Diagnostic Imaging : Ultrasound

The machinery

Very high frequency vibration, above the frequency of hearing (i.e. ultra-sound frequency) is transmitted from a probe into the tissues via a liquid or gel contact medium. The sound penetrates the tissues, being absorbed and/or bounced back to the probe where the echos are recorded and used to measure depths into the tissue. The ultrasound machine then presents the information as a one, two or three dimensional image of the subject of the scan.

To the left is a 2-D image showing a cross section through a dog's heart. Different types of probes are used for different purposes. Linear array probes produce an image like the one above right, whilst the results from sector probesare similar to the image below.

Common Uses

Ultrasound scanning is commonly used for assessment of babies during pregnancy. It can be used for preganancy diagnosis and assessment of foetal development in animals. More frequently it is used for evaluation of cardiac function and of abdominal organ assessments. The image here on the right shows an ultrasound image of a normal kidney.

The adrenal glands (left) and digestive system are often investigated using ultrasound. stomach and intestines show up well but it is not possible to assess every bit of them using ultrasound and it is typically used as an adjunct to other digestive stystem investigations. Below you can see blood vessels within the liver, and below that a bladder tumour.

Ultrasound is very useful for assessing blood flow in vessels, particularly when there is an abnormality causing turbulence as in this porto-caval shunt. The shunt, and abnormal connection between two vessels, needs to be occluded surgically to redirect blood flow to where it should be going.

Other parts of the body are can also be scanned:.

• Muscles, tendons, blood vessels, lymph nodes
• The larynx andsalivary glands
• The eyes and orbit:

Here the detached retina is seen as a white line across the dark area of the vitreus space at the back of a dog's eye. In cases like this it is often possible to use laser surgery to help prevent further detachment and in some cases reattach a detached retina.