Particularly for medical purposes, an image which is stored in a storage layer as a latent image is produced from an object, for example a patient, by means of X-ray radiation. It is mostly a phosphor layer which is used as the storage layer in this case. The storage layer is excited by means of a radiation source in order to read out the X-ray image stored in the storage layer. Therefore, on the basis of this excitation the storage layer emits light which has an intensity corresponding to the stored X-ray image. The light emitted by the storage layer is received by a receiving means and subsequently converted into electric signals such that the X-ray image stored in the storage layer can subsequently be visualized. The X-ray image can be displayed, for example, directly on a monitor, or else be written onto a photographic X-ray film which can be used specifically for X-ray images. After the X-ray image has been read out from the storage layer, the latter is erased by an erasing device, in order to be able to store a subsequent X-ray image.
Such storage layers can be arranged in an X-ray cassette. European patent EP 0 288 014 B1 discloses erasing a storage layer which is located in an X-ray cassette. The X-ray cassette contains an opening mechanism such that the X-ray cassette can be opened in order to erase information stored in the storage layer. Present outside the X-ray cassette is an erasing means which outputs an erasure radiation. This erasure radiation is irradiated into the open X-ray cassette and projected onto the storage layer. The irradiation of the storage layer by means of the erasure radiation erases the information stored in the storage layer. The known X-ray cassette contains a reflector or a diffusing means for the purpose of reflecting the erasure radiation irradiated into the cassette, and of scattering it over the width of the storage layer.
A device for reading out information stored in a storage layer is disclosed in patent U.S. Pat. No. 5,038,037. An X-ray table for X-raying patients is described therein. The X-ray table contains two phosphor layers which are fitted on the top side and underside of a tape and serve for storing X-ray information. Both for the phosphor layer fitted on the top side and for that fitted on the underside of the tape, the known X-ray table has a dedicated device for reading out information from this phosphor layer. Furthermore, the X-ray table contains two erasing means which are used to erase the phosphor layers. A dedicated erasing means is provided for each of the phosphor layers. Serving as erasing means is an erasing lamp which—viewed in the transport direction of the tape—is arranged upstream of that point at which the X-ray image of the patient is taken. As a result, an “old” X-ray image stored in the phosphor layer is erased before a “new” X-ray image is taken. A plurality of erasing lamps arranged next to one another are likewise used as erasing means, being arranged in the X-ray table below that position at which the X-ray image is projected onto the stationary tape with the phosphor layers. Before the taping of a “new” X-ray image, the “old” X-ray image is therefore firstly erased with the aid of this erasing means, the tape being stationary. In this type of erasing means, the phosphor layer cannot be used directly for a “new” picture. The erasure of the phosphor layers does not take place until immediately before the subsequent taking of a “new” X-ray image. This means that time is lost and tuning takes place between the operations of erasure and subsequent storage. The erasure must firstly be terminated before the next X-ray image can begin to be taken.
Patent application WO 99/28765 discloses an X-ray cassette in which both a device for reading out information stored in the storage layer and an erasing means for erasing information stored in the storage layer are present. The erasing lamp extends over the entire width of the storage layer in which information can be stored. By means of a drive, the erasing means is guided over the storage layer along a transport direction running perpendicular to the line direction. The storage layer can be erased in this way line by line.