Cancer Diagnosis - Diagnostic Imaging
How is cancer diagnosed?
There is no single test that can accurately diagnose cancer. The complete evaluation of a patient usually requires a thorough history and physical examination along with diagnostic testing. Many tests are needed to determine whether 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 for "staging," to determine the extent of cancer and if it has spread, or they may be done to assess prognosis or select specific therapies. In some cases, it is necessary to repeat testing 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, laboratory tests (including tests for tumor markers), tumor biopsy, endoscopic examination, surgery, or genetic testing. Tests are often repeated regularly throughout treatment to "re-stage," that is, to determine the effectiveness of treatment and the cancer's response to it.
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 detect tumors and other abnormalities, determine the extent of disease, and evaluate the effectiveness of treatment. Imaging may also be used when performing biopsies and other surgical procedures. There are three types of imaging used for diagnosing cancer: transmission imaging, reflection imaging, and emission imaging. Each uses a different process.
X-rays, computed tomography scans (CT scans), and fluoroscopy are radiological examinations whose images are produced by transmission. In transmission imaging, a beam of high-energy photons is produced and passed through the body structure being examined. The beam passes very quickly through less dense types of tissue such as watery secretions, blood, and fat, leaving a darkened area on the x-ray film. Muscle and connective tissues (ligaments, tendons, and cartilage) appear gray. Bones will appear white.
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.
Computed tomography scan (also called a CT scan or computed axial tomography or CAT scan)
A CT scan is a diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce both horizontal and vertical cross-sectional 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 lymphangiogram is an imaging study that can detect cancer cells or abnormalities in the lymphatic system and structures. It involves a dye being injected into the lymph system.
A mammogram is an x-ray examination of the breast. It is used to detect and diagnose breast disease in women who either have breast problems such as a lump, pain, or nipple discharge, as well as for women who have no breast complaints. Mammography cannot prove that an abnormal area is cancerous, but if it raises a significant suspicion of cancer, a biopsy may be performed. Tissue may be removed by needle or open surgical biopsy and examined under a microscope to determine if it is cancer. Mammography has been used for about 30 years, and in the past 15 years technical advancements have greatly improved both the technique and results. Today, dedicated 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 negligible.
Reflection imaging refers to the type of imaging produced by sending high-frequency sounds to the body part or organ being studied. These sound waves "bounce" off of the various types of body tissues and structures at varying speeds, depending on the density of the tissues present. The bounced sound waves are sent to a computer that analyzes the sound waves and produces a visual image of the body part or structure.
Ultrasound, or sonography, is the most commonly used type of reflection imaging. This technique 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 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.
Emission imaging occurs when tiny nuclear particles or magnetic energy are detected by a scanner and analyzed by computer to produce an image of the body structure or organ being examined. Nuclear medicine uses emission of nuclear particles from nuclear substances introduced into the body specifically for the examination.
Magnetic resonance imaging (MRI)
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. This means that a tiny amount of a radioactive substance, called a radionuclide (a radiopharmaceutical or radioactive tracer), 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 detect biochemical changes in an organ or tissue that can identify the onset of a disease process before anatomical changes related to the disease can be seen with other imaging processes, such as computed tomography (CT) or magnetic resonance imaging (MRI). More recently, PET/CT performs PET and CT at the same time and produces a composite image that can both produce a picture of an organ and measure its utilization of sugar.
Bone scans are pictures or x-rays taken of the bone after a radioactive material has been injected that is absorbed by bone tissue. These scans are used to detect tumors and bone abnormalities.