Cancer may be difficult to detect, but for some types of cancer, the earlier it is detected, the better are the chances of treating it effectively. Imaging techniques - methods of producing pictures of the body - have become an important element of early detection for many cancers. But imaging is not simply used for detection. Imaging is also important for determining the stage (telling how advanced the cancer is) and the precise locations of cancer to aid in directing surgery and other cancer treatments, or to check if a cancer has returned.

Clinical trials, research studies involving people, play an essential role in determining whether emerging imaging techniques are effective and safe. For more information, see Cancer Imaging Clinical Trials ¹.

RadiologyInfo ²
RadiologyInfo is designed to answer patient questions related to many radiologic procedures and therapies. It includes images from diagnostic radiology, interventional radiology and radiation therapy, has an alphabetical procedures list and galleries of images. There is access to descriptive material for radiologists to use in their waiting rooms.

Additional discussion of imaging instrument questions and utilities is available at the Medical Imaging web site ³ supported by the National Association of Electrical Manufacturers (NEMA).

Uses of Imaging

Imaging, by itself, is not a treatment but can help in making better decisions about treatments. The same imaging technique can help doctors find cancer, tell how far a cancer has spread, guide delivery of specific treatments, or find out if a treatment is working.

Here is some information about the uses of imaging:

Screening for cancer: Imaging can be used to determine if a person has any suspicious areas or abnormalities that might be cancerous. Mammograms are an example of a familiar imaging tool used to screen for breast cancer. Screening for cancer is usually recommended for people who are at increased risk (due to their family history, lifestyle, or age) for developing a particular type of cancer.

Diagnosis/staging: Imaging can be used to find out where a cancer is located in the body, if it has spread, and how much is present. Used in this way, imaging can help determine what stage (how advanced) the cancer is, and if the cancer is in, around, or near important organs and blood vessels. If a biopsy (taking a small amount of the tumor for laboratory examination) is necessary, imaging may be used to help guide doctors to the tumor and take a sample of it.

Guiding cancer treatments: Imaging can be used to make cancer treatments less invasive by narrowly focusing treatments on the tumors. For instance, ultrasound, MRI, or CT scans may be used to determine exact tumor locations so that therapy procedures can be focused on the tumor, minimizing damage to surrounding tissue.

Determining if a treatment is working: Imaging can be used to see if a tumor is shrinking or if the tumor has changed and is using less of the body's resources than before treatment. For example, in some current cancer treatment trials, X-rays, MRIs, and CT scans are done at intervals to see if a treatment is working and the tumor is shrinking. PET and other nuclear medicine techniques are used to monitor the ways the tumor uses the body's resources. Magnetic resonance spectroscopy is used to study chemical changes in the tumor.

Monitoring for cancer recurrence: Imaging can be used to see if a previously treated cancer has returned or if the cancer is spreading to other locations.

X-Ray Imaging

X-ray imaging is perhaps the most familiar type of imaging. Images produced by X-rays are due to the different absorption rates of different tissues. Calcium in bones absorbs X-rays the most, so bones look white on a film recording of the X-ray image, called a radiograph. Fat and other soft tissues absorb less, and look gray. Air absorbs least, so lungs look black on a radiograph. The most familiar use of X-rays is checking for broken bones, but X-rays are also used in cancer diagnosis. For example, chest radiographs and mammograms are often used for early cancer detection or to see if cancer has spread to the lungs or other areas in the chest. Mammograms use X-rays to look for tumors or suspicious areas in the breasts.

CT Scans

A computed tomography scan (CT scan, also called a CAT scan) uses computer-controlled X-rays to create images of the body. However a radiograph and a CT scan show different types of information. Although an experienced radiologist can get a sense for the approximate three-dimensional location of a tumor from a radiograph, in general, a plain radiograph is two-dimensional.

An arm or chest radiograph looks all the way through a body without being able to tell how deep anything is. A CT scan is three-dimensional. By imaging and looking at several three-dimensional slices of a body (like slices of bread) a doctor could not only tell if a tumor is present, but roughly how deep it is in the body. A CT scan can be three dimensional because the information about how much of the X-rays are passing through a body is collected not just on a flat piece of film, but on a computer.

The data from a CT scan can be enhanced to be more vivid than a plain radiograph. For both plain radiographs and CT scans, the patient may be given a contrast agent to drink and/or by injection to more clearly show the boundaries between organs or between organs and tumors.

_{(Left) A 1 mm spiral CT "slice" through the mid-chest region, showing both lungs. The white spot in the right lung is a suspicious nodule that could be biopsied to see if it is cancerous. (Right) A close-up view of 8 "slices" focused on a lung nodule. Compared with a traditional X-ray, a series of CT images gives the radiologist a much better sense of nodule size and its potential threat. Images courtesy of A. P. Reeves, Cornell University.}

Recent technical advances in CT scanning dramatically increased its speed and effectiveness by a process called multi-slice or helical (spiral) scanning.

_{(Figure A:) Conventional CT scan. (Figure B:) Spiral CT scan.}

Conventional CT scans take pictures of slices of the body (like slices of bread). These slices are a few millimeters apart. The newer spiral (also called helical) CT scan takes continuous pictures of the body in a rapid spiral motion, so that there are no gaps in the pictures collected.

_{(Left) Conventional CT scan without contrast showing possible tumor in the liver. (Right) Conventional CT scan of the same patient using contrast. Images courtesy of Dr. Peter Choyke, Department of Radiology, Clinical Center, National Institutes of Health.}

Nuclear Imaging (PET and SPECT)

Nuclear imaging uses low doses of radioactive substances linked to compounds used by the body's cells or compounds that attach to tumor cells. Using special detection equipment, the radioactive substances can be traced in the body to see where and when they concentrate. Two major instruments of nuclear imaging used for cancer imaging are PET and SPECT scanners.

PET Scan

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

After receiving the radioactive sugar, the patient lies still for about 60 minutes while the radioactively labeled sugar 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 45-60-minute period. The PET scanner is used to detect the distribution of the sugar in the tumor and in the body. By the combined matching of a CT scan with PET images, there is an improved capacity to discriminate normal from abnormal tissues. A computer translates this information into the images that are interpreted by a radiologist.

PET scans may play a role in determining whether a 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). PET scans are beginning to be used to check if a treatment is working - if a tumor cells are dying and thus using less sugar.

SPECT Scan

Similar to PET, single photon emission computed tomography (SPECT) uses radioactive tracers and a scanner to record data that a computer constructs into two- or three-dimensional images. A small amount of a radioactive drug is injected into a vein and a scanner is used to make detailed images of areas inside the body where the radioactive material is taken up by the cells. SPECT can give information about blood flow to tissues and chemical reactions (metabolism) in the body.

In this procedure, antibodies (proteins that recognize and stick to tumor cells) can be linked to a radioactive substance. If a tumor is present, the antibodies will stick to it. Then a SPECT scan can be done to detect the radioactive substance and reveal where the tumor is located.

SPECT scan. High levels of antibody in pelvis and axilla (red) and uptake in skin of the thigh and right shoulder (green) showing areas of cutaneous T-cell lymphoma. Image courtesy of Dr. Jorge Carrasquillo, Nuclear Medicine Department, Clinical Center, National Institutes of Health.

Ultrasound

Ultrasound uses sound waves with frequencies above those humans can hear. A transducer sends sound waves traveling into the body which are reflected back from organs and tissues, allowing a picture to be made of the internal organs. Ultrasound can show tumors, and can also guide doctors doing biopsies or treating tumors.

Magnetic Resonance Imaging (MRI)

Magnetic Resonance Imaging (MRI) uses radio waves in the presence of a strong magnetic field that surrounds the opening of the MRI machine where the patient lies to get tissues to emit radio waves of their own.

Different tissues (including tumors) emit a more or less intense signal based on their chemical makeup, so a picture of the body organs can be displayed on a computer screen. Much like CT scans, MRI can produce three-dimensional images of sections of the body, but MRI is sometimes more sensitive than CT scans for distinguishing soft tissues.

(Top) MRI scan without contrast showing possible tumor in the liver. (Bottom) MRI scan of the same patient using contrast. Images courtesy of Dr. Peter Choyke, Clinical Center, NIH.

Digital Mammography

Conventional mammography uses X-rays to look for tumors or suspicious areas in the breasts. Digital mammography also uses X-rays, but the data is collected on computer instead of on a piece of film. This means that the image can be computer-enhanced, or areas can be magnified. Eventually, a computer could in certain appropriate situations, screen digital mammograms, theoretically detecting suspicious areas that human error might miss.

(Top) Breast images using conventional mammography. (Bottom) Digital mammography images of the same woman. Images courtesy of Dr. Laurie Fajardo, Johns Hopkins Medical Institutions

Virtual Colonoscopy

Virtual colonoscopy (VC) (or Computerized Tomographic Colonography (CTC)) uses x rays and computers to produce two- and three-dimensional images of the colon (large intestine) from the lowest part, the rectum, all the way to the lower end of the small intestine and display them on a screen. The procedure is used to diagnose colon and bowel disease, including polyps, diverticulosis, and cancer. VC can be performed with computed tomography (CT), sometimes called a CAT scan, or with magnetic resonance imaging (MRI).

Watch a video of a virtual colonoscopy 4

Virtual Colonoscopy Procedure

While preparations for VC vary, you will usually be asked to take laxatives or other oral agents at home the day before the procedure to clear stool from your colon. You may also be asked to use a suppository to cleanse your rectum of any remaining fecal matter.

VC takes place in the radiology department of a hospital or medical center. The examination takes about 10 minutes and does not require sedatives. During the procedure,

• The doctor will ask you to lie on your back on a table.
• A thin tube will be inserted into your rectum, and air will be pumped through the tube to inflate the colon for better viewing.
• The table moves through the scanner to produce a series of two-dimensional cross-sections along the length of the colon. A computer program puts these images together to create a three-dimensional picture that can be viewed on the video screen.
• You will be asked to hold your breath during the scan to avoid distortion on the images.
• The scanning procedure is then repeated with you lying on your stomach.

After the examination, the information from the scanner must be processed to create the computer picture or image of your colon. A radiologist evaluates the results to identify any abnormalities.

You may resume normal activity after the procedure, although your doctor may ask you to wait while the test results are analyzed. If abnormalities are found and you need conventional colonoscopy, it may be performed the same day.

Conventional Colonoscopy

In a conventional colonoscopy, the doctor inserts a colonoscope--a long, flexible, lighted tube--into the patient's rectum and slowly guides it up through the colon. Pain medication and a mild sedative help the patient stay relaxed and comfortable during the 30- to 60-minute procedure. A tiny camera in the scope transmits an image of the lining of the colon, so the doctor can examine it on a video monitor. If an abnormality is detected, the doctor can remove it or take tissue samples using tiny instruments passed through the scope.

For more information about conventional colonoscopy, please see the Colonoscopy fact sheet ⁵ from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

Advantages of Virtual Colonoscopy

VC is more comfortable than conventional colonoscopy for some people because it does not use a colonoscope. As a result, no sedation is needed, and you can return to your usual activities or go home after the procedure without the aid of another person. VC provides clearer, more detailed images than a conventional x ray using a barium enema, sometimes called a lower gastrointestinal (GI) series. It also takes less time than either a conventional colonoscopy or a lower GI series.

Disadvantages of Virtual Colonoscopy

The doctor cannot take tissue samples or remove polyps during VC, so a conventional colonoscopy must be performed if abnormalities are found. Also, VC does not show as much detail as a conventional colonoscopy, so polyps smaller than 10 millimeters in diameter may not show up on the images.

Computerized Tomographic Colonography (CTC) images of a colon (left, with the patient scanned supine; right, with the patient scanned prone). The red colored area indicates a polyp detected by computer-aided detection (CAD). Images courtesy of Dr. Ronald M. Summers, Diagnostic Radiology Department, Clinical Center, National Institutes of Health.

Virtual colonoscopy image of the inside of a colon. The red colored area indicates a polyp detected by computer-aided detection (CAD). Image courtesy of Dr. Ronald M. Summers, Diagnostic Radiology Department, Clinical Center, National Institutes of Health.

Sentinel Node Mapping for Breast Cancer Staging

These trials illustrate how imaging may be able to reduce the need for extensive diagnostic surgery. When patients are being diagnosed with breast cancer it has been standard practice to surgically remove all of the lymph nodes under the arm to determine if the cancer has spread beyond the breast and what treatment is appropriate. Removing all the lymph nodes can result in long-term complications and discomfort for the patient from lymphedema (a condition where excess lymph fluid collects in tissues and causes swelling). Trials are underway now; however, to test an alternative, less damaging procedure in which imaging plays an important role.

In this alternative procedure, called sentinel node mapping, only the sentinel node (the first lymph node to which breast cancer is likely to spread) is removed rather than all the lymph nodes. In order to identify the sentinel node, the doctors inject either a blue dye or a relatively non-toxic radioactive substance and see which lymph node it reaches first. This lymph node is the sentinel node, and is surgically removed.

Image-Guided Brain Surgery

This "hi-tech" concept has become a reality in the last several years. A conventional video image of a patient lying on the operating table is combined with MRI scans to locate key structural components of the brain and tumor. This allows the surgeon to see into the brain of a patient in a new way - virtually. Using this virtual image, the surgeon can make the best plan to enter the brain and remove the tumor, avoiding important brain structures and blood vessels.

Once the surgery is underway, taking new MRI images of the patient's brain allows the surgeon to check his or her progress, see if the position of anything has changed, and look for remaining pieces of the tumor. This new technology helps make brain surgery safer and less damaging, can help reduce the time spent in surgery, reduce blood loss, allows for removal of all the accessible tumor in one operation and sometimes allows operations that before would have been considered too risky.