AskDefine | Define radiology

Dictionary Definition



1 the branch of medical science dealing with the medical use of X-rays or other penetrating radiation
2 (radiology) examination of the inner structure of opaque objects using X rays or other penetrating radiation [syn: radioscopy]

User Contributed Dictionary



  1. the use of radioactive substances in diagnosis and treatment
  2. the use of radiation (including ionizing radiation, especially X-rays) in diagnosis, usually through the formation of images
  3. radioscopy


Related terms

Extensive Definition

Radiology is the specialty directing medical imaging technologies to diagnose and sometimes treat diseases. Originally it was the aspect of medical science dealing with the medical use of electromagnetic energy emitted by X-ray machines or other such radiation devices for the purpose of obtaining visual information as part of medical imaging. Radiology that involves use of x-ray is called roentgenology.
Wilhelm Conrad Roentgen first discovered x-radiation on 8 November 1895 at the Physical Institute of Wuerzburg University. He named the radiation he had discovered "X-radiation". This term is still in use today in the Anglo-American region. His work was first published in a meeting protocol of the Wuerzburg Physical-Medical Society in the 1895 volume; the article was submitted by W.C. Roentgen on 28 December 1895.
Today, following extensive training, radiologists direct an array of imaging technologies (such as ultrasound, computed tomography (CT) nuclear medicine, and magnetic resonance imaging) to diagnose or treat disease. Interventional radiology is the performance of (usually minimally invasive) medical procedures with the guidance of imaging technologies. The acquisition of medical imaging is usually carried out by the radiographer or radiologic technologist. Outside of the medical field, radiology also encompasses the examination of the inner structure of objects using X-rays or other penetrating radiation.


As a medical specialty, radiology can be classified broadly into Diagnostic radiology and Therapeutic radiology.
  • Diagnostic radiology is the interpretation of images of the human body to aid in the diagnosis or prognosis of disease. It is divided into subfields by anatomic location and in some cases method:
    • Chest radiology.
    • Abdominal & Pelvic radiology. Sometimes together termed "Body Imaging."
    • Interventional radiology uses imaging to guide therapeutic and angiographic procedures. Also known as Vascular & Interventional radiology.
    • Neuroradiology is the sub-specialty in the field of central nervous system, i.e. brain and spinal cord, peripheral nervous system, osseous spine and its neural contents, and head and neck imaging.
    • Musculoskeletal radiology is the sub-specialty in the field of bone, joint, and muscular imaging.
    • Pediatric radiology.
    • Mammography Subdivision of radiology that images the breast tissue.
    • Emergency radiology. Subdivision of radiology involved in the diagnosis and treatment of acutely ill or injured patients.
    • Nuclear Medicine is a subdivision of radiology that uses radioisotopes in the characterization of lesions and disease processes, and often yields functional information.
  • A Radiologist is a subspecialty physician trained in all areas of diagnostic radiology. Board certification is earned through the American Board of Radiology (ABR).
    • Nuclear Medicine, Interventional radiology, Neuroradiology and Pediatric radiology have optional subspecialty Board qualifications under the American Board of Radiology.
    • Certification in Nuclear Medicine alone can be earned as a non-radiologist physician through the American Board of Nuclear Medicine.
  • Therapeutic radiology utilizes radiation (radiation therapy) for therapy of diseases such as cancer.
    • While originally encompassed within radiology, radiation oncology is now a separate field.
    • Radiation Oncology specialty certification is earned through the American Board of Radiology.

Acquisition of radiological images

Patients have the following procedures to provide images for Radiological decisions to be made.

Projection (plain) radiography

Radiographs (or Roentgenographs, named after the discoverer of X-rays, Wilhelm Conrad Roentgen (1845–1923)) are often used for evaluation of bony structures and soft tissues. An X-Ray machine directs electromagnetic radiation upon a specified region in the body. This radiation tends to pass through less dense matter (air, fat, muscle, and other tissues), but is absorbed or scattered by denser materials (bones, tumors, lungs affected by severe pneumonia). In Film-Screen Radiography, radiation which has passed through a patient then strikes a cassette containing a screen of fluorescent phosphors and exposes x-ray film. Areas of film exposed to higher amounts of radiation will appear as black or grey on X-ray film while areas exposed to less radiation will appear lighter or white. In Computed Radiography (CR), the x-rays passing through the patient strike a sensitized plate which is then read and digitized into a computer image by a separate machine. In Digital Radiography the x-rays strike a plate of x-ray sensors producing a digital computer image directly. While all three methods are currently in use, the trend in the U.S. is away from film and toward digital imaging.
Plain radiography was the only imaging modality available during the first 50 years of Radiology. It is still the first study ordered in evaluation of the lungs, heart and skeleton because of its wide availability, speed and relative low cost.


Fluoroscopy and angiography are special applications of X-ray imaging, in which a fluorescent screen or image intensifier tube is connected to a closed-circuit television system, which allows real-time imaging of structures in motion or augmented with a radiocontrast agent. Radiocontrast agents are administered, often swallowed or injected into the body of the patient, to delineate anatomy and functioning of the blood vessels, the genitourinary system or the gastrointestinal tract.Two radiocontrasts are presently in use. Barium (as BaSO4) may be given orally or rectally for evaluation of the GI tract. Iodine, in multiple proprietary forms, may be given by oral, rectal, intraarterial or intravenous routes. These radiocontrast agents strongly absorb or scatter X-ray radiation, and in conjunction with the real-time imaging allows demonstration of dynamic processes, such as peristalsis in the digestive tract or blood flow in arteries and veins. Iodine contrast may also be concentrated in abnormal areas more or less than in normal tissues and make abnormalities (tumors, cysts, inflammation) more conspicuous. Additionally, in specific circumstances air can be used as a contrast agent for the gastrointestinal system and carbon dioxide can be used as a contrast agent in the venous system; in these cases, the contrast agent attenuates the X-ray radiation less than the surrounding tissues.

CT scanning

CT imaging uses X-rays in conjunction with computing algorithms to image the body. In CT, an X-ray generating tube opposite an X-ray detector (or detectors) in a ring shaped apparatus rotate around a patient producing a computer generated cross-sectional image (tomogram). CT is acquired in the axial plane, while coronal and sagittal images can be rendered by computer reconstruction. Radiocontrast agents are often used with CT for enhanced delineation of anatomy. Intravenous contrast can allow 3D reconstructions of arteries and veins. Although radiographs provide higher spatial resolution, CT can detect more subtle variations in attenuation of X-rays. CT exposes the patient to more ionizing radiation than a radiograph. Spiral Multi-detector CT utilizes 8,16 or 64 detectors during continuous motion of the patient through the radiation beam to obtain much finer detail images in a shorter exam time. With computer manipulation these images can be reconstructed into 3D images of carotid, cerebral and coronary arteries. Faster scanning times in modern equipment has been associated with increased utilization.
The first commercially viable CT scanner was invented by Sir Godfrey Hounsfield at EMI Central Research Labs, Great Britain in 1972. EMI owned the distribution rights to The Beatles music and it was their profits which funded the research. Sir Hounsfield and Alan McLeod McCormick shared the Nobel Prize for Medicine in 1979 for the invention of CT scanning. The first CT scanner in North America was installed at the Mayo Clinic in Rochester, MN in 1972.


Medical ultrasonography uses ultrasound (high-frequency sound waves) to visualize soft tissue structures in the body in real time. No ionizing radiation is involved, but the quality of the images obtained using ultrasound is highly dependent on the skill of the person (ultrasonographer) performing the exam. Ultrasound is also limited by its inability to image through air (lungs, bowel loops) or bone. The use of ultrasound in medical imaging has developed mostly within the last 30 years. The first ultrasound images were static and two dimensional (2D), but with modern-day ultrasonography 3D reconstructions can be observed in real-time; effectively becoming 4D.
Because ultrasound does not utilize ionizing radiation, unlike radiography, CT scans, and nuclear medicine imaging techniques, it is generally considered safer. For this reason, this modality plays a vital role in obstetrical imaging. Fetal anatomic development can be thoroughly evaluated allowing early diagnosis of many fetal anomalies. Growth can be assessed over time, important in patients with chronic disease or gestation-induced disease, and in multiple gestations (twins, triplets etc.). Color-Flow Doppler Ultrasound measures the severity of peripheral vascular disease and is used by Cardiology for dynamic evaluation of the heart, heart valves and major vessels. Stenosis of the carotid arteries can presage cerebral infarcts (strokes). DVT in the legs can be found via ultrasound before it dislodges and travels to the lungs (pulmonary embolism), which can be fatal if left untreated. Ultrasound is useful for image-guided interventions like biopsies and drainages such as thoracentesis). It is also used in the treatment of kidney stones (renal lithiasis) via lithotripsy. Small portable ultrasound devices now replace peritoneal lavage in the triage of trauma victims by directly assessing for the presence of hemorrhage in the peritoneum and the integrity of the major viscera including the liver, spleen and kidneys. Extensive hemoperitoneum (bleeding inside the body cavity) or injury to the major organs may require emergent surgical exploration and repair.

External links

radiology in Bulgarian: Радиология
radiology in Czech: Radiologie
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radiology in Modern Greek (1453-): Ακτινολογία
radiology in Spanish: Radiología
radiology in Basque: Erradiologia
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radiology in Japanese: 放射線医学
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radiology in Russian: Рентгенология
radiology in Albanian: Radiologjia
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radiology in Thai: รังสีวิทยา
radiology in Turkish: Radyoloji
radiology in Ukrainian: Рентгенологія
radiology in Chinese: 影像诊断学

Synonyms, Antonyms and Related Words

X-ray photometry, X-ray spectrometry, atom-tagging, atomic science, atomics, atomistics, atomology, curiescopy, fluoroscopy, mass spectrography, mass spectrometry, molecular physics, nuclear chemistry, nuclear physics, orthodiagraphy, photofluorography, quantum mechanics, radiation physics, radiobiology, radiochemistry, radiography, radiological physics, radiometallography, radiometry, radiopathology, radioscopy, radiotechnology, radiotherapy, roentgenography, roentgenology, roentgenoscopy, spectroradiometry, thermionics, tracer investigation, wave mechanics
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