Advanced equine diagnostics — magnetic resonance imaging

Lameness is one of the most common issues seen in equine practice, historically complex to diagnose, many practitioners and owners can be frustrated with the ever-eluding causation of lameness. Traditional methods of imaging can be insensitive to subtle changes in the equine patient which can cause significant discomfort. Routine nerve-blocking with local-anaesthetic and lameness assessments alone can be timely, costly, and a painstaking process, which can often leave a lot unanswered. However, over the last decade magnetic resonance imaging (MRI) has become more accessible and commonly utilised in veterinary diagnostics (Smith, 2015a; Mizobe et al, 2016). Having been the case for years within human medicine, specialist facilities and public perception have aligned to enable practitioners the scope to advance their field and, in turn, provide outstanding quality images and accurate diagnoses; promoting animal welfare (Swagemakers et al, 2016). With the ability to depict bone, tendon, ligament, and other soft tissue lesions including those within the hoof capsule, MRI supersedes the accuracy and detail capability of many other imaging techniques (Dyson et al, 2003) (Figure 1). Within the UK the majority of equine MRI scanners are low-field standing units, with only three high-field general anaesthetic units in the country. Both modalities have opposing merit, however, the field of interest, cost and the holistic presentation of the patient play a vital role in making informed choice between the two (Biggi and Dyson, 2018). Although considered safer, there are still some patient considerations to be addressed when using the lowfield scanners; long periods of sedation and a lack of food and water can lead to a higher probability of gut stasis and impaction (Bailey et al, 2016). Low-field scanners are often limited to the distal limb, due to the structure of the machine and movement artefacts associated with standing sedation. Although movement is alleviated via general anaesthetic in high-field, high-field scanners also have a better capacity to image the proximal limb structures, head, and cervical vertebrae of the horse. However, this is accompanied by the risk of general anaesthesia, which is widely known in horses to carry a high morbidity and mortality risk (Johnston et al, 1995; Senior, 2013).