An
X-ray generator is a device used to generate X-rays. These devices are commonly used by radiographers to acquire an
x-rayX-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 10 to 0.01 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays...
image of the inside of an object (as in medicine or non-destructive testing) but they are also used in
sterilizationSterilization can refer to:* Sterilization , an operation which renders an animal or human unable to procreate** Compulsory sterilization, where the government forces particular members of society to undergo the procedure...
or
fluorescenceFluorescence is the emission of visible light by a substance that has absorbed light of a differing, usually invisible, wavelength. Absorption of a photon triggers the emission of a photon with a longer wavelength. A shorter wavelength emission is sometimes observed from multiple photon absorption...
.
History
Shay M. Anderson and Ryan W. Preuninger formulated mathematical equations for X-rays. Physicist Johann Hittorf observed tubes with energy rays extending from a negative electrode.
William CrookesSir William cookies, OM, FRS was a chemist and physicist who attended the Royal College of Chemistry, in London, and worked on spectroscopy.He was pioneer of vacuum tubes, inventing the Crookes tube.-Early years:...
investigated the effects of energy discharges on rare gases. Heinrich Hertz began experimenting and demonstrated that cathode rays could penetrate very thin metal foil (such as aluminium). In 1887,
Nikola TeslaNikola Tesla was an inventor and a mechanical and electrical engineer. He is frequently cited as one of the most important contributors to the birth of commercial electricity and is best known for his many revolutionary developments in the field of electromagnetism in the late 19th and early 20th...
began to investigate X-rays and produced the
bremsstrahlungBremsstrahlung , is electromagnetic radiation produced by the acceleration of a charged particle, such as an electron, when deflected by another charged particle, such as an atomic nucleus. The term is also used to refer to the process of producing the radiation...
process. In 1895, Wilhelm Röntgen began observing and further documenting X-rays while experimenting with vacuum tubes.
One of the first X-ray photographs was made of the hand of Röntgen's wife. The image displayed both her wedding ring and bones. as the new scientific wonder and seized upon by entertainers. Circus patrons viewed their own skeletons and were given pictures of their own bony hands wearing silhouetted jewelry. While many people were fascinated by this discovery, others feared that it would allow strangers to look through doors and invade people's privacy.
In the 1940s and 50s, (real time) X-ray machines were used in stores to help sell footwear. These were known as fluoroscopes. However, as the harmful effects of
X-rayX-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 10 to 0.01 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays...
radiationIn physics, radiation describes any process in which energy emitted by one body travels through a medium or through space, ultimately to be absorbed by another body...
were properly considered, they finally fell out of use. Shoe-fitting use of the device was first banned by the state of
PennsylvaniaThe Commonwealth of Pennsylvania , often colloquially referred to as PA by natives and Northeasterners, is a state located in the Northeastern and Middle Atlantic regions of the United States...
in 1957. (They were more a clever marketing tool to attract customers, rather than a fitting aid.)
Overview
An X-ray imaging system consists of a X-ray source or generator (
X-ray tubeAn X-ray tube is a vacuum tube that produces X-rays. They are used in X-ray machines. X-rays are part of the electromagnetic spectrum, an ionizing radiation with wavelengths shorter than ultraviolet light...
), and an image detection system which can be either a film (analog technology) or a digital capture system, in addition to a
PACSIn medical imaging, picture archiving and communication systems are computers, commonly servers, dedicated to the storage, retrieval, distribution and presentation of images. The medical images are stored in an independent format. The most common format for image storage is DICOM...
.
X-ray sources
In the typical X-ray source of less than 450 kV,
X-rayX-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 10 to 0.01 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays...
photons are produced by an electron beam striking a target. The electrons that make up the beam are emitted from a heated cathode filament. The electrons are then focused and accelerated towards an angled anode target. The point where the electron beam strikes the target is called the focal spot. Most of the
kinetic energyThe kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its current velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its...
contained in the electron beam is converted to heat, but around 1% of the energy is converted into X-ray photons, the excess heat is dissipated via a heat sink. At the focal spot, X-ray photons are emitted in all directions from the target surface, the highest intensity being around 60deg to 90deg from the beam due to the angle of the anode target to the approaching X-ray photons. There is a small round window in the X-ray tube directly above the angled target. This window allows the X-ray to exit the tube with little attenuation while maintaining a vacuum seal required for the X-ray tube operation.
X-ray machines work by applying controlled
voltageVoltage is commonly used as a short name for electrical potential difference. Its corresponding SI unit is the volt...
and
currentElectric current can mean, depending on the context, a flow of electric charge or the rate of flow of electric charge ....
to the
X-ray tubeAn X-ray tube is a vacuum tube that produces X-rays. They are used in X-ray machines. X-rays are part of the electromagnetic spectrum, an ionizing radiation with wavelengths shorter than ultraviolet light...
, which results in a beam of
X-rayX-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 10 to 0.01 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays...
s. The beam is projected on
matterThe term matter traditionally refers to the substance that all objects are made of. One common way to identify this "substance" is through its physical properties; a common definition of matter is anything that has mass and occupies a volume...
. Some of the X-ray beam will pass through the object, while some are absorbed. The resulting pattern of the radiation is then ultimately detected by a detection medium including
rare earthAs defined by IUPAC, rare earth elements or rare earth metals are a collection of seventeen chemical elements in the periodic table, namely scandium, yttrium, and the fifteen lanthanoids...
screens (which surround photographic film), semiconductor detectors, or
X-ray image intensifierAn X-ray image intensifier , sometimes referred to as a C-Arm or Fluoroscope in medical settings, is a highly complex piece of equipment which uses x-rays and produces a 'live' image feed which is displayed on a TV screen....
s.
Detection
In healthcare applications in particular, the x-ray detection system rarely consists of the detection medium. For example, a typical stationary radiographic x-ray machine also includes an ion chamber and grid. The ion chamber is basically a hollow plate located between the detection medium and the object being imaged. It determines the level of exposure by measuring the amount of x-rays that have passed through the electrically charged, gas-filled gap inside the plate. This allows for minimization of patient radiation exposure by both ensuring that an image is not underdeveloped to the point the exam needs to be repeated and ensuring that more radiation than needed is not applied. The grid is usually located between the ion chamber and object and consists of many aluminum slats stacked next to each other (resembling a polaroid lens). In this manner, the grid allows straight x-rays to pass through to the detection medium but absorbs reflected x-rays. This improves image quality by preventing scattered (non-diagnostic) x-rays from reaching the detection medium, but using a grid creates higher exam radiation doses overall.
ImageAn image is an artifact, for example a two-dimensional picture, that has a similar appearance to some subject—usually a physical object or a person....
s taken with such devices are known as X-ray photographs or radiographs.
Applications
X-ray machines are used in
health careHealth care , is the treatment and management of illness, and the preservation of health through services offered by the medical, dental, complementary and alternative medicine, pharmaceutical, clinical laboratory sciences , nursing, and allied health professions...
for visualising bone structures and other dense tissues such as tumours. Non-medicial applications include
securitySecurity is the degree of protection against danger, loss, and criminals.Security has to be compared and contrasted with other related concepts: Safety, continuity, reliability...
and material analysis.
Medicine
The two main fields in which x-ray machines are used in medicine are
radiographyRadiography is the use of the property of X-rays to cross materials to view inside objects. The impact on society of this technique has also been immense : application fields are medical, non-destructive testing, food inspection, security, archeology, ......
and
dentistryDentistry is the known evaluation, diagnosis, prevention, and treatment of diseases, disorders and conditions of the soft and hard tissues of the jaw , the oral cavity, maxillofacial area and the adjacent and associated structures and their impact on the human body. Dentistry is a part of stomatology...
.
RadiographyRadiography is the use of the property of X-rays to cross materials to view inside objects. The impact on society of this technique has also been immense : application fields are medical, non-destructive testing, food inspection, security, archeology, ......
is used for fast, highly penetrating images, and is usually used in areas with a high bone content. Some forms of radiography include:
- orthopantomogram
An Orthopantomogram , also known as an "orthopantogram" or "panorex", is a panoramic scanning dental X-ray of the upper and lower jaw. It shows a two-dimensional view of a half-circle from ear to ear.-Equipment:...
— a panoramic x-ray of the jawThe jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...
showing all the teeth at once
- mammography
Mammography is the process of using low-dose amplitude-X-rays to examine the human breast and is used as a diagnostic as well as a screening tool. The goal of mammography is the early detection of breast cancer, typically through detection of characteristic masses and/or microcalcifications....
— x-rays of breast tissue
- tomography
Tomography is imaging by sections or sectioning, through the use of wave of energy. A device used in tomography is called a tomograph, while the image produced is a tomogram. The method is used in medicine, archaeology, biology, geophysics, oceanography, materials science, astrophysics and other...
— x-ray imaging in sections
Radiotherapy — the use of x-ray radiation to treat malignant
cancer cellCancer Cell is the first Cell Press journal to focus on a specific disease field, with an editorial scope spanning from basic to clinical-oriented researches and a strong emphasis on translational research...
s, a non-imaging application
FluoroscopyFluoroscopy is an imaging technique commonly used by physicians to obtain real-time moving images of the internal structures of a patient through the use of a fluoroscope. In its simplest form, a fluoroscope consists of an x-ray source and fluorescent screen between which a patient is placed...
is used in cases where real-time visualization is necessary (and is most commonly encountered in everyday life at
airport securityAirport security refers to the techniques and methods used in protecting airports and aircraft from crime.Large numbers of people pass through airports. Such gatherings present a target for terrorism and other forms of crime due to the number of people located in a small area...
). Some medical applications of fluorography include:
- angiography — used to examine blood vessel
The blood vessels are the part of the circulatory system that transport blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart, the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s in real time
- barium enema
A lower gastrointestinal series, also called a barium enema, is a medical procedure used to examine and diagnose problems with the human colon . X-ray pictures are taken while barium sulfate fills the colon via the rectum.-Procedure:...
— a procedure used to examine problems of the colonThe colon is the last portion of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body....
and lower gastrointestinal tractThe human gastrointestinal tract , digestive tract, guts or gut is the system of organs within humans that takes in food, digests it to extract energy and nutrients, and expels the remaining matter...
- barium swallow
A barium swallow is a medical imaging procedure used to examine the upper GI tract, which includes the esophagus and, to a lesser extent, the stomach.-Principle:...
— similar to a barium enema, but used to examine the upper gastroinstestional tract
- biopsy
A biopsy is a medical test involving the removal of cells or tissues for examination. It is the removal of tissue from a living subject to determine the presence or extent of a disease. The tissue is generally examined under a microscope by a pathologist, and can also be analyzed chemically...
— the removal of tissue for examination
X-rays are highly penetrating,
ionizing radiationIonizing radiation consists of subatomic particles or electromagnetic waves that are energetic enough to detach electrons from atoms or molecules, ionizing them. The occurrence of ionization depends on the energy of the impinging individual particles or waves, and not on their number...
, therefore X-ray machines are used to take pictures of dense tissues such as bones and teeth. This is because bones absorb the radiation more than the less dense
soft tissueIn medicine, the term soft tissue refers to tissues that connect, support, or surround other structures and organs of the body.Soft tissue includes tendons, ligaments, fascia, fibrous tissues, fat, and synovial membranes , and muscles, nerves and blood vessels .It is sometimes defined by what it is...
. X-rays from a source pass through the body and onto a photographic cassette. Areas where radiation is absorbed show up as lighter shades of grey (closer to white). This can be used to diagnose broken or fractured bones. In fluoroscopy, imaging of the digestive tract is done with the help of a
radiocontrast agentRadiocontrast agents are a type of medical contrast medium used to improve the visibility of internal bodily structures in an X-ray based imaging techniques such as Computed tomography or Radiography...
such as
barium sulfateBarium sulfate is a white crystalline solid with the chemical formula BaSO4. It is insoluble in water and other traditional solvents but is soluble in concentrated sulfuric acid. The mineral barite is composed largely of barium sulfate and is a common ore of barium...
, which is opaque to X-rays.
Security
X-ray machines are used to screen objects non-invasively. Luggage at
airportAirport security refers to the techniques and methods used in protecting airports and aircraft from crime.Large numbers of people pass through airports. Such gatherings present a target for terrorism and other forms of crime due to the number of people located in a small area...
s and student baggage at many schools are examined for possible weapons, including bombs. These machines are very low dose and safe to be around. The main parts of an X-ray Baggage Inspection System are the generator used to generate x-rays, the detector to detect radiation after passing through the baggage, signal processor unit (usually a PC) to process the incoming signal from the detector, and a conveyor system for moving baggage into the system.
Operation
When baggage is placed on the conveyor, it is moved into the machine by the operator. There is an
infraredInfrared radiation is electromagnetic radiation whose wavelength is longer than that of visible light , but shorter than that of terahertz radiation and microwaves...
transmitter and receiver assembly to detect the baggage when it enters the tunnel. This assembly gives the signal to switch on the generator and signal processing system. The signal processing system processes incoming signals from the detector and reproduce an image based upon the type of material and material density inside the baggage. This image is then sent to the display unit.
Colour classification
The colour of the image displayed depends upon the material and material density : organic material such as paper, clothes and most explosives are dispayed in al costs.
See also
- Fluoroscope
- Backscatter X-ray
In contrast to the traditional X-ray machine, which detects hard and soft materials by the variation in transmission through the target, backscatter X-ray is a newer imaging system which detects the radiation which comes back from the target...
e.g., for security scanning passengers (rather than baggage)
- X-ray crystallography
X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and diffracts into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a three-dimensional picture...
- Radiography
Radiography is the use of the property of X-rays to cross materials to view inside objects. The impact on society of this technique has also been immense : application fields are medical, non-destructive testing, food inspection, security, archeology, ......
- X-ray fluorescence
X-ray fluorescence is the emission of characteristic "secondary" X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays...
- X-ray astronomy
X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray emission from celestial objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and satellites...
Just detectors.
External links