Discovering Medical Imaging and Radiation Therapy


The definitions on this page ​will help you understand the terms used in Radcademy.

Radcademy Glossary


    Acronym for “as low as reasonably achievable,” which means keeping the radiation dose as low as possible when performing medical imaging procedures.

  • ARRT

    The American Registry of Radiologic Technologists (ARRT) is the world’s largest credentialing organization that seeks to ensure high-quality patient care in medical imaging, interventional procedures and radiation therapy. ARRT certifies and registers radiologic technologists. 

  • ASRT

    The American Society of Radiologic Technologists (ASRT) is the premier professional association of people working in medical imaging and radiation therapy. 

  • Bone densitometry

    The practice of bone densitometry is an enhanced form of x-ray technology that is used to measure bone loss. 

  • Cardiovascular-interventional

    ​This term describes sophisticated imaging practices that allow cardiac procedures to be performed without invasive surgery. 

  • Certification

    The recognition of an individual who satisfies certain standards within a profession. ARRT certifies radiologic technologists who have met recognized national standards for medical imaging, interventional procedures and radiation therapy. To be certified, individuals must meet basic educational, ethical and examination requirements of eligibility. 

  • Continuing education

    Radiologic technologists are required to earn 24 continuing education (CE) credits every other year to maintain their credentials. They must take approved classes or participate in approved activities until they have earned the necessary credits, and the courses or activities must be approved by ARRT. 

  • Computed tomography

    A kind of imaging procedure that produces cross-sectional images or “slices” of structures in the human body including organs like the brain, heart and lungs, as well as soft tissue in the abdomen and pelvis, which can form a more complete picture than x-ray images. 

  • Discipline

    An area of expertise. The five disciplines in radiologic technology are radiography, radiation therapy, magnetic resonance imaging, sonography and nuclear medicine.

  • Disease

    A disease is a lesion, abnormality or illness.

  • Ionizing vs. nonionizing radiation

    Ionizing radiation has enough energy to remove tightly bound electrons from atoms, thus creating ions. This is the type of radiation that people usually think of as 'radiation.' We take advantage of its properties to generate electric power, to kill cancer cells, and in many manufacturing processes. Nonionizing radiation has enough energy to move atoms in a molecule around or cause them to vibrate, but not enough to remove electrons. Examples of this kind of radiation are sound waves, visible light and microwaves.

  • Magnetic resonance imaging

    Magnetic resonance imaging uses a magnetic field and radio waves to create detailed images of the body’s organs and tissues. The MRI machine is essentially a large, tube-shaped magnet. When you lie inside the machine, the magnetic field temporarily realigns hydrogen atoms in your body and radio waves cause the aligned atoms to produce faint signals that are used to create several “slices,” which are layered together to create a complete picture.

  • Mammography

    Mammography is a special kind of x-ray technique used to screen for breast cancer. Mammograms can be used either for screening or diagnostic purposes.

  • Medical dosimetry

    Medical dosimetry refers to the measurement of absorbed dose from exposure to ionizing radiation.

  • Modality

    Modality refers to a type of technology (for example, magnetic resonance or computed tomography).

  • Nuclear medicine

    Nuclear medicine is a branch of radiologic technology that uses small amounts of radioactive material to diagnose, determine the severity of, and/or treat a variety of diseases including many types of cancers, heart disease, neurological disorders and more.

  • Radiation therapy

    Radiation therapy uses high-energy (ionizing) radiation to shrink or kill tumors. Because radiation damages cells and destroys their ability to divide, external beam radiation therapy uses focused radiation beams produced by a machine outside the body to target tumor cells inside the body.

  • Radiography

    Radiography is the process of obtaining an image for diagnostic examination using x-rays.

  • Radiologic technologists

    Radiologic technologists are the personnel working in any discipline or specialty area of radiologic technology. People who practice in this profession may also be known as medical imaging or radiation therapy professionals or as medical imaging technologists and radiation therapists.

  • Radiologists

    Radiologists are medical doctors who specialize in diagnosing and treating diseases and injuries using medical imaging techniques. They are educated in radiation safety and protection, the effects of radiation on the human body, and performance and interpretation of medical imaging studies.

  • Radiologist assistants

    Radiologist assistants are experienced, registered radiographers who have obtained additional education and certification that qualifies them to serve as radiologist extenders. They work under the supervision of a radiologist to provide patient care in the diagnostic imaging environment.

  • Radiopharmaceutical

    Radiopharmaceuticals are small amounts of radioactive materials that are attracted to specific bones, organs or tissues. They are taken by mouth, inhaled or injected​. A special type of camera then detects radioactive emissions that travel through the body to the area being imaged and records the information on a computer screen or film.
  • Regulations

    Regulations are the rules governed by ARRT and individual states that radiologic technologists must follow. Regulations help ensure that patients are treated consistently by R.T.s regardless of where they live or what procedure they need to have done.

  • Shielding

    Shielding means having something that will absorb radiation between you and the source of the radiation (but using another person to absorb the radiation doesn't count as shielding). The amount of shielding required to protect against different kinds of radiation depends on how much energy they have.

  • Sonography

    Sonography (or ultrasound) uses high-frequency sound waves to create images of organs, tissues or blood flow.

  • Specialties

    Specialties in radiologic technology include mammography, magnetic resonance imaging, cardiovascular-interventional radiography, computed tomography and other specialty imaging areas.

  • X-rays

    X-rays are beams that pass through the body to produce images of anatomical structures. The beams are absorbed in different amounts depending on the density of the material they pass through. The resulting image analyzed by the radiologist is called a radiograph.