Dog - Diagnostic Imaging

Until relatively recently the only images used for diagnostic purposes in small animal practice were x-rays (radiographs). By the mid 1980s few small animal practices were without their own in-house radiographic facilities. Over the last decade radiology has expanded to become Diagnostic Imaging using a variety of other techniques to produce recorded images of parts of the body. These include:

• Ultrasonography
• Computer tomography (CT)
• Magnetic Resonance Imaging (MRI)

These and other techniques are all readily available in human medicine and are now increasingly being employed in diagnosis and also the planning of treatment in respect of our dogs and cats.

This handout is intended to give an insight into these techniques and the reason they are sometimes recommended instead of radiography.

Radiography: x-ray examination

This is still a very important diagnostic tool in canine practice. However with the dog as the patient it tends to be a little more complicated in that usually general anaesthesia or at least heavy sedation is required. This is in order that the patient can be correctly positioned.

Used irresponsibly x-rays carry considerable risks so there are strict health and safety regulations regarding their use in veterinary practice. For example, one specific requirement of the Health and Safety Executive (HSE) is that the subject must be adequately restrained and not hand held by any practice personnel.

Today computerised radiography has taken a big leap forward, the images can be electronically stored and thus instantly available for viewing both at the practice and by any consultant involved with the case.

Ultrasonography: ultrasound scanning

The advantages of ultrasonography as an alternative form of diagnostic imaging was realised by the veterinary profession about twenty years ago. Today ultrasound is available in many practices. Instead of radiation (x-rays) to 'see inside the body', very high frequency sound waves emitted by a transducer placed on the body wall are used. Echoes reflected back from the structures within the body are then picked up by the same transducer, and converted into images by a computer and displayed on a screen at the time of the examination.

Ultrasound is very safe and is useful for various diseases and conditions, particularly pregnancy diagnosis and the evaluation of cardiac (heart) function. It does not usually require anaesthesia and in many cases not even sedation.

Various modes of ultrasound scanning are available. These enable determination of anatomy and also movement. This is particularly useful with pregnancy diagnosis and detection of live foetuses and also cardiac examination and detection of heart wall and valvular defects.

A further refinement, Doppler ultrasound, enables determination of blood flow, blood pressure and cardiac output to be made. This is particularly useful since the patient can be examined conscious. Heart function is not influenced by the use of any anaesthetic or sedative. Further, there is usually no discomfort for the animal during ultrasound examinations.

Computer tomography

Unlike x-rays and ultrasound scans which are presently available in-house at many first opinion practices in the UK, CT and magnetic resonance imaging (MRI) are becoming increasingly available in veterinary practice but facilities are confined largely to the veterinary schools and larger referral practices due to the high initial cost of the equipment.

CT scanning is a British invention and was developed in the early 1970s. It is based on conventional x-rays but the x-ray tube rotates very rapidly around the patient and the emergent x-ray beam is picked up by electronic means and ultimately turned into high definition images which are shown on a screen.

CT scans in veterinary work are invaluable in the diagnosis of conditions affecting the brain and also for the investigation of skeletal problems since the definition of the images is far superior to that obtained with x-rays.

Magnetic Resonance Imaging: MRI

This was developed in the mid 20th century and scanning times are much longer than with CT, therefore general anaesthesia is necessary in most cases. The definition of the resultant images however is far superior. The technique is used in veterinary work mainly for the diagnosis of problems affecting the brain.

Please feel free to call us to discuss any of the imaging techniques that may be necessary for the diagnosis of your pet’s condition.