When physicians need to peer inside the body, they have a variety of radiological techniques at their disposal. Some of these diagnostic tools employ widely different technologies: X-ray, ultra-high-frequency sound, radioactive substances or a radio-wave effect of atomic nuclei called nuclear magnetic resonance.
Some technologies allow physicians to see not only how an organ looks but how it is working, sparing patients the pain and trauma of exploratory surgery.
Which test your doctor orders will depend on the organ or body part of interest and the problem being investigated. Here are a few of the more common imaging techniques, why they’re used and what you can expect if you have to undergo an exam by one.
Despite development of more sophisticated technologies, the X-ray remains the workhorse of diagnostic imaging. “X-ray is the quick, simple, cheap and effective tool that’s tried and true,” says Dr. Anush Parikh, of Mid-Delaware Imaging in Dover.
X-rays are waves that have a relatively high frequency along the electromagnetic spectrum. They are absorbed in varying amounts by different parts of the body. In general, bones appear white, soft tissue appears gray, and air appears black.
The basic type of X-ray imaging is plain radiography. This involves an X-ray machine aimed at the body with a recording plate placed behind the area of interest. Once the machine delivers its radiation, an image is captured on the plate. It is a useful tool for detecting pneumonia and broken bones.
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Fluoroscopy is the study of moving body structures, a “video clip,” says Dr. Kert Anzilotti, chairman of the department of radiology at Christiana Care Health System. In fluoroscopy, a continuous X-ray beam is passed through the body part examined and is transmitted to a monitor so its motion can be observed in detail in real time.
Fluoroscopy has a number of applications. A barium X-ray allows the physician to observe the movement of the intestines. Cardiac catheterization monitors the blood flow through the coronary arteries to see if there is a blockage. Fluoroscopy can also be used to check for obstruction in a woman’s Fallopian tubes that can cause infertility. The videofluoroscope swallow test evaluates an individual’s ability to handle a variety of foods and liquids.
Though much of fluoroscopy’s diagnostic capabilities have been taken over by the colonoscopy and endoscopy, fluoroscopy plays an integral role in interventional radiology, where it is used to guide injections of pain medication or cartilage replacement into joints or in procedures to treat compression fractures of spinal vertebrae.
The CT scan uses specialized X-ray equipment to obtain images of bones, muscles and organs from different angles around the body. “It is an incredibly powerful tool that is used to look at everything from the top of your head to the bottom of your toes,” Anzilotti says.
A CT scan is used to detect fractures, stroke and intracranial bleeding; to see abdominal pathologies; to pinpoint a tumor, infection, blood clot or internal bleeding; and to detect and monitor cancers, as well as degenerative disease of the lumbar spine.
During the procedure, the patient is placed on a table that moves through a doughnut-shaped device housing an X-ray tube and detectors. The X-ray tube and detectors spin inside the doughnut, around the table, taking thousands of X-ray images. Each image is reconstructed by a computer into a two- or three-dimensional image of the body.
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Magnetic Resonance Imaging
Unlike X-ray imaging, the MRI does not use radiation. Instead, MRI works on the basis of strong magnetic waves and the spin of atomic particles. Compared with CT, images produced by MRI have more detail, which makes it the preferred test for analyzing pathologies of the brain, spine, joints, muscles, tendons and ligaments. “The MRI is the king of the soft tissue,” says Dr. Jonathan L. Patterson of Ocean Medical Imaging in Milton. Like the CT, the MRI can be done with or without contrast.
Almost anyone can have an MRI exam. However, it is not safe for individuals with metallic devices such as cochlear implants or aneurysm clips, or for people with implanted electrical devices such as pacemakers. The procedure may also cause problems for metal workers such as welders who may have metallic fragments lodged in their eyes. These patients must have their eyes X-rayed before being cleared for an MRI.
In addition, an MRI places the patient in a long narrow tube for up to 45 minutes which can feel uncomfortable for some individuals. An open MRI is an option, but physicians caution that the magnetic fields in this type of MRI are weaker, thus may produce an image of lower quality. Breast imaging must be performed in a closed MRI.
Ultrasound technology obtains images by using high-frequency sound waves. These sound waves enter the body when a probe called a transducer is placed directly on the skin. A gel is placed between the transducer and the patient’s body to maximize the clarity of the image. A computer processes the data and converts it to an image.
“It doesn’t give you as high a resolution as a CT or MRI, but it gives you quick information at a relatively low cost with no radiation,” Parikh says.
Some ultrasound studies utilize the additional component of a Doppler ultrasound, which visualizes the movement of blood cells through the arteries of the heart, the carotid artery and blood vessels of the legs. Because it does not use radiation, the ultrasound is especially useful in monitoring fetal movement. It can also be used to check for abnormalities in abdominal organs and in reproductive organs.
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Bone densitometry uses special X-ray equipment to measure the density of bones to help determine who may have or may be at risk for osteoporosis and to monitor changes in bone density for those under treatment.
During the exam, patients lie on their backs on a padded table. A scanning device moves above, taking X-rays of the lower back and hip. Patients must avoid nuclear, barium and contrast studies seven days prior to the test. Calcium supplements may not be taken 24 hours prior to the procedure.
Though women are the most likely candidates for bone density screening, anyone taking medications that could decrease bone density and anyone who experiences frequent fractures should be monitored.
Mammography uses X-rays to take a picture of inner breast tissue. In standard mammography, images are recorded on a film using an X-ray cassette. The film is viewed by the radiologist using a light box, then stored in a jacket in the facility’s archives.
Digital mammography uses a special electronic X-ray detector to convert the image into a digital picture for review on a computer monitor. With digital mammography, the magnification, orientation, brightness, and contrast of the image can be altered after the exam is completed to help the radiologist see certain areas better. In addition, digital technology allows the image to be viewed by more than one physician at a time. Digital mammography is also more effective at detecting cancers in women with dense breasts, women under age 50, and those who are pre- or perimenopausal, Parikh says.
Patients are advised to schedule their mammography during the week after a menstrual period when the breasts are less tender. They should also refrain from using deodorants, antiperspirants, powder, lotions, creams, and perfumes under the arms or on the breasts because metallic particles in these products can show up on the mammogram, causing confusion.
Because breast tissue is nodular, the breasts must be compressed with a special machine to obtain a clear image. This can be painful, especially for women with large breasts. Taking an over-the-counter pain medication about an hour before the procedure can help minimize discomfort.
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Nuclear medicine can be thought of as a “reverse X-ray” because it records radiation emitting from the patient’s body instead of radiation that is directed through the patient’s body. Nuclear medicine uses small amounts of radioactive materials called radiopharmaceuticals that are attracted to specific organs, bones or tissues. These substances are introduced into the patient’s body by injection, swallowing or inhalation. A special type of camera detects these emissions, then records them on a computer or film.
Nuclear medicine allows doctors to study the physiology or function of tissues and organs, as opposed to their structure, says Dr. Timothy A. Manzone, director of nuclear medicine at Christiana Care Health System. Common nuclear procedures include thyroid studies, brain scans, bone scans, lung scans, cardiac stress tests, and liver and gallbladder procedures.
The terms PET and SPECT are often used in conjunction with nuclear medicine. Single photon emission computerized tomography, or SPECT, produces a cross-sectional image of the area scanned. Positron emission tomography, or PET, uses a special camera to construct a 3-D image of the area scanned.
The PET-CT has proven invaluable in diagnosing and detecting the spread of cancer and in determining which treatments are best for the patient.
“One of the ways PET has been found to be very useful is, if you can identify those patients who are not likely to benefit from surgery because they’re not curable, you can then avoid putting them through the trauma,” Manzone says.