The original diagnostic images, radiographs are produced by exploiting the difference in absorbtion of x-rays between tissues of varying radiographic density, for example highlighting the difference between soft tissues through which the x-rays can pass relatively easily, and bone which by comparison is more radio-opaque. Previously the images were formed on x-ray film but now most are developed digitally on screens. In order to properly image an organ or limb for example, often multiple views from different angles are taken. X-Rays are harmful to living tissues so equipment operators avoid exposure and may wear protective clothing like aprons or gloves made from lead rubber which is impervious to normal clinical x-rays.
Because of the size of horses some areas are difficult to image using x-rays due to the thickness of the trunk and upper limbs – very high energy x-ray beams are needed to penetrate the thick tissue mass, which also scatters the radiation and reduces contrast in the image.
One standardized set of radiographs are ‘’Sales X-Rays’’ used to evaluate potential problems prior to Thoroughbred yearling sales. These comprise 36 images of the main joints of all four legs taken no more than six weeks pre- sale and are available for viewing by veterinarians on behalf of interested purchasers. The system in Australia began in 20003 and aids clients evaluation of potential problems with young horses and enables better assessment of risks attendant on purchase.