What is an ultrasound?
Ultrasound is an imaging technique used to examine the organs. Ultrasound images are created by passing sound waves from a probe into the body, then recording them as they bounce back. The sound waves are absorbed by some tissues, with hardly any waves bouncing back, while other tissues reflect most of the waves. The ultrasound probe detects the different amounts of sound waves registering in each area and translates this into an image. The picture is grey scale, with white areas showing more solid tissue and black areas showing less solid tissue.
What are ultrasounds used for?
- Ultrasound is very good for examining the abdominal organs, such as the liver, kidneys and bladder, and is sometimes used to examine the lungs.
- Ultrasound images are created in real-time, so can be used to assess active processes like movement of the intestines.
- Ultrasound is commonly used to examine the heart, known as echocardiography. Ultrasound can show us the shape and size of the heart chambers as well as how the heart is contracting.
- You will be asked to leave your pet at the practice for the morning, as ultrasound scans are often part of a larger procedure list (we do not know an exact time the exam will take place, occasionally you may be given a specific time slot for the scan).
- You may be asked to withhold food the night before an ultrasound, so the stomach is empty. If the problem includes the bladder, you may be asked not to let your pet pass urine in the morning.
- To allow the ultrasound waves to enter the body, the probe must be placed as close to the skin as possible. This requires the fur to be clipped from the area. An ultrasound gel is applied to remove any tiny air pockets between the probe and the skin. This is cleaned off afterwards, and is non-toxic, but may leave a sticky residue.
- Ultrasound waves cannot be felt or heard, so ultrasound examination itself is not painful. Often, the disease process that requires a scan may be uncomfortable. Sometimes we need to push the probe into the skin quite firmly to create a clear image.
- Some animals may allow ultrasound with them awake; though often it is recommended to perform the scan under sedation. Your vet will advise if this is needed and discuss any risks.
- It may be advised to take samples from the organs during an ultrasound scan. This is usually performed using a thin needle to take a sample of cells and is known as a fine needle aspirate (FNA). This will usually be sent to a specialist lab for analysis but can give your vet more information about what is causing any changes seen.
- If samples are taken, the pet will usually require sedation, and may also require blood tests prior to the appointment to check clotting factors.
Ultrasound images are created instantly during the examination, this allows us to immediately screen for serious problems. Often it is helpful to spend time analysing the images after the scan is completed. Depending on the case, your vet may be happy to report results within a few hours. Sometimes they want a second opinion on interpreting the images, they may get back to you a few days later.
Unfortunately, not every problem can be identified on ultrasound, and sometimes images are more useful for ruling things out than providing a positive answer. Sometimes ultrasound shows us that there is something abnormal, but we cannot be certain exactly what is causing the changes. For example, an organ may look larger than normal. Images tell us that there is a structural change, but do not tell us whether the organ is working normally, or whether the increase in size is due to swelling, infection, or a mass.
Depending on what is seen on the ultrasound this may be enough to make a diagnosis and plan treatment. If the ultrasound shows changes but is inconclusive, we will need to gather more information. This may include x-rays, taking a sample of cells (as described above), a surgical biopsy, taking organ-specific blood tests, or even exploratory surgery. Sometimes advanced imaging such as a CT scan is required. This is significantly more expensive, and may require referral to another centre, but gives a much more detailed image.