Radiography is the oldest and best-known diagnostic imaging system available for use in people and animals. Basically, X-rays can pass through solid material, although more will travel through soft tissues, such as skin, tendons and muscle, than bone. X-rays will turn a photographic film black, which accounts for the negative image produced on X-ray film, where the surroundings are black, soft tissues appear grey, and bones rather whiter. Most radiographs are still produced on film, although systems are now available for digital radiography involving electronic image capture and storage. X-rays are also used in computed tomography which allows the generation of 3D images.

Radiographs are particularly useful for diagnosing bone and joint problems, such as fractures of bones and arthritis. This is in contrast to ultrasonography, which is most useful for imaging soft tissues, such as tendons and ligaments. X-ray machines come in various sizes, ranging from small, portable units to large, fixed machines which hang from the ceilings of X-ray rooms on cranes. The portable machines are useful for the distal limb, such as problems involving the foot, pastern and fetlock, and even the knee and hock. However, as these machines generate a lower intensity of X-rays than the fixed machines, exposure times are longer, therefore movement blur is more likely. The larger, fixed machines can be used with higher definition film, producing more detailed pictures, and they also allow pictures to be produced of horses’ chests, backs, and upper limb joints, such as the shoulder and hip, which are outside the range of portable machines.

(Left) Some equine hospitals use a mobile XRay unit such as this one. (Above) A portable X Ray unit, of the type carried by some vets in practice.

Horse being positioned for X-Ray of the foot using a fixed X-Ray machine