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.

Imaging, by itself, is not a treatment but is a tool that 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 and 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 help guide delivery of cancer treatments in numerous ways. Imaging can help make 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 molecular imaging and 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.

Sometimes patients get frightened by the word "nuclear". Did you know that the peaceful uses of nuclear material for medical purposes predates World War II? Also, when used to look for disease (diagnosis), X ray tests like a chest X ray or a hand X ray have a very small radiation dose. Your Doctors are concerned about keeping these radiation doses as low as possible. So the risk to you as a patient is similar to driving a few miles or smoking a few cigarettes. For CT scans, PET and Nuclear Medicine exams, the radiation dose is greater and varies depending on the exam. Here, the Doctor orders an exam when it might change your diagnosis or treatment. For example, if you are a smoker and begin to cough up blood, your Doctor might order a chest X ray. If the chest X ray is abnormal, a CT scan might be ordered next. (Certainly better than a trip to the operating room, especially if you only have a small infection, etc). If the CT shows something that could be a tumor or a cancer a PET scan could follow. The radiation dose from these diagnostic exams (looking to find out what is wrong) is similar to living in Denver or a high altitude ski resort for several years.

The Doctors also look at the risk to benefit ratio. If a test has a very small risk (much less than surgery) and has the potential benefit of greatly changing your treatment for the better, the decision to do the test becomes easy.

Some tests, like diagnostic MRI and diagnostic ultrasound do not have any radiation that might hurt you.

The ability of CT, MRI, PET and / or Nuclear Medicine to do an Imaging "exploratory surgery" has made them very popular. Low risk or no risk imaging procedures combined with excellent results has been the key to imaging's success and growth over the past 20 years. Sometimes the only way to tell if a treatment is working (except for a procedure like surgery or a biopsy) is by imaging.

We can also use nuclear materials to treat tumors. The use of radioactive iodine to treat some thyroid diseases also predates the US entry into World War II. It was very successful back then, and we still use it today!

For pregnant women, those with very young children and with kids in general, there many additional safety rules. As Hippocrates said, "Above all, do no harm".

X-ray imaging is perhaps the most familiar type of imaging. Most adults have had a chest X-ray to look for an infection or maybe just as part of an employment health check. Some people have had X-rays obtained of a hand or a foot looking for a fracture or metallic splinter. 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. We can also use X-rays to look for cancer. 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.

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.

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

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.

CT scanning is very common. Doctors will order a CT scan or MRI exam on most every patient with a suspect cancer.

Molecular and Nuclear imaging use 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.

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 incrementally several times during a 15-60-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 a pinky nail (or half of a thumb nail) and/or less aggressive cancers. The size of smallest tumor mass that can be found at PET is constantly improving. 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 also commonly 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.

Ultrasound (US) 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. Most people know about US images when a woman is pregnant, for example — boy or girl. As with diagnostic MRI, there is no harmful radiation from diagnostic US. (Keep in mind, both MRI and US can be used for treatment under certain conditions - but this very uncommon currently.) Unfortunately, while US is very useful for imaging certain body parts, it is not as useful as other imaging techniques for looking at the brain, lungs or an entire abdomen or pelvis. Because masses can sometimes be tiny and far from the skin surface, we usually need CT, MRI and / or PET to find these places of suspect tumor spread.

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.

Many people know that MR scanners are noisy. Most every MR technologist has a big supply of ear plugs or an over the ear headphone for the patient to use. Some people get claustrophobic in the MR units. The Doctors and technologists are accustomed to helping patients deal with this.

MR is safe — so long as there is no metal in your body.

MR is safe for pregnant women and kids — there is no harmful radiation from MRI.

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. There are both 2D and 3D forms of mammography available today.

In addition to "regular" mammograms, additional or spot views might be needed if a suspicious finding is noted on a screening mammogram (meaning no tumor was suspected by history nor by physical exam when the test was ordered).

US and MRI are other types of diagnostic tests that might be obtained to assess the breast.

Sometimes a biopsy is recommended in order to get a piece of tissue for the Pathologist to examine. This will determine if a tumor might be present.

In most every part of the body except for the breast, most biopsies find cancer or something else bad. In the breast, 80-90% of biopsies do not show any tumor. However, because imaging findings for cancer and non-cancerous abnormalities are similar, we have not yet found a way to improve on this low yield.

Breast cancer also occurs in men. So a man with a new chest mass should also see his doctor.

This technique illustrates 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 bad arm swelling called 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.

This has been done since the 1990s at many centers. It is becoming more common outside of assessment of breast tumor spread.

Image Guided Surgery is most commonly used by Brain surgeons. When you hear about a brain surgery patient having a big metal or plastic frame around their head, this part of the localization system.

Various techniques for this have been around since the 1990s. These systems fuse imaging data from a pre-surgical CT or MRI to location information which can be used by the surgeon during the neuro-surgical procedure. This can make the procedure both faster and safer.

There are multiple techniques for using imaging to guide surgery in the body, for example in the liver. This is an area where technique changes occur often.