Indications and Procedures (Magill’s Medical Guide, Sixth Edition)
Sound waves are mechanical pressure waves that can propagate through liquids, solids, and, to some extent, gases. A sound wave is composed of cyclic variations that occur over time; one cycle per second is called 1 hertz (Hz). Ultrasound waves have a frequency of oscillation that is higher than 20,000 hertz, placing ultrasound above the audible range for humans. The useful frequency range for medical diagnostic ultrasound is between 1 and 10 megahertz (10 million hertz), although surgical instruments often use carrier frequencies greater than 20 megahertz.
The basic ultrasound system has two principal components. The first, and perhaps more important, component is the transducer, or probe. The transducer converts electrical pulses into mechanical pressure (sound) waves that are transmitted into the tissues. It then detects the echoes that are reflected from the tissues and transforms those echoes into electrical voltages. The second component is the audiovisual electronic component, which processes and displays the reflected echoes in the form of an image of internal organs and structures or an image of the movement of red blood cells.
Ultrasound waves are created when the crystalline material within the transducer is excited by an electrical voltage produced by the instrument’s oscillator. The application of an electrical charge causes the crystalline particles to expand and contract, producing...
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Uses and Complications (Magill’s Medical Guide, Sixth Edition)
High-resolution abdominal ultrasonography is a valuable technique for the visualization of intra-abdominal organs and disease processes. For example, liver conditions such as parenchymal abnormalities, abscesses, hematomas, cysts, and cancerous lesions can be identified easily by means of this technique. B-mode and Doppler color-flow imaging are particularly valuable technologies that can be used to evaluate the tissue characteristics and blood flow patterns of transplanted organs. An ultrasound examination of the gallbladder may reveal gallstones, obstruction of the common bile duct, or inflammatory disease. Ultrasound imaging of the pancreas is used to identify pancreatitis, pancreatic pseudocysts, and carcinoma of this organ. An ultrasound examination of the spleen may reveal splenomegaly, or enlargement of the spleen in response to disease or trauma. Additionally, ultrasonography can be used to evaluate splenic volume and to identify hematomas, congenital cysts, infarctions, and tumors within the organ. The technology is particularly well suited for the study of tumors and abscesses within the abdomen. Ascites and other fluid collections may be recognized, and primary tumors and lymph node metastases within the abdominal cavity may be identified by means of pulse-echo imaging.
Ultrasound has certain characteristics that make it particularly valuable for examining the kidneys and the genitourinary tract. The ability...
(The entire section is 827 words.)
Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
Ultrasonic techniques have assumed a preferred role in the diagnosis of many diseases and have become an essential component of quality medical care. In contrast to the rapid development and use of X-ray technology in medical diagnosis, the application of diagnostic ultrasound has been relatively slow. Progress depended in large part on the development of high-resolution electronic devices and transducers. Early research into medical applications involved the adaptation of instruments that had been designed for industrial or military purposes.
The first attempts to locate objects with ultrasound probably occurred following the sinking of the Titanic in 1912. Improvements in the technology led to the widespread industrial and military use of ultrasound for the detection of flaws in metals, for the determination of range and depth information, and for navigation. The first application of ultrasound to medical diagnosis occurred in 1937, when K. T. Dussik attempted to image the cerebral ventricles by measuring the attenuation of a sound beam transmitted through the head. In 1947, Douglas H. Howry pioneered the ultrasonic imaging of soft tissues and constructed a pulse-echo system that utilized a transducer submerged in water. The system utilized surplus Navy sonar equipment, a high-fidelity recorder power supply, and a metal cattle-watering trough in which the patient and the transducer were immersed....
(The entire section is 516 words.)
For Further Information: (Magill’s Medical Guide, Sixth Edition)
Bates, Jane A. Abdominal Ultrasound. 2d ed. New York: Churchill Livingstone/Elsevier, 2004. Offers a wealth of practical clinical information on normal and abnormal anatomy and sonographic techniques.
Bernstein, Eugene F., ed. Vascular Diagnosis. 4th ed. St. Louis, Mo.: Mosby, 1993. This bible of noninvasive vascular technology contains chapters written by experts in the field. This important text not only presents updated information on diagnostic vascular ultrasonography but also takes a futuristic look at the clinical applications of this technology.
Griffith, H. Winter. Complete Guide to Symptoms, Illness, and Surgery. Revised and updated by Stephen Moore and Kenneth Yoder. 5th ed. New York: Perigee, 2006. Covers more than five hundred diseases and disorders and includes information about causes and risk factors, preventive techniques, diagnostic tests, and surgical treatment.
Hagan, Arthur D., and Anthony N. DeMaria. Clinical Applications of Two-Dimensional Echocardiography and Cardiac Doppler. 2d ed. Boston: Little, Brown, 1989. This exceptional textbook correlates normal and abnormal cardiac anatomy with two-dimensional echocardiography and pathophysiology.
Kremkau, Frederick W. Diagnostic Ultrasound: Principles and Instruments. 7th ed. St. Louis, Mo.: Saunders/Elsevier, 2006. A well-organized, programmed text for the student of ultrasound. Each...
(The entire section is 262 words.)
Ultrasonography (Encyclopedia of Cancer)
Ultrasonography is the study of internal organs or blood vessels using high-frequency sound waves. The actual test is called an ultrasound scan or sonogram. Duplex ultrasonography uses Doppler technology to study blood cells moving through major veins and arteries. There are several types of ultrasound. Each is used in diagnosing specific parts of the body.
An ultrasound is a noninvasive, safe method of examining a patient's eyes, pelvic or abdominal organs, breast, heart, or arteries and veins. It is often used to diagnosis disease, locate the source of pain, or look for stones in the kidney or gallbladder. Ultrasound produces images in real time. Images appear on the screen instantly. It may also be used to guide doctors who are performing a needle biopsy to locate a mass. (Needle biopsies are often used to obtain a sample of breast tissue to test for cancer cells.) Duplex/Doppler ultrasound aids in diagnosing a blockage in or a malformation of the vessel. Different color flows aid in identifying problem areas in smaller vessels. Endoscopic ultrasound combines a visual endoscopic exam, during which a flexible tube called an endoscope is threaded down the throat, with an ultrasound test. The ultrasound probe is...
(The entire section is 854 words.)
Ultrasonography (Encyclopedia of Neurological Disorders)
Ultrasonography is a diagnostic technique that involves directing high frequency sound waves at tissues in the body to generate images of anatomical structures. Ultrasonography is also called sonography, diagnostic sonography, and echocardiography when it is used to image the heart.
Ultrasonography has a variety of uses in medical diagnostics. It is most well suited for imaging soft tissues that are solid and uniform or filled with fluid. It does not perform well when imaging calcified objects such as bone or objects filled with air like the bowel. Some of the more common uses for ultrasonography include imaging fetus development during pregnancy, diagnosing gallbladder disease and some forms of cancer, and evaluating abnormalities in the scrotum and prostate, heart, and thyroid gland. Ultrasound can also be used to perform breast exams. A technique called Doppler imaging ultrasonography can also be used to view the movement of blood through blood vessels and to guide needles through anatomical structures for obtaining specimens for biopsy. Three-dimensional ultrasounds provide detailed images of fetuses in the uterus.
The majority of ultrasonic exams are performed externally by running a transducer over the surface of the skin. Usually a gel is applied to the skin on which the transducer...
(The entire section is 1897 words.)