Magnetic resonance imaging (MRI) provides detailed 3-dimensional information of both soft tissues and bones and can provide diagnosis when the results of radiography and ultrasonography do not explain the lameness. During an MRI examination only a small area can be evaluated and therefore it is important that the lameness is localised as much as possible. High-field MRI is performed with the horse under general anaesthesia and provides more detailed information than the low-field system. It is very useful in horses with mild lameness related to the foot or fetlock, when relatively mild lesions are expected. Low-field MRI is performed under standing sedation and it is possible to examine the limbs up to and including the carpus (knee) and the hock.
MRI is an imaging technique that uses a strong magnet to create detailed images of bones and soft tissues within a patient. MRI is a non-invasive technique used widely in humans, and increasingly in horses for detection of damage to a wide range of tissues. MRI is particularly useful for orthopaedic injuries affecting bones, joints and soft tissues. Unlike x-rays, MRI does not require the use of ionising radiation. MRI is very versatile in the ability to provide images sliced in many planes, and is capable of producing 3-dimensional images in a variety of orientations.
We routinely scan horses with proximal metacarpal and metatarsal pain, and are detecting damage to single lobes of the suspensory ligament, osseous changes or interosseous ligament pathology. MRI of horses with fetlock region pain may show joint and osseous damage, pre-fracture pathology, distal sesamoidean ligament or intersesamoidean ligament abnormality. MRI of horses with pain localised to the carpus or tarsus has allowed us to identify subtle joint or intertarsal/intercarpal ligament abnormalities.
Transverse T1W gradient echo magnetic resonance image of the proximal metacarpal region of a dressage horse with no detectable radiological or ultrasonographic abnormalities. Medial is to the left. The medial lobe of the suspensory ligament has diffuse increased signal intensity. The palmar cortex of the third metacarpal bone is thickened, with extensive endosteal reaction. This is consistent with proximal suspensory injury and osseous reaction at the enthesis.
We have over 10 years experience interpreting equine MR images using high and low systems. We have validated MR images in horses against post-mortem, histology, radiography, ultrasonography and scintigraphy so can provide a clinical service based on real facts. We are regularly consulted on MRI image acquisition and interpretation by equine clinics worldwide and have published and presented more papers on equine MRI than any other equine practice.