Frequently Asked QuestionsFrequently asked questions about ultrasound
Ultrasound (US), also called sonography, is a method of dynamically imaging the body through the use of high-frequency sound waves beyond the range of hearing for humans and animals. A microphone-like instrument (transducer) is scanned over the skin. Gel is placed on the skin to improve the contact of the transducer to the area being examined. The sound waves are recorded and displayed as a real-time visual image. US can be used to examine many parts of the body including the abdomen, chest, heart, eyes, muscles and blood vessels, as well as the fetus during pregnancy. Because no ionizing radiation (x-ray) is involved, ultrasound is an extremely safe imaging modality. The procedure is painless and generally takes about 60 to 90 minutes to complete. An ultrasound exam is a minimally invasive technology that gives the pet owner and the veterinarian a great deal of information about the patient quickly and safely. Along with lab tests, radiographs and the physical exam, ultrasound can help your veterinarian diagnose quickly, saving time, costs, stress and most importantly, lives. Ultrasound imaging is based on the same principles involved in the sonar used by bats or ships at sea. As the sound passes through the body, echoes are produced that can be used to identify how far away an object is, how large it is, its shape and its consistency (fluid, solid or mixed). The ultrasound transducer functions as both a generator of sound (like a speaker) and a detector (like a microphone). When the transducer is pressed against the skin it directs inaudible, high-frequency sound waves into the body. As the sound echoes from the body's fluids and tissues the transducer records the strength and character of the reflected waves. These echoes are instantly measured and displayed by a computer, which in turn creates a real-time picture on the monitor. The "live" images of the examination may be "frozen" to capture a still image. What
are the common uses of this procedure in veterinary medicine?
What are the benefits of ultrasound?
Is
ultrasound safe? What are the limitations of ultrasound imaging? Ultrasound has difficulty penetrating bone and therefore can only see the outer surface of bony structures and not what lies within. For visualization of bone, other imaging modalities such as magnetic resonance imaging (MRI) may be selected. Because ultrasound waves do not pass through air, an evaluation of the stomach, small intestine and large intestine may be limited. Intestinal gas may also prevent visualization of deeper structures such as the pancreas and aorta. Obese patients are also more difficult to image because tissue attenuates (weakens) the sound waves as they pass deeper into the body. When should I ask for an ultrasound examination? If you notice your pet has one or more of these symptoms, consider calling your veterinarian for an ultrasound examination right away:
How do I prepare my pet for an ultrasound examination? Patients should be off food for 12 hours prior to an abdominal ultrasound. Water is allowed up to four hours before the procedure. No food or water withholding is needed for a cardiac exam or a thoracic (chest) exam. It is advisable to bring the patient into the hospital and drop them off the morning of the procedure. This allows the pet an opportunity to get used to the hospital environment and be shaved in an unhurried, relaxed atmosphere. This will help alleviate undue anxiety in the patient. This is especially important for cardiac exams. The rapid heartbeat associated with stress can interfere with the accurate interpretation of the examination.
If you have any questions about an ultrasound exam for your pet, your veterinarian is your best source of information about your pet's health care. How long will the appointment take? This can vary depending on the nature of the problem your pet for which your pet is examined. In general though, most ultrasound exams require approximately 1 ½ hours once your pet is shaved and ready for the exam. Will my pet be painful or sick after the procedure? One of the advantages of ultrasound is that it is a non-invasive procedure. Even when a biopsy is needed (a minimally invasive procedure), this is performed through an incision that is less than ½ inch long using a local anesthetic. In most cases you will not notice any changes in your pet after the procedure and your pet should not experience any discomfort afterwards. Why do you want my pet to have a full bladder for the ultrasound examination? A distended bladder acts as a "window" through which the sound waves travel and allows the sonographer to visualize the pelvic organs. A distended bladder also displaces bowel, which can prevent visualization of the pelvic organs. Why does my pet have to fast for an abdominal ultrasound? Fasting reduces the amount of air in the stomach and intestines which can interfere with visualization of the abdominal organs. It also ensures that the gallbladder will be distended so it can be thoroughly evaluated. How is the ultrasound performed? For an abdominal exam your pet will lay on his or her back in a padded trough. Hair is shaved from the abdominal area. For a cardiac exam (echocardiogram) your pet will lay on a specially designed padded and elevated table with a hole in it that allows the sonographer to bring the transducer up under the patient. A strip of hair on either side of the breast bone is shaved. In both cases a water-soluble non-toxic gel similar to KY jelly is used on the skin to improve transducer contact. Will my pet need to be sedated or anesthetized for the ultrasound? Many clients ask if sedation will be needed for an ultrasound exam. In most circumstances, the answer is no. We prefer not to give any drugs to patients undergoing a cardiac scan as this makes the results easier to interpret although the consequences of extreme patient anxiety with rapid heartbeat and panting can create equal difficulty in interpretation. In cases of extreme patient anxiety the appropriate use of anxiety-relieving medication is the most humane approach. Most abdominal scans, with or without fine needle aspirate, can be completed without the need for sedation. There are circumstances that make sedation/analgesia preferable or absolutely necessary: Very nervous patients that will not allow shaving or restraint without struggling or suffering great anxiety; patients undergoing a Tru-cut biopsy, patients that are painful. A Tru-cut type biopsy, while still a minimally invasive and very safe procedure, does involve the use of a biopsy needle that will be inside an abdominal organ. For safety reasons, it is important that the patient not make sudden movements while the biopsy sample is collected. Good images of the adrenal glands require a fair amount of pressure on the abdomen to bring the probe within 2 -3 cm of the glands. Some dogs will find this uncomfortable, especially if they are larger or overweight. Modern medications are very safe and many can be completely reversed when the procedure is over. Ultimately, the need for tranquilization is determined by the need for patient comfort and safety and the need to obtain good images. |
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Chris D. Miller, D.V.M.