The Science behind it
Ultrasound scanning is one of the most commonly used methods of imaging in horses. It is easily portable and very safe with no risks of radiation. Ultrasound machines work by emitting sound waves into the tissues of the body which are reflected to different degrees by different tissue types. Ultrasound waves are reflected very well wherever soft tissue meets air, or soft tissue meets bone. Waves are not reflected when they meet fluid but penetrate completely through it. This means that bone appears white when viewed on an ultrasound scanner, soft tissues are varying shades of grey and fluid is black.
Uses in Practice
Ultrasound examination remains the gold standard technique for diagnosing tendon and ligament injuries e.g. superficial digital flexor tendon ('bowed' tendons), suspensory ligament or check ligament injuries. These will appear as loss of the normal tendon fibre pattern or accumulation of fluid within the torn areas of tendon. In addition, early tendon damage signs e.g. enlargement of the overall size of the tendon can provide useful information and allow adjustments in training to prevent further injury. Ultrasound is used in the diagnosis of other types of orthopaedic injury e.g. to examine joints and diagnose conditions such as bone cysts and chip fractures or collateral ligament or meniscal injuries.
It is also used routinely at our clinic as part of the workup and assessment of colic cases. Evaluation of intestinal motility, bowel wall thickness and signs of small intestinal distension can be assessed along with identification of potential large colon displacements e.g. nephrosplenic ligament entrapment. Ultrasound guided belly taps (abdominocentesis) are frequently performed. Ultrasound guidance is also very useful in obtaining biopsies of abdominal organs such as the liver.
Ultrasound evaluation is important in the assessment of pneumonia cases, particularly in adult horses where radiographic evaluation is limited due to the horse's size. It also provides vital information regarding build up of fluid around the lungs ('pleural effusion'), which in severe pneumonia can make breathing even more difficult.
Echocardiography is a specific form of ultrasound examination used to examine the heart. The strength and function of the heart muscle can be assessed in combination with evaluation of the heart valves e.g. if a murmur has been detected on routine examination.
Ultrasound is invaluable for investigating sick foals- It can be used to diagnose respiratory disease such as pneumonia and to check for ruptured bladders, umbilical remnant infections, meconium impactions and hernias as well as being part of the investigation for sepsis in foals.