Diagnostic Imaging



A type of high-energy radiation. In low doses, x-rays are used to diagnose diseases by making pictures of the inside of the body. In high doses, x-rays are used to treat cancer.

Types of Diagnostic Imaging Ultrasound

Ultrasound, also called sonography, is an imaging technique in which high-frequency sound waves that cannot be heard by humans are bounced off tissues and internal organs. Their echoes produce a picture called a sonogram. Ultrasound imaging of the breast is used to distinguish between solid tumors and fluid-filled cysts. Ultrasound can also be used to evaluate lumps that are hard to see on a mammogram. Sometimes, ultrasound is used as part of other diagnostic procedures, such as fine needle aspiration (also called needle biopsy). Fine needle aspiration is the removal of tissue or fluid with a needle for examination under a microscope to check for signs of disease.

Ultrasound is not used for routine breast cancer screening because it does not consistently detect certain early signs of cancer such as microcalcifications (tiny deposits of calcium in the breast that cannot be felt but can be seen on a conventional mammogram). A cluster of microcalcifications may indicate that cancer is present.

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computed tomography

Computed tomography (CT) is a diagnostic procedure that uses special x-ray equipment to obtain cross-sectional pictures of the body. The CT computer displays these pictures as detailed images of organs, bones, and other tissues. This procedure is also called CT scanning, computerized tomography, or computerized axial tomography (CAT).
    How is CT used in cancer?

    Computed tomography is used in several ways:
      To detect or confirm the presence of a tumor;
      To provide information about the size and location of the tumor and whether it has spread;
      To guide a biopsy (the removal of cells or tissues for examination under a microscope);
      To help plan radiation therapy or surgery;
      To determine whether the cancer is responding to treatment.

    What can a person expect during the CT procedure?

    During a CT scan, the person lies very still on a table. The table slowly passes through the center of a large x-ray machine. The person might hear whirring sounds during the procedure. People may be asked to hold their breath at times, to prevent blurring of the pictures.

    Often, a contrast agent, or “dye,” may be given by mouth, injected into a vein, given by enema, or given in all three ways before the CT scan is done. The contrast dye can highlight specific areas inside the body, resulting in a clearer picture.

    Computed tomography scans do not cause any pain. However, lying in one position during the procedure may be slightly uncomfortable. The length of the procedure depends on the size of the area being x-rayed; CT scans take from 15 minutes to 1 hour to complete. For most people, the CT scan is performed on an outpatient basis at a hospital or a doctor’s office, without an overnight hospital stay.

    Are there risks associated with a CT scan?

    Some people may be concerned about the amount of radiation they receive during a CT scan. It is true that the radiation exposure from a CT scan can be higher than from a regular x-ray. However, not having the procedure can be more risky than having it, especially if cancer is suspected. People considering CT must weigh the risks and benefits.

    In very rare cases, contrast agents can cause allergic reactions. Some people experience mild itching or hives (small bumps on the skin). Symptoms of a more serious allergic reaction include shortness of breath and swelling of the throat or other parts of the body. People should tell the technologist immediately if they experience any of these symptoms, so they can be treated promptly.

    What is spiral CT?

    A spiral (or helical) CT scan is a new kind of CT. During a spiral CT, the x-ray machine rotates continuously around the body, following a spiral path to make cross-sectional pictures of the body. Benefits of spiral CT include:
      It can be used to make 3–dimensional pictures of areas inside the body;
      It may detect small abnormal areas better than conventional CT; and
      It is faster, so the test takes less time than a conventional CT.

    What is total or whole body CT? Should a person have one?

    A total or whole body CT scan creates images of nearly the entire body—from the chin to below the hips. This test has not been shown to have any value as a screening tool. (“Screening” means checking for signs of a disease when a person has no symptoms.)

    The American College of Radiology (as well as most doctors) does not recommend scanning a person’s body on the chance of finding signs of any sort of disease. In most cases abnormal findings do not indicate a serious health problem; however, a person must often undergo more tests to find this out. The additional tests can be expensive, inconvenient, and uncomfortable. The disadvantages of total body CT almost always outweigh the benefits.

    What is virtual endoscopy?

    Virtual endoscopy is a new technique that uses spiral CT. It allows doctors to see inside organs and other structures without surgery or special instruments. One type of virtual endoscopy, known as CT colonography or virtual colonoscopy, is under study as a screening technique for colon cancer.

    What is combined PET/CT scanning?

    Combined PET/CT scanning joins two imaging tests, CT and positron emission tomography (PET), into one procedure. A PET scan creates colored pictures of chemical changes (metabolic activity) in tissues. Because cancerous tumors usually are more active than normal tissue, they appear different on a PET scan.

    Combining CT with PET scanning may provide a more complete picture of a tumor’s location and growth or spread than either test alone. Researchers hope that the combined procedure will improve health care professionals’ ability to diagnose cancer, determine how far it has spread, and follow patients’ responses to treatment. The combined PET/CT scan may also reduce the number of additional imaging tests and other procedures a patient needs. However, this new technology is currently available only at some facilities.

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Digital Mammography

Digital mammography is a technique for recording x-ray images in computer code instead of on x-ray film, as with conventional mammography. The images are displayed on a computer monitor and can be enhanced (lightened or darkened) before they are printed on film. Images can also be manipulated; the radiologist (a doctor who specializes in creating and interpreting pictures of areas inside the body) can magnify or zoom in on an area. From the patient’s perspective, the procedure for a mammogram with a digital system is the same as for conventional mammography.

Digital mammography may have some advantages over conventional mammography. The images can be stored and retrieved electronically, which makes long-distance consultations with other mammography specialists easier. Because the images can be adjusted by the radiologist, subtle differences between tissues may be noted. The improved accuracy of digital mammography may reduce the number of followup procedures. Despite these benefits, studies have not yet shown that digital mammography is more effective in finding cancer than conventional mammography.

Women considering digital mammography should talk with their doctor or contact a local FDA-certified mammography center to find out if this technique is available at that location. Only facilities that have been certified to practice conventional mammography and have FDA approval for digital mammography may offer the digital system.

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MRI

In magnetic resonance imaging (MRI), a magnet linked to a computer creates detailed pictures of areas inside the body without the use of radiation. Each MRI produces hundreds of images of the breast from side-to-side, top-to-bottom, and front-to-back. The images are then interpreted by a radiologist.

During an MRI of the breast, the patient lies on her stomach on the scanning table. The breast hangs into a depression or hollow in the table, which contains coils that detect the magnetic signal. The table is moved into a tube-like machine that contains the magnet. After an initial series of images has been taken, the patient may be given a contrast agent intravenously (by injection into a vein). The contrast agent is not radioactive; it is sometimes used to improve the visibility of a tumor. Additional images are then taken. The entire imaging session takes about 1 hour.

Breast MRI is not used for routine breast cancer screening, but clinical trials (research studies with people) are being performed to determine if MRI is valuable for screening certain women, such as young women at high risk for breast cancer. MRI cannot always accurately distinguish between cancer and benign (noncancerous) breast conditions. Like ultrasound, MRI cannot detect microcalcifications.

MRI is used primarily to evaluate breast implants for leaks or ruptures, and to assess abnormal areas that are seen on a mammogram or are felt after breast surgery or radiation therapy. It can be used after breast cancer is diagnosed to determine the extent of the tumor in the breast. MRI is also sometimes useful in imaging dense breast tissue, which is often found in younger women, and in viewing breast abnormalities that can be felt but are not visible with conventional mammography or ultrasound.

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PET Scan

The positron emission tomography (PET) scan creates computerized images of chemical changes that take place in tissue. The patient is given an injection of a substance that consists of a combination of a sugar and a small amount of radioactive material. The radioactive sugar can help in locating a tumor, because cancer cells take up or absorb sugar faster than other tissues in the body.

After receiving the radioactive drug, the patient lies still for about 45 minutes while the drug circulates throughout the body. If a tumor is present, the radioactive sugar will accumulate in the tumor. The patient then lies on a table, which gradually moves through the PET scanner 6 to 7 times during a 45-minute period. The PET scanner is used to detect the radiation. A computer translates this information into the images that are interpreted by a radiologist.

PET scans may play a role in determining whether a breast mass is cancerous. However, PET scans are more accurate in detecting larger and more aggressive tumors than they are in locating tumors that are smaller than 8 mm and/or less aggressive. They may also detect cancer when other imaging techniques show normal results. PET scans may be helpful in evaluating and staging recurrent disease (cancer that has come back).

An NCI-sponsored clinical trial is evaluating the usefulness of PET scan results in women who have breast cancer compared with the findings from other imaging and diagnostic techniques. This trial is also studying the effectiveness of PET scans in tracking the response of a tumor to treatment.

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Electrical Impedance Scanning

Different types of tissue have different electrical impedance levels (electrical impedance is a measurement of how fast electricity travels through a given material). Some types of tissue have high electrical impedance, while others have low electrical impedance. Breast tissue that is cancerous has a much lower electrical impedance (conducts electricity much better) than normal breast tissue. Electrical impedance scanning devices are used along with conventional mammography to detect breast cancer. The T-Scan 2000, also known as the T-Scan, is an example of such a device. The FDA approved the T-Scan 2000 in 1999.

This device can confirm the location of abnormal areas that were detected by a conventional mammogram. The scanner sends the image directly to a computer, allowing the radiologist to move the probe around the breast to get the best view of the area being examined. The device may reduce the number of biopsies needed to determine whether a mass is cancerous. It may also improve the identification of women who should have a biopsy.

The scanner is not approved as a screening device for breast cancer, and is not used when mammography or other findings clearly indicate the need for a biopsy. This device has not been studied with patients who have implanted electronic devices, such as pacemakers. It is not recommended for use on such patients.

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Image-Guided Breast Biopsy Techniques

Imaging techniques play an important role in helping doctors perform breast biopsies, especially of abnormal areas that cannot be felt but can be seen on a conventional mammogram or with ultrasound. One type of needle biopsy, the stereotactic-guided biopsy, involves the precise location of the abnormal area in three dimensions using conventional mammography. (Stereotactic refers to the use of a computer and scanning devices to create three-dimensional images.) A needle is then inserted into the breast and a tissue sample is obtained. Additional samples can be obtained by moving the needle within the abnormal area.

There have been no reports of serious complications resulting from the Mammotome breast biopsy system. Women interested in this procedure should talk with their doctor.

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Ductal Lavage

Ductal lavage is an investigational technique for collecting samples of cells from breast ducts for analysis under a microscope. A saline (salt water) solution is introduced into a milk duct through a catheter (a thin, flexible tube) that is inserted into the opening of the duct on the surface of the nipple. Fluid, which contains cells from the duct, is withdrawn through the catheter. The cells are checked under a microscope to identify changes that may indicate cancer or changes that may increase the risk for breast cancer. The usefulness of ductal lavage is still under study.

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Colonoscopy

A colonoscopy allows a doctor to look inside the entire large intestine. The procedure enables the physician to see things such as inflamed tissue, abnormal growths, and ulcers. It is most often used to look for early signs of cancer in the colon and rectum. It is also used to look for causes of unexplained changes in bowel habits and to evaluate symptoms like abdominal pain, rectal bleeding, and weight loss.

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Endoscopic Retrograde Cholangiopancreatography

Endoscopic retrograde cholangiopancreatography (ERCP) enables the physician to diagnose problems in the liver, gallbladder, bile ducts, and pancreas. ERCP is used primarily to diagnose and treat conditions of the bile ducts, including gallstones, inflammatory strictures (scars), leaks (from trauma and surgery), and cancer. ERCP combines the use of x rays and an endoscope, which is a long, flexible, lighted tube. Through the endoscope, the physician can see the inside of the stomach and duodenum, and inject dyes into the ducts in the biliary tree and pancreas so they can be seen on x-rays.

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Flexible Sigmoidoscopy

Flexible sigmoidoscopy enables the physician to look at the inside of the large intestine from the rectum through the last part of the colon, called the sigmoid or descending colon. Physicians may use the procedure to find the cause of diarrhea, abdominal pain, or constipation. They also use it to look for early signs of cancer in the descending colon and rectum. With flexible sigmoidoscopy, the physician can see bleeding, inflammation, abnormal growths, and ulcers in the descending colon and rectum. Flexible sigmoidoscopy is not sufficient to detect polyps or cancer in the ascending or transverse colon (two-thirds of the colon).

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Upper Endoscopy

Upper endoscopy enables the physician to look inside the esophagus, stomach, and duodenum (first part of the small intestine). The procedure might be used to discover the reason for swallowing difficulties, nausea, vomiting, reflux, bleeding, indigestion, abdominal pain, or chest pain. Upper endoscopy is also called EGD, which stands for esophagogastroduodenoscopy.

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Information obtained from National Institute of Health
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