Ultrasound Explained--Answering Clients' Questions About Ultrasound
World Small Animal Veterinary Association World Congress Proceedings, 2008
Emma Tobin, MVB, CertVR, DECVDI, MVM
Coolgreaney, Castlewarren, Co. Kilkenny, Ireland

What is an Ultrasound Scan?

Ultrasound is a scan used to study internal body structures. It works by sending out high frequency sound waves, directed at the internal body part being examined. The reflected sounds, or 'echoes', are recorded to create an image that can be viewed on a monitor. The sound waves are emitted from a small, hand-held probe. The high frequency of the sound means the human ear can't hear it.

What is it Used For in Veterinary Practice?

Ultrasound allows us to visualize the internal architecture of many organs. Radiographically inapparent internal abnormalities such as nodules, masses, cysts and abscesses can be seen, counted and measured. Many organs that are difficult to see on plain film radiographs (for example the prostate gland) can be easily seen with ultrasound. Real-time echocardiography (ultrasound examination of the heart) also allows us to see the heart in motion. From these images, measurements of cardiac contractility, areas of abnormal wall motion, chamber dilatation and wall thickening are made and compared to normal values.

Why Use Ultrasound Instead of Radiography?

Ultrasound studies allow your vet to see changes occurring within the organs in the body. Regular radiographs (x-rays) allow determination of the sizes and shapes of structures within the body, but they do not allow for visualisation inside of these structures. Ultrasound allows us to see inside the organs of the body and to internally assess and measure them.

How Will it Help in the Diagnosis of My Pet's Disease?

It depends on what is wrong with your pet. Following a full and thorough clinical examination, blood results etc, your veterinary surgeon may elect that an ultrasound examination of a particular area is the next diagnostic test that needs to be performed.

Ultrasound is very useful in diagnosing abnormalities that are discrete and may be missed on a plain radiograph. An example of this type of lesion would include a mass (tumour) in the liver. Once detected, the mass can be accurately measured for later comparison; careful examination of the other organs for the presence of metastatic disease (tumour spread) is needed prior to obtaining an accurate prognosis.

Ultrasound is especially useful in diagnosing inflammation of the pancreas (pancreatitis), adrenal gland abnormalities, bladder wall tumours, uterine infections (pyometra) and masses that are located behind the eyeball (retrobulbar masses). Ultrasound can often differentiate benign prostatic enlargement from prostatic cancer.

In animals with a history of vomiting, ultrasound can be used to evaluate whether the problem is within the stomach, liver, gall bladder or pancreas. It can often diagnose problems that are associated with the stomach or small intestinal wall such as neoplasia, or detect an intestinal foreign body, thus preventing a labour intensive and costly upper gastrointestinal barium study.

The diagnosis of pregnancy is commonly performed 21 days post-conception with ultrasound--much earlier than is possible with x-rays (42 days).

In imaging the heart, ultrasound is at its best, as the heart is a fluid filled organ. Abnormalities such as diseased heart muscle (hypertrophic and dilated cardiomyopathy), fluid around the heart (pericardial effusion), and congenital abnormalities can be diagnosed and their severity can be assessed. Heart-base tumors, which are rarely visible on radiographs, are easily visualised with ultrasonography.

Although the ultrasound examination alone is in many cases non-specific for a particular disease, in conjunction with the animal's age, sex, breed, history, physical exam, radiographic findings and lab work, as well as ultrasound guided fine needle aspirates or true-cut biopsies, the specificity for disease can be high.

Will it Hurt My Pet?

Ultrasound is not a painful procedure as it is non-invasive, however a small amount of pressure may have to be applied to the patient with the probe. This is usually well tolerated unless the patient has a painful condition such as pancreatitis. In these cases, pain-relieving medication may be administered to the patient.

Will My Pet Have to be Sedated or Anaesthetised?

The typical ultrasound examination requires no sedation or anesthesia and is easily performed on awake animals.

Will You Have to Clip Hair?

The only patient preparation necessary is clipping of the hair overlying the area to be scanned and placing coupling gel on the skin surface just prior to the exam process. Since ultrasound waves cannot travel through the air, your pet will need to have hair removed (clipped) in the area to be examined before the ultrasound study. Hair traps air and will interfere with the quality of the ultrasound study.

Can I Stay?

This depends mostly on the owner or patient. Some patients are more co-operative without the owner present. Some owners would prefer not to stay. However for the most part, owners benefit from seeing the ultrasound scan and realizing exactly what is wrong with their pet.

Does My Pet Need to Be Fasted?

It depends on what type of ultrasound examination is about to be performed. Most routine scans do not need the patient to be fasting, however if your pet is going to have an anaesthetic or sedation then the vet may request you to fast your pet.

How Long Will An Ultrasound Scan Take?

The entire scanning process takes 30-40 minutes. Images are acquired on the monitor of the ultrasound machine as well as on film for later viewing.

What is an Ultrasound Guided Biopsy or Fine Needle Aspirate?

Ultrasound guided fine needle aspirate or biopsy is a relatively safe and non-invasive way to reach a definitive diagnosis. The ultrasound may be used to 'guide' the veterinarian to a specific area for biopsy or aspirate of an organ or tissue. A biopsy obtains a core of tissue, whereas an aspirate collects a group of cell from the tissue. The major risk associated with an ultrasound-guided biopsy or aspirate is bleeding from the biopsy or aspirate site. Some diseases can affect the body's ability to form a blood clot. Testing for this ability may be required before the biopsy or aspirate is done, in order to ensure that your pet can properly form a clot and to minimize the chance of potentially fatal bleeding. In some situations, bleeding will still occur, and if severe, may require a blood transfusion.

There are certain conditions that make it difficult or impossible to perform an ultrasound-guided biopsy or aspirate. These include delayed clotting ability, fluid within the abdomen or chest cavity, or the organ being too small or too far away from the body wall to be within reach. Because the size of the biopsy obtained with an ultrasound guided needle is smaller than that obtained via surgery or laparoscopy, a disease that is localized may not be found, or if more than one condition is occurring the biopsy may not be big enough to allow the pathologist to evaluate all the changes occurring.

The advantage of ultrasound guided biopsy and aspirates is that they are 'non-invasive'. In other words, a body wall incision is not needed. Recuperation consists of restricted activity for the first 24 hours. An aspirate can usually be done without using anesthesia in a cooperative animal; a biopsy requires anesthesia and intravenous fluids. Anesthetic recovery is typically 3-4 hours, if severe bleeding occurs recovery could be longer.

Conditions Where Diagnosis Can Be Aided By Ultrasound


 Chamber enlargement (dilated and hypertrophic cardiomyopathy and congenital abnormalities)

 Contractility (dilated cardiomyopathy)

 Valvular insufficiency (endocardiosis and congenital abnormalities)

 Pericardial effusion

 Response to therapy


 Liver: ultrasound can help in the diagnosis of hepatitis, hepatic neoplasms, gall bladder stones, hepatic congestion, portosystemic shunts

 Kidneys: hydronephrosis, neoplasia, calculi, ectopic ureters, pyelonephritis, chronic renal failure, toxicities

 Spleen: haemangiosarcoma, haemangioma, haematoma, ruptured spleen

 Bladder: calculi, cystitis, neoplasia (transitional cell carcinoma), ectopic ureters

 Prostate: prostatic cysts, prostatic abscesses, prostatic neoplasia, benign prostatic hyperplasia

 Uterus: pregnancy can be detected as early as 21 days with ultrasound and ultrasound is very sensitive at detecting pyometras.

 Adrenals: ultrasound can help in the diagnosis of hyperadrenocorticism (Cushing's disease) and is useful in ensuring that adrenal neoplasia is not the cause.

 Pancreas: ultrasound allows visualisation of the pancreas for pancreatitis, pancreatic neoplasia and insulinomas.

 GIT: the gastrointestinal tract can be imaged in detail with ultrasound, this allows for the detection of foreign bodies, neoplasms and wall thickening.

Ultrasound can also help to confirm the presence of free abdominal fluid, check for peritonitis, and assess the mesenteric and iliac lymph nodes for tumour spread.


Ultrasound is very useful in imaging retrobulbar masses and assessing intraocular masses, retinal detachment and congenital eye abnormalities.


Ultrasound is useful in shoulder lameness, in the diagnosis of biceps and supraspinatus tendon abnormalities and in the assessment of osteochondrosis.


Ultrasound has been proven to be useful in assessing stifle and shoulder joints.

Speaker Information
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Emma Tobin, MVB, CertVR, DECVDI, MVM
Castlewarren, Co. Kilkenny, Ireland

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