This page explains about having an MRI scan under oral sedation, and what to expect when your child comes to Great Ormond Street Hospital (GOSH) to have this procedure.
An MRI (magnetic resonance imaging) scan uses a magnetic field rather than x-rays to take pictures of your child’s body. The MRI scanner is a hollow machine with a tube running horizontally through its middle. Your child will lie on a bed that slides into the tube. An MRI scan usually lasts between 20 minutes and an hour.
Watch our short video about having an MRI scan or listen to our audio podcast. If you would like further advice about preparing your child for the scan, please ring the department’s play specialist on the numbers below.
Is an MRI scan safe for everyone?
No. If your child has a cardiac pacemaker or other metal devices in their chest or body, aneurysm clips in their head, dental braces within the last six weeks, or history of metal fragments in the eyes then the magnetic field of the MRI scanner may not be safe for them. Please call the department immediately when you get the appointment letter if you have any questions about safety.
You (or whoever comes with your child to the scan) will need to know your child’s full medical history from birth to the present day, including any operations they have had and will need to sign a metal check form stating that it is safe for your child to enter the MRI scanner. If this information is not known we may have to cancel the scan.
Why does my child need sedation for the MRI scan?
Some children find it difficult to lie still for the scan – either because of their age or their medical condition – so we might suggest they have sedation for the MRI scan. We assess all children to see if they might benefit from sedation. Your appointment letter will state whether your child is having sedation so you can follow the instructions below to prepare them.
Are there any alternatives?
Your child may need this scan so that their doctors can get detailed pictures of the size and shape of part of your child’s body. Various types of scan such as CT, ultrasound and x-rays can show the size and shape of parts of your child’s body but not in as much detail as an MRI scan. The information from the scan is then used to help with diagnosis and plan their treatment.
When you receive your appointment letter
If you are unable to keep this appointment, please inform the department as soon as possible beforehand. Sometimes, we can offer the appointment to another child on the waiting list.
Preparing for the sedation
- The evening before the scan, reduce the amount of sleep your child has by allowing them to go to bed an hour later than usual.
- On the day of the scan, wake your child at least one hour earlier than usual and try to keep them awake on the way to GOSH.
- It is important that your child does not eat or drink anything for a few hours before the sedation. This is called ‘fasting’ or ‘nil by mouth’. Fasting reduces the risk of stomach contents entering the lungs during and after the procedure.
- You will be informed the night before the procedure of the time that your child should be ‘nil by mouth’ – in other words, have nothing to eat or drink before the sedation.
The day of the scan
When you arrive at the hospital, you should report to the Otter Imaging Suite on level 1 Variety Club Building. Some scans need additional preparation – details about whether your child needs any additional preparation is in your appointment letter.
We will give you your arrival time when we call you the night before. Appointment times are staggered to avoid prolonged waiting times. We need this time to prepare you and your child, for instance, completing the metal check described below and to apply some local anaesthetic cream in case your child needs an injection.
Your child should wear clothes without zips or metal poppers for the scan – otherwise they will need to change into a gown. Before the scan starts, the nurse or radiographer will check your child does not have a pacemaker, metal implants or clips, dental braces, a history of metal fragments in the eyes or any allergies. We will ask you to sign a form to confirm this. If your child is wearing a medication patch, for instance, for pain relief, please remove this before you go into the scanner room. You will also need to leave metallic objects like jewellery, watches, keys, pens or cards with metallic strips like bank cards and train tickets outside the scanner room.
You are welcome to stay with your child until they are asleep and then again when they are in recovery until they are ready to go home.
What does the scan involve?
Your child will have the sedation medicine as a liquid to swallow about 20 to 45 minutes before the scan is scheduled. Some children also need ‘top up’ sedation, which is given into a vein (intravenously). We will put some local anaesthetic cream on your child’s skin to numb it, just in case intravenous sedation or a contrast injection is needed. Contrast is a liquid that shows up well on scans.
Your child will need to lie on the bed for the scan. Depending on the part of their body being scanned, they may need to have a coil over part of their body or wear a head coil (this will not touch their head).
When your child is in the correct position, the radiographer will move the bed inside the scanner and then go into the control room. A nurse will stay with your child throughout the scan. The scanner will make a continuous knocking sound throughout the scan, which can be quite loud, but we will give your child ear protectors to minimise any discomfort. When the scan has finished, the radiographer will move the bed out of the scanner.
They will then move your child into the recovery area to wake up from the sedation. You should be prepared to stay in the department until your child is fully awake and has had something to eat and drink. Most families are able to go home a couple of hours or so after the scan.
Sedative medicines given
Your child will have one or more of these sedative medicines:
Chloral Hydrate – Belongs to the group of medications known as sedatives and hypnotics. It promotes sedation and sleep by acting on certain areas of the brain. It is given orally. Possible side effects include: slow breathing rate, vomiting, irritability and prolonged sleepiness.
Alimemazine – Works by blocking a natural substance (histamine) that the body makes during an allergic reaction. It also works directly on the brain to help your child feel more relaxed. It is given orally. Possible side effects include: slow breathing rate, vomiting, irritability and prolonged sleepiness.
Midazolam – Works by slowing activity in the brain to allow relaxation and decreased consciousness. This is given intravenously when oral sedation has not been effective
after 45 minutes. Possible side effects include: slow breathing rate, low blood pressure, irritability and prolonged sleepiness.
Flumazinil – Is given intravenously and maybe used to reverse the effects of midazolam. Side effects are vomiting, palpitations and anxiety.
Dexmedetomidine – Is notable for its ability to provide sedation without risk of respiratory depression and can provide cooperative or semi-arousable. sedation. This is given intravenous or intranasal route. Possible side effects include irritability, prolonged sleepiness and low blood pressure. You can reduce the side effects of low blood pressure by encouraging your child to drink plenty of fluids in the hours after the scan.
Are there any risks?
There are no risks associated with MRI scans. They are painless and generally quick with no lasting effects. The scanner does not touch your child during the scan.
MRI scans are not suitable for people with certain metal implants inside them (such as pacemakers) because the scanner emits a strong magnetic field. This is why we carry out a thorough metal check before your child has the scan.
Risks of sedation are rare and these will be discussed fully on the day before you sign the consent form. The side effects of the medication however are more common, these can involve vomiting when giving the medication, increased sleepiness through the day and irritability. Your child may feel a bit wobbly and unsteady on their legs afterwards so please bring a pushchair
or buggy with you for the journey home if needed. The sedation nurse is very experienced and is trained to deal with any complications.
What happens afterwards?
When your child has recovered fully from the sedation and has had something to eat and drink, you will be able to go home. The radiologist (doctor specialising in scans) will send a report of the scan to your child’s doctor in time for their next appointment. If you have not been given a follow up appointment to see your consultant, please contact their secretary after two weeks.
When you get home
- Children are generally sleepier than usual for 24 hours after a scan with sedation. This is because the effects of the sedative last for about a day.
- If your child complains of feeling dizzy or faint, basic first is usually helpful:
- Sit them down and put their head between their knees
- Lie them down with their legs raised
- Offer them a sugary drink
- If your child is unduly sleepy or difficult to rouse, make sure they are in a safe position on their side and telephone your family doctor (GP).
- Make sure your child has plenty of fluid for the next 24 hours. If your child is tolerating fluids, you can offer them something to eat.
- Give milk only if your child does not feel sick or has vomited.
- Your child may have mood changes which can make them irritable. This is temporary.
- Keep a close watch on your child until they are back to normal. Do not leave them with an inexperienced carer.
- If your child is taking any medications, please give this as normal.
- Your child should be well enough to go to school a day or two after the scan.
- Let your child rest and sleep for the rest of the day.
Please note this is a generic GOSH information sheet. If you have specific questions about how this relates to your child, please ask your doctor. Please note this information may not necessarily reflect treatment at other hospitals.