CT Scans of the Spine: What They Show and When They Are Used

By Mr Ahmed-Ramadan Sadek, Neurosurgeon · Last reviewed October 2026 · 7 min read

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On this page

What a CT scan is
CT and MRI: how they differ
When CT is used in spinal care
How much radiation is involved?
Before your scan
During the scan
After the scan
Further reading

Key points

A CT scan uses X-rays and a computer to build detailed pictures of the inside of the body. In the spine its main strength is showing bone.
MRI is still the main scan for discs, nerves and the spinal cord. CT is usually added when the fine shape of the bone matters, or when MRI is not possible.
Common reasons for a spinal CT include injuries, stress fractures of the pars, planning an operation and checking whether a fusion has healed.
The scan itself usually takes 10 to 20 minutes and you can normally go home straight afterwards.
CT involves more radiation than a plain X-ray, so it is only requested when the result is likely to help with your care.

What a CT scan is

CT stands for computed tomography. The scanner is a large ring, and you lie on a flat bed that moves slowly through it while X-ray pictures are taken from many angles. A radiographer runs the scanner from a neighbouring room but can see, hear and talk to you throughout. The whole appointment in the scanner usually takes 10 to 20 minutes.^[1]

A computer turns the X-ray information into thin slices through the body. These can be rebuilt in different planes, so your surgeon can look at the spine from the side, the front or above. National guidance on spinal injury, for example, asks for the scan to be reformatted into side-on and front-on views so that the whole column can be checked.^[2]

CT and MRI: how they differ

For most spinal problems an MRI scan is the first choice. It gives a very clear picture of the discs, nerves and spinal cord and uses magnets and radio waves rather than X-rays, so there is no radiation, as the British Association of Spine Surgeons (BASS) explains.^[3]

CT works the other way round. Soft tissues such as discs and nerves show up less well, but the outline of the bone is very sharp. It is often the better test when the question is about the bone itself: is it broken, has it healed, how much room is there in a bony channel, or where exactly should a screw go?

MRI: best for discs, nerves, spinal cord, infection and tumours. No radiation, but it is not suitable for everyone.
CT: best for fine bony detail, fractures, metal implants and bone healing. Quick, but uses X-rays.

When CT is used in spinal care

Injuries

After an accident, CT is the standard first scan for adults with a suspected neck injury who meet the criteria for imaging. It is also used for suspected injuries of the middle and lower back when there are abnormal nerve signs, or when a plain X-ray is abnormal. If there is any sign that the spinal cord may be affected, an MRI is done after the CT.^[2]

Pars defects (spondylolysis)

The pars is a narrow bridge of bone at the back of each vertebra. A stress fracture here is called spondylolysis and is a common cause of back pain in young people who play sport. A 2024 review describes CT as the gold standard for this condition because it shows the fracture line, how far it extends and which way it runs. MRI has a role in catching the problem early, before a clear break has formed, and avoids radiation.^[4]

Bone spurs and bony narrowing

As the spine ages, the small facet joints can thicken and grow bony spurs (osteophytes). These can narrow the openings through which nerves leave the spine. MRI shows that a nerve is squeezed; CT can help to show whether the squeeze is coming mainly from bone, which can affect how much bone a surgeon needs to remove.

Planning surgery and checking a fusion

Before some operations, especially those using screws, surgeons use CT to measure the size and angle of the bones. After a lumbar spinal fusion, CT is one of the main ways of checking whether the bones have knitted together. A 2025 systematic review recommended CT for people with ongoing back pain after fusion. Signs of a solid fusion included bone bridging across the level, no dark halo around the implants and no broken bone or metalwork. The authors also stressed that symptoms matter as much as pictures, and that pain persisting beyond a year should be taken seriously whatever the scan shows.^[5]

CT myelogram when MRI is not possible

Some people cannot have MRI, for example because of certain implanted devices; the NHS MRI safety checklist asks specifically about pacemakers and other metal in the body.^[6] For them, a CT myelogram is an option. A contrast dye is injected into the fluid around the nerves, usually through a fine needle in the lower back, and CT pictures are then taken. The dye outlines the nerves and spinal cord so that pressure on them can be seen. A review in Radiographics notes that this test is used far less since MRI became widely available, but that it is still often performed when the nerve sac needs to be assessed and MRI cannot be done.^[7]

How much radiation is involved?

We are all exposed to natural background radiation from the ground, the air and space. In the UK the average is about 2.1 millisieverts (mSv) a year. The UK Health Security Agency (UKHSA) publishes typical doses for common tests, set against how long it would take to receive the same amount from background radiation.^[8]

Test (UKHSA figures)	Typical dose	Similar to natural background over
Chest X-ray (single film)	0.02 mSv	3 days
Lumbar spine X-ray	1.3 mSv	7 months
CT head	2 mSv	1 year
CT chest	8 mSv	3.6 years
CT abdomen and pelvis	10 mSv	4.5 years

UKHSA does not list spinal CT separately, so the CT figures above are for other parts of the body; the dose for your scan depends on how much of the spine is covered. UKHSA estimates that a CT of the abdomen and pelvis adds a lifetime risk of fatal cancer of about 1 in 2,000 for adults aged 16 to 69, and that the risk for older people is roughly five times lower.^[8] The NHS describes the cancer risk from CT as very small, and says doctors weigh it against the benefit before requesting a scan.^[1]

Before your scan

Your hospital will tell you if you need to prepare. You might be asked not to eat for a few hours, or to avoid clothing with metal, such as zips, poppers, underwired bras, hair clips or jewellery.^[1]

Tell the hospital before the scan if you:

are, or might be, pregnant
are breastfeeding
have kidney or thyroid problems
have diabetes or asthma
take any medicines
have any allergies, particularly a previous reaction to contrast dye

This information comes from the NHS guide to CT scans.^[1]

If you feel anxious, mention it in advance. A CT scanner is a ring rather than an enclosed tube, but the team may still be able to offer something to help you relax, and you can ask whether someone may come with you.^[1]

During the scan

You lie on the bed, usually on your back, and the bed moves through the ring. You need to keep still and may be asked to hold your breath briefly. Some scans need a contrast dye injected into a vein. It can cause a warm, flushed feeling, a metallic taste or an odd sensation of needing to pass urine, all of which settle quickly.^[1]

After the scan

Most people go home soon afterwards. If you had contrast dye you may be asked to wait for up to 30 minutes in case of a reaction, which is rare. Tell the radiographer if you feel unwell.^[1]

A radiologist, a doctor who specialises in reading scans, reports the images to the doctor who requested them. Results usually take 1 to 2 weeks and occasionally up to 4. If you have heard nothing after 4 weeks, contact the doctor who referred you.^[1] The report may mention changes such as disc bulges or wear in the joints. BASS points out that some of these changes, such as a darker or bulging disc, can be entirely normal, so the findings are best discussed with your specialist alongside your symptoms.^[3]