BACKGROUND OF THE INVENTION Detectors utilized in the art of acquisition and reproduction of ionizing radiation images are well known in the art. The images stored in these detectors are read out by stimulating the crystals to radiate. This radiation reproduces the stored image. A detector that may be stimulated to radiate is called a stimulatable detector or a storage phosphor. When such a storage phosphor is irradiated with ionizing radiation carrying a pattern (e. g., x-rays which passed through a human body), electron-hole pairs are created whose distribution depends on the pattern carried by the radiation. Reading out the stored pattern is performed by stimulating the detector with a light (photo-stimulation) at a suitable wave length or alternatively, by heating the detector (thermo-stimulation). The stimulated crystal emits light that reproduces the stored pattern. Typically, the stimulating light is red or infra-red while the emitted light is visible in the violet-green spectral range.

Description of exemplary such stimulatable phosphors as well as apparatus and methods concerning their photo-stimulation mechanisms are to be found in US patents 4,239,968, 4,261,854,5,028,509,5,180,610,5,227,097,5,360,697 and papers:"Luminescent Alkali Halide Crystal Memory Elements"by I. K. Plyavin, V. P. Objedkov, G. K. Vale, R. A. Kalnin and L.

E. Nagli in Luminescence of Crystals, Molecules and Solutions, The proceedings of the International Conference on Luminescence, Leningrad USSR, August 1972, edited by Fred Williams, published by Plenum Press, New York, 1973;"Photostimulation mechanisms of X- ray irradiated RbBr: Tl" by H. Von Seggem, A. Meijernik, T. Vogt and A. Winacker in Journal of Applied Physics Vol. 66, pp. 4418-4424 (1989) and PCT patent publication WO 00/10035 the disclosures of all of which are incorporated herein by reference.

Detectors utilized in the art may be polycrystalline or single crystals, which may be substantially transparent to stimulating and/or fluorescent light and substantially permeable to the pattern carrying radiation. For convenience, the term"crystalline"will be used to denote both single and polycrystalline materials. These crystals may have structural defects and/or non controlled impurities which scatter the stimulating and/or the emitted light. As a consequence, the spatial resolution and/or the sensitivity of the final image may be poor. Activated alkali- halide crystallines such as RbBr: Tl, KBr : doped with Tit In+, Ga+, Ag+, Cu+, Sn++, Pb++,

Eu++, etc., Europium or Cerium activated Barium Fluoro-halides such as BaFBr: Eu and/or Silver activated Zinc Sulfide are some examples of crystallines utilized in radiography. Ideally, these crystallines must have a high absorption coefficient for the ionizing radiation and must be transparent to stimulating and fluorescence light; in practice they only represent a compromise between these parameters.

PCT patent publication WO 00/10033, the disclosure of which is incorporated by reference, describes a system in which the storage phosphor material has a pattern of luminescent centers (formed, for example by ionizing radiation), the material is excited with excitation radiation, and the light emitted by the centers is acquired. In exemplary embodiments disclosed therein excitation radiation does not cause electron-hole recombinations. Thus, the material can be read more than once.

SUMMARY OF THE INVENTION A general aspect of some embodiments of the invention is concerned with the construction of radiation detectors.

In some exemplary embodiments of the invention, the radiation detectors, comprising for example, stimulatable detectors formed of storage phosphors or other detector materials, are packaged in a manner that provides one or more of the following: Integration of filters to protect the detector from environmental light which could erase the stored image, while allowing sufficient transmission of emitted light and stimulating light when the image is being read.

Protection of the fragile detector material against shock and/or bending stress.

. Protection from humidity.

More comfortable insertion of detectors for imaging the oral cavity, into the mouth.

Integration of filters and other optical elements useful for increasing the light output of the detectors when excited.

. Compensation for surface irregularities of the detectors, to increase the light output.

Detection of the emitted light from only one side of the detector, for example, by transmission.

Marking and/or coding of the detectors, to provide one or more of identification of the patient/study ; identification of the material in the detector and calibration.

Facilitation of the positioning of the detectors and/or aiming of the ionizing radiation.

In some embodiments of the invention, the detector material is packaged between two stiff plates. These plates may be bonded to the detector material with a resilient adhesive to

provide shock protection. Optionally, the adhesive provides an optical match between the detector material and the plate, to reduce internal reflections. Optionally, the adhesive has the same index of refraction as the detector material. Use of such adhesive reduces the effects of surface irregularities in the detector material on the transmission of light. The edges of the plate/detector material sandwich may be sealed, for example with silicone, to protect the detector material from humidity. The plates may be flat or may be formed to fit the site at which they are to be used for imaging, such as the inside of the mouth. Optionally, one of the plates may be in the form of a"bathtub"structure, and optionally there may be space between the"bathtub"and the detector material, which may be filled with a resilient plastic filling, at least partially and, optionally, completely encapsulating the fragile detector material, protecting it from shock, bending, and humidity. Optionally, the resilient plastic filling may replace one of the plates, the one which does not form part of the"bathtub,"since the"bathtub"may give the package sufficient rigidity without the need for a rigid plate on the other side. Optionally, there may be no rigid plate on either face, but only a rigid frame around the edges.

In some embodiments of the invention, the plates and/or the resilient plastic filling act as filters which protect the detector from environmental light that could erase the image by causing recombination of electron-hole pairs. Such light tends to be in a wavelength range, 500 to 700 nm in the case of a doped KBr detector, that includes the wavelengths used for reading the stored image by exciting the detector material. The detector must be protected from environmental light of these wavelengths, once it has been exposed. In the art described in PCT Application No. PCT/IL00/00776 from which this application claims priority, the detector was enclosed in a sheath that was opaque to visible light, although it was transparent to x-rays, during exposure and while stored after exposure. In order to read the image, this sheath had to be removed, and the detectors had to be placed in a reader, while in an environment with a low level of light, typically less than 100 lux. In some embodiments of the invention, the plates attached to the detector are filters which block a large fraction of red light, for example 80% to 99%, and a large fraction of other wavelengths that can erase the image, while allowing transmission of a large fraction of the emitted light, typically blue light. The reader includes a red laser, used to excite the detector and read the stored image, sufficiently powerful that it can cause the detector to emit useful amounts of light even though only a small fraction of the laser light, for example 1% to 20%, is transmitted through the filter and reaches the detector. These filters block enough of the harmful wavelengths of environmental light that the stored image is effectively protected from erasure during the short time required to take the detector out of an

opaque container that it is stored in after exposure and load it in the reader. (Optionally the opaque container is a bag that the detector was packaged in, and the detector can remain inside the bag while the detector is being exposed in the patient's mouth. Then the detector will not be exposed to any harmful environmental light between the time it is exposed and the time it is removed from the bag just before reading it.) For example, if the filter transmits 10% of red light, then typically 50% of the image will be erased if the detector is exposed to indoor environmental light for five minutes. Thus 1% transmission would allow even easier handling and 20% transmission would require subdued lighting. While lower and higher transmissions are possible, the required strength of the laser increases with reduction of the percent transmission. Too much transmission may make handling difficult. The exact amount of time of course depends on the type of storage phosphor, the transmission spectrum of the filter, and the level of environmental light. Hence there is no need to use a room with an especially low level of light. But the filters transmit enough red light from the powerful laser in the reader that the images can be read. Optionally, the detector material could be KBr doped with In++, and the laser light used to excite the stored image could have a wavelength in the range between 633 nm and 660 nm. Although KBr doped with In++ is more sensitive to 633 nm light than to light at longer wavelengths, lasers producing light at longer wavelengths are more powerful and cheaper.

In some embodiments of the invention, the plates are filters and/or have surfaces that enhance the light output of the radiation detector when the detector material is excited.

Optionally, an input plate comprises a filter that passes enough of the excitation radiation and reflects light that is emitted upon excitation. Thus, all of the emitted light passes through a single face of the detector. Optionally, additionally or alternatively, the output plate absorbs the exciting light and/or diffuses the emitted light. The absorption of the excitation light reduces noise in the detection systems. Diffusing the emitted light increases the output by reducing the amount of light reflected back into the detector. However, since it is not generally desirable that the exciting radiation be reflected from the output, when the output is diffusive, the output plate should absorb the exciting radiation. Diffusion reduces the amount of emitted light that is totally reflected.

Alternatively to diffusion, the outer side of the output plate is formed with grooves to reduce the amount of reflection of the emitted light.

Optionally, the edges of the storage phosphor crystal or the edge of the detector sandwich are coated with a light reflective coating, such as titanium oxide, to increase the light

output. The reflections may optionally be substantially Lambertian. In the absence of such a reflective coating at the edges, for a typical index of refraction of the storage phosphor, most of the emitted light will be totally internally reflected and exit the detector through one of the edges. If the reflection from the edges were specular rather than Lambertian, and the edge surfaces are perpendicular to the faces of the detector, then any emitted light which is totally internally reflected from the faces will continue to be totally internally reflected from the faces after reflecting from the edges, and will travel back and forth inside the detector until it is absorbed. With a Lambertian coating on the edges, the direction of the light is randomized each time it reflects from the edge, so even if it totally internally reflected from the faces before it reflects from the edge, almost all of the light will be able to exit through the faces after reflecting a few times from the edges. Although it is possible to accomplish the same thing by beveling the edges at an angle, that solution (which is prior art) is more expensive than applying a white Lambertian reflective coating to the edges.

In some of these embodiments of the invention, the exciting radiation enters one face and the substantially all the emitted light leaves via the other face, because the input face of the detector has a filter which reflects the emitted light, while the output face has a filter which transmits the emitted light. This can allow for a more simplified and efficient system for reading the images.

In some embodiments of the invention, the packaging of the detectors or the detector itself is coded to facilitate use. Optionally, the coding comprises a color code, a bar code or a serial number that identifies the specific detector. In some embodiments, the bar code or number is written in radio-opaque ink or in ink that blocks the exciting radiation, so that, when the device is scanned, the identification is acquired by the image readout device. In others, the identification it is optically read by a reader of the detectors. In still others the identification is read by an operator. The identification can optionally be used to provide one or more of the following: A reference to a calibration map, to allow correction of the image for non-uniformity in sensitivity of the detector.

Identification of the type of material used.

Matching of the image with a patient/study, where the identification is previously associated with the patient/study.

In some embodiments of the invention, for example for use with dental detectors, the packaging is formed with position indicators. Such indicators may be, for example a bump or

indentation on one corner of one face of the package to indicate whether that side is the input or output side and/or to aid in orienting the detector.

In an embodiment of the invention, the detector packaging includes an extension for positioning and aiming. For example, a package used for dental imaging may have a bent arm in the shape of a"U". The detector is placed at one end of the U-shape. When the detector is placed in the mouth, the other end of the U projects out of the mouth, in line with the position of the detector. Thus the other end of the U provides both an indication of the position of the detector in the mouth and an aiming point for the x-ray. This aiming and positioning structure can be part of the package of the detector or the detector may be inserted into and removed from the structure, so that the structure can be reused. This structure can be used for film as well as for stimulatable detectors.

An aspect of some embodiments of the invention is concerned with image readers for radiation detectors.

In some embodiments of the invention, a reader is provided that utilizes a laser having a wavelength that excites a stimulatable phosphor so that it emits light. A beam generated by the laser scans across the detector. Light is emitted when the laser excites a particular point on the detector. This light is generated by stimulatable centers at that point and, to some degree by centers that were excited just prior to the laser reaching the point. When a detector is provided with a filter system, as described above, with input and optionally with output filters and/or diffuser, light exits substantially only, or at least to a much greater degree, in the direction opposite that of the input beam. A relatively simple detector system can be used to detect this light.

As the beam scans the detector, a map of the emission is formed, which is optionally corrected for light emitted by points previously scanned. The correction can be performed, for example, by deconvolving the emitted light image utilizing a decay function for the detector material, a known spatial intensity profile of the laser and/or a known temporal response of the detector.

In some embodiments of the invention, the reader is also used to scan ordinary x-ray films. This would be convenient for a dentist who wants to input both older x-ray films and newer stimulatable detectors into one database, for example. When the reader is used to scan x- ray films, no color filters are needed. However, the"excitation"radiation needed for the x-ray film is much lower than that for reading stimulatable detectors, especially when the stimulatable detectors have a filter on them which blocks 80% to 99% of the excitation light.

Thus, exemplary embodiments of such dual mode readers are provided with means for reducing the amount of light in the scanning beam. Such means may include optical attenuators or means for reducing the output power of the laser itself or an attenuator attached to the film.

In some embodiments of the invention, the radiation detectors or films are loaded into a magazine which is then loaded into the reader. The reader can then automatically read several detectors or films, one after the other, at an appropriate pace. The magazine used for film could be different from the magazine used for radiation detectors, and could include an attenuator to reduce the amount of light in the scanning beam. The magazine for radiation detectors could be designed to make it impossible to load the detectors in the wrong orientation.

In some embodiments of the invention, the reader determines the quality level of a detector. One method for doing this is to measure the noise level of emitted light while scanning the detector. Degeneration of the detector generally results in increased noise. In addition, the absolute level of the excitation output can be used as an indication of detector quality. Such periodic checking will detect, for example, scratches.

In some embodiments of the invention, the reader includes an optical reader that reads markings such as bar code or other markings on the detector package. As indicated above, these markings, which may include one or more of bar codes, numbers, color coding or other markings, may include information as to corrections to be made when reading the detector or may be associated with a particular patient/study. In general, the information is stored in a controller of the reader, to which the image or bar code number is sent.

There is thus provided an integrated radiation detector comprising: a storage phosphor having first, input, face and a second, output, face, the phosphor being excitable by radiation at a first wavelength and emitting radiation at a second wavelength when excited; and at least one input filter optically juxtaposed to the input face which at least one filter blocks at least 80% of radiation at wavelengths that can erase a stored image in the storage phosphor, but passes at least 0.1 % of radiation at the first wavelength.

In an embodiment of the invention, the at least one input filter reflects radiation at the second wavelength.

In an embodiment of the invention, the said at least one input filter blocks enough of the radiation at wavelengths that can erase a stored image in the storage phosphor, so that said detector can be safely inserted into a device for reading the storage phosphor, at a light level of 150 lux.

Optionally, the said at least one input filter blocks enough of the radiation at wavelengths that can erase a stored image in the storage phosphor, so that said detector can be safely inserted into a device for reading the storage phosphor, at a light level of 300 lux.

Optionally, the said at least one input filter blocks enough of the radiation at wavelengths that can erase a stored image in the storage phosphor, so that said detector can be safely inserted into a device for reading the storage phosphor, at a light level of 500 lux.

Optionally, the said at least one input filter allows approximately 20% or less of radiation at the first wavelength to pass.

Optionally, the said at least one input filter allows approximately 10% or less of radiation at the first wavelength to pass.

Optionally, the said at least one input filter allows approximately 5% or less of radiation at the first wavelength to pass.

Optionally, the said at least one input filter allows approximately 1% or less of radiation at the first wavelength to pass.

Optionally, the said at least one input filter allows approximately 0.5% or less of radiation at the first wavelength to pass.

In some embodiments of the invention, at least one of the at least one input filters is deposited on the input face.

Optionally, at least one of the at least one input filters is a dichroic filter.

Alternatively or additionally, at least one of the at least one input filters is a partially silvered mirror.

Optionally, the at least one input filters also include a filter that substantially transmits light at the first wavelength, and substantially blocks light at wavelengths which are harmful to the stored image but are not suitable for excitation of the storage phosphor.

In some embodiments of the invention, the detector includes an input rigidizing plate attached to said input face.

Optionally, at least one of the at least one input filters is comprised in the input rigidizing plate.

Optionally, the input rigidizing plate is attached to the input face using an optical glue.

Optionally, the optical glue is resilient, so that it absorbs shock.

In some embodiments of the invention, the detector includes at least one output filter optically juxtaposed to the output face.

Optionally, the at least one output filter substantially blocks radiation at the first wavelength and passes at least 50% of radiation at the second wavelength.

Optionally, the at least one output filter passes at least 75% of radiation at the second wavelength.

Optionally, the at least one output filter passes at least 90% of radiation at the second wavelength.

Optionally, the at least one output filter substantially blocks radiation of wavelengths that could erase an image in the phosphor.

Optionally, the at least one output filter diffuses radiation at the second wavelength.

Optionally, at least one of the at least one output filters is deposited on the output face.

In some embodiments of the invention, the detector includes an output rigidizing plate attached to said output face.

Optionally, the output rigidizing plate is attached to the output face using an optical glue. Optionally, the optical glue is resilient, so that it absorbs shock.

In some embodiments of the invention, the detector includes a resilient plastic filler attached to the input face.

Optionally, the resilient plastic filler comprises at least one of the at least one input filters.

In some embodiments of the invention, the detector includes a layer of a resilient plastic filler attached to the output face.

Optionally, the storage phosphor is completely encapsulated in the resilient plastic filler.

In some embodiments of the invention, the plastic filler is contained by an external rigid structure.

Optionally, the rigid structure comprises at least one of the at least one input filters.

In some embodiments of the invention, the output rigidizing plate comprises at least one of the at least one output filters.

Alternatively or additionally, the layer of resilient plastic filler attached to the output face comprises at least one of the at least one output filters.

Alternatively or additionally, the rigid structure comprises at least one of the at least one output filters.

In some embodiments of the invention, the radiation detector is sealed against humidity.

In some embodiments of the invention, the detector includes a visible marking identifying the particular detector.

In some embodiments of the invention, the detector includes a radio-opaque marking identifying the particular detector.

In some embodiments of the invention, the detector includes an elastomer sheath at least partially covering the detector.

Optionally, the sheath is removable.

In some embodiments of the invention, the detector includes at least one bumper, made of a resilient material, attached to the outside of the detector, to protect the detector from damage if it falls.

Optionally, there are four bumpers, one attached to each corner of the detector.

There is thus also provided a reader for reading storage phosphors, comprising: at least one holder for a storage phosphor; a scanner that scans a phosphor when such is held in said holder; a detector that detects light exiting substantially from the phosphor, and a removable receptacle capable of holding more than one storage phosphor, wherein the reader reads the storage phosphors sequentially when the removable receptacle is loaded into the reader.

Optionally, the removable receptacle comprises one holder for each storage phosphor that it holds.

Alternatively, the reader causes each storage phosphor to be transferred into one holder and read, after the removable receptacle is loaded into the reader.

In some embodiments of the invention: the scanner scans a phosphor via a first side thereof, when such is held in said holder; the scanner detects light exiting substantially only from a second side of the held phosphor; and the receptacle is constructed so that it is not possible to insert a storage phosphor facing the wrong way for reading.

In some embodiments of the invention, the reader can be set to scan the image at any of at least two different resolutions.

Optionally, an optical element increases the spot size of the excitation radiation, when a lower resolution setting is used.

In some embodiments of the invention, the scanner is a two-dimensional scanner, including a slow-axis mirror and a fast-axis mirror.

Optionally, the fast-axis mirror is driven by a galvanometer.

Optionally, the slow-axis mirror is driven by a stepper motor.

In some embodiments of the invention, the reader includes a correcting lens between the scanner and storage phosphor, wherein the virtual fulcrum or approximate virtual fulcrum at which light from the scanner originates, taking into account the refraction of the light in the correcting lens and in the storage phosphor, is substantially the same distance from the storage phosphor as the x-ray source was when the storage phosphor was exposed.

Optionally, the correcting lens substantially preserves the flatness of the focal plane.

In some embodiments of the invention, the light detector covers a substantial area, and the reader includes an optical element which spreads the emitted light from the phosphor over all or a substantial part of the light detector.

In some embodiments of the invention, the reader includes an optical element which directs toward the light detector light emitted from the phosphor that would otherwise miss the light detector.

In some embodiments of the invention, the reader is adapted to read film as well as a storage phosphor.

Optionally: the reader operates in a first mode, when a film is held, in which an attenuator is present between the scanner and the detector; and the reader operates in a second mode, when a storage phosphor is held, in which the attenuator is not present between the scanner and the detector.

Optionally, different types of holders are used for storage phosphors and films and the attenuator is included in the holder for films.

Optionally, different types of holders are used for storage phosphors and films, and the holder for films includes a diffuser on the output side.

In some embodiments of the invention, the reader includes a marking reader that reads an identification marking on the storage phosphor.

Optionally, the identification mark is a radio-opaque marking the shadow of which becomes incorporated in the stored image, and said identification mark is read by the scanner.

Optionally, the reader includes a controller that receives said identification and an output of the detector and generates an image based on the output.

Optionally, the controller receives the identification and corrects the image based on the identification.

Optionally, the correction is based on a correction table associated with the particular detector.

Alternatively or additionally, correcting the image is based on a speed of the scanner and a decay time of the phosphor.

In some embodiments of the invention, the reader includes at least one erasure light for erasing the stored image or remnants of the stored image on the phosphor.

BRIEF DESCRIPTION OF THE DRAWINGS Exemplary embodiments of the invention are described with reference to the following drawings, in which the same or similar reference symbols are used to denote the same or similar features.

Figs. lA-1F show schematic cross-sectional views of exemplary detectors systems, in accordance with an aspect of the invention; Figs. 2A-2C show an exemplary elastomer package.

Fig. 3 shows a side view of the detector of Fig. 1B, including exemplary markings of the detector; Fig. 4 shows a dental detector, in accordance with an exemplary embodiment of the invention; Fig. 5 is a schematic diagram of a reader for reading detectors, in accordance with an exemplary embodiment of the invention; Fig. 6 shows a perspective view of a detector, in accordance with an exemplary working embodiment of the invention.

Figs. 7A and 7B show a perspective view and a cutaway top view of a reader, for an exemplary working embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS Fig. 1A schematically shows an integrated detector system 10. Detector system 10 comprises a stimulatable storage phosphor 12 sandwiched between an input plate 14 with a coating 15, and an output plate 16. In Fig. 1A, coating 15 is shown on the side of input plate 14 adjacent to phosphor 12, but in some embodiments of the invention coating 15 could also be located on the outer side of input plate 14. Although coating 15 is not shown explicitly in Figs.

1B through 1E, coating 15 can also be present in the embodiments shown in Figs. 1B through 1E. Optionally, plates 14 and 16 are adhered to phosphor 12 using an optical glue 18 that matches the indices of refraction of the materials being joined. Optionally, coating 15 could be replaced by a separate filter, which could be joined to plate 14 using optical glue 18 as well.

Optionally, optical glue 18 is relatively soft so that it absorbs shocks to which detector system may, inadvertently, be subject. Generally, the crystal has an index of refraction of the same order (1.4-1.6) as some glasses and some plastic materials, so that an adhesive such as Norland Optical Adhesive types 61,65 or 68 (Edmund Scientific) or Dow Coming Dielectric Gel Sylgard 527 or 518 can be used.

Exemplary input and output plates are on the order of 0.3-1 mm thick, although they do not have to be the same thickness, and the phosphor plate is of the order of 0.5-3 mm thick, although all can be either thinner or thicker than the above values.

The edges of the phosphor crystal or detector sandwich are coated with a reflecting material 20, such as a Lambertian paint based on titanium dioxide, to avoid loss of light. If there were no reflective coating on the edges, or if the coating were not substantially Lambertian, then, for a typical index of refraction of the storage phosphor, most of the emitted light would totally internally reflect from the faces, and would either go out the edges of the detector, or would be absorbed in the detector after reflecting several times from the edges.

With a Lambertian coating, the direction of the light is randomized each time it reflects from the edge, so even light which is totally internally reflected from the faces before it reflects from an edge, will almost all be able to exit through the faces by the time it has a reflected a few times from the edges.

Optionally the edges are encased, for example in a silicone material 22, to provide greater strength to the structure, further shock absorption and/or a humidity seal to protect phosphor 12.

In the following discussion, it is assumed that the storage phosphor is KBr doped with In++. This material can be written on with x-rays to form a pattern of excitable centers, which can be excited with red light to emit blue light. However, it should be understood that any known storage phosphor can be used in almost all embodiments of the invention, with self- evident changes in the color properties of the filters, described below.

Plates 14 and 16 can be separate plates as shown in Fig. 1A, or can be part of a "bathtub"and cover structure 14'and 16'as shown in Fig. 1B. Plates 14 and 16 can be flat as shown in Figs. 1A and 1B or one of them (generally the output plate 16") may be curved or formed to fit the structure of the mouth which is to be imaged as shown in Fig. 1C.

Alternatively or additionally, a soft section 24 for cushioning the detector system against the inside of the mouth is provided as shown in Fig. 1D. Optionally, soft section 24 is removable,

for ease of reading of the detector. Alternatively or additionally, a very resilient bumper 25 may be attached to each of the four corners of the detector.

Fig. 1E shows one of bumpers 25 attached to a corner of detector 10. If the detector falls down on a flat surface, it will always hit only on one, two or three of the bumpers, which will provide shock attenuation. The bumpers will also reduce discomfort when the detector is inserted in the mouth. When plate 14 and/or plate 16 forms a"bathtub"structure as in Fig. 1B, then, as shown in Fig. IF, a resilient plastic filling 26 may optionally be placed between the plates and phosphor 12, completely encapsulating phosphor 12, providing additional shock attenuation.

In Fig. IF, output plate 16 forms a bathtub structure, and part of filling 26 functions as the input plate, but input plate 14 could form the bathtub structure and filling 26 could function as the output plate instead. In the configuration shown in Fig. IF, coating 15, or a separate filter which serves the same purpose, may deposited on the input side of phosphor 12 before it is encapsulated. Alternatively, a coating 17, which serves the same purpose, may be deposited on the surface of filling 25 after filling 25 is formed. In some embodiments of the invention, plates 14 and 16 are made of glass or plastic. However, other materials may be used.

In some embodiments of the invention, there is no rigid plate on either face, but the resilient plastic protects both faces, and there is a rigid frame around the edges. Optionally, such a configuration is manufactured by first using a bathtub structure to contain the resilient plastic filling, and then machining away or otherwise removing the bottom of the bathtub structure once the filling is set, leaving only the sides of the bathtub.

In some embodiments of the invention, any or all of plates 14 and 16, and resilient filling 25, are provided with optical properties to enhance the amount of light detected when the phosphor is excited, and to protect the detector from environmental light that can erase it. These properties can include one or more of : Coating 15 of input plate 14, which could also be a separate filter attached to input plate 14, reflects the light emitted by the storage phosphor. This enhances the amount of light that leaves the output plate by about a factor of two. Optionally this coating or filter passes the excitation light without substantial attenuation. A dichroic coating or filter may be used.

A filter at input plate 14 that blocks a large fraction of the harmful environmental light in the wavelength range, about 500 nm to 700 nm for a KBr detector, that can erase the image.

Although such a filter will necessarily block a large fraction of the excitation light as well,

the filter should transmit enough of the excitation light (for example, 1% to 20%) so that the image can be read.

Alternatively, instead of a dichroic filter at the input face, there is a partially reflective coating with optical properties that are not wavelength dependent, for example a partially silvered mirror coating. If this coating reflects a large fraction of light that hits it, for example 80% to 99%, then it would also play the role of the input filter which blocks the harmful environmental light, and it would be almost as effective as a dichroic filter for reflecting the blue light emitted inside the detector. Such a partially reflective coating would be less expensive than a dichroic filter. Since such a partially reflective mirror would reflect 80% to 99% of incoming red light as well as internally emitted blue light, it can be used with an input filter that transmits most of the red light, but blocks a substantial portion of light in the intermediate range of wavelengths (typically 500 to 630 nm) that is harmful to the stored image but is not used for reading the image. Alternatively, a partially reflective coating is used together with a dichroic filter and/or input filter.

A filter at the output plate that passes the blue light and preferably absorbs the red light.

Absorption of the red light results in a lower light output than its reflection, but preserves the resolution. This filter should pass the emitted blue light, in the 400 nm to 500 nm range, substantially without absorption. Optionally, this filter substantially blocks the harmful environmental light in the 500 nm to 700 nm wavelength range which can erase the image.

Optionally, this filter can be made of the same material as the filter at the input plate which blocks the harmful environmental light. Optionally this output filter can be thicker than the input filter which blocks the harmful environmental light. Because there is no need for this output filter to pass any of the excitation (red) light, there is no need to compromise on how much of the harmful environmental light it absorbs, and optionally it absorbs much more of the harmful environmental light than the input filter blocks.

A diffusive surface or grooves at the output plate that reduces specular reflection from the output plate. This reduces the effects of total internal reflection from the outside face of the output plate.

The above described filters may be part of the plates or may be glued between the plates and the storage phosphor. Alternatively, they can be deposited directly on the surface of the storage phosphor. In some embodiments of the invention, the radiation detector is supported by a plate on only one side thereof.

Furthermore, in some embodiments of the invention, the detectors are packaged in a disposable film package, for example a bag. The detector, in the film package, is placed in the mouth of the patient, for irradiation by the x-rays. The film is removed for reading the detector.

The bag can block exciting wavelengths to avoid discharging the image inadvertently.

Alternatively, the detector sandwich may be placed in an elastomer package that blocks at least the wavelengths of the excitation radiation. An exemplary elastomer package 30 is shown in an open state in Figs. 2A and 2B and in a closed state, in which the detector is covered, in Fig. 2C. The optional end cover 32 is one way to completely cover and protect the detector and block the excitation wavelengths. End cover 32 is may be integrally formed with the body of package 30. In the open state the cover has an opening 34 facing away from the opening in the body. After the detector is inserted, the cover is stretched, inside out over the opening, to completely cover the opening. Alternatively, other cover types, including separate covers or no cover at all (open end) can be used. The elastomer can be silicone or any other suitable material.

Fig. 3 shows a side view of detector 10'of Fig. 1B.

In some embodiments of the invention, the packaging of the detectors or the detector itself is coded 28, to facilitate use. Optionally, coding 28 comprises a color code, a bar code or a serial number that identifies the specific detector. In some embodiments, the bar code or number is written in radio-opaque ink or in ink that blocks the exciting radiation, so that, when the device is scanned, the identification is acquired by the image readout device. In others, the identification is optically read by a reader of the detector, for example, as described below with respect to Fig. 5. In still others the identification is read by an operator. In some embodiments, the same identification is both visible and radio-opaque or present in both visible and radio- opaque form, so that it can be read in various ways. The identification can be used, for example, to provide one or more of the following: A reference to a calibration map, to allow correction of the image for non-uniformity in sensitivity of the detector.

Identification of the type of material used.

. Matching of the image with a patient/study, where the identification is previously associated with the patient/study.

These possibilities are discussed further with respect to Fig. 5. Furthermore, it should be understood that the markings should be so placed, or be of such a material that they do not interfere with the operation of the detector. Thus, placement on the side of the code on the side

of the detector is ideal, where it is possible. However, where the code must, for practical reasons, be placed on a face of detector 10, it may be formed of a material that neither reflects nor absorbs x-rays and does not absorb or reflect either the exciting radiation or the emitted light. Thus it may be colored to reflect light at a third wavelength or may be an IR or UV ink, if reading is to be performed by the reader.

If the ink is radio-opaque, then it must be on the face, and the identification will be read more clearly if it is close to the detector material itself. However, it should be very close to an edge of the detector so that it does not interfere with image capture over important parts of the image.

In some embodiments of the invention, for example for use with dental detectors, the packaging is formed with position indicators. Such indicators may be, for example a bump or indentation (not shown) on one corner of one face of the package or a particular shape for the detector package to indicate whether that side is the input or output side and/or to aid in orienting the detector.

Fig. 4 shows a dental detector 40, including an aiming and positioning housing 42.

Housing 42 has a generally"U"shape. At an end 44 of one arm 46 of the"U"shape, a radiation detector 48 is placed. Radiation detector 48 may be similar to those described above, with relation to Figs. 1 and 3, or may be another type of ionizing radiation image detector, such as for example, a dental film.

At an end 50 of the other arm 52, a cross, or other optional aiming device is marked, although the end of the arm itself can act as such a mark. Alternatively, as shown in Fig. 4, end 50 is formed with an opening 54 that matches the size and position of radiation detector 48.

When end 44 is placed against the inside of the mouth, the mark or opening 54 indicates the position of radiation detector 48, to aid in positioning the detector and aiming the x-ray beam.

In general, the x-ray dosage for stimulatable detectors is lower than for film. This lower dosage can generally be achieved by reducing the power output of the x-ray generator.

However, in some older x-ray machines, the power can not be sufficiently reduced. For these machines additional attenuation must be provided. This attenuation can be provided by adding external attenuation on the x-ray generator.

When end 50 (or a cross thereon) acts as the aiming device, the material of the device should be radio-lucent. However, if end 50 is formed with an aiming window, the area surrounding the window need not be radio-lucent and may be radio-opaque to block radiation that is not detectable by the detector.

Housing 42 can be part of the package of the detector 48 or the detector may be inserted into and removed from the housing, so that it can be reused.

Standard dental holders such as RINN 54-0862 (RINN Corporation, Elgin, IL) modified to the detector thickness, can also be used.

According to some embodiments of the invention, a reader for reading the latent images on a storage phosphor is provided. An exemplary embodiment of a reader 60, is schematically illustrated in Fig. 5.

Reader 60 comprises a scanner 62 for providing a scanning light beam 64 across a radiation detector 66. A light collecting system 68 collects light emitted by radiation detector 66 and concentrates it on a light detector 70. Light detector 70 may be a point detector with a large acceptance angle and/or coupled to a lens with a large acceptance angle or it may be a line, or area detector. When detector 66 comprises a storage phosphor, the scanning light should match the excitation wavelength required for exciting the phosphor. For the exemplary embodiment given above this wavelength is 633-660 nm. A suitable source is based on a diode laser and any scanning system as known in the art. In order to assure focus across the scanned device, a mechanical scanner in which the beam has a constant focal position may be used. In general, scanning by the scanner is linear, with the scanner as a whole moving more slowly with respect to the rest of the reader (or vice-versa) in the cross-scan direction. Alternatively a two-dimensional optical scanner that performs a TV-like raster scan can be used. The scanner could have two mirrors, a slow-axis mirror is driven by a geared stepping motor and a fast-axis mirror is driven by a galvanometer. Such mechanisms are well known in the art and are not shown in Fig. 5.

Optionally, a correcting lens 72 is located between scanner 62 and radiation detector 66, to provide the right virtual fulcrum. When radiation detector 66 is exposed to x-rays, the x-rays do not follow paths that are parallel to each other, but their paths radiate out from an origin that is a finite distance away. If the light used to scan the radiation detector originates at a different distance from the radiation detector, then the image will be distorted and smeared out, due to the finite thickness of the radiation detector. Even if the light used for scanning originates at the same distance as the x-rays did, there will still be distortion due to refraction of the light in the radiation detector. Correcting lens 72 compensates for these effects, while still keeping the focal plane of the scanner substantially flat.

If the light detector covers a large area, then the light collecting system optionally could distribute the light over a large fraction of that area, rather than concentrating it in a small

region, in order to make the reader less sensitive to imhomogeneities in the light detector. A pyramidal reflector could be used for this purpose. A pyramidal mirror would also collect light emitted from the radiation detector at angles that otherwise would not reach the light detector, and direct this light to the light detector.

Radiation detector 66is inserted so that its entrance face faces the scanner. The correct way to insert the detector can be indicated by a mark or bump or by the detector having a characteristic shape that allows for insertion in only one direction. For example, Fig. 6 shows a detector with a truncated corner 67, which matches the shape of a slot in a magazine 90 (see Fig. 7), and makes it impossible to insert the detector the wrong way. Although magazine 90 in Fig. 7 holds more than one detector, the same thing could also be done with a holder that only holds a single detector. If detector 66 has a filter blocking a sufficiently large fraction of the environmental light that can erase the stored image, but allowing enough excitation light to pass so that it can be read, then detector 66 can be inserted into the reader in ordinary indoor light.

If the detector is lacking such a filter, then it is necessary to remove it from its opaque storage container or sheath or other packaging in an environment with a low level of light, typically less than 100 lux, and then insert it in the reader.

As indicated above, for the radiation detectors of Figs. 1 and 2, all of the emitted light leaves the detector via the face opposite that from which it is scanned. Optics for light collecting system 68 is schematically shown in Fig. 4. Light detector 70 detects the emitted light and provides an electrical signal responsive to the light intensity to a controller 73.

Alternatively, collector 68 and detector 70 are replaced by a photomultiplier that covers substantially the whole output face and collects all the light therefrom.

Controller 73 also controls the position of the beam of scanner 62 and the cross-scan position of beam with respect to detector 66 and/or receives an indication of the positions.

Based on this knowledge of the beam position, controller 73 associates a light intensity with each position of the beam, i. e., with locations on the detector.

To optimize the MTF of the resulting image, the beam is focused so that its waist is at about 1/3 of the active depth of the storage phosphor. The active depth is a weighted average of the actual doping profile and the x-ray absorption profile and corresponds to the mid depth of the light emission from the phosphor. Corrective optics may be used to assure that the beam stays in focus.

Optionally, the controller corrects the resulting map of light intensity values for turn-on and decay function of the emission, which is also a function of the type of detector material.

For example, the image may be deconvolved with the function to correct for the finite turn-on and decay times and spreading of the beam. It should be understood that the correction may not be necessary, especially if the scanning is not very fast.

Optimally, the beam scanning/light detection is carried out continuously. The sampling of the signal produced by detector is carried out at several times the pixel rate, to provide greater accuracy in the readout. In an exemplary embodiment of the invention, 16 samples per pixel are taken and averaged.

In an exemplary embodiments of the invention the pixel size is about 25-50 micrometers, the scanning beam moves in the scan direction at about a rate of 5-20 microseconds per pixel, which is approximately the same as the decay time of the emitted light.

Optionally, reader 60 could be capable of scanning at two or more different resolutions, by changing the scanner step size or sampling rate, and by incorporating in optics 68 a smearing optical element that can increase the focused spot size for lower resolution scans.

Lower resolution scans could be used to read detectors which intrinsically have lower resolution, or to decrease the time required to perform a scan when high resolution is not needed.

In accordance with some embodiments of the invention, reader 60 provides an identification of the detector used. To facilitate this identification, an optical reader 74, such as a camera or bar code reader, reads a code marked on detector 66. As indicated above, this code can be used in a number of ways. Additionally, reader 74 can be used to determine if the detector is inserted in the correct direction and/or orientation.

The detectors can be associated with a particular patient/study, so that there is no mix- up between studies. For example, when the image is formed in the phosphor, a bar code reader 76 or other device reads the code on the detector. This reader may also read a bar code associated with the patient/study being performed. Alternatively, identification information can be entered by hand via an input device 78. When the same detector is inserted into the reader, optical reader reads the code and controller 73 associates the image read from the detector with the patient/study.

The identification of the detector can also associate the particular detector with a look- up table, stored in the system, for example in the controller, which contains a map of sensitivity as a function of location for the detector. Controller 73 corrects any images generated to correct for any non-uniformity, responsive to the look-up table.

Additionally or alternatively, the identification can be read during the scanning. In some embodiments, as described above, the identification marking is radio-opaque. Thus, if the detector is exposed to the ionizing radiation through the marking, the marking will be impressed on the latent image formed in the detector and will be read out by the scanner.

Controller 73 can identify this marking and thus identify the detector. Alternatively, a properly colored blocking marking on the input and/or output can also result in the marking being read by the scanner. Alternatively, the doping can be adjusted to provide such marking. Since these markings are generally not visible, this identification is best used for the mapping correction described above. A separate identification may be used for patient/study.

The final image may be displayed on a display 80 and/or a hard copy device 82.

Alternatively or additionally, the images can be stored in an electronic archive, shown schematically at 84. This archive can be a large memory, a CD ROM, magnetic tape or any other of the many available storage devices. The images can also be sent from place to place, by teleradiology. Standard post-processing and image enhancement can be performed as well.

In some embodiments of the invention, reader 60 can be used for reading either detectors based on storage detectors or film. However, if film is used, the light levels needed for reading are lower. Thus, in some embodiments of a dual purpose reader, an attenuator, such as a neutral density filter, is placed between scanner 62 and light detector 70 to reduce the light level. This attenuator may be moved into place by an operator or by the device itself on command from controller 73. Also, in some embodiments of a dual purpose reader, a diffuser is placed between the film and light detector 70, when film is being read. This will make the output light from the film more omnidirectional, simulating the light emitted from a storage phosphor, so that light detector 70 will respond to a film in the same way as if a storage phosphor were being read.

Optionally, the storage detectors or films can be preloaded in a magazine 90 (shown in Fig. 7) which, in turn, is inserted into reader 60. Alternatively, the storage detectors or films are dropped into a receptacle in reader 60 at a pace which suits the operator, and reader 60 takes them up automatically at an appropriate pace. Different kinds of magazines can be used for storage detectors and for films, and for different sizes of storage detectors and films.

Magazines designed for films as opposed to storage detectors can have an attenuator built into them to reduce the light level, and/or a diffuser built into them at the output side. The magazines can be built so that the storage devices and/or films can only be inserted in the correct orientation.

Fig. 7A is a perspective view and Fig. 7B is a cutaway top view of an exemplary working embodiment of a reader. A laser 92 produces a beam of red light which bounces off a fast oscillating mirror 94 driven by a galvanometer 96, and off a slow oscillating mirror 98 driven by a stepping motor 100, producing a raster pattern of laser light on detector 66 in magazine 90. Magazine 90 has slots for loading six detectors, but Fig. 7A shows only one detector in magazine 90, and the other slots are shown empty. A corner piece 102 in the corner of each slot fits the truncated corner 67 on each detector (shown in Fig. 6), and makes it impossible to insert the detector into the magazine the wrong way.

A magazine drive motor 104 causes a magazine drive shaft 106 to turn by means of a belt 108, and drive shaft 104 moves magazine 90 back and forth, bringing each slot of the magazine sequentially in front of a photomultiplier tube 110. An optional pyramidal mirror 112 helps to spread out the emitted blue light from the detector uniformly over the photomuliplier tube, so that the signal will not be affected by nonuniformities in the sensitivity of the photomuliplier tube. An optional filter wheel 114, between the detector and the photomuliplier tube, has a filter which is used to attenuate laser light if film is being read instead of a detector (storage phosphor). Alternatively or additionally, filter wheel 114 has a blue filter, optionally used when a detector is being read, to filter out red laser light that might scatter into the photomuliplier tube after reflecting from part of the reader. This allows only blue light, emitted by the detector, to enter the photomultiplier tube. Once all the detectors in a magazine have been read and their images have been archive if desired, there are two erasure lights 116, which optionally are used to erase any remnants of the stored images that were not erased during the reading process, so the detectors can be used over again. If the detectors did not have filters which block most of the environmental light of wavelengths that can erase the stored image, then they could be erased easily by just exposing them to typical levels of indoor light for a short time. But with the filters that block most light of these wavelengths, the detectors would have to be left out for a long time to completely erase the image. Erasure lights 116 provide strong light in the right wavelength range to erase the image, at a wavelength that is not completely blocked by the filters, for example at the excitation wavelength. The erasure lights illuminate the detectors for the time required to erase the stored images sufficiently so that the earlier image will not be noticeable the next time the detector is used. In the embodiment of the invention shown in Figs. 7A and 7B, two 20 watt halogen lights are used, and they require about 2 seconds to effectively erase the stored image, even when the detectors have an input filter that blocks 90% of the red light.

Figs. 7A and 7B show only one design for a reader, but other designs are possible. For example, the reader could be made like a slide projector, with a mechanism for transferring each detector from the magazine to a holder in the reader before it is read, and then transferring the detector back to the magazine after it is read. However, the design shown in Figs. 7A and 7B has the advantage that the detectors do not have to be handled once they have been loaded into the magazine. Other designs will occur to someone skilled in the art.

While the invention has been described with an emphasis on storage phosphors for dental imaging (with a typical size of about 3x4 cm.), the system can also generate larger images, utilizing larger plates, for mammography, in which the high dynamic range of the detectors is especially useful.

The invention has been described in the context of the best mode for carrying it out. It should be understood that not all the features shown in any one drawing may be present in an actual device, in accordance with some embodiments of the invention and that some features described with respect to one figure may be in another embodiment as well. Furthermore, variations on the methods and apparatus shown are included within the scope of the invention, which is limited only by the claims. Such variations may include use of a computer program to carry out some of the methods, the replacement of hardware by software, software by hardware and the replacement of hardware or software by firmware.

As used herein, the terms"have","include"and"comprise"or their conjugates, as used herein mean"including but not limited to". The term"detector"as used herein sometimes refers to the x-ray detector, which is also called a radiation detector, stimulatable detector, phosphor or storage phosphor, and sometimes refers to the light detector which detects emitted light when the image is scanned in the reader. The word"attached"as used herein means "attached directly or indirectly,"and does not necessarily mean permanently attached.