Patent Application
20080035839
CsBr:Eu storage phosphors are advantageously prepared by mixing CsBr as an alkali metal halide salt and a lanthanide dopant salt in a form of EuX2, EuX3, EuOX or EuXz, wherein 2<z<3 and wherein X is one of Br, Cl or a combination thereof. In another embodiment as in U.S. Pat. No. 6,802,991 said CsBr:Eu phosphor is advantageously prepared by mixing CsBr as an alkali metal halide salt and wherein between 10−3 and 5 mol % of a Europium compound selected from the group consisting of EuX2, EuX3, EuOX, or EuXz, wherein 2<z<3 and wherein X is one of Br, Cl or a combination thereof, firing the mixture at a temperature above 450° C., cooling said mixture, and recovering the CsBr:Eu phosphor. Depending on the inert gas pressure and substrate temperature the crystallinity of the CsBr:Eu phosphor is changed as in US-Applications 2003/0091729 and 2004/0081750. In still another embodiment said CsBr:Eu phosphor is advantageously prepared by mixing CsBr as an alkali metal halide salt and a combination of an alkali metal halide salt and a lanthanide dopant salt according to the formula CsxEuyX′x+αγ, wherein x/y>0.25, wherein α>2 and wherein X′ is a halide selected from the group consisting of Cl, Br and I and combinations thereof as in US-Applications 2005/0184250, 2005/0184271 and 2005/0186329. CsBr:Eu phosphor screens are advantageously prepared by applying said phosphor on a substrate by a method selected from the group consisting of physical vapor deposition, thermal vapor deposition, chemical vapor deposition, radio frequency deposition and pulsed laser deposition. In that case binderless, needle-shaped phosphors are obtained with a high sensitivity, thanks to the morphology of the crystals, with a high sharpness, as disclosed in U.S. Pat. Nos. 6,967,339 and 6,740,897. Such needle-shaped crystals may also, e.g. after having been ground, be coated in a binder material, such as a polymer or a polymer mixture, in a binder layer of a phosphor screen or panel, as e.g. disclosed in US-Applications 2005/0087707 and 2005/0106490. These very particular CsBr:Eu phosphors are the basic phosphors of storage phosphor screens or panels used in the methods according to the present invention, more details of which are presented hereinafter.
According to the present invention a method is provided of reading out energy stored in a CsBr:Eu stimulable phosphor plate, having been exposed to high energy radiation, wherein said method comprises the step of detecting radiation emitted upon photostimulation of said phosphor plate, wherein said method is performed in two steps: a first read-out step while irradiating said phosphor plate with stimulating energy from an infrared radiation stimulation source, followed by a second read-out step, wherein said second read-out step proceeds while providing stimulation radiation having a higher energy than stimulation radiation energy provided during said first read-out step.
In the method according to the present invention, said phosphor plate has been exposed to high energy radiation from X-rays, α-, β- or γ-rays, or ultraviolet radiation.
According to the method of the present invention, during said first read-out step said infrared radiation stimulation source is a Nd:YAG laser emitting radiation having a wavelength of 1064 nm or a Nd:YLF laser emitting radiation having a wavelength of 1053 nm. Both particular wavelengths are indicating that no use is made of the corresponding frequency-doubled lasers, having only one half of the wavelenghts of both particular lasers respectively. In still another embodiment according to the method of the present invention, said infrared radiation stimulation source is a diode laser emitting radiation in a wavelength range from 1000 nm up to 1200 nm.
In a particular embodiment the method according to the present invention is provided by a first step of reading out energy stored in a CsBr:Eu stimulable (storage) phosphor plate, having been exposed to high energy radiation, wherein said method comprises as a first step of detecting radiation emitted upon photostimulation of said phosphor plate, while irradiating said phosphor plate with stimulating energy from an infrared (IR) radiation stimulation source, emitting radiation energy in a wavelength range of more than 1300 nm.
According to the method of the present invention, said infrared radiation stimulation source advantageously emits radiation energy in a wavelength range from 1350 nm to 1400 nm.
It has been found to be advantageous in the method of the present invention to provide an optical filter between said infrared radiation stimulation source and said phosphor plate in order to attenuate radiation from said infrared radiation stimulation source in a wavelength range shorter than 800 nm as stimulation by radiation having higher energy should be avoided.
In the method according to the present invention, separating stimulation radiation and radiation emitted upon stimulation proceeds by providing one or more optical filter(s) allowing transmission for blue light. According to the present invention said optical filter allows transmission for blue light in an amount of more than 95%, and even up to 100%.
According to the method of the present invention said higher energy, while performing said second read-out step, is provided by stimulation with radiation energy from a light source emitting light in a wavelength range from 550 nm to 800 nm.
Moreover between said first and said second read-out step a calibration step is advantageously performed, according to the method of the present invention, in order to allow performance of said second read-out step with a PMT or a CCD as a detector having an optimized sensitivity or with a laser having an optimized power.
In another aspect of the present invention the method wherein said first and said second read-out steps are performed with a different read-out depth, it is envisaged to obtain an image with a low sensitivity and a high sharpness and an image with a high sensitivity and low sharpness respectively.
It has been found to be advantageous, according to the method of the present invention, when said image obtained from a first read-out step and said image obtained from a second read-out step are combined in one image, more particularly when said image with a low sensitivity and high sharpness and said image with a high sensitivity and low sharpness as set out hereinbefore are combined in one image, i.e. a so-called “dual-energy” image.
Particular advantages related with the method of the present invention, without however limiting the invention thereto, are following.
Separation between stimulation radiation and radiation emitted upon stimulation is simple, in that well-known optical filters as, e.g., the well-known optical filters KG1®, KG3® and KG5®, from SCHOTT AG, Mainz, Germany, can be used as such, as the transmission for blue light, corresponding with light emitted by the CsBr:Eu phosphor upon photostimulation is almost 100%.
Requirements for the optical filters are much less stringent as the photomultiplier used is much less sensitive to radiation in the infrared wavelength ranges as applicable when performing photostimulation.
Due to the low read-out energy used when photostimulating with infrared waves in the regions as set forth, the latent X-ray image remains present in the CsBr:Eu storage phosphor plate as a stored latent image, providing further read-out by radiation having a higher energy as e.g. red (laser) light, e.g. such as with a HeNe-laser at 632 nm.
Capturing of the latent X-ray image after having read out said image by means of infrared rays allows analysis of said image (“pre-scan image”) in order to beforehand allow calibration and to provide an optimized read-out with the said higher read-out energy during a second read-out step, after the first read-out step has been performed with lower (infrared) energy.
While the sensitivity depends on the “hardness” of the X-ray radiation exposure of the storage phosphor plate and while this sensitivity behavior is different for deep traps and for shallow traps, it is possible to combine the image, read-out with the IR-lasers emitting radiation of more than 1000 nm, with the image, read-out with of red laser emitting in a wavelength range between 550 and 800 nm, as e.g. a HeNe laser (emitting at 632 nm) in order to make a system for dual energy.
A lower intensity of light is needed for erasing the plate and to make it ready for re-use, while these IR-stimulable traps are easy to erase.
Scanning may proceed by a flying spot scanner, wherein a photomultiplier (PMT) is used as a detector, as well as by an array of lasers, wherein a CCD is detector. When used in a scanner as e.g. DX-S®, trade name of the needle image plate scanner from Agfa-Gevaert, Mortsel, it is clear that the diode laser, normally present therein and emitting light having a shorter wavelength, must be replaced by a diode laser emitting radiation of a longer wavelength, i.e. in the wavelength range from 1050 to 1150 nm.
As a particularly advantageous aspect, the method of the present invention allows a pre-scan by (far) infrared radiation of a stored X-ray image in a CsBr:Eu storage phosphor plate, thus reading out shallow traps and providing ability to set parameters for a following scan with radiation of higher energy, so that dual energy applications thereby become available.
Having described in detail preferred embodiments of the current invention, it will now be apparent to those skilled in the art that numerous modifications can be made therein without departing from the scope of the invention as defined in the appending claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06120277.6 | Aug 2006 | EP | regional |
This application claims the benefit of U.S. Provisional Application No. 60/844,018 filed Sep. 12, 2006, which is incorporated by reference. In addition, this application claims the benefit of European Application No. 06120277.6 filed Sep. 07, 2006, which is also incorporated by reference. It is understood that the entire contents of all references cited in this specification is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60844018 | Sep 2006 | US |
