What is an Ultrasound?

An ultrasound test is a radiology technique, which uses high- frequency sound waves to produce images of the organs and structures of the body. The sound waves are sent through body tissues with a device called a transducer. The transducer is placed directly on top of the skin, which has a gel applied to the surface. The sound waves that are sent by the transducer through the body are then reflected by internal structures as "echoes." These echoes return to the transducer and are transmitted electrically onto a viewing monitor. The echo images are then recorded on a plane film and can also be recorded on videotape. After the ultrasound, the gel is easily wiped off.

The technical term for ultrasound testing and recording is "sonography." Ultrasound testing is painless and harmless. Ultrasound tests involve no radiation and studies have not revealed any adverse effects.

For what purposes are ultrasounds performed?

Ultrasound examinations can be used in various areas of the body for a variety of purposes. These purposes include examination of the chest, abdomen, blood vessels (such as to detect blood clots in leg veins) and the evaluation of pregnancy. In the chest, ultrasound can be used to obtain detailed images of the size and function of the heart. Ultrasound can detect abnormalities of the heart valves, such as mitral valve prolapse, aortic stenosis, and infection (endocarditis). Ultrasound is commonly used to guide fluid withdrawal (aspiration) from the chest, lungs, or around the heart. Ultrasound is also commonly used to examine internal structures of the abdomen. Gallstones in the gallbladder are easily detected, as are kidney stones. The size and structure of the kidneys, the ureters, liver, spleen, pancreas, and aorta within the abdomen can be examined. Ultrasound can detect fluid, cysts, tumors or abscess in the abdomen or liver. Impaired blood flow from clots or arteriosclerosis in the legs can be detected by ultrasound. Aneurysms of the aorta can also be seen. Ultrasound is also commonly used to evaluate the structure of the thyroid gland in the neck.

During pregnancy, an ultrasound can be used to evaluate the size, gender, movement, and position of the growing baby. The baby's heart is usually visible early, and as the baby ages, body motion becomes more apparent. The baby can often be visualized by the mother during the ultrasound, and the gender of the baby is sometimes detectable.

How do patients prepare for an ultrasound?

Preparation for ultrasound is minimal. Generally, if internal organs such as the gallbladder are to be examined, patients are requested to avoid eating and drinking with the exception of water for six to eight hours prior to the examination. This is because food causes gallbladder contraction, minimizing the size, which would be visible during the ultrasound. In preparation for examination of the baby and womb during pregnancy, it is recommended that mothers drink at least four to six glasses of water approximately one to two hours prior to the examination for the purpose of filling the bladder. The extra fluid in the bladder moves air-filled bowel loops away from the womb so that the baby and womb are more visible during the ultrasound test.

How are results transmitted to the patient and doctor?

The ultrasound is generally performed by a technician. The technician will notice preliminary structures and may point out several of these structures during the examination. The official reading of the ultrasound is given by a radiologist, a physician who is an expert at interpreting ultrasound images. The radiologist records the interpretation and transmits it to the practitioner requesting the test. Occasionally, during the ultrasound test the radiologist will ask questions of the patient and/or perform an examination in order to further define the purpose for which the test is ordered or to clarify preliminary findings. Plain x-rays might be ordered to further evaluate early findings. A summary of results of all of the above is reported to the practitioner who requested the ultrasound. They then are discussed with the patient in the context of overall health status.

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Six Ways to Get the Inside Picture: A Quick Reference for Students of Radiology

Projection radiography, you may call them radiographs or more formally Roentgenographs, as they're named after the discoverer of X-rays, Wilhelm Conrad Roentgen. These are often used for evaluation of bony structures and soft tissues. An X-Ray machine directs electromagnetic radiation upon a region in the body. The lower the density of the object, the more light passes through. Thus radiation tends to pass through skin, fat, muscle, and other tissues, but is absorbed by bones, tumors, and lungs affected by severe pneumonia. Radiation which has passed through a patient then exposes onto an X-ray film. Areas of film exposed to higher amounts of radiation will usually appear dark gray after development. The unexposed areas of film of course stay white. Fluoroscopy and angiography are special applications of X-ray imaging, in which a fluorescent screen or image intensifier tube is connected to a small television system, which allows real-time imaging of structures in motion. Radiocontrast agents are administered, which are often swallowed or injected into the body of the patient, that help delineate anatomy such as the blood vessels, the genitourinary system or the gastrointestinal tract. There is a radiocontrast agent for each specific type of evaluation. For example, barium in a suspension is administered into the gastrointestinal tract and the image is taken with fluoroscopy or radiography. Radiocontrast agents, which 'soak up' X-ray radiation, in conjunction with the real-time imaging allows demonstration of dynamic processes. Peristalsis in the digestive tract or blood flow in arteries and veins can easily be seen dynamically this way, for instance.

CT scanning/CT imaging uses X-rays in conjunction with computing algorithms to take an image of a variety of soft tissues in the body. CT is acquired in the axial plane, while coronal and sagittal images can be rendered by computer software reconstruction. It is of course only recently that the combined studies of computer imaging such as 3D ray-tracing and Computer Assisted Design have made this process possible. Yes, CT imaging owes a little debt to movies like "Tron"! Radiocontrast agents are often used with CT for enhanced delineation of the patient's anatomy. Intravenous contrast allows 3D reconstructions of arteries and veins, showing them as a network of branching tunnels in real-time space. While radiographs provide higher resolution for bone X-rays, CT can generate much more detailed images of the soft tissues. CT exposes the patient to more ionizing radiation than a radiograph, which is the main reason it isn't used any more oftan than it needs to be.

Ultrasound/Medical ultrasonography uses ultrasound, literal high-frequency sound waves, to visualize soft tissue structures in the body in real time. No ionizing radiation is involved, but the quality of the images obtained using ultrasound is highly dependent on the skill of the person performing the exam, who is known as the ultrasonographer. The use of ultrasound in medical imaging has developed mostly within the last thirty years. The first ultrasound images were static and two dimensional, but with modern-day ultrasonography 3D reconstructions can be observed in real-time. Because ultrasound does not utilize ionizing radiation like radiography, CT scans, and nuclear medicine imaging techniques, it is generally considered safer. For this reason, this imaging method plays a vital role in obstetrical imaging. Fetal development can be thoroughly evaluated, allowing early diagnosis of fetal anomalies or confirmation of a normal gestation.

MRI/NMR MRI uses strong magnetic fields to align spinning hydrogen proton nuclei within body tissues, then uses a radio signal to disturb the axis of rotation of these nuclei. It then observes the radio frequency signal generated as the nuclei return to their baseline states. MRI scans give the highest quality soft tissue contrast of all the imaging modalities. With advances in scanning speed and spatial resolution and improvements in computer 3D algorithms and hardware, MRI has made greatleaps forward in the recent years. One distinct disadvantage is that the patient has to hold still for long periods of time in a noisy, cramped space while the imaging is performed. Recent improvements in magnet design like wider, shorter magnet bores and more open magnet designs, have brought some relief for claustrophobic patients, who previously had to be sedated - unfortunate if you are looking at the brain on the MRI, since the brain shows different activity when sedated. MRI has it's best benefit in imaging the brain, spine, and musculoskeletal system. The modality can be contraindicated for patients with pacemakers (watch out for those magnets!), certain types of cerebral aneurysmal clips or metallic hardware due to the strong magnetic fields. Areas of present advancement include functional imaging, cardiovascular MRI, as well as MR image guided therapy.

Nuclear medicine imaging, our newest technology, involves the administration into the patient of substances labeled with radioactive tracers which have affinity for particular tissues. The heart, lungs, thyroid, liver, gallbladder, and bones are commonly evaluated for particular conditions using nuclear medicine techniques. While anatomical detail is limited in these kinds of images, nuclear medicine is useful in displaying physiological functions. For instance, processes such as the growth of a tumor can often be monitored, even when the tumor cannot be adequately visualized using any of the other methods. The principal imaging device is the gamma camera which detects the radiation emitted by the tracer in the body and displays it as an image on a computer monitor. Often the information is converted into a series of slices through the body like a loaf of bread. In the most modern devices, nuclear medicine images can be fused with a CT scan taken at the same time so that the physiological information can be super-imposed with the anatomical structures to improve diagnostic accuracy. PET scanning is another kind of nuclear medicine. The applications of nuclear medicine can include the scanning of bones, which traditionally has had a strong role in the staging of cancers. Molecular Imaging is the new and exciting frontier in this field. They say that a picture is worth a thousand words, but the development of each of these technologies to show doctors what's happening inside the body in a non-invasive fashion has been worthwhile for saving many times a thousand lives!