X-ray or gamma ray systems or devices – Specific application – Xeroradiography
Reexamination Certificate
2003-01-27
2004-10-12
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Xeroradiography
C378S029000, C378S032000
Reexamination Certificate
active
06804322
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is based on a device and a method for recording, processing and illustrating X-ray images using an X-ray image converter for recording and evaluating information which can be detected within suitable radiation regions for e.g. X-ray examination of people, animals or objects for scientific and technical purposes to e.g. analyze or control, the converter having a carrier on which the X-ray radiation impinges to effect characteristic changes.
Medicine uses X-rays for diagnosis. In technology, X-rays are used for testing e.g. of materials. Towards this end, the object to be examined is subjected to X-ray radiation. The rays passing through the object are recorded by an X-ray image converter. Known X-ray image converters use e.g. X-ray film which directly records the contrasted, negative projected image. Moreover, polyester sheets coated with barium halogenide crystals are known which are scanned by a laser beam after exposure to X-ray radiation and thereby emit light pulses of an intensity which corresponds to the intensity of the X-rays. The light pulses are evaluated after digital image processing in a computer and can be printed out. A further possibility of visualization of the X-ray image is the use of fluorescence of different substances in the X-ray radiation. X-rays are also used in science and research for a wide range of applications.
Disadvantageously, known X-ray image converters require a considerably high radiation dose for satisfactory evaluation and visualization. This is particularly disadvantageous since recordings must often be repeated. If e.g. CCD cameras or other detector systems are used for recording the light pulses emitted by a crystal coating, the known methods have the further disadvantage that such systems may be damaged with time by the X-ray radiation.
SUMMARY OF THE INVENTION
In contrast thereto, the inventive X-ray image converter having the characterizing features of the present invention as claimed has the advantage that a carrier is used for recordings which is an inexpensive, disposable component which can be replaced after repeated use and having e.g. charge carriers which are detectably changed by the impinging X-ray radiation. Evaluation is carried out not optically via a lens or via secondary light emissions on a screen, but electrically. The inventive system has the further advantage that it is considerably more sensitive than the known methods and image converters and therefore requires a considerably smaller radiation dose. The increased sensitivity is also very advantageous in other applications such as analysis, measuring, control and observation devices.
In accordance with an advantageous design of the inventive X-ray image converter for electrostatic methods, the carrier consists of an insulating, electrically well chargeable material, in particular a plastic sheet. This material may contain air or gas in small cavities. This material has the advantage that even low radiation energy deposition already causes changes in the charge carriers which, however, do not discharge immediately. Scanning of the change in the charge carriers is thereby possible within a certain time after exposure to the X-ray radiation.
In accordance with a further advantageous embodiment of the invention, one side of the carrier is provided with an electrically conducting coating. This causes uniform electric charging of that side and also direct contact with the carrier, which is an insulator and which only becomes weakly conducting during irradiation. This coating permits an increase in sensitivity and uniformity.
In accordance with a further advantageous embodiment of the invention, the other side of the carrier is provided with a plurality of electrically conducting surfaces which are electrically insulated from one another. They are also electrically insulated from the conducting layer described in the above paragraph. The plurality of surfaces form, together with the opposite surface, a plurality of separate capacitors having a certain capacitance. These surfaces form so-called pixels which are ideally square and uniform but may also have other shapes. The size, number and distribution of these surfaces depend on the required resolution and also on other parameters such as sensitivity, noise and scanning methods.
Immediately before recording with e.g. X-rays, the two sides are charged (polarized) with a constant D.C. voltage applied across the two sides. If the surface is fully covered, one single contact is sufficient. In the case of one side having pixels, all surfaces must be contacted. This may be effected e.g. by a roller or in an analogous fashion. The detecting device or scanning device can also be configured to perform this task. The charging contacts are then removed and irradiation follows to effect charge exchange and thereby a voltage drop at the individual capacitors or pixels. The voltage drop at each individual pixel is a function of the radiation intensity at this pixel or in the carrier layer (dielectric) of this pixel. After irradiation, the pixels are scanned as quickly as possible which may occur through contact or without contact (capacitively, through electrostatic induction) or in a different conventional manner.
To increase the capacitance on the pixel surfaces, several layers of conducting laminates can be used, which are connected as required. In the basic version, the layers are parallel to the carrier. However, to increase the capacitance, facilitate production, or for other reasons, the conducting layers must not necessarily be parallel to the carrier.
The principle of operation in the above embodiment can be modified while still maintaining an operable device. The conducting surfaces increase the scanning capability and the signal-to-noise ratio. In accordance with further advantageous embodiments of the invention, solutions other than conducting surfaces are possible. Omission of the pixel layer may produce a better resolution. There is, however, the associated risk of systematic errors and increased noise. Moreover, other conventional physical methods which react to irradiation may be utilized optionally, and if advantageous, combined with the embodiment described above.
The carrier is basically passive. In accordance with an advantageous embodiment, electric conductors and current circuits, and furthermore passive and/or active elements may be used on or in the carrier, e.g. to generate or prolong maintenance of the polarization voltage, to intensify signals or to improve transmission to the detector device. Such devices can be powered and the information read-out via contacts, inductively, capacitively or in a different conventional fashion.
In an advantageous embodiment of the invention, the measurement of the electric voltage at the individual pixels may occur simultaneously with irradiation. In this case, the current to or from the pixels or the resistance may be measured, since each of these quantities depends on the intensity of the rays at the respective pixel. The information content can be read out from the carrier during or following irradiation. In this case as well, the pixels must be charged before or during irradiation.
To extend the time between charging, irradiation and scanning, or for other reasons, one or more masks can be used, having specific geometric and electric properties with respect to the carrier, which influence the pixel surfaces just before irradiation, using contacts or in a different fashion. An analogous or the same method may be carried out between irradiation and scanning. Even during irradiation, the use of a mask may be advantageous. The mask is preferably disposed parallel to the carrier and can possibly contact or nearly contact the carrier. In another embodiment, the mask may be a roller which rolls over the carrier or vice versa. In a further embodiment, the mask completely or partially follows the movements of the carrier on the surface to be irradiated for imaging. The mask may also be on the side facing the rays as long as radiation att
Bruce David V.
Thomas Courtney
Vincent Paul
LandOfFree
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