What is a magnetic resonance imaging (MRI) scan?

MRI uses a strong magnetic field and radio waves to take detailed pictures of the inside of your body. A special contrast dye may be used so that the images are clearer.

When it’s used to look at your urinary system, this procedure is sometimes called an MR urogram.

What does it involve? 

MRI is carried out as a day procedure in hospital.

You lie inside a large tube that’s open at both ends, while the scanner takes images. A contrast dye is injected into your vein and travels through your blood until it reaches your urinary system. The dye helps the medical team see your urinary system in greater detail.

Who is MRI scanning for?

MRI can give your kidney doctor more information to help them make a diagnosis. You may have already had other tests, such as an ultrasound scan or X-ray, but these may not have given your doctor enough detail.

Is it safe? Are there any alternatives?

MRI is generally considered very safe.

There’s no evidence that the magnetic fields used are harmful, and MRI departments have safety procedures in place.

Some MRI scanners can affect the functioning of implanted devices, including pacemakers and cochlear implants. The hospital will carry out a safety assessment in advance. This will include questions about whether you have any implanted devices or any metal in your body that can’t be removed, such as piercings you can’t take out.

There’s no evidence that MRI is harmful in pregnancy.

If you are breastfeeding, it is safe to continue breastfeeding after the contrast dye is given. It is not thought to present any danger to your child as the amount received by your baby through breast milk is small.

Severe allergic reactions to contrast dye are rare but if you do have a have a reaction, the hospital team are trained to manage it. You’ll be asked if you’ve previously had reactions to contrast dye.

Where will the MRI scan take place? 

In the radiology/X-ray department of the hospital.

It will be carried out by a radiographer, who is trained in this type of imaging test and will operate the scanner.

What happens before the scan? 

• Some medications may need to be stopped before the procedure. You’ll be asked in advance about any medications you take, so follow the guidance you’re given.
• You may be asked to avoid wearing anything containing metal on the day, including anything with zippers or metal buttons.
• You’ll need to remove items such as hearing aids, watches and jewellery before going into the scanner. A locker will be provided in the hospital.

What happens during the scan? 

The radiographer will discuss your safety assessment and you may have a blood test to look at blood clotting, blood count and kidney function.

You may be given fluid to drink. You’ll empty your bladder before the scan.

If contrast dye is used, you’ll have it as an injection.

Then you’ll be asked to lie on a bed, and you’ll be given ear protection to wear because MRI scanners make loud noises when the small magnets inside click on and off. You’ll have a call button, which you can use if you need to stop the scan.

The radiographer will go into another room to operate the scanner. You’ll be able to hear and speak to them throughout the scan.

The procedure may be uncomfortable because you’ll need to lie very still to ensure the pictures aren’t blurred, and you may be asked to hold your breath at certain points.

The scan usually takes between 20 minutes and an hour.

What happens immediately after the scan?

If contrast dye was used, you may be asked to stay in the department for about 30 minutes so that staff can make sure you don’t have a reaction.

What should I expect when I get home? 

You should be able to carry on with your usual activities when you get home.

How will I get the results? 

A radiologist – a doctor who specialises in interpreting images – will look at the pictures and prepare a report to send to your kidney doctor. Your doctor will discuss the results with you.

Is there anything else I need to know? 

Tell the hospital team if you’re worried about feeling claustrophobic in the MRI scanner. The scanner is open-ended so you will not be fully enclosed. Your hospital team can help you to manage any anxiety.

Publication date: 01/2026

Review date: 01/2029