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, to determine the extent of disease, and to evaluate the effectiveness of treatment. Imaging also may 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.
Transmission imaging
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 tumor (or cancer) cells.
- Computed tomography scan (also called a CT scan or computed axial tomography or CAT scan) is a diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce cross-sectional images (often called slices), both horizontally and vertically, 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.
- Bone scans are pictures or X-rays taken of the bone after a dye has been injected that is absorbed by bone tissue. These scans are used to detect tumors and bone abnormalities.
- Lymphangiogram (LAG) 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.
- 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.
- Ultrasoundor 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 often can be seen with an ultrasound.
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 uses radio waves with a machine that creates a strong magnetic field that in turn causes cells to emit their own radio frequencies.
- Magnetic resonance imaging is a diagnostic procedure that uses a combination of a large magnet, radio frequencies 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.