Photostimulated luminescence
Encyclopedia
Photostimulated luminescence (PSL) is the release of stored energy within a phosphor
by stimulation with visible light, to produce a luminescent signal. Commonly this is used to allow the storage of a weak radioactive signal in a phosphor plate that takes the place of X-ray film, potentially over a prolonged period, which PSL transforms to obtain a highly sensitive image of the original pattern of radiation. Also known as an image plate, a photostimulable phosphor (PSP) plate can be used record a two-dimensional image
of the intensity short-wavelength
(typically, X-ray
) electromagnetic radiation
. The device to read such a plate is known as a phosphorimager (occasionally abbreviated to phosphoimager, perhaps reflecting its common application in molecular biology
of detecting radiolabeled phosphorylated proteins and nucleic acids).
Creating an image requires illuminating the plate
twice: the first exposure, to the radiation
of interest, "writes" the image, and a later, second illumination (typically by a visible-wavelength laser
) "reads" the image.
material remain 'trapped' in 'colour centres' in the crystal
lattice
until stimulated by the second illumination. For example, Fuji's photostimulable phosphor is deposited on a flexible polyester film support with grain size about 5 micrometers, and is described as "barium fluorobromide containing a trace amount of bivalent europium
as a luminescence center". Europium is a divalent cation that replaces barium to create a solid solution
. When Eu2+ ions are struck by ionizing radiation, they lose an additional electron to become Eu3+ ions. These electrons enter the conduction band
of the crystal and become trapped in the bromine ion empty lattice of the crystal. This metastable state is higher in energy than the original condition, so a lower-frequency light source that is insufficient in energy to create more Eu3+ ions can return the trapped electrons to the conduction band. As these mobilized electrons encounter Eu3+ ions, they release a blue-violet 400 nm luminescence. This light is produced in proportion to the number of trapped electrons, and thus in proportion to the original X-ray signal. It can be collected (often by a photomultiplier tube
), enabling the resulting signal to be converted into a digital image
.
This process is also known as Photostimulable Luminescence (PSL).
Unlike film
, a PSP plate can be reused: plates can be "erased," by exposing the plate to room-intensity white light
.
s, a PSP plate is used for X-ray imaging in place of the photographic plate, in a process called computed radiography
. The PSP plate can be used over and over again.
studies.
Phosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
by stimulation with visible light, to produce a luminescent signal. Commonly this is used to allow the storage of a weak radioactive signal in a phosphor plate that takes the place of X-ray film, potentially over a prolonged period, which PSL transforms to obtain a highly sensitive image of the original pattern of radiation. Also known as an image plate, a photostimulable phosphor (PSP) plate can be used record a two-dimensional image
Image
An 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.-Characteristics:...
of the intensity short-wavelength
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
(typically, X-ray
X-ray
X-radiation 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 and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
) electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
. The device to read such a plate is known as a phosphorimager (occasionally abbreviated to phosphoimager, perhaps reflecting its common application in molecular biology
Molecular biology
Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...
of detecting radiolabeled phosphorylated proteins and nucleic acids).
Creating an image requires illuminating the plate
Photographic plate
Photographic plates preceded photographic film as a means of photography. A light-sensitive emulsion of silver salts was applied to a glass plate. This form of photographic material largely faded from the consumer market in the early years of the 20th century, as more convenient and less fragile...
twice: the first exposure, to the radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
of interest, "writes" the image, and a later, second illumination (typically by a visible-wavelength laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
) "reads" the image.
Basic Explanation
After the initial exposure, excited electrons in the phosphorPhosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
material remain 'trapped' in 'colour centres' in the crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
lattice
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
until stimulated by the second illumination. For example, Fuji's photostimulable phosphor is deposited on a flexible polyester film support with grain size about 5 micrometers, and is described as "barium fluorobromide containing a trace amount of bivalent europium
Europium
Europium is a chemical element with the symbol Eu and atomic number 63. It is named after the continent of Europe. It is a moderately hard silvery metal which readily oxidizes in air and water...
as a luminescence center". Europium is a divalent cation that replaces barium to create a solid solution
Solid solution
A solid solution is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase...
. When Eu2+ ions are struck by ionizing radiation, they lose an additional electron to become Eu3+ ions. These electrons enter the conduction band
Conduction band
In the solid-state physics field of semiconductors and insulators, the conduction band is the range of electron energies, higher than that of the valence band, sufficient to free an electron from binding with its individual atom and allow it to move freely within the atomic lattice of the material...
of the crystal and become trapped in the bromine ion empty lattice of the crystal. This metastable state is higher in energy than the original condition, so a lower-frequency light source that is insufficient in energy to create more Eu3+ ions can return the trapped electrons to the conduction band. As these mobilized electrons encounter Eu3+ ions, they release a blue-violet 400 nm luminescence. This light is produced in proportion to the number of trapped electrons, and thus in proportion to the original X-ray signal. It can be collected (often by a photomultiplier tube
Photomultiplier
Photomultiplier tubes , members of the class of vacuum tubes, and more specifically phototubes, are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum...
), enabling the resulting signal to be converted into a digital image
Digital image
A digital image is a numeric representation of a two-dimensional image. Depending on whether or not the image resolution is fixed, it may be of vector or raster type...
.
This process is also known as Photostimulable Luminescence (PSL).
Unlike film
Film
A film, also called a movie or motion picture, is a series of still or moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects...
, a PSP plate can be reused: plates can be "erased," by exposing the plate to room-intensity white light
White Light
White Light may refer to:*Light with the color white*White Light , a 1980 novel by Rudy Rucke*White Light , 1971 album*White Light , 2010 album...
.
Medical X-ray Imaging
In modern hospitalHospital
A hospital is a health care institution providing patient treatment by specialized staff and equipment. Hospitals often, but not always, provide for inpatient care or longer-term patient stays....
s, a PSP plate is used for X-ray imaging in place of the photographic plate, in a process called computed radiography
Computed radiography
Computed Radiography uses very similar equipment to conventional radiography except that in place of a film to create the image, an imaging plate made of photostimulable phosphor is used. The imaging plate housed in a special cassette and placed under the body part or object to be examined and...
. The PSP plate can be used over and over again.
X-ray Diffraction Studies
Image plate detectors have been used in numerous crystallographyCrystallography
Crystallography is the experimental science of the arrangement of atoms in solids. The word "crystallography" derives from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and grapho = write.Before the development of...
studies.
See also
- X-ray image intensifierX-ray image intensifierAn x-ray image intensifier , is an imaging component which converts x-rays into a visible image.The term image intensifier refers to a specific component of an x-ray imaging system, which allows low intensity x-rays to be converted to a visible light output...
- RadioluminescenceRadioluminescenceRadioluminescence is the phenomenon by which luminescence is produced in a material by the bombardment of ionizing radiation such as beta particles.-Tritium:...
- SpinthariscopeSpinthariscopeA Spinthariscope is a device for observing individual nuclear disintegrations caused by the interaction of ionizing radiation with a phosphor or scintillator.The spinthariscope was invented by William Crookes in 1903...
- FluoroscopyFluoroscopyFluoroscopy 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...