable, but it cannot see bone or inside the skull the way CT and MRI can.
How does the doctor choose?
The choice is not arbitrary, and more expensive does not mean better. It rests on the clinical question being asked, the organ involved, how urgent the situation is, and your medical history. In short:
- Bones and fractures → usually plain X-ray
- Emergencies, trauma, rapid assessment → CT
- Soft tissue, brain and nerves, cartilage and ligaments → MRI
- Pregnancy, abdomen, thyroid, flow assessment → ultrasound
Sometimes more than one scan is requested. That is not duplication — each answers a different part of the picture.
Preparing for your scan
Preparation varies by type and the team will guide you in detail when you book, but in general:
- Some abdominal ultrasound scans require fasting for a number of hours; others require a full bladder
- For MRI you must remove all metal (bags, jewellery, watches) and tell the team immediately if you have any metallic device or implant such as a pacemaker, plates or screws
- If you have claustrophobia, say so before the scan — there are ways to help you complete it comfortably
- If there is any chance you are pregnant, tell the doctor or radiographer before any scan, particularly X-ray and CT
- Bring any previous scans or reports — comparison makes a real difference to the accuracy of the report
Is there radiation, and is it dangerous?
MRI and ultrasound involve no ionising radiation. X-ray and CT do, but a scan is performed when its medical benefit outweighs any potential risk, using the lowest dose that achieves the diagnostic purpose.
If you are concerned about repeated scans, ask your doctor directly — they can weigh the need against the alternatives in your case.
When is a scan urgent?
Some situations should not wait for a routine appointment. Go to the nearest emergency department immediately if there is:
- A head injury with loss of consciousness, repeated vomiting, or confusion
- Sudden weakness or numbness on one side of the body, or difficulty speaking
- Sudden severe chest or abdominal pain
- An obvious injury with deformity of a limb or inability to move it
How Town Hospital helps you
In Town Hospital's Diagnostics and Radiology department, scans are performed on modern equipment, reports are written by consultant radiologists, and findings are discussed with your treating doctor when the case calls for it. The aim is for the scan to answer a clear clinical question and move you a step closer to the right diagnosis — not simply to produce an image.
Frequently Asked Questions
What is the difference between a CT scan and an MRI?
CT is faster and better in emergencies, for bone and for bleeding. MRI gives finer detail in soft tissue such as the brain, nerves and cartilage. CT involves radiation; MRI does not.
What exactly does an ultrasound show?
It is used in pregnancy monitoring, examining abdominal organs such as the liver, gallbladder and kidneys, the thyroid, and assessing blood flow in vessels. It is not suitable for imaging bone or inside the skull.
Is the radiation from a CT scan harmful?
There is radiation, but a scan is requested when its diagnostic benefit outweighs the potential risk, using the lowest dose that achieves the purpose. If you are worried about repeated scans, discuss it with your doctor.
Does an MRI require preparation?
Usually no fasting, but you must remove all metal and tell the team if you have implants or metallic devices in your body. If you have claustrophobia, mention it before the scan.
I am pregnant — can I have a scan?
You must tell the doctor or radiographer before any scan. Ultrasound is used routinely in pregnancy care; scans involving radiation are used only where medical necessity requires it, after your doctor's assessment.
How soon are results ready?
It depends on the type of scan and your case — some results are available the same day, while cases needing closer review or comparison with previous scans may take longer. The team will explain the expected timing when you book.
To book a scan or ask about the preparation required, call 15276 or book through our website.