Introduction: X-radiation (composed of X-rays) is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0. 01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3? 1016 Hz to 3? 1019 Hz) X-rays up to about 10 keV (10 to 0. 10 nm wavelength) are classified as “soft” X-rays, and from about 10 to 120 keV (0. 10 to 0. 01 nm wavelength) as “hard” X-rays, due to their penetrating abilities. [3] Hard X-rays can penetrate some solids and liquids, and all uncompressed gases, and their most common use is to image of the inside of objects in diagnostic radiography and crystallography.
As a result, the term X-ray is metonymically used to refer to a radiographic image produced using this method, in addition to the method itself. By contrast, soft X-rays hardly penetrate matter at all; the attenuation length of 600 eV (~2 nm) X-rays in water is less than 1 micrometer. [4] The distinction between X-rays and gamma rays has changed in recent decades. Originally, the electromagnetic radiation emitted by X-ray tubes had a longer wavelength than the radiation emitted by radioactive nuclei (gamma rays).
[5] Older literature distinguished between X- and gamma radiation on the basis of wavelength, with radiation shorter than some arbitrary wavelength, such as 10? 11 m, defined as gamma rays. [6] However, as shorter wavelength continuous spectrum “X-ray” sources such as linear accelerators and longer wavelength “gamma ray” emitters were discovered, the wavelength bands largely overlapped. The two types of radiation are now usually distinguished by their origin: X-rays are emitted by electrons outside the nucleus, while gamma rays are emitted by the nucleus. [5][7][8][9] Medical applications:
During the first four decades of this century many advances in medical radiation uses came from gradual improvements in equipment and techniques. The availability of X-ray machines in military hospitals during World War I convinced many physicians of the usefulness of X-ray studies in detection of somatic problems, as well as trauma. A chest X ray became the standard method of diagnosing tuberculosis. About all that could be offered the active tubercular patient was nursing care but isolation of such patients helped to break the spread of the highly contagious disease to other family members and co-workers.
Tuberculosis was the target of the ? rst X-ray population screening efforts The creation of arti? cial isotopes in the 1930s by Frederic Joliot and Irene Curie, daughter of Pierre and Marie ,opened new dimensions in radiation science. Soon, Ernest Lawrence was making arti? cial isotopes in the cyclotron of the Donner Laboratory at the University of California in Berkeley. Lawrence invited Robert Stone, the chief of radiologyat the University of California Medical Center in San Francisco, to bring cancer patients for treatment with neutrons produced in the Donner lab.
Cancers treated with neutrons melted away. Soon, so did the cancer patients. Neutrons had more energy and different biological characteristics than high energy X rays. Stone discontinued his treatments until the characteristics of neutrons could be understood better World War II arrived, and in quick succession Lawrence, Stone, and most of the leading radiation scientists in the free world were drawn into the Manhattan project to develop an atomic bomb.
Wartime imperatives drive science more strongly than peaceful objectives. But there was an appreciation within the Manhattan project that biological problems were created by the physical and chemical advances, and after the war, the congress created the Atomic Energy Commission to further peaceful applications of the new radiation science. FOR PHYSICIANS, these peaceful applications took two directions. One was the development of arti? cial reactor-produced isotopes as high energy sources for radiation treatment.
During the war years, there had been development of Robert van de Graaff’s million volt static generators and Donald Kerst’s high energy betatron, the first supervoltage therapy machines. But the simplicity of using cobalt 60or cesium 137 in rotating-head treatment devices soon eclipsed the early electronic generators. Cobalt 60, with an energy of 1. 33 million electron volts, emerged in the late 1950s as the workhorse for radiation therapy . The second direction was the development of lower energy isotopes such as iodine 131 for use as diagnostic tools.
Trace amounts of iodine or other isotopes could be given a patient. By measuring the output of urine, for example, using a Geiger counter, a physician could assess kidney function. With scintillation crystal detectors, a doctor could study an image of radioactive iodine uptake in the thyroid gland, to study function and to infer the presence of tumors. Advances in X-ray techniques continued apace. Russell Morgan at the University of Chicago developed phototiming, a method of matching exposures to physical characteristics of patients.
Morgan, Edward Chamberlain of Temple University and, principally, John Coltman of the Westinghouse Corporation are credited with the conceptual development of electronic image intensification, together bringing fluoroscopic studies out of darkened rooms. Reduced amounts of radiation could be fed into a fluoroscopic screen and brightened several thousandfold before being displayed on an output screen. This procedure allowed recording of motion, such as the ? utter of a heart valve, on motion picture ? lm or videotape without subjecting patients to unacceptable levels of radiation.
Radiologists and some other physicians began to expand the uses of hollow catheters to inject contrast liquids into the vascular system and other body channels. The skills needed to thread a catheter tip into position to visualize the coronary arteries or the vessels of the head were compared by one investigator to the task of pushing a rope through twisted passageways. A major advance in isotopic diagnosis resulted from the development by Harold Anger of the University of California of the gamma camera, with its array of photomultiplier tubes and a large crystal which shortened scanning time.
This was coupled with the development of various chemical forms of technetium 99m, an isotope with a six-hour half life. Technetium could be tagged to various chemicals to allow concentration in different organs of interest. Given its six-hour decay period, relatively larger amounts of isotope could be used without increasing patient exposures. Since Rontgen’s discovery that X-rays can identify bone structures, X-rays have been use for medical imaging. The first medical use was less than a month after his paper on the subject. [25] In 2010, 5 billion medical imaging studies were done worldwide.
[26] Radiation exposure from medical imaging in 2006 made up about 50% of total ionizing radiation exposure in the United States. [19] Plain X-rays X-rays are useful in the detection of pathology of the skeletal system as well as for detecting some disease processes in soft tissue. Some notable examples are the very common chest X-ray, which can be used to identify lung diseases such as pneumonia, lung cancer or pulmonary edema, and the abdominal X-ray, which can detect intestinal obstruction, free air (from visceral perforations) and free fluid (inascites).
X-rays may also be used to detect pathology such as gallstones (which are rarely radiopaque) or kidney stones which are often (but not always) visible. Traditional plain X-rays are less useful in the imaging of soft tissues such as the brain or muscle. X-rays are also commonly used in dentistry, as X-ray imaging is useful in the diagnoses of common oral problems, such as cavities. Computer tomography Imaging alternatives for soft tissues are computed axial tomography (CAT or CT scanning). [27] Fluoroscopy Fluoroscopy is another X-ray test methodology. This method may use a contrast material.
Examples include cardiac catheterization (to examine for coronary artery blockages) and Barium swallow (to examine for esophageal disorders). Radiotherapy The use of X-rays as a treatment is known as radiation therapy and is largely used for the management (including palliation) of cancer; it requires higher radiation energies than for imaging alone. Most applications of X rays are based on their ability to pass through matter. This ability varies with different substances; e. g. , wood and flesh are easily penetrated, but denser substances such as lead and bone are more opaque.
The penetrating power of X rays also depends on their energy. The more penetrating X rays, known as hard X rays, are of higher frequency and are thus more energetic, while the less penetrating X rays, called soft X rays, have lower energies. X rays that have passed through a body provide a visual image of its interior structure when they strike a photographic plate or a fluorescent screen; the darkness of the shadows produced on the plate or screen depends on the relative opacity of different parts of the body. Photographs made with X.
rays are known as radiographs or skiagraphs. Radiography has applications in both medicine and industry, where it is valuable for diagnosis and nondestructive testing of products for defects. Fluoroscopy is based on the same techniques, with the photographic plate replaced by a fluorescent screen (see fluorescence; fluoroscope); its advantages over radiography in time and cost are balanced by some loss in sharpness of the image. X rays are also used with computers in CAT (computerized axial tomography) scans to produce cross-sectional images of the inside of the body.
Another use of radiography is in the examination and analysis of paintings, where studies can reveal such details as the age of a painting and underlying brushstroke techniques that help to identify or verify the artist. X rays are used in several techniques that can provide enlarged images of the structure of opaque objects. These techniques, collectively referred to as X-ray microscopy or microradiography, can also be used in the quantitative analysis of many materials. One of the dangers in the use of X rays is that they can destroy living tissue and can cause severe skin burns on human flesh exposed for too long a time.
This destructive power is used in X-ray therapy to destroy diseased cells. References: 1. ^ Novelline, Robert. Squire’s Fundamentals of Radiology. Harvard University Press. 5th edition. 1997. ISBN 0674833392. 2. ^ “X-ray”. Oxford English Dictionary. Oxford University Press. 3rd ed. 2001. 3. ^ Holman, Gordon; Benedict, Sarah (1996-09-23). “Hard X-Rays”.
Solar Flare Theory Educational Web Pages. Goddard Space Flight Center. Retrieved 2011-03-09. 4. ^ “Physics. nist. gov”. Physics. nist. gov. Retrieved 2011-11-08. 5. ^ a b Dendy, P. P. ; B. Heaton (1999).
Physics for Diagnostic Radiology. USA: CRC Press. p. 12. ISBN 0750305916. 6. ^ Charles Hodgman, Ed. (1961). CRC Handbook of Chemistry and Physics, 44th Ed.. USA: Chemical Rubber Co.. p. 2850. 7. ^ Feynman, Richard; Robert Leighton, Matthew Sands (1963). The Feynman Lectures on Physics, Vol. 1. USA: Addison-Wesley. pp. 2–5. ISBN 0201021161. 8. ^ L’Annunziata, Michael; Mohammad Baradei (2003). Handbook of Radioactivity Analysis. Academic Press. p. 58. ISBN 0124366031. 9. ^ Grupen, Claus; G. Cowan, S. D. Eidelman, T. Stroh (2005). Astroparticle Physics. Springer. p. 109.