American Medical Association Family Medical Guide - American Medical Association [89]
Doppler ultrasound is an ultrasound technique that can evaluate movement such as blood flow through the beating heart of a fetus or through arteries and veins. Because flowing blood cells in a blood vessel reflect sound waves, the speed and direction of blood flow through the vessels can be measured and analyzed with ultrasound. This information is displayed on a screen as a graph. Doppler ultrasound is often used along with or, in some cases, instead of angiography (see previous page).
THE PROCEDURE
If you are having an ultrasound of the abdominal area, you will be asked to fast for at least 12 hours before the procedure. If the scan involves the pelvic area (such as to examine pelvic organs or to view a fetus), you will be asked to drink three or four glasses of water about 20 to 30 minutes before the examination to fill your bladder (so it will reflect sound waves). The technician will spread a gel on your skin over the area to be examined; the gel provides good contact for the transducer and allows it to move easily and smoothly over the skin. The room is darkened slightly to make the images on the computer screen clearly visible to the technician. Most ultrasounds take about 15 to 30 minutes. The procedure is very safe and has no known side effects or risks.
Gallstone in gallbladder
This ultrasound scan of the gallbladder (the dark oval area at the top of the image) shows a gallstone (arrow) inside the gallbladder. Gallstones form when bile (which is stored in the gallbladder) hardens. The major component of most gallstones is cholesterol.
Four-month-old fetus
During pregnancy, ultrasound is a safe method for determining the approximate age, rate of growth, and position of a fetus. This ultrasound image is of a healthy 4-month-old fetus (the head of the fetus is at the left, facing up).
Heart
An ultrasound of the heart (called an echocardiogram) can help diagnose heart abnormalities. This echocardiogram shows a healthy heart. The four chambers of the heart are numbered, and appear as dark spaces surrounded by the walls of the chambers: 1 indicates the right ventricle; 2, the left ventricle; 3, the right atrium; and 4, the left atrium.
Vein in leg
This Doppler ultrasound shows blood flow (orange) through the longest vein in the body—the vein in the leg from the foot to the groin that drains blood back to the heart.
CT scanning
Computed tomography (CT) uses a combination of X-rays (see page 109) and a computer to create images. A CT scanner uses X-rays in a different way than a conventional X-ray machine does. Instead of taking an X-ray photograph, a CT scanner sends large numbers of X-ray beams from many directions through the part of the body being examined, records the amount of radiation that has been absorbed, and uses an internal computer to construct an image. In CT, the computer produces a series of horizontal or vertical (or even three-dimensional) cross-sectional slice images of the body. These images offer clear pictures of all the organs in the part of the body being studied. CT scanning is able to create more fully defined pictures of the head and body than conventional X-rays and has reduced the need for uncomfortable, invasive, and risky diagnostic procedures such as exploratory surgery.
A newer type of CT—called electron beam tomography (EBT)—is ten times faster than any other scanning technique. EBT is also called spiral, or helical, tomography. The EBT X-ray tube revolves around the body, allowing a continuous flow of images. The data are collected on a computer, and can be enhanced to provide clearer and more detailed images than those produced with conventional CT. Three-dimensional