Magnetic Resonance Imaging (MRI)
MRI is a diagnostic imaging technique that involves placing the part of the body to be imaged inside a strong magnetic field. This is a relatively new technique in equine medicine that can be used to image the lower part of the leg in standing horses. Our clinic was the first veterinary clinic in the world to use this technology (the first scanner was installed in 2002, and has since been upgraded) and has played a central role in its development. Prior to this MRI could only be undertaken in horses at a few centres around the world using human MRI scanners under general anaesthesia.
The standing equine MRI scanner uses low magnetic field (0.27 Tesla) technology and horses are scanned standing under sedation. Both front and / or hind shoes (depending on the affected limbs) need to be removed prior to undertaking the procedure. The entire scanning process (from preparation to scanning) usually takes between 3 and 5 hours, depending on the area being scanned and the temperament of the horse. However, in some complicated cases, the procedure may take even longer than this. As far as it is known, the procedure is perfectly safe and it does not involve exposure to any form of ionising radiation.
MRI allows evaluation of both bone and soft tissues at the same time. The technique has specific indications for the evaluation of certain types of lameness. In most cases the area being scanned must be accurately localised by means of nerve blocks, prior to the procedure taking place as scanning even a small region (eg the feet) will take several hours.
One of the most useful indications for standing MRI is in the evaluation of horses with lameness originating in the foot. Our experience has shown that many horses with chronic foot lameness have a variety of concurrent soft tissue injuries. These particular injuries cannot be accurately diagnosed using more conventional techniques (X-ray or ultrasound). MRI has also proven to be very accurate in diagnosing some bone diseases which can be difficult or impossible to diagnose in any other way.
MRI also has many applications in evaluating other diseases in the lower legs and our knowledge concerning its value is expanding all the time.
Guidance notes for owners of horses having MRI
MRI Guidance Notes
- If your horse is insured, you should inform the insurance company that we intend to undertake a MRI examination and, where appropriate, check that the insurers are prepared to cover the costs of this. Wherever possible this should be done well in advance of your appointment date. You can download our guide for insurance claims for day-case appointments Here.
- Please bring details of your insurance policy (company name and policy numbers) with you to the appointment, in addition to an insurance continuation form.
- We will provide an estimate for the costs of the MRI examination, but in some cases we will determine that further scanning of more areas of the limb(s) with be required – this may incur extra cost, but we will discuss this with you (and usually your veterinary surgeon) before incurring further costs.
- Please bring the horse’s passport with you.
- Shoes need to be removed before the procedure can be carried out, so please organise for them to be removed prior to the horse’s arrival at the clinic. There will be a small charge if shoes are removed at the clinic and this would need to be arrange before the scan. If your horse is having its forelimbs scanned, only its front shoes need to be removed and only hind shoes for scanning hind limbs. If your horse is coming specifically for MRI, then shoes need to be removed before the horse arrives at the clinic, however, if your horse is being examined for a lameness problem prior to an MRI at Bell Equine, shoes should be left on so we can assess the lameness accurately.
- If scans of multiple areas (eg feet and fetlocks) are required, then we normally recommend that the horse stays overnight and is imaged over 2 days to avoid very large amounts of sedation on one day.
- Horses should be clean and dry when they arrive for the scan to aid the technicians in preparing and handling the horse for scanning. In particular, the feet should be clean and dry. Unfortunately any purple or blue spray applied to the feet can seriously affect the image quality. To avoid this please stop using the product at least 5 days prior to the scan and make sure that any spray left on your horse is thoroughly cleaned off.
- Your horse will need to be sedated for the scan. If you know of any reason why this cannot be done safely or if you know of any previous problems that the horse has encountered when being sedated, please inform us prior to arrival.
- In order to avoid repeated intravenous injections of sedation, a catheter will be placed into the jugular vein prior to scanning. This will be removed once scanning is complete. Occasionally a small swelling (haematoma) can develope at the catheter site following removal, but this should have resolved by the following day.
- MRI scanning can be a slow process, particularly if the horse moves during the scans. The process (preparation and initial scanning) will normally take between 3-4 hours, but can take longer. Further scans may be required one the initial images have been reviewed by the imaging specialist. Additionally, your horse will need to come round from the sedation after the scans are completed. As the duration can be variable and we cannot say exactly how long it will take for each horse, you are very welcome to drop your horse off to stay at the clinic for the day and pick up later if that is more convenient than waiting.
- You will be informed when the scanning is complete, with an estimate of time at which your horse can leave the clinic; we want the horse fully awake before they leave. Arrangements to collect the horse can be made at this time.
- Unfortunately, due to the large number of images obtained during in an MRI scan, reviewing and interpreting all of the images takes some time. It is therefore unlikely that you will receive any ‘results’ on the day of the scan. In most cases a full report will be produced within 3-5 days and copies will be sent to yourself and your referring vet.
- Routine X-rays will be taken of horses having MRI of the feet prior to the procedure. This is for our own research and development purposes and there will not be a charge for this. It also gives us the opportunity to check for any broken clenches or rust that has been left in the feet which will have to be removed as they would adversely affect the image quality.
- In some cases, the MRI scans will identify a problem where we believe further imaging (such as radiography, ultrasonography or nuclear scintigraphy) will be helpful in providing more information. In such cases, we may request permission to perform these added tests before the horse goes home.
- In a small number of horses, sedation may predispose them to mild colic. If your horse is prone to colic, it might be prudent to feed a laxative diet or add extra table salt to the feed (eg one tablespoon per feed) for 24 hours or so before coming for the MRI and after your horse returns home. In a few cases we may recommend giving the horse an electrolyte solution by stomach tube before travelling home to gut contents and promote motility. If feasible, walking exercise can also be helpful to promote gut motility.
In view of our interests in researching the applications of MRI to lameness diagnosis in horses, we are always interested in hearing how individual horses have fared after they have returned home from having a MRI scan. We may contact owners in the future to find out how the horse has got on.
Equine MRI is still in its infancy, and it continues to reveal new conditions that it is discovering all the time. An important way of increasing our knowledge is by correlating the results of MRI and post-mortem examinations. If, for any reason, a horse that has previously had an MRI scan has to be euthanased, then we would welcome the opportunity to perform a post-mortem examination of the scanned area. In this way we can further increase our knowledge and expertise for the benefit of horses in the future.
If you have any further questions or require more information, then please do not hesitate to contact us on 01622 813700 and ask for the hospital team.