What is an ultrasound?
An ultrasound (also called a sonogram) is another diagnostic test used to evaluate internal organs and tissues. It is most commonly used to evaluate abdominal organs or the heart, although can also be utilized to examine the eyes, lungs, bony lesions, or subcutaneous space (under the skin). Ultrasound is generally much more sensitive and specific when it comes to detecting and characterizing internal abnormalities compared to radiographs, especially since it allows the clinician to evaluate the entire tissue structure (including inside various organs). Despite this, it is important to know that in some cases both radiographs and ultrasound are recommended, since radiographs may be better at showing the size, shape, and position of various internal organs and tissues.
An abdominal ultrasound is generally recommended by a clinician in patients with abnormal abdominal x-rays, in patients with persistent clinical signs (such as vomiting, diarrhea, inappetence, bloody urine, abdominal discomfort, weight loss, fever), and in patients with abnormal bloodwork/urine findings (such as elevated liver or kidney values, abnormal urine concentration). In addition, ultrasonography is commonly utilized with cancer patients (see below). A cardiac ultrasound (called an echocardiogram) may be recommended in cases where a heart murmur or abnormal rhythm is heard on physical examination or in patients where underlying heart disease is suspected. In some patients where systemic disease is present, an ultrasound may be prescribed to rule out specific internal abnormalities that would prompt initiation of further diagnostics and/or treatment. Ultrasound can also be used as a guide during specific procedures, such as fine needle aspiration of internal organs, tumors, lymph nodes, acquisition of fluid within the chest/abdominal cavity, or removal of urine from the bladder.
How is are ultrasound images obtained and is this procedure safe?
Ultrasound requires specialized equipment and a skilled professional (usually a board certified radiologist, an internal medicine specialist, a cardiologist [for echocardiograms], or a veterinarian that has ample training and experience with ultrasonography). The hair over the area being imaged (eg the abdomen or small square over the heart) is shaved and the patient is placed on a table (usually on his side or back) for the duration of the exam. Gel and/or alcohol is placed on the surface of the skin or in some cases gel is placed directly on the transducer, which is attached to the ultrasound machine and transmits the images. The transducer (also called probe) is placed on the skin and moved around to evaluate the area; during this process ultrasound waves are transmitted into the patient and are absorbed or echo back depending on the type of tissue or organ is encountered. This ultimately creates an image that is interpreted by the ultrasonographer. In addition to imaging, flow of blood (eg through the heart, arteries, or veins) can also be evaluated with ultrasonography.
Ultrasound is non-invasive and relatively painless. The procedure generally takes 20-40 minutes (depending on the area being evaluated), and usually does not require sedation. In rare cases where the patient is stressed, anxious, or painful (due to underlying disease), mild sedation may be administered. The only time there is any risk with ultrasound is when ultrasound guided fine needle aspirates or biopsies are performed. These procedures require sedation or light anesthesia, and in rare cases can cause internal bleeding or leakage of air (ie if lung is tissue is aspirated causing difficulty breathing). The majority of the time the patient tolerates the procedure well with no significant issues.
How is an ultrasound used in cancer patients?
Similar to radiographs, ultrasonography is commonly used as a staging test to search for evidence of spread of cancer to other areas of the body (particularly the abdominal cavity). Common sites of metastasis include liver, spleen, and abdominal lymph nodes. Ultrasound guided fine needle aspirates are commonly performed to further characterize splenic and liver nodules/masses, enlarged lymph nodes, or tumors within the abdomen, and also to distinguish between benign and malignant changes. Ultrasonography is also used often to assess response to treatment in patients receiving systemic therapy.