Cancer Diagnostic Imaging
How is cancer diagnosed?
There is no single imaging test that can accurately diagnose cancer. A complete evaluation usually requires a detailed health history and physical exam along with diagnostic testing. Many tests are needed to determine if a person has cancer, or if another condition (such as an infection) is mimicking the symptoms of cancer. Effective diagnostic testing is used to confirm or eliminate the presence of disease, monitor the disease process, and plan for and evaluate the effectiveness of treatment. Tests may be done for staging, to determine the extent of cancer and if it has spread. Or tests may be done to assess prognosis or select specific therapies. In some cases, repeat testing is needed when a person’s condition has changed, or if a sample collected was not of good quality, or an abnormal test result needs to be confirmed. Diagnostic procedures for cancer may include imaging, lab tests (including tests for tumor markers), tumor biopsy, endoscopic exam, surgery, or genetic testing. Tests are often repeated regularly throughout treatment to determine the treatment's effectiveness of treatment and the cancer's response to it. This is called restaging. A cancer diagnosis requires a biopsy or analysis of involved tissue or blood. An imaging test can’t diagnose cancer.
What are the different types of diagnostic imaging?
Imaging is the process of producing valuable pictures of body structures and organs. It is used to find or detect tumors and other abnormalities, determine the extent of disease, and evaluate the effectiveness of treatment. Imaging may also be used when doing biopsies and other surgical procedures. Listed below are various types of imaging tests that may be used.
X-rays are diagnostic tests that use invisible electromagnetic energy beams to produce images of internal tissues, bones, and organs on film. X-rays may be taken of any part of the body to detect a tumor or cancer.
A noninvasive diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce both horizontal, or axial, images (often called slices) of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, and organs. CT scans are more detailed than general X-rays.
A mammogram is an X-ray exam of the breast. It is used to detect and diagnose breast disease in women who have breast problems such as a lump, pain, or nipple discharge. It is also used for women who have no breast complaints. Mammography can’t prove that an abnormal area is cancerous. But if it raises a significant suspicion of cancer, a biopsy must be done to confirm a cancer diagnosis. During a biopsy procedure, a tissue sample is removed by needle or open surgical biopsy. Then the tissue is checked under a microscope to see if it is cancer. Mammography has been used for about 30 years. In the past 15 years technical advancements have greatly improved both the technique and results. Today, special equipment, used only for breast X-rays, produces studies that are high in quality but low in radiation dose. Radiation risks are considered to be very minor.
This diagnostic procedure uses high-frequency sound waves and a computer to create images, called sonograms, of blood vessels, tissues, and organs. Sonograms are used to view internal organs as they function and to assess blood flow through various vessels. Tumors in the belly (abdomen), liver, and kidneys can often be seen with an ultrasound. (Ultrasound is not useful in the chest because the ribs block the sound waves.) Ultrasound can be used through a probe that can be inserted into organs, such as the anus, vagina, or esophagus and brought closer to the internal organs, producing a more accurate picture.
MRI is a diagnostic procedure that uses a combination of a large magnet, radiofrequencies, and a computer to produce detailed images of organs and structures within the body. An MRI is often used to examine the heart, brain, liver, pancreas, male and female reproductive organs, and other soft tissues. It can assess blood flow, detect tumors and diagnose many forms of cancer, evaluate infections, and assess injuries to bones and joints.
Positron emission tomography (PET)
PET is a specialized radiology procedure used to examine various body tissues to identify certain conditions. PET may also be used to follow the progress of the treatment of certain conditions. PET is a type of nuclear medicine procedure. It uses a tiny amount of a radioactive substance, called a radionuclide (a radiopharmaceutical or radioactive tracer). The radionuclide is injected into the body during the procedure to assist in the examination of the tissue under study. A special type of camera can then detect the radioactivity in the body. Specifically, PET studies evaluate the metabolism (utilization of tagged glucose molecules) of a particular organ or tissue, so that information about the physiology (functionality) and anatomy (structure) of the organ or tissue is evaluated, as well as its biochemical properties. Thus, PET may find biochemical changes in an organ or tissue. These changes can identify the start of a disease process before anatomical changes related to the disease can be seen with other imaging processes, such as CT or MRI. More recently, PET/CT does PET and CT at the same time and produces a composite image that can both produce a picture of an organ and measure its use of sugar.
Nuclear medicine scan
These scans take pictures after injecting into the body a substance called radionuclides that release a low level of radiation. Special cameras create pictures of where the material travels and collects. A tumor may show up as a "hot spot." These scans are used to detect tumors and bone abnormalities. Some common nuclear scans are bone scan, PET scan, thyroid scan, MUGA scan, or gallium scan.