MRI (magnetic resonance imaging) is an imaging technique that produces highly detailed anatomical images of the bone and soft tissue structures of the area being examined.

Images are produced by placing the body part in a strong magnetic field and applying pulses of radiowaves to the part via a radiofrequency coil. A signal is received back via the coil which is then generated into a detailed image by computer software. MRI is a very safe imaging technique as, unlike other imaging techniques (eg. radiography, scintigraphy and CT), it does not involve ionising radiation.

Prior to 2002, MRI was only available for horses in a few centres worldwide which had access to high field human MR scanners. These required horses to be placed under general anaesthesia before scanning could be performed. A new low field (0.2 Tesla) MRI system was developed specifically for use in the horse by Hallmarq at the beginning of this century which allowed scans to be performed in horses under standing sedation. The Liphook Equine Hospital was the third equine hospital worldwide to install this pioneering system and since 2004 we have developed a wealth of experience in using this technique to assist in the diagnosis of equine lameness. Our MRI unit was moved to a new, purpose-built suite in 2009 which means that, if required (eg. due to a horse’s temperament), as well as performing MR scans under standing sedation we can also perform scans on horses under general anaesthesia.

The low field MR scanner can be used to image any part of the equine lower limb up to and including the carpus and hock. MRI requires the horse to stand still within the magnet with a coil around the area of interest and therefore most horses require sedation as scanning can take between 1 and 3 hours. Horse’s shoes must be removed before entering the magnet to prevent interference with the strong magnetic field.

MRI is particularly useful for evaluating the bony and soft tissue (eg tendons and ligaments) within the equine foot. Our experience has shown that many horses with chronic lameness affecting the front feet have a variety of soft tissue injuries which cannot be accurately diagnosed using more conventional techniques. Furthermore the increasing use of MRI in horses over the last decade has increased our ability to diagnose and understand of many causes of lameness in the fetlock and proximal metacarpal/metatarsal regions. It is important that the results of MRI are interpreted in conjunction with other clinical findings and diagnostic investigations (eg. regional analgesia and radiography).

Click here for more information about the Hallmarq low field equine scanner.