Abdominal Ultrasound


Abdominal Ultrasound

 

Definition

Ultrasound technology allows doctors to "see" inside a patient without resorting to surgery. A transmitter sends high frequency sound waves into the body, where they bounce off the different tissues and organs to produce a distinctive pattern of echoes. A receiver "hears" the returning echo pattern and forwards it to a computer, which translates the data into an image on a television screen. Because ultrasound can distinguish subtle variations between soft, fluid-filled tissues, it is particularly useful in providing diagnostic images of the abdomen. Ultrasound can also be used in treatment.

Purpose

The potential medical applications of ultrasound were first recognized in the 1940s as an outgrowth of the sonar technology developed to detect submarines during World War II. The first useful medical images were produced in the early 1950s, and, by 1965, ultrasound quality had improved to the point that it came into general medical use. Improvements in the technology, application, and interpretation of ultrasound continue. Its low cost, versatility, safety and speed have brought it into the top drawer of medical imaging techniques.While pelvic ultrasound is widely known and commonly used for fetal monitoring during pregnancy, ultrasound is also routinely used for general abdominal imaging. It has great advantage over x-ray imaging technologies in that it does not damage tissues with ionizing radiation. Ultrasound is also generally far better than plain x rays at distinguishing the subtle variations of soft tissue structures, and can be used in any of several modes, depending on the need at hand.As an imaging tool, abdominal ultrasound generally is warranted for patients afflicted with: chronic or acute abdominal pain; abdominal trauma; an obvious or suspected abdominal mass; symptoms of liver disease, pancreatic disease, gallstones, spleen disease, kidney disease and urinary blockage; or symptoms of an abdominal aortic aneurysm. Specifically:
  • Abdominal pain. Whether acute or chronic, pain can signal a serious problem—from organ malfunction or injury to the presence of malignant growths. Ultrasound scanning can help doctors quickly sort through potential causes when presented with general or ambiguous symptoms. All of the major abdominal organs can be studied for signs of disease that appear as changes in size, shape and internal structure.
  • Abdominal trauma. After a serious accident, such as a car crash or a fall, internal bleeding from injured abdominal organs is often the most serious threat to survival. Neither the injuries nor the bleeding are immediately apparent. Ultrasound is very useful as an initial scan when abdominal trauma is suspected, and it can be used to pinpoint the location, cause, and severity of hemorrhaging. In the case of puncture wounds, from a bullet for example, ultrasound can locate the foreign object and provide a preliminary survey of the damage. The easy portability and versatility of ultrasound technology has brought it into common emergency room use, and even into limited ambulance service.
  • Abdominal mass. Abnormal growths—tumors, cysts, abscesses, scar tissue and accessory organs—can be located and tentatively identified with ultrasound. In particular, potentially malignant solid tumors can be distinguished from benign fluid-filled cysts and abscesses. Masses and malformations in any organ or part of the abdomen can be found.
  • Liver disease. The types and underlying causes of liver disease are numerous, though jaundice tends to be a general symptom. Ultrasound can differentiate between many of the types and causes of liver malfunction, and is particularly good at identifying obstruction of the bile ducts and cirrhosis, which is characterized by abnormal fibrous growths and reduced blood flow.
  • Pancreatic disease. Inflammation and malformation of the pancreas are readily identified by ultrasound, as are pancreatic stones (calculi), which can disrupt proper functioning.
  • Gallstones. Gallstones cause more hospital admissions than any other digestive malady. These calculi can cause painful inflammation of the gallbladder and also obstruct the bile ducts that carry digestive enzymes from the gallbladder and liver to the intestines. Gallstones are readily identifiable with ultrasound.
  • Spleen disease. The spleen is particularly prone to injury during abdominal trauma. It may also become painfully inflamed when beset with infection or cancer. These conditions also lend themselves well to ultrasonic inspection and diagnosis.
  • Kidney disease. The kidneys are also prone to traumatic injury and are the organs most likely to form calculi, which can block the flow of urine and cause blood poisoning (uremia). A variety of diseases causing distinct changes in kidney morphology can also lead to complete kidney failure. Ultrasound imaging has proven extremely useful in diagnosing kidney disorders.
  • Abdominal aortic aneurysm. This is a bulging weak spot in the abdominal aorta, which supplies blood directly from the heart to the entire lower body. These aneurysms are relatively common and increase in prevalence with age. A burst aortic aneurysm is imminently life-threatening. However, they can be readily identified and monitored with ultrasound before acute complications result.
Ultrasound technology can also be used for treatment purposes, most frequently as a visual aid during surgical procedures—such as guiding needle placement to drain fluid from a cyst, or to extract tumor cells for biopsy. Increasingly, direct therapeutic applications for ultrasound are being developed.The direct therapeutic value of ultrasonic waves lies in their mechanical nature. They are shock waves, just like audible sound, and vibrate the materials through which they pass. These vibrations are mild, virtually unnoticeable at the frequencies and intensities used for imaging. Properly focused however, high-intensity ultrasound can be used to heat and physically agitate targeted tissues.High-intensity ultrasound is used routinely to treat soft tissue injuries, such as strains, tears and associated scarring. The heating and agitation are believed to promote rapid healing through increased circulation. Strongly focused, high-intensity, high-frequency ultrasound can also be used to physically destroy certain types of tumors, as well as gallstones and other types of calculi. Developing new treatment applications for ultrasound is an active area of medical research.

Precautions

Properly performed, ultrasound imaging is virtually without risk or side effects. Some patients report feeling a slight tingling and/or warmth while being scanned, but most feel nothing at all. Ultrasound waves of appropriate frequency and intensity are not known to cause or aggravate any medical condition, though any woman who thinks she might be pregnant should raise the issue with her doctor before undergoing an abdominal ultrasound.The value of ultrasound imaging as a medical tool, however, depends greatly on the quality of the equipment used and the skill of the medical personnel operating it. Improperly performed and/or interpreted, ultrasound can be worse than useless if it indicates that a problem exists where there is none, or fails to detect a significant condition. Basic ultrasound equipment is relatively inexpensive to obtain, and any doctor with the equipment can perform the procedure whether qualified or not. Patients should not hesitate to verify the credentials of technicians and doctors performing ultrasounds, as well as the quality of the equipment used and the benefits of the proposed procedure.In cases where ultrasound is used as a treatment tool, patients should educate themselves about the proposed procedure with the help of their doctors—as is appropriate before any surgical procedure. Also, any abdominal ultrasound procedure, diagnostic or therapeutic, may be hampered by a patient's body type or other factors, such as the presence of excessive bowel gas (which is opaque to ultrasound). In particular, very obese people are often not good candidates for abdominal ultrasound.

Key terms

Accessory organ — A lump of tissue adjacent to an organ that is similar to it, but which serves no important purpose, if functional at all. While not necessarily harmful, such organs can cause problems if they grow too large or become cancerous. In any case, their presence points to an underlying abnormality in the parent organ.Benign — In medical usage, benign is the opposite of malignant. It describes an abnormal growth that is stable, treatable and generally not life-threatening.Biopsy — The surgical removal and analysis of a tissue sample for diagnostic purposes. Usually, the term refers to the collection and analysis of tissue from a suspected tumor to establish malignancy.Calculus — Any type of hard concretion (stone) in the body, but usually found in the gallbladder, pancreas and kidneys. They are formed by the accumulation of excess mineral salts and other organic material such as blood or mucous. Calculi (pl.) can cause problems by lodging in and obstructing the proper flow of fluids, such as bile to the intestines or urine to the bladder.Cirrhosis — A chronic liver disease characterized by the invasion of connective tissue and the degeneration of proper functioning—jaundice is often an accompanying symptom. Causes of cirrhosis include alcoholism, metabolic diseases, syphilis and congestive heart disease.Common bile duct — The branching passage through which bile—a necessary digestive enzyme—travels from the liver and gallbladder into the small intestine. Digestive enzymes from the pancreas also enter the intestines through the common bile duct.Computed tomography scan (CT scan) — A specialized type of x-ray imaging that uses highly focused and relatively low energy radiation to produce detailed two-dimensional images of soft tissue structures, particularly the brain. CT scans are the chief competitor to ultrasound and can yield higher quality images not disrupted by bone or gas. They are, however, more cumbersome, time consuming and expensive to perform, and they use ionizing electromagnetic radiation.Doppler — The Doppler effect refers to the apparent change in frequency of sound wave echoes returning to a stationary source from a moving target. If the object is moving toward the source, the frequency increases; if the object is moving away, the frequency decreases. The size of this frequency shift can be used to compute the object's speed—be it a car on the road or blood in an artery. The Doppler effect holds true for all types of radiation, not just sound.Frequency — Sound, whether traveling through air or the human body, produces vibrations—molecules bouncing into each other—as the shock wave travels along. The frequency of a sound is the number of vibrations per second. Within the audible range, frequency means pitch—the higher the frequency, the higher a sound's pitch.Ionizing radiation — Radiation that can damage living tissue by disrupting and destroying individual cells at the molecular level. All types of nuclear radiation—x rays, gamma rays and beta rays—are potentially ionizing. Sound waves physically vibrate the material through which they pass, but do not ionize it.Jaundice — A condition that results in a yellow tint to the skin, eyes and body fluids. Bile retention in the liver, gallbladder and pancreas is the immediate cause, but the underlying cause could be as simple as obstruction of the common bile duct by a gallstone or as serious as pancreatic cancer. Ultrasound can distinguish between these conditions.Malignant — The term literally means growing worse and resisting treatment. It is used as a synonym for cancerous and connotes a harmful condition that generally is life-threatening.Morphology — Literally, the study of form. In medicine, morphology refers to the size, shape and structure rather than the function of a given organ. As a diagnostic imaging technique, ultrasound facilitates the recognition of abnormal morphologies as symptoms of underlying conditions.

Description

Ultrasound includes all sound waves above the frequency of human hearing—about 20 thousand hertz, or cycles per second. Medical ultrasound generally uses frequencies between one and 10 million hertz (1-10 MHz). Higher frequency ultrasound waves produce more detailed images, but are also more readily absorbed and so cannot penetrate as deeply into the body. Abdominal ultrasound imaging is generally performed at frequencies between 2-5 MHz.An ultrasound machine consists of two parts: the transducer and the analyzer. The transducer both produces the sound waves that penetrate the body and receives the reflected echoes. Transducers are built around piezoelectric ceramic chips. (Piezoelectric refers to electricity that is produced when you put pressure on certain crystals such as quartz). These ceramic chips react to electric pulses by producing sound waves (they are transmitting waves) and react to sound waves by producing electric pulses (receiving). Bursts of high frequency electric pulses supplied to the transducer causes it to produce the scanning sound waves. The transducer then receives the returning echoes, translates them back into electric pulses and sends them to the analyzer—a computer that organizes the data into an image on a television screen.Because sound waves travel through all the body's tissues at nearly the same speed—about 3,400 miles per hour—the microseconds it takes for each echo to be received can be plotted on the screen as a distance into the body. The relative strength of each echo, a function of the specific tissue or organ boundary that produced it, can be plotted as a point of varying brightness. In this way, the echoes are translated into a picture. Tissues surrounded by bone or filled with gas (the stomach, intestines and bowel) cannot be imaged using ultrasound, because the waves are blocked or become randomly scattered.Four different modes of ultrasound are used in medical imaging:
  • A-mode. This is the simplest type of ultrasound in which a single transducer scans a line through the body with the echoes plotted on screen as a function of depth. This method is used to measure distances within the body and the size of internal organs. Therapeutic ultrasound aimed at a specific tumor or calculus is also A-mode, to allow for pinpoint accurate focus of the destructive wave energy.
  • B-mode. In B-mode ultrasound, a linear array of transducers simultaneously scans a plane through the body that can be viewed as a two-dimensional image on screen. Ultrasound probes containing more than 100 transducers in sequence form the basis for these most commonly used scanners, which cost about $50,000.
  • M-Mode. The M stands for motion. A rapid sequence of B-mode scans whose images follow each other in sequence on screen enables doctors to see and measure range of motion, as the organ boundaries that produce reflections move relative to the probe. M-mode ultrasound has been put to particular use in studying heart motion.
  • Doppler mode. Doppler ultrasonography includes the capability of accurately measuring velocities of moving material, such as blood in arteries and veins. The principle is the same as that used in radar guns that measure the speed of a car on the highway. Doppler capability is most often combined with B-mode scanning to produce images of blood vessels from which blood flow can be directly measured. This technique is used extensively to investigate valve defects, arteriosclerosis and hypertension, particularly in the heart, but also in the abdominal aorta and the portal vein of the liver. These machines cost about $250,000.
The actual procedure for a patient undergoing an abdominal ultrasound is relatively simple, regardless of the type of scan or its purpose. Fasting for at least eight hours prior to the procedure ensures that the stomach is empty and as small as possible, and that the intestines and bowels are relatively inactive. Fasting also allows the gall bladder to be seen, as it contracts after eating and may not be seen if the stomach is full. In some cases, a full bladder helps to push intestinal folds out of the way so that the gas they contain does not disrupt the image. The patient's abdomen is then greased with a special gel that allows the ultrasound probe to glide easily across the skin while transmitting and receiving ultrasonic pulses.This procedure is conducted by a doctor with the assistance of a technologist skilled in operating the equipment. The probe is moved around the abdomen to obtain different views of the target areas. The patient will likely be asked to change positions from side to side and to hold their breath as necessary to obtain the desired views. Discomfort during the procedure is minimal.The many types and uses of ultrasound technology makes it difficult to generalize about the time and costs involved. Relatively simple imaging—scanning a suspicious abdominal mass or a suspected abdominal aortic aneurysm—will take about half an hour to perform and will cost a few hundred dollars or more, depending on the quality of the equipment, the operator and other factors. More involved techniques such as multiple M-mode and Doppler-enhanced scans, or cases where the targets not well defined in advance, generally take more time and are more expensive.Regardless of the type of scan used and the potential difficulties encountered, ultrasound remains faster and less expensive than computed tomography scans (CT), its primary rival in abdominal imaging. Furthermore, as abdominal ultrasounds are generally undertaken as "medically necessary" procedures designed to detect the presence of suspected abnormalities, they are covered under most types of major medical insurance. As always, though, the patient would be wise to confirm that their coverage extends to the specific procedure proposed. For nonemergency situations, most underwriters stipulate prior approval as a condition of coverage.Specific conditions for which ultrasound may be selected as a treatment option—certain types of tumors, lesions, kidney stones and other calculi, muscle and ligament injuries, etc.—are described in detail under the appropriate entries in this encyclopedia.

Preparation

A patient undergoing abdominal ultrasound will be advised by their physician about what to expect and how to prepare. As mentioned above, preparations generally include fasting and arriving for the procedure with a full bladder, if necessary. This preparation is particularly useful if the gallbladder, ovaries or veins are to be examined.

Aftercare

In general, no aftercare related to the abdominal ultrasound procedure itself is required.

Risks

Abdominal ultrasound carries with it no recognized risks or side effects, if properly performed using appropriate frequency and intensity ranges. Sensitive tissues, particularly those of the reproductive organs, could possibly sustain damage if violently vibrated by overly intense ultrasound waves. In general though, such damage would only result from improper use of the equipment.Any woman who thinks she might be pregnant should raise this issue with her doctor before undergoing an abdominal ultrasound, as a fetus in the early stages of development could be injured by ultrasound meant to probe deeply recessed abdominal organs.

Normal results

As a diagnostic imaging technique, a normal abdominal ultrasound is one that indicates the absence of the suspected condition that prompted the scan. For example, symptoms such as a persistent cough, labored breathing, and upper abdominal pain suggest the possibility of, among other things, an abdominal aortic aneurysm. An ultrasound scan that indicates the absence of an aneurysm would rule out this life-threatening condition and point to other, less serious causes.

Abnormal results

Because abdominal ultrasound imaging is generally undertaken to confirm a suspected condition, the results of a scan often will prove abnormal—that is they will confirm the diagnosis, be it kidney stones, cirrhosis of the liver or an aortic aneurysm. At that point, appropriate medical treatment as prescribed by a patient's doctor is in order. See the relevant disease and disorder entries in this encyclopedia for more information.

Resources

Periodicals

Freundlich, Naomi. "Ultrasound: What's Wrong with this Picture?" Business Week September 15, 1997:84-5.

Organizations

American College of Gastroenterology. 4900 B South 31st St., Arlington, VA 22206-1656. (703) 820-7400. http://www.acg.gi.org.American Institute of Ultrasound in Medicine. 14750 Sweitzer Lane, Suite 100, Laurel, MD 20707-5906. (800) 638-5352. http://www.aium.org.American Society of Radiologic Technologists. 15000 Central Ave., SE, Albuquerque, NM 87123-3917. (505) 298-4500. http://www.asrt.org.

Ultrasound, Abdomen

Synonym/acronym: Abdominal ultrasound, abdomen sonography.

Common use

To visualize and assess the solid organs of the abdomen, including the aorta, bile ducts, gallbladder, kidneys, pancreas, spleen, and other large abdominal blood vessels. This study is used to perform biopsies and assist in diagnosing disorders such as aortic aneurysm, infections, fluid collections, masses, and obstructions. This procedure can also be used to evaluate therapeutic interventions such as organ transplants.

Area of application

Abdomen from the xiphoid process to the umbilicus.

Contrast

Done without contrast.

Description

Ultrasound (US) procedures are diagnostic, noninvasive, and relatively inexpensive. They take a short time to complete, do not use radiation, and cause no harm to the patient. High-frequency sound waves of various intensities are delivered by a transducer, a flashlight-shaped device, pressed against the skin. The waves are bounced back off internal anatomical structures and fluids, converted to electrical energy, amplified by the transducer, and displayed as images on a monitor. US is often used as a diagnostic and therapeutic tool for guiding minimally invasive procedures such as needle biopsies and fluid aspiration (paracentesis). The contraindications and complications for biopsy and fluid aspiration are discussed in detail in the individual monographs.

Abdominal US is valuable in determining aortic aneurysms, the internal components of organ masses (solid versus cystic), and for evaluating other abdominal diseases, ascites, and abdominal obstruction. Abdominal US can be performed on the same day as a radionuclide scan or other radiological procedure and is especially valuable in patients who have hypersensitivity to contrast medium or are pregnant. US is also widely used for pediatric patients to help diagnose appendicitis and for infants to assign cause for recurrent vomiting.

This procedure is contraindicated for

    N/A

Indications

  • Determine the patency and function of abdominal blood vessels, including the abdominal aorta; vena cava; and portal, splenic, renal, and superior and inferior mesenteric veins
  • Detect and measure an abdominal aortic aneurysm
  • Monitor abdominal aortic aneurysm expansion to prevent rupture
  • Determine changes within small aortic aneurysms pre- and postsurgery
  • Evaluate abdominal ascites
  • Evaluate size, shape, and pathology of intra-abdominal organs

Potential diagnosis

Normal findings

  • Absence of ascites, aortic aneurysm, cysts, obstruction, or tumors
  • Normal size, position, and shape of intra-abdominal organs and associated structures

Abnormal findings related to

  • Abdominal abscess, ascitic fluid, or hematoma
  • Aortic aneurysm greater than 4 cm
  • Congenital absence or malplacement of organs
  • Gallbladder or renal calculi
  • Tumor, liver, spleen, or retroperitoneal space

Critical findings

  • Aortic aneurysm measuring 5 cm or more in diameter.

  • It is essential that a critical finding be communicated immediately to the requesting health-care provider (HCP). A listing of these findings varies among facilities.

  • Timely notification of a critical finding for lab or diagnostic studies is a role expectation of the professional nurse. Notification processes will vary among facilities. Upon receipt of the critical value the information should be read back to the caller to verify accuracy. Most policies require immediate notification of the primary HCP, Hospitalist, or on-call HCP. Reported information includes the patient’s name, unique identifiers, critical value, name of the person giving the report, and name of the person receiving the report. Documentation of notification should be made in the medical record with the name of the HCP notified, time and date of notification, and any orders received. Any delay in a timely report of a critical finding may require completion of a notification form with review by Risk Management.

Interfering factors

  • Factors that may impair clear imaging

    • Attenuation of the sound waves by the ribs, which can impair clear imaging of the upper abdominal structures
    • Incorrect placement of the transducer over the desired test site; quality of the US study is very dependent upon the skill of the ultrasonographer
    • Metallic objects (e.g., jewelry, body rings) within the examination field, which may inhibit organ visualization and cause unclear images
    • Inability of the patient to cooperate or remain still during the procedure because of age, significant pain, or mental status
    • Retained gas or barium from a previous radiological procedure

  • Other considerations

    • Failure to follow dietary and fluid restrictions and other pretesting preparations may cause the procedure to be canceled or repeated.

Nursing Implications and Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Inform the patient this procedure can assist in assessing abdominal abnormalities.
  • Obtain a history of the patient’s complaints or clinical symptoms, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of results of the patient’s cardiovascular, gastrointestinal, genitourinary, and hepatobiliary systems, symptoms, and results of previously performed laboratory tests, diagnostic and surgical procedures.
  • Note any recent procedures that can interfere with test results (i.e., barium procedures, surgery, or biopsy). There should be 24 hours between administration of barium and this test.
  • Endoscopic retrograde cholangiopancreatography, colonoscopy, and computed tomography of the abdomen, if ordered, should be scheduled after this procedure.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
  • Review the procedure with the patient. Address concerns about pain related to the procedure. Explain to the patient that there may be moments of discomfort experienced during the test. Inform the patient that the procedure is performed in a ultrasound department, by a health-care provider (HCP) specializing in this procedure, with support staff, and takes approximately 30 to 60 minutes.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Instruct the patient to remove jewelry and other metallic objects in the area to be examined.
  • Note that there are no food or fluid restrictions for US of the aorta. Restrictions for US studies of other abdominal organs may be imposed by medical direction.

Intratest

  • Potential complications: N/A
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient.
  • Ensure that food and fluids have been restricted, if required, prior to the procedure.
  • Ensure that the patient has removed external metallic objects prior to the procedure.
  • Instruct the patient to void prior to the procedure and to change into the gown, robe, and foot coverings provided.
  • Instruct the patient to cooperate fully and to follow directions. Instruct the patient to remain still throughout the procedure because movement produces unreliable results.
  • Place the patient in the supine position on an examination table. The right- or left-side-up positions may be used to allow gravity to reposition the liver, gas, and fluid to facilitate better organ visualization.
  • Expose the abdominal area and drape the patient.
  • Conductive gel is applied to the skin, and a Doppler transducer is moved over the skin to obtain images of the area of interest.
  • Ask the patient to breathe normally during the examination. If necessary for better organ visualization, ask the patient to inhale deeply and hold his or her breath.

Post-Test

  • Inform the patient that a report of the results will be sent to the requesting HCP, who will discuss the results with the patient.
  • When the study is completed, remove the gel from the skin.
  • Instruct the patient to resume usual diet and fluids, as directed by the HCP.
  • Recognize anxiety related to test results. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be needed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include ACTH and challenge tests, albumin, ALKP, ALT, amylase, angiography abdomen, AST, biopsy intestinal, biopsy liver, bilirubin and fractions, BUN, calcium, calculus kidney stone panel, cancer antigens, carbon dioxide, CBC, CBC hematocrit, CBC hemoglobin, CBC WBC and differential, chloride, cortisol and challenge tests, creatinine, CT abdomen, GGT, HCG, hepatobiliary scan, infectious mononucleosis, IVP, KUB, LDH, lipase, magnesium, MRI abdomen, peritoneal fluid analysis, phosphorus, potassium, PT/INR, renogram, sodium, US kidney, US liver and biliary, US pancreas, US spleen, uric acid, urinalysis, and WBC scan.
  • Refer to the Cardiovascular, Gastrointestinal, Genitourinary, and Hepatobiliary systems tables at the end of the book for related tests by body system.