Method of image formation, dosimetry and personal monitoring

Details Method of image formation, dosimetry and personal monitoring Method of image formation, dosimetry and personal monitoring

2000-06-22

2002-07-16

Hannaher, Constantine (Department: 2878)

Radiant energy

Source with recording detector

Using a stimulable phosphor

C250S484200, C250S484500, C250S459100, C250S362000

Reexamination Certificate

active

06420724

ABSTRACT:

FIELD OF THE INVENTION
The present invention is related with a novel method of image formation (whether or not radiographic), dosimetry or personal monitoring, and more particularly, to a method to release energy stored in stimulable phosphors, coated in storage phosphor screens or panels.
BACKGROUND OF THE INVENTION
Well-known in diagnostic imaging is the use of phosphors in the production of X-ray images. In a conventional radiographic system an X-ray radiographic image is obtained by X-rays transmitted imagewise through an object and converted into light of corresponding intensity in a so-called intensifying screen (X-ray conversion screen) wherein phosphor particles absorb transmitted X-rays and convert them into visible light and/or ultraviolet radiation. As silver halide grains or crystals, present in emulsions coated in layers of a silver halide photographic film material are more sensitive to the thus converted X-ray energy than to direct impact of X-rays (due to a less effective absorption of those energetic X-rays) the said conversion is in favour of image formation on the film material.
According to another method of recording and reproducing an X-ray pattern disclosed e.g. in U.S. Pat. No. 3,859,527 a special type of phosphor is used, known as a photostimulable phosphor, which being incorporated in a panel is exposed to incident pattern-wise modulated X-rays and as a result thereof temporarily stores energy contained in the X-ray radiation pattern. At some interval after the exposure, a beam of visible or infra-red light scans the panel in order to stimulate the release of stored energy as light that is detected and converted to sequential electrical signals which can be processed in order to produce a visible image. For this purpose, the phosphor should store as much as possible of the incident X-ray energy and emit as little as possible of the stored energy until stimulated by the scanning beam. This is called “digital radiography” or “computed radiography”.
Use of alkali metal halide phosphors in storage screens or panels is well known in the art of storage phosphor radiology, wherein at least part of the energy contained in an X-ray pattern is temporarily stored. The high crystal symmetry of these phosphors makes it possible to provide structured screens and binderless screens, in favour of image quality. Examples of such alkali metal phosphor can be found in several documents. In e.g. U.S. Pat. No. 5,028,509 a phosphor corresponding to general formula:
(M
1−x
.M′
x
)X.aM
2+
X′
2
.bM
3+
X″
3
:dB,
wherein M is Cs or Rb, M′ is at least one metal selected from the group consisting of Li, Na, K, Rb, and Cs, M
2+
is at least one metal selected from the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu and Ni, M
3+
is at least one metal selected from the group Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga and In; X, X′ and X″ can be the same or different and each represents a halogen atom selected from the group consisting of F, Br, Cl, I with the proviso that all X′ atoms are the same, B is an element selected from the group consisting of Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Gd, Lu, Sm, Y, Tl, Na, Ag, Cu, Mg, Pb, Bi, Mn, and In. 0≦x≦1 en 0≦a≦1 en 0≦b≦0.5 en 0≦d≦0.2.
In U.S. Pat. No. 5,055,681 a binderless screen comprising the phosphor as disclosed in U.S. Pat. No. 5,028,509 has been disclosed.
In U.S. Pat. No. 4,806,757 a CsI phosphor has been disclosed, comprising between 0.0001 to 1 mole % of at least one element selected from the group consisting of Li, K, Rb, Cu, Au, Be, Mg, Ca, Sr, Ba, Zn, Cd, Hg, B, Al, Ga, In, Tl, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Si, Ti, Zr, Ge, Sn, Pb, As, Sb and Bi.
Alkali metal halide phosphors performing as desired qualities absorption characteristics, speed, storage capabilities etc. have been disclosed in EP-A 0 751 200, wherein besides high speed also high chemical stability and low sensitivity to humidity have been appreciated as well as ability to produce screens comprising vapour deposited phosphor layers providing high image definition.
The radiation image storage phosphor screen according to that invention comprises an alkali metal halide phosphor characterized in that said phosphor contains a dopant selected from the group consisting of Ga
1+
, Ge
2+
, Sn
2+
, Sb
3+
and As
3+
. In a preferred embodiment thereof the alkali metal is Cs and/or Rb.
In order to provide a method for recording X-rays following steps were recommended:
(i) exposing a photostimulable storage phosphor screen, comprising novel alkali metal halide phosphors,
(ii) stimulating said photostimulable screen in order to release the stored X-ray energy as stimulated light and
(iii) collecting said stimulated light.
In order to release energy stored by a stimulable phosphor use has hitherto often been made of optical light sources as mentioned hereinbefore. As a consequence thereof optical filters are required in order to separate light emitted by the storage phosphors after stimulation and light originating from the stimulation source. In order to develop a scan-head in order to scan a plate or panel built-up with stimulable phosphors in order to release said stored energy, it is recommended to reduce the volume of such a scan-head to a minimum. Especially when the detector, collecting said stimulated light is a CCD with Fiber Optic Plate (FOP), the image plate should be placed in direct contact with this fiber optic plate in order to obtain a sufficiently good resolution. Presence of any extra intermediate layer, as e.g. a filter layer, may lay burden thereupon and any measure in order to simplify the process of reading out a storage phosphor is welcome.
OBJECTS OF THE INVENTION
Therefore it is an object of the present invention to provide an easy method in order to stimulate storage phosphors and panels built up with said storage phosphors.
Moreover it is an object to provide easy detection means for the energy release by the said storage phosphors and panels, more particularly with respect to (radiographic) image formation, dosimetry and personal monitoring.
Other objects will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
The above mentioned objects are realized by providing a method of image formation, dosimetry or personal monitoring wherein said method comprises the steps of
(a) storing energy in stimulable phosphors, and more particularly with tribostimulable phosphors, coated in one or more layers of said screen or panel;
(b) converting said energy to emission energy and
(c) detecting said energy,
characterized in that said converting step proceeds by means of a source of pressure energy.
Because the emitted light energy is proportional with the pressure applied to the tribostimulable phosphors coated in said storage screen or panel, this technique is also suitable for measuring pressure forces.
Specific features for preferred embodiments of the invention are disclosed in the dependent claims.
Further advantages and embodiments of the present invention will become apparent from the following description and drawings.


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B.P. Chandra et al: “Classification of Mechanoluminescence”, Crystal Research and Technology, 19

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