Ultrasound
The RVC Equine Referral Hospital has major expertise in equine ultrasonography and has several ultrasound machines to suit specific purposes. Two hospital based systems are used for advanced clinical applications, including orthopaedic, abdominal and thoracic ultrasonography. Four portable units are available for ambulatory use.
Ultrasonography is widely used at the RVC Equine Referral Hospital. It is non-invasive, non-radioactive and relatively inexpensive compared to other imaging modalities. It is the standard imaging modality for examination of the reproductive tract in the breeding mare. It is also used widely in equine lameness diagnosis to evaluate soft tissue structures of the limbs, such as tendons, ligaments, joints, tendon sheaths, bursae, muscles and blood vessels.
Ultrasonography can also aid in the examination of the bone surface, and confirm fractures in regions that are difficult to radiograph e.g. the pelvis and ribs. For horses that have undergone trauma to tendons or ligaments, ultrasound is an effective way of monitoring the healing process of these structures as well as in the initial diagnosis.
Other uses of ultrasonography include:
- Investigation of cardiac disease.
- Evaluation of the eye.
- Investigation of respiratory disease, especially in foals.
- Imaging the abdomen, for example in horses with colic.
How are ultrasound images acquired?
Ultrasound waves in the frequency range of 1.5-15 megahertz (MHz) are used to create images of body structures based on the pattern of echoes reflected from the tissues and organs. A transducer (probe) has to be placed in contact with the horse. It is very important that the transducer is placed as close to the tissue being examined as possible, therefore most horses undergoing ultrasonography of their distal limbs, abdomen or thorax will be usually be required to have the area under examination clipped prior.
The transducer produces sound waves which penetrate through the tissues until they meet a tissue of different density. At the interface between tissues, the waves are reflected back and used to create an image on the screen. The reflected sound waves are known as ‘echoes’ and tissues that reflect sounds are described as ‘echogenic’. Bone is highly reflective and appears as a bright white line on the screen. If the sound waves pass readily through less dense tissues and there is little reflection, these appear as black (anechoic) areas on the screen. The soft tissues of the body have a characteristic appearance with many shades of grey (>250) between the extreme of the black and white at the end of each scale.