X-ray radiation, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 nanometers to 10 picometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×1016 Hz to 3×1019 Hz) and energies in the range 124 keV to 145 eV, respectively. X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays. In many languages, X-radiation is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it on November 8, 1895. He named it X-radiation to signify an unknown type of radiation. Spellings of X-ray(s) in English include the variants x-ray(s), xray(s), and X ray(s).
A computed tomography scan is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or radiology technologists.
Radiography is an imaging technique using X-rays, gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical radiography and industrial radiography. Similar techniques are used in airport security. To create an image in conventional radiography, a beam of X-rays is produced by an X-ray generator and is projected toward the object. A certain amount of the X-rays or other radiation is absorbed by the object, dependent on the object's density and structural composition. The X-rays that pass through the object are captured behind the object by a detector. The generation of flat two dimensional images by this technique is called projectional radiography. In computed tomography an X-ray source and its associated detectors rotate around the subject which itself moves through the conical X-ray beam produced. Any given point within the subject is crossed from many directions by many different beams at different times. Information regarding attenuation of these beams is collated and subjected to computation to generate two dimensional images in three planes which can be further processed to produce a three dimensional image.
Radiology is the medical discipline that uses medical imaging to diagnose diseases and guide their treatment, within the bodies of humans and other animals. It began with radiography, but today it includes all imaging modalities, including those that use no electromagnetic radiation, as well as others that do, such as computed tomography (CT), fluoroscopy, and nuclear medicine including positron emission tomography (PET). Interventional radiology is the performance of usually minimally invasive medical procedures with the guidance of imaging technologies such as those mentioned above.
Medical imaging is the technique and process of imaging the interior of a body for clinical analysis and medical intervention, as well as visual representation of the function of some organs or tissues (physiology). Medical imaging seeks to reveal internal structures hidden by the skin and bones, as well as to diagnose and treat disease. Medical imaging also establishes a database of normal anatomy and physiology to make it possible to identify abnormalities. Although imaging of removed organs and tissues can be performed for medical reasons, such procedures are usually considered part of pathology instead of medical imaging.
An X-ray generator is a device that produces X-rays. Together with an X-ray detector, it is commonly used in a variety of applications including medicine, X-ray fluorescence, electronic assembly inspection, and measurement of material thickness in manufacturing operations. In medical applications, X-ray generators are used by radiographers to acquire x-ray images of the internal structures of living organisms, and also in sterilization.
Fluoroscopy is an imaging technique that uses X-rays to obtain real-time moving images of the interior of an object. In its primary application of medical imaging, a fluoroscope allows a surgeon to see the internal structure and function of a patient, so that the pumping action of the heart or the motion of swallowing, for example, can be watched. This is useful for both diagnosis and therapy and occurs in general radiology, interventional radiology, and image-guided surgery.
An X-ray image intensifier (XRII) is an image intensifier that converts X-rays into visible light at higher intensity than the more traditional fluorescent screens can. Such intensifiers are used in X-ray imaging systems to allow low-intensity X-rays to be converted to a conveniently bright visible light output. The device contains a low absorbency/scatter input window, typically aluminum, input fluorescent screen, photocathode, electron optics, output fluorescent screen and output window. These parts are all mounted in a high vacuum environment within glass or, more recently, metal/ceramic. By its intensifying effect, It allows the viewer to more easily see the structure of the object being imaged than fluorescent screens alone, whose images are dim. The XRII requires lower absorbed doses due to more efficient conversion of X-ray quanta to visible light. This device was originally introduced in 1948.
Digital radiography is a form of radiography that uses x-ray–sensitive plates to directly capture data during the patient examination, immediately transferring it to a computer system without the use of an intermediate cassette. Advantages include time efficiency through bypassing chemical processing and the ability to digitally transfer and enhance images. Also, less radiation can be used to produce an image of similar contrast to conventional radiography.
Projectional radiography, also known as conventional radiography, is a form of radiography and medical imaging that produces two-dimensional images by X-ray radiation. The image acquisition is generally performed by radiographers, and the images are often examined by radiologists. Both the procedure and any resultant images are often simply called 'X-ray'. Plain radiography or roentgenography generally refers to projectional radiography. Plain radiography can also refer to radiography without a radiocontrast agent or radiography that generates single static images, as contrasted to fluoroscopy, which are technically also projectional.
Image-guided radiation therapy is the process of frequent imaging, during a course of radiation treatment, used to direct the treatment, position the patient, and compare to the pre-therapy imaging from the treatment plan. Immediately prior to, or during, a treatment fraction, the patient is localized in the treatment room in the same position as planned from the reference imaging dataset. An example of IGRT would include comparison of a cone beam computed tomography (CBCT) dataset, acquired on the treatment machine, with the computed tomography (CT) dataset from planning. IGRT would also include matching planar kilovoltage (kV) radiographs or megavoltage (MV) images with digital reconstructed radiographs (DRRs) from the planning CT.
The computed tomography dose index (CTDI) is a commonly used radiation exposure index in X-ray computed tomography (CT), first defined in 1981. The unit of CTDI is the gray (Gy) and it can be used in conjunction with patient size to estimate the absorbed dose. The CTDI and absorbed dose may differ by more than a factor of two for small patients such as children.
Cone beam computed tomography is a medical imaging technique consisting of X-ray computed tomography where the X-rays are divergent, forming a cone.
Coronary CT angiography is the use of computed tomography (CT) angiography to assess the coronary arteries of the heart. The patient receives an intravenous injection of radiocontrast and then the heart is scanned using a high speed CT scanner, allowing physicians to assess the extent of occlusion in the coronary arteries, usually in order to diagnose coronary artery disease.
Neutron imaging is the process of making an image with neutrons. The resulting image is based on the neutron attenuation properties of the imaged object. The resulting images have much in common with industrial X-ray images, but since the image is based on neutron attenuating properties instead of X-ray attenuation properties, some things easily visible with neutron imaging may be very challenging or impossible to see with X-ray imaging techniques.
Rotational angiography is a medical imaging technique based on x-ray, that allows to acquire CT-like 3D volumes during hybrid surgery or during a catheter intervention using a fixed C-Arm. The fixed C-Arm thereby rotates around the patient and acquires a series of x-ray images that are then reconstructed through software algorithms into a 3D image. Synonyms for rotational angiography include flat-panel volume CT and cone-beam CT.
X-ray detectors are devices used to measure the flux, spatial distribution, spectrum, and/or other properties of X-rays.
In radiography, focal plane tomography is tomography by simultaneously moving the X-ray generator and X-ray detector so as to keep a consistent exposure of only the plane of interest during image acquisition. This was the main method of obtaining tomographs in medical imaging until the late-1970s. It has since been largely replaced by more advanced imaging techniques such as CT and MRI. It remains in use today in a few specialized applications, such as for acquiring orthopantomographs of the jaw in dental radiography.
X-ray computed tomography operates by using an X-ray generator that rotates around the object; X-ray detectors are positioned on the opposite side of the circle from the X-ray source.
The history of X-ray computed tomography dates back to at least 1917 with the mathematical theory of the Radon transform In October 1963, William H. Oldendorf received a U.S. patent for a "radiant energy apparatus for investigating selected areas of interior objects obscured by dense material". The first clinical CT scan was performed in 1971 using a scanner invented by Sir Godfrey Hounsfield.
