CT of the Equine Head – A Clinical Perspective

CT of the equine head – a clinical perspective

Introduction
The anatomy of the equine head is very complex with very dense structures (teeth and bones) being located next to less dense structures (soft tissues, including brain) and air (paranasal sinuses) in a rather small space. Conventional radiographs depict a three dimensional object as a two dimensional image. Their main limitation is that overlying tissues are superimposed over each other and summed up to produce an image. This makes the radiographic differentiation of individual structures in the head a challenge and hence the acquisition and interpretation of radiographs difficult. Tomographic methods such as computed tomography (CT) and magnetic resonance imaging (MRI) overcome this problem by producing a series of cross sectional slices of the structure of interest, thus virtually slicing the body up and in humans and small animals tomographic methods have long replaced radiography for many applications. In CT X-ray slice data is generated using an X-ray source that rotates around the object with X-ray sensors positioned on the opposite side of the circle from the X-ray source. Many consecutive scans are taken as the object is gradually passed through the gantry and combined to allow 3D visualisation of the patient. The use of CT for evaluation of the horse’s head has been described two decades ago in horses under general anaesthesia. Due to the high risk and costs of GA in the horse, the use of CT has only become more widespread since 2006 when the late Alistair Nelson, an equine practitioner in Yorkshire, came up with a design that allowed the CT scanning of the head in a standing horse. The size of the opening of the scanner (usually 60-80cm) and the external dimensions of the gantry limits its use in the standing horse to the head, cranial half of the neck and distal limbs. […]