Ultrasound represents a technique for imaging internal organs without x-ray radiation. Instead, the ultrasound uses the reflection of high-frequency sound waves to evaluate the size, shape and position of soft tissues.
Ultrasound does not replace traditional x-ray examination of the organs. Instead, it complements the x-ray and can provide information that the x-ray does not, and vice versa. It does offer several advantages over x-rays. It is safer for the operator than x-rays because sound waves do not represent a dangerous energy source. Also, organs that may not be visible at all on x-rays, such as lymph nodes and the pancreas, can be seen on ultrasound. Additionally the internal structure of many organs is visible on ultrasound, whereas a x-ray will only show a solid structure. Also, “real time” or moving images may be produced. At the Animal Clinic at Thorndale, we use our ultrasound for screening purposes and for guidance collecting samples from the urinary bladder or other areas of the body. We are very fortunate to have a number of board certified veterinary radiologists within a short drive of our hospital. When we determine that your dog could best be served by a more detailed ultrasound examination, we will recommend a referral to area specialist.
Air and bone are the enemies of ultrasound waves. Since the lungs are air-filled, they cannot be studied. The exception is a mass located within or fluid around the lungs. Bones cannot be studied because they reflect the sound waves back to the ultrasound machine without producing an image. Because of the problems with imaging bone, the brain and spinal cord are not seen with an ultrasound study. MRI and Ct Scan are needed to image bone and structures contained within bone.
Prior to the study, the hair must be clipped over the area of interest. Next, a water-based gel is smoothed over the skin to improve the contact between the transducer and skin. The transducer is held in the operator’s hand and moved over the skin. When sound waves are emitted from the transducer, they are reflected back to the ultrasound machine. The pattern of the reflected sound waves creates an image that is viewed on a screen.
In general, the ultrasound is used to examine the heart or to study organs within the abdomen, such as the liver, kidneys, spleen, or bladder. The cardiac ultrasound, also called an echocardiogram or an “echo,” can measure the thickness of the heart wall and the size of the individual heart chambers. The heart valves can be examined for normal motion and any thickened areas. Motion can be detected so that an assessment can be made of the ability of the heart of move blood.
Some specific diseases can be diagnosed because they have a specific ultrasound appearance. However, other diseases cause ultrasound findings that are not unique.
Even when non-specific findings are detected, the ultrasound is still very helpful in detecting abnormal areas within a particular organ. Determination of an abnormality allows the veterinarian obtain a fine-needle aspirate or biopsy of the precise site. The needle aspirate produces a preparation of cells which are smeared on a slide. It does not usually require sedation because it is no more painful than a blood sample collection. It is a good screening tool but, in some cases, may not provide a diagnosis. In these situations, it may be necessary to obtain a biopsy. A biopsy provides an actual piece of tissue for the pathologist to examine under the microscope for more information. Sedation is often needed when ultrasound guided biopsies are performed. In many cases, the pathologist, receiving the tissue samples, makes the final diagnosis.
No special preparation is needed if the heart is to be studied. If organs in the abdomen are to be studied, your dog should be withheld from food for 16-18 hours. The urinary bladder is best visualized if it is full of urine. Therefore, do not let your dog urinate within 3-6 hours of the study, if possible.
If your dog is cooperative, no anesthesia or sedation is needed to ultrasound the heart or the abdomen. However, if biopsies are to be taken, a short-acting anesthetic will be needed to prevent complications.
Since an ultrasound study is performed in real time, the results of what is seen are known immediately. In some cases, the ultrasound images are sent to a veterinary radiologist for further consultation. If this happens, the final report may not be available for a few days.