WO2002063338A1

WO2002063338A1 - X-ray detector

Info

Publication number: WO2002063338A1
Application number: PCT/SE2002/000149
Authority: WO
Inventors: Per Nelvig
Original assignee: Lp Röntgenteknik Ab
Priority date: 2001-02-07
Filing date: 2002-01-29
Publication date: 2002-08-15
Also published as: SE0100382D0

Abstract

A thin photo detector (5) forming a single sensitive surface is positioned in front of a scintillating or fluorescent material (3) in front of an image detector (1). The light created in the scintillating or fluorescent material when the present device is subject to X-ray radiation then will hit both the photo detector and the image detector. An electric signal created in the photo detector (5) may then be utilised for deciding status of the imaging system and define a status of the imaging system dependent on whether exposure (radiation source active) takes place or not. The photo detector may in a preferred embodiment for instance constitute amorphous silicon deposited onto a substratre transparent for X-ray radiation and positioned close to a scintillating or fluorescent material in front of an image detector. However the photo detector in still another embodiment may as well be made from a semiconductor polymer. The three main components, photo detector (5), fluorescent screen (3) and image detector (1) are easily integrated into one imaging component. Due to the compact design possible, the present invention may advantageously be used for instance for dental X-ray examinations.

Description

X-ray detector

TECHNICAL FIELD The present invention relates to a detector device and more exactly to an X- ray image detector provided with a photo detector generating control signals.

BACKGROUND

In X-ray techniques today electronic detectors tend to replace the earlier utilised ordinary film, which after exposure had to be developed. Since 1986 different products have for instance been marketed for direct dental X-ray examinations. Most of the devices rely on Charge Coupled Device detector techniques (CCD). During last years also CMOS detectors have been introduced for imaging purposes in connection with X-ray examinations. The silicon based detectors all have been combined with an energy converter consisting of a fluorescent or scintillating material in order to increase efficiency.

Typical X-ray sources for dental X-ray imaging generally operate with an accelerating voltage of 60 - 90 kV giving a mean photon energy in the range 30 - 40 keV. The material thickness required to stop 80 % of the X-ray photons is found to be in the range 150 - 500 μm for commonly used scintillators. The primary interaction between a photon and the material, photoelectric absorption, is a single event. The light in the scintillator material is then generated by a large number of secondary reactions taking place within a few microns from the location of the primary interaction. As a result a flash of light is generated close to the spot of the primary interaction and radiated in all directions. Materials often used as scintillators have been based on cesium iodide (Csl) or terbium doped gadolinium oxy-sulphide (Gd₂O₂S:Tb) phosphor.

In many cases a thin plate of fibre optics has been used between the silicon detector and the fluorescent component in order to decrease the amount of X-ray radiation reaching the silicon detector and absorbed directly therein. Regarding the CCD detector different methods to increase its durability have been used. Among other things the method of creating the channel limitations has been crucial as for commercial CCD detectors as the common LOCOS structure was considered to result in deficient radiation durability. Additionally a so called inverted mode or using another expression, MPP, has essentially increased the durability and decreased the dark current which in principle has made the fibre optical component unnecessary.

A further approach for increasing efficiency with improved resolution when using a scintillator device together with an image detector was recently demonstrated in an International Application WO00/43810 (Swedish patent SE-C2-513 538) to handle a situation whenever the X-ray photon absorption distance is much longer than the required pixel size.

To synchronise an imaging detector system and the radiation source (e.g. a dental X-ray apparatus) different methods have been used. EP-A1-0 415 075 discloses a dental X-ray diagnostic device using a radiation sensitive sensor at the back or at the side of an image detector for use in dental X-ray imaging. The detector could also be integrated in the silicon substrate forming a CCD. In WO92/22188 (US-A-6 002 742) a further method and system for triggering of an X-ray image sensor is disclosed using a number of X-ray sensitive diodes distributed over the back surface of a CCD image detector for dental X-ray examinations.

In GB-A-2 303 772 and GB-A-2 303 017 a manner to read and analyse the dark current of the CCD detector is disclosed. When the achieved signal suddenly overrides a threshold value defined this indicates that exposure has started and the CCD is then set to an integration state until enough time passed for a fully exposed image to be read out.

For CMOS detectors a non-destructive readout of pixels for instance has been used as well as other methods to discover and establish whether radiation is present or not in order to control and indicate a system status. However there is still a need for a technique to easily obtain a general indication of X-ray radiation of the image sensor, which independent of the imaging detector itself provides a high sensitivity over the entire imaging surface.

SUMMARY OF THE INVENTION According to the present invention a thin photo detector is additionally positioned in front of a scintillating or fluorescent material in front of an image detector. Generally a scintillating or fluorescent material is used to convert X-ray radiation into visible light. The light created in the scintillating or fluorescent material when the present device is subject to X-ray radiation then will hit both the photo detector and the image detector. An electric signal is then created in the photo detector, which signal may be utilised for deciding status of the imaging system and define a status of the imaging system dependent on whether exposure (radiation source active) takes place or not. The photo detector may in a preferred embodiment for instance constitute amorphous silicon deposited onto a substrate transparent for X- ray radiation and positioned close to a scintillating or fluorescent material in front of an image detector. However the photo detector in still another embodiment may as well be made from a semiconducting polymer. The three main components, photo detector, fluorescent screen and image detector are easily integrated into one imaging component. Due to the possible compact design, the present invention may advantageously be used for instance for dental X-ray examinations.

An X-ray image detector device for simultaneous imaging and creation of a status signal according to the present invention is set forth by the independent claim 1, and further embodiments are set forth by the dependent claims 2 to 8.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described by the following description to be read together with the appended drawings, wherein: FIG. 1 illustrates a general view of an illustrative embodiment of a image detector according to the present invention;

FIG. 2 illustrates in a general view a second embodiment of an image detector according to the present invention, and

FIG. 3 illustrates a cross section of a third embodiment of an X-ray image detector according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 illustrates a general embodiment of an image detector realising the techniques according to the present invention. On top of an image detector 1, preferably a CCD or a CMOS image detector, a fluorescent material 3 is positioned. Additionally a thin photo detector 5 is placed on top of the fluorescent material 3. The fluorescent material 3 may typically be a Csl material, but may also constitute a terbium doped gadolinium oxy-sulphide phosphor (Gd₂O₂S:Tb).

Light arising in the fluorescent material layer 3 will hit both the photo detector 5 and the image sensor 1 when the device is subject to an X-ray radiation. An electric signal then will be created in the photo detector. For instance this signal is extracted for use as a measure indicating that an exposure is ongoing. In other words, an indication is achieved that the radiation source is active. This electric signal, as is apparent to a person skilled in the art, may by ordinary electronic means easily be integrated and used for a highly sensitive exposure control.

The photo detector in a preferred embodiment is advantageously a thin film cell of for instance amorphous silicon deposited onto a substrate fully transparent for X-ray radiation. The silicon surface of this photo detector is for highest possible sensitivity brought in direct contact with the fluorescent material 3. The photo detector, according to the state of the art is provided with electrical terminals for access of the current induced by light generated from the fluorescent material 3 when subject to X-ray radiation.

In a further embodiment this front photo detector may also be made from a semiconducting polymer and brought in contact with the surface of the fluorescent material facing the radiation source.

Figure 2 indicates a second embodiment of an X-ray imaging detector provided with the present photo detector. In Figure 2 a fibre optical interface 7 is inserted between the fluorescent material 3 and the imaging detector 1 to further utilise the possible resolution of the imager, for instance a CCD cell. The three main components, photo detector 5, fluorescent screen 3 and image detector 1 are easily integrated into one imaging component. Due to the compact design possible, the present invention may advantageously be used for instance for dental X-ray examinations.

In yet another embodiment the fluorescent material layer 3 and the fibre optical interface 7 may be replaced by a fluorescent screen forming tubes of fluorescent material of for instance Csl having a diameter corresponding to the pixel size of the image detector 1. Such an interface to the imager will for instance be equal to what is disclosed by the previously mentioned International Publication WO00/43810, however with the difference that the pore matrix, forming tubes for fluorescent material, will be open in both ends to transmit light also to the additional photo detector. In Figure 3 is demonstrated an embodiment illustrating an interface combining a photo detector 5 according to the present invention and a pore matrix 13 filled with scintillating material 11. Some of the high efficiency of the original matrix device will be lost but resolution will still be gained in the same way as disclosed by the International Publication WO00/43810. It may be noticed that the pore channels of the matrix filled with scintillating material 11 are aligned with each pixel 15 of the image detector 1. The silicon 5 on the X-ray transparent material 9 of the photo detector will serve as one single photo element covering the entire surface of the image detector 1. As illustrated an X-ray photon will give rise to several photons producing visible light, which due to the channels of the matrix will be transferred both to a specific pixel of the image detector and to the photo detector. The detector will integrate all photons arising from X-ray radiation over the entire detector surface. A similar function is also obtained in the second embodiment of Figure 2 utilising fibre optics between the fluorescent material and the image detector.

It will be apparent to a person skilled in the art that the present invention may be modified and altered in many ways without departing from the scope of the invention, which is defined by the appended claims.

Claims

1. An X-ray image detector device for simultaneous imaging and creation of a status signal, characterised in an imaging detector device (1); a fluorescent component (3) positioned above a surface of the imaging detector device (1) facing an X-ray radiation source; an additional photo detector (5) overlying a surface of the fluorescent component (3) facing the X-ray radiation source, the additional photo detector simultaneously with the imaging detector receiving light created by the fluorescent component for generating a signal indicating presence of X-ray radiation.

2. The device according to claim 1, characterised in that the imaging detector device (1) constitutes a Charge Coupled Device (CCD).

3. The device according to claim 1, characterised in that the imaging detector device (1) constitutes a CMOS image detector.

4. The device according to claim 1, characterised in that the fluorescent or scintillating component (3) contains cesium iodide (Csl) or terbium doped gadolinium oxy-sulphide (Gd₂O₂S:Tb) phosphor.

5. The device according to claim 1, characterised in that the additional photo detector (5) is a thin cell deposited onto a surface of the fluorescent component facing the X-ray radiation source.

6. The device according to claim 5, characterised in that the thin cell constitutes amorphous silicon deposited onto the fluorescent component.

7. The device according to claim 5, characterised in that the thin cell constitutes a semiconducting polymer.

8. The device according to claim 1 , characterised in that a fibre optical device (7) is inserted between the fluorescent material (3) and the image detector (1) in order to increase imaging resolution.

9. The device according to claim 1, characterised in that that a pore matrix (13) filled with fluorescent material (3) or scintillating material (11) is inserted between the photo detector (5) and the image detector (1).