What is diagnostic imaging?

This is a term used to describe the various ways in which doctors and vets obtain pictures or images of the inside of the body. Until the last decade or so this could only be achieved using X-ray pictures or radiographs, but now there are other techniques such as ultrasound, CT scanning (computerised tomography) and MRI (magnetic resonance imaging). A specialist in the interpretation of such pictures is called a radiologist.
 

Which of these techniques is most commonly used by vets in practice?

The mainstay of veterinary diagnostic imaging is radiography, and almost all small animal veterinary practices will own an X-ray machine. However, more and more practices are acquiring ultrasound machines, and expertise in diagnostic ultrasound is increasing rapidly. Private veterinary practices are unlikely to own CT or MRI scanners because of the expense and the space needed to house them.
However, some veterinary schools and referral practices have been able to
arrange access to scanners in hospitals or medical schools.
 

What are the main uses of radiography?

Radiographs are a very effective way of looking at bone tissue and of course
radiographs can be used to diagnose fractures and to monitor the healing
process. Radiography can also be used to diagnose osteoarthritis,
osteochondrosis (OCD) bone tumours, hip dysplasia and a host of other skeletal diseases. However, radiographs can also be used to look at the soft tissues in the body, such as the heart, lungs and abdominal organs. Using special ‘contrast techniques’ such as barium meals and myelography (as in human medicine) we can make many diagnoses using radiography alone.
 

Can I hold my dog for his X-ray?

It has long been known that x-rays are potentially harmful to normal tissues and even tiny doses can accumulate over a lifetime and cause cancer or gene
mutation decades later. New safety laws introduced in the mid 1980s have
indicated that animals should only be held for radiography in very exceptional
circumstances. A pre-planned procedure such as a hip x-ray on a healthy dog
does not justify the danger of its owner holding it and, in any case, it is much
easier for the vet and less stressful for the dog to use sedation or anaesthesia.
 

When should my vet use ultrasound?

Radiographs do not show the difference between sold soft tissue and fluid such
as blood or urine; everything appears a uniform grey shade. Ultrasound clearly
shows not only the difference between fluids and s olid tissues but also shows the internal architecture of solid organs such as the liver. This allows, for example, the presence of tumours to be identified. One of the commonest uses of the techniques is early pregnancy diagnosis. Ultrasound produces a moving picture so the contractions of the heart can be seen and measured, and advanced techniques called M-mode and Doppler echocardiography provide more functional information about the heart than is possible with any other method. However, ultrasound doesn’t penetrate bone so is not used for diagnosis of skeletal diseases.

 When would CT or MRI be used?

CT, and more especially MRI, produce cross-sectional pictures of the body in
fantastic detail and can show the inside of organs which cannot otherwise be
examined in live animals. CT uses x-rays in a more complicated way than normal radiography and MRI is a new method of imaging which combines magnetism and radio signals. Although CT and MRI have many uses in man, their main value in dogs and cats is for investigation of brain diseases such as tumours and meningitis, and for ruling out gross disease in epileptic pets. The Animal Health Trust has its own MRI scanner which is the only one Europe dedicated to dogs and cats. As well as scanning our own patients, we also offer a scanning service to the veterinary schools and referral practices. However, the time-consuming nature of the scans and their expense mean that they are never likely to replace radiography and ultrasound completely.