About a CT scan of the lumbar spine
The lumbar spine is the lower back, made up of five large vertebrae (L1 to L5) between the ribcage and the pelvis, with discs between them that act as cushions. The nerves that run to the legs leave the spine here. A CT (computed tomography) scan uses X-rays and a computer to make detailed cross-section pictures of the vertebrae, which can be turned into 3D images.
Most lower back pain gets better on its own, and NICE advises that imaging is not routinely needed. When a scan is needed for sciatica, disc problems or trapped nerves, a lumbar spine MRI is usually the right test, as it shows the discs, nerves and soft tissues much more clearly and does not use radiation.
A lumbar spine CT is used when the question is about the bones, for example:
- fractures, including fractures caused by osteoporosis or injury, and how they are healing
- spondylolysis, a stress fracture in a small part of the vertebra, often in young athletes, and spondylolisthesis, where one vertebra slips forward on another
- bony narrowing of the spinal canal or nerve openings caused by bone spurs and arthritis of the facet joints
- the position of screws and rods and whether bones have fused after spinal surgery
- back problems when MRI is not possible, for example if you have a pacemaker or other device that is not safe for MRI
If several parts of the spine need to be seen, a whole spine CT may be used. You can read more in our article on lumbar spine imaging.
What happens during the scan
You lie on your back on the scanner bed, often with a cushion under your knees to make you more comfortable. The bed moves through a short, open ring while your lower back is scanned. The radiographer controls the scanner from the next room, but can see, hear and talk to you throughout. The scan itself takes only a few minutes. Contrast dye is not usually needed; where contrast is needed, it is charged separately.
Is CT safe?
CT uses X-rays, which are a type of ionising radiation. A lumbar spine CT gives a higher dose than an X-ray of the back, and the reproductive organs are close to the area scanned, so the scan is only done when it is likely to change your treatment. The risk from a single scan is very small, and every CT scan is checked by a radiologist or radiographer to make sure the benefit of the scan outweighs the risk, as required by the Ionising Radiation (Medical Exposure) Regulations. If you have had other CT scans recently, tell us when you book.
What the scan can show
A CT scan of the lumbar spine can help to look at:
- fractures and fracture healing
- spondylolysis and spondylolisthesis
- bony narrowing of the spinal canal and nerve openings
- facet joint arthritis and bone spurs
- spinal fusion and metalwork after surgery
- bone lumps and changes in the shape of the spine
When to get urgent help: call 999 or go to A&E if you have back pain with numbness around your genitals or bottom, new problems controlling your bladder or bowel, or new weakness in both legs. These can be signs of cauda equina syndrome, which needs emergency treatment. Do not wait for a private scan.
Preparing for your scan
No special preparation is needed, and you can eat and drink normally. If lying flat is painful, you may want to take your usual painkillers before your appointment. Upload any previous X-ray, MRI or scan reports and letters from your surgeon when you book.
Wear loose, comfortable clothing without metal zips, poppers or buttons, and leave jewellery at home, as metal in the scan area can affect the pictures. You may be asked to change into a gown. Unlike MRI, CT is not affected by pacemakers or most metal implants, and the scanner is a short open ring rather than a tunnel, so it is usually easier for people who feel anxious in enclosed spaces.
Tell the team before your scan if you are, or might be, pregnant or breastfeeding, if you have kidney problems, diabetes (especially if you take metformin), asthma, thyroid problems or allergies, or if you have had a reaction to contrast dye before. If you need contrast, you may be asked for a recent kidney blood test result.
Frequently asked questions
Should I have a CT or MRI for back pain?
Most back pain does not need a scan. When a scan is needed for sciatica or disc problems, MRI is usually better and does not use radiation. CT is better for the bones, such as fractures, spondylolysis and checking spinal surgery. Your referrer will say which is needed; if you are unsure, contact us before booking.
Can a CT show a slipped disc?
CT can sometimes show a large disc bulge, but it does not show discs and nerves as clearly as MRI.
I have had spinal surgery with screws. Can I have a CT?
Yes. CT is often used after spinal surgery to check the position of screws and whether the bones have fused. Tell us about any implants when you book.
Do I need a referral?
Because CT uses radiation, each scan has to be justified by a qualified professional before it can go ahead. Upload a referral from your GP or consultant when you book if you have one. If you do not, select “no referral” and the scanning centre will review your request and confirm the next steps with you, which may include arranging a referral.
Sources
- NICE NG59 – Low back pain and sciatica in over 16s: assessment and management
- NHS – Sciatica
- NHS – Spondylolisthesis
- RadiologyInfo.org – CT of the Spine
- NHS – CT scan
- UKHSA – Patient dose information: guidance
The information on this page has been gathered from various sources and is provided for general information only. It is not medical advice. TOP MRI is not liable for the accuracy or completeness of this information. Please speak to your doctor or the scanning centre about your own situation.