Patent Application
20060091337
The invention relates generally to a storage phosphor plate for the storage of X-ray information and a corresponding system or device for reading out the X-ray information. Furthermore, the invention relates to a corresponding radiography module or cassette for housing a system and storage phosphor plate for reading out the X-ray information.
Generic storage phosphor plates and devices are used, in particular for medical purposes, in the field of computer radiography (CR). Here, X-rays are recorded in so-called storage phosphor layers, whereby the X-ray radiation passing through an object, for example a patient, is stored as a latent picture in the storage phosphor layer. In order to read out the stored picture, the storage phosphor layer is irradiated with stimulation light, and so stimulated into emitting emission light, the intensity of which is dependent upon the respectively stored picture information. The emission light is collected by an optical detector and converted into electric signals which can be further processed as required and shown on a monitor or on a corresponding display unit, such as eg. a printer.
In certain applications, the storage phosphor layer is applied to a support layer which is partially transparent for the stimulation light so that the storage phosphor layer can be stimulated by irradiating with stimulation light from the side of the support layer.
The problem can arise here that part of the stimulation light in the region of the upper boundary surface between the support layer and storage phosphor layer is reflected or dispersed back into the support layer by reflection and/or dispersion and reflected back in the direction of the storage phosphor layer on the lower boundary surface of the support layer. In such cases, in particular with support layers with a large thickness, regions of the storage phosphor layer are stimulated which are so far away from the region of the storage phosphor layer currently to be read out that the emission light emitted from them can no longer be collected. The consequence of this so-called advance read-out of individual regions is that with a subsequent, actual read-out of these regions, a reduced intensity of the emission light is obtained, and this leads overall to a detrimental effect upon the picture quality.
It is the objective of the invention to provide a storage phosphor plate and a corresponding device and a radiography module for reading out this type of storage phosphor plate with which an improved picture quality can be achieved.
The above and other problems in the prior art are solved by use of a storage phosphor plate for the storage of X-ray information, including a storage phosphor layer which stores the X-ray information and can be stimulated by stimulation light into emitting emission light, and a support layer on which the storage phosphor layer is located, the support layer being partially transparent for the stimulation light, and having a thickness d and an absorption coefficient k for the stimulation light, where (k times d)≧0.2.
Due to the combination of a specific thickness of the support layer with the absorption properties for stimulation light of the same according to the invention, an efficient weakening of the light beams of the stimulation light relevant to the advance read-out is achieved, and so the picture quality improved. In particular, with relatively large thicknesses of the support layer with which the effect of the advance read-out has a particularly unfavourable effect upon the picture quality, using a support material with relatively small absorption coefficients, the advance read-out can be prevented, or at least greatly reduced. By using this type of relatively weakly absorbent support materials, the costs of appropriate support materials can be substantially reduced.
In a preferred embodiment of the invention it is proposed that the thickness of the support layer comes within the range of between 1 mm and 10 mm. In this thickness range, the carrying capacity and mechanical stability of the support layer is sufficient for most applications. Any distortion of the storage phosphor layer positioned on the support layer is in this way sufficiently reduced so as to prevent any damage to the phosphor layer. The strongly pronounced effect of the advance read-out in this thickness range is prevented, or at least reduced, by the choice of the absorption coefficient of the support layer for stimulation light according to the invention.
Preferably, the storage phosphor plate is self-supporting. The thickness of the support layer is chosen here as regards its length/width ratio such that it can be held at the edges along with the storage phosphor layer positioned on top of it, without it becoming substantially distorted. In this way, any additional mechanically stabilising layers or supports can be dispensed with so that the storage phosphor layer can be irradiated, unimpeded, with stimulation light on its lower side, i.e. from the transparent support layer.
Preferably, the absorption coefficient of the support layer for the stimulation light is less than 1 mm−1 and greater than 0.02 mm−1. This makes it possible to use materials which require a relatively small degree of light weakening by absorption for the stimulation light, and are therefore correspondingly inexpensive.
In a particularly preferred embodiment of the invention, the support layer includes a colouring which can partially absorb the stimulation light. This can be achieved, for example, by selecting an appropriately coloured glass or synthetic material for the support layer. The colouring here can either be distributed evenly over the whole thickness of the support layer or be contained in at least a first partial layer of the support layer. With the latterly specified alternative, the support layer preferably has two layers, namely one layer which does not substantially absorb the stimulation light, and an additional layer of colouring which partially absorbs the stimulation light. The desired absorption coefficient of the support layer can then be achieved simply by an appropriate choice of coloured layer.
Preferably, the support layer has a lower and an upper boundary surface, the storage phosphor layer being located on the upper boundary surface and the at least one first partial layer being located in the region of the upper and/or lower boundary surface of the support layer. By locating the first partial layer in the region of the upper or lower boundary surface of the support layer, it is possible to particularly efficiently avoid or reduce the re-entry of dispersed radiation into the support layer or the reflection of the dispersed radiation on the lower boundary surface.
In one variation of the invention, it is proposed that the support layer can partially absorb the stimulation light dependent upon polarisation of the same. This variation is advantageous when using polarised stimulation light, such as laser light. The absorption properties of the support layer are chosen here such that the originally polarised stimulation layer can pass through the support layer without any loss, and can stimulate the storage phosphor light located on the same into emitting emission light. The stimulation light thus dispersed on the upper boundary surface of the support layer is, however, no longer polarised as it was originally due to the dispersion process, and is absorbed by the support layer so that advance read-out of the storage phosphor layer is reduced or prevented. The absorption coefficient for stimulation light in the sense of the invention identifies in this variation the absorption coefficient for that portion of the stimulation light which does not have a preferred polarisation direction, i.e. is polarised isotropically.
Preferably, the support layer has at least a second partial layer in which the stimulation light can be partially absorbed dependent upon polarisation of the same. The second partial layer is preferably located in the region of the lower boundary surface of the support layer. In this way, it is particularly easy to create a polarisation-dependent absorbent support layer.
It is also preferred that the storage phosphor layer comprises a large number of oblong, in particular needle-shaped storage phosphor particles. These so-called needle phosphors are characterised by a particularly high intensity of stimulated emission light and so by a particularly high picture quality. Corresponding storage phosphor plates are also called Needle Image Plates (NIP).
With the device according to the invention for reading out from the storage phosphor layer, the irradiation device for irradiating the storage phosphor layer with stimulation light is disposed on the side of the support layer facing away from the storage phosphor layer. The storage phosphor layer is therefore irradiated with stimulation light from the upper boundary surface of the support layer.
The detection device for collecting emission light is preferably disposed on the side of the support layer facing towards the storage phosphor layer. In this way it is possible to carry out an efficient read-out of the storage phosphor layer in transmission geometry. In this way, a particularly high picture quality is achieved, with at the same time a very compact device, in particular in connection with oblong, needle-shaped storage phosphor particles which act like small light conductors for the stimulation and/or emission light.
Further features and advantages of the invention are given in the following description of preferred embodiments and examples of applications, reference being made to the attached drawings, not necessarily drawn to scale.
An irradiation device 6, in particular a laser or a laser diode line, serves to irradiate the storage phosphor layer 2 with stimulation light 4 which can stimulate the storage phosphor layer 2 into emitting emission light 5, the intensity of which is dependent upon the X-ray information stored in the storage phosphor layer 2. The emission light 5 emitted is detected with a detection device 7, in particular a photomultiplier or a line detector. The irradiation device 6 and the detection device 7 are preferably combined in a reading head (scan head) which is moved over the storage phosphor plate 1 in conveyance direction T so that the X-ray information stored in the storage phosphor layer 2 is successively read out. Alternatively however, the reading head can also be fixed. In this case, the storage phosphor plate 1 is moved past the reading head.
The reading head is preferably in the form of a so-called line scanner, with which, at a particular point in time, one whole line of the storage phosphor layer 2 is respectively read out. In this case, the irradiation device 6 has a line light source, in particular in the form of laser diodes arranged in a line, and the detection device 7 includes a large number of light-sensitive detectors, in particular a photo diode or CCD array, arranged in a line.
The support layer 3 is partially transparent for the stimulation light 4 so that part of the stimulation light 4 entering into the support layer 3 finally strikes the lower side of the storage phosphor layer 2, and can be stimulated into emitting emission light 5. However, only part of the stimulation light 4 striking the storage phosphor layer 2 is absorbed. Other parts of the stimulation light 4 are reflected on the upper boundary surface 11 of the support layer 3 or are dispersed on the storage phosphor layer 2, and partially arrive back at the support layer 3. These portions are shown for example in
The first light beam 4′ strikes the lower boundary surface 10 of the support layer 3, is at least partially reflected back to the storage phosphor layer 2, and finally strikes the lower side of the storage phosphor layer 2 once again. In the region where the reflected stimulation light 4′ strikes, the storage phosphor layer 2 is also stimulated into emitting emission light which, however, can not be collected by the detection device 7 due to the limited space of its aperture. The consequence of this so-called advance read-out is that the intensity of the emission light collected in a subsequent, actual read-out process in this region is lowered, and because of this, the quality of the X-ray picture read out is reduced.
In order to reduce or avoid advance read-out, the support layer 3 is designed in such a way that it has a specific absorption coefficient k for the stimulation light 4 and 4′, and a specific thickness d, where the product of the thickness d and the absorption coefficient k is greater than or equal to 0.2, mathematically expressed as (k times d)≧0.2.
The typical thickness d preferably lies within the range of between 1 and 10 mm. The absorption coefficient k for the stimulation light preferably lies within the range of between 0.02 and 1 mm−1, in particular between 0.02 and 0.4 mm−1. The maximum intensity of the stimulation light typically lies within the range of between 620 nm and 700 nm, in particular approximately 680 nm.
With the above selected values for the thickness d and the absorption coefficient k, the first light beams 4′ which strike the lower boundary surface 10 of the support layer 3 at an angle α, which is greater than or equal to the limit angle of the total reflection, are weakened so that advance read-out caused by these first light beams 4′ is prevented. For a support layer 3 made from glass the limit angle of the total reflection is 41.8°.
In this first embodiment, the support layer 3 is in the form of a glass plate which includes colouring which partially absorbs the stimulation light 4 and 4′. The colouring is chosen here such that light can be absorbed either in broad bands or only in certain wavelength regions. Suitable absorbent glass materials can be obtained, for example, from the companies Saint Gobain Glass (eg. glass type SGG Parsol) or Schott (eg. glass type NG11).
With the second embodiment shown in
In this embodiment, the first partial layer 8 is located in the region of the lower boundary surface 10 of the support layer 3. Alternatively or in addition, the first support layer 8 can also be disposed in the region of the upper boundary surface 11 of the support layer 3.
With the examples shown in
With the third embodiment shown in
In contrast with the examples of
Alternatively or in addition, the second partial layer 9, which can absorb the stimulation light 4 or 4′ dependent upon polarisation, is also disposed in the region of the upper boundary surface 11 of the support layer 3.
The radiography module 70 includes a housing 77 in which the storage phosphor plate 1, the detection device 7 and the irradiation device are integrated. However in
With the radiography module 70 shown, the storage phosphor plate 1 is disposed in the housing 77 such that it is fixed, i.e. the storage phosphor plate 1 is securely connected to the housing 77 by means of appropriate connection elements. The connection to the housing 77 here can be fixed or swinging, for instance, using appropriate suspension elements in order to dampen any external impacts to the housing 77 and transfer of the same to the storage phosphor plate 1.
The reading head which includes the detection device 7 and the irradiation device (see description to
In addition to the reading head, a deletion lamp 74 is provided which is also driven by the drive 73 and can be moved over the storage phosphor plate 1 in order to delete any information remaining in the storage phosphor layer which could still be present after read-out.
Furthermore, a control device 75 is provided which controls or implements the read-out and deletion process as well as any signal processing processes. Interfaces 76 are provided on the control device 75 which are required for transferring energy, if required air pressure, control signals and/or image signals to or from the radiography module 70.
| Number | Date | Country | Kind |
|---|---|---|---|
| EP04105391.9 | Oct 2004 | EP | regional |
