Abstract:
An X-ray image converter ( 2 ) for recording and evaluating information gained from X-ray investigations of persons ( 3 ), animals or objects is suggested, which comprises a carrier ( 4 ) of a material in which the impinging X-ray radiation causes detectable changes, as well as a method for recording X-ray images, wherein changes in charge carriers on the surface of a carrier ( 4 ) are determined for evaluation of the radiation from the object ( 3 ) being observed.

Description:
[0001]    This application is a continuation of Ser. No. 09/832,985 filed Apr. 12, 2001 the entire disclosure of which is hereby incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    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.  
           [0003]    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.  
           [0004]    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  
         [0005]    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.  
           [0006]    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.  
           [0007]    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.  
           [0008]    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.  
           [0009]    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.  
           [0010]    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.  
           [0011]    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.  
           [0012]    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.  
           [0013]    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.  
           [0014]    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 attenuation is negligible or can be compensated for. In that case, it could be combined with a shadow casting device.  
           [0015]    The carrier may consist of more than one layer (sheet) or several carriers can be used at the same time. The different layers or carriers can have specialized functions, can supplement one another, and can cooperate. They can move together, partially together, or differently.  
           [0016]    The invention may also be used with radiation other than X-rays, depending on the purpose and type of carrier, e.g. with alpha, beta and gamma radiation. Detection of other particles and their tracks or of cosmic radiation is also possible in this fashion.  
           [0017]    In accordance with an advantageous embodiment of the invention, magnetic fields or magnetic field changes can be recorded which can also be processed and represented as two- or three-dimensional images. The carrier is equipped with appropriate conventional devices such as electric circuits and/or materials having magnetic properties and the detector device is correspondingly adjusted. To increase the sensitivity and accuracy, the carrier, its materials or parts thereof may be pre-magnetized or saturated before and/or during recording.  
           [0018]    In accordance with a further advantageous embodiment of the invention, a detector device is provided which can be moved relative to the carrier for detecting the information contained on the carrier. The movement between the detector device and the carrier is parallel to the carrier surface, in one or two directions. After the action of the incident radiation, the carrier is scanned by the detector device. Since the carrier material is insulating, scanning can occur within a certain time following action of the X-rays. The detector device can thereby easily be protected from the radiation and is therefore not damaged.  
           [0019]    In accordance with a further advantageous embodiment of the invention, the detector device can be moved over the carrier in two directions. The carrier itself is thereby stationary. The detector of the detector device may be punctiform. If several detectors are disposed next to one another to produce a detector device with one-dimensional extent, it is sufficient to move same in one direction relative to the carrier.  
           [0020]    In accordance with a further advantageous embodiment of the invention, the carrier, e.g. the plastic sheet, is disposed on rollers or cylinders to permit movement of the carrier relative to the detector device.  
           [0021]    In accordance with a further advantageous embodiment of the invention, the detection device within the detector is a field effect transistor or an integrated amplifier provided with a field effect transistor at the input thereof.  
           [0022]    In accordance with a further advantageous embodiment of the invention, a field effect transistor is used as the detection device in the detector, however, without a gate. The electric field of the carrier surface thereby directly influences the current between the source and drain, instead of the controlling gate electrode. This influence is recorded and evaluated. Scanning of the carrier surface may be effected without contact. Therein, it is possible that many measuring points simultaneously act over a complete line width, similar to fax devices or paper sheet scanners.  
           [0023]    In accordance with a further advantageous embodiment of the invention, several carriers are disposed in different spatial positions relative to the object to be recorded for recording spatially resolved information. In this case, at least 2 X-ray radiation sources should be provided or the position of the source should be changed relative to the object.  
           [0024]    In accordance with a further advantageous embodiment of the invention, the information recorded by the detector device is evaluated and displayed by means of a computer. The X-ray images may be stored in the computer, printed out by printers or processed in a different fashion.  
           [0025]    In a preferred embodiment, scanning is effected, e.g. immediately in front of the rollers.  
           [0026]    In an advantageous embodiment, the detection device and method depend on the physical properties of the carrier. The scanning roller may e.g. have contact points which contact the pixels individually to scan the information, or conducting surfaces, optionally below a thin insulator, which scan the pixels without electric contact, e.g. capacitively. If deflecting rollers simultaneously carry out scanning, the pixels are usually on the side facing the scanning rollers.  
           [0027]    For certain cases, it is sufficient to move the detector device in only one direction, e.g. across the longer side of a rectangle, if its detectors are distributed over the entire width, i.e. across the shorter side of the rectangle, similar to a flat bed scanner for paper sheets. The detector device must have a number of detector points required for the resolution.  
           [0028]    In accordance with an embodiment of the invention, two or more information planes permit calculation of e.g. improved image resolution and three-dimensional information, since i.a. the positions of radiation sources, objects and carrier levels are known. The planes can be parallel to one another in their simplest embodiment or may also have different orientations.  
           [0029]    Intermediate layers can be used to increase sensitivity by, e.g. increasing the capacitance or through the addition of active agents.  
           [0030]    In an embodiment of the invention, the recording planes are disposed not one behind the other but next to one another, with respect to the path of the rays.  
           [0031]    In embodiments of the invention, the image converter does not record the radiation originating directly from the radiation source as influenced by the absorption effects of the objects being examined. Rather, radiation sources within the object itself become sources following irradiation by the actual primary radiation source. This point is partially related to applications using optical microscopes with which the object is not observed using transmitted light but rather e.g. in the dark field. In this case, the image converters are usually not in the path of the rays of the radiation source, as in classical X-ray recordings, but lateral or transverse thereto and are shielded from the primary radiation. It is possible to simultaneously use several converters in accordance with the invention, even with only one primary radiation source. The optimum angle or orientation depends on the physical mechanism utilized. Deflection angles and other parameters which are further processed later for evaluation and representation can be calculated numerically in a computer using the inventive converter and must not necessarily be searched for through mechanical adjustments, if the converters are sufficiently large. A special case of this embodiment involves sources in an object which are not secondary but actually primary, i.e. real sources, in particular radioactive sources, such as radioactively marked capsules, agents, medication, tools, instruments, and also sources in space or on the earth. When the effects and the inventive converter are reasonably combined, e.g. through application of fluorescence effects, use of selective filters and spatial image recording, and/or through orientation of X-ray source and converter in a same direction, even in close proximity to one another, or installed in the same housing, e.g. mines, explosives or other objects can be detected at large distances. With substances comprising phosphorescence effects, the primary source is switched on for illumination, is then switched off and the recording is started immediately thereafter.  
           [0032]    To improve contrast, selectivity and sensitivity, reference recordings are taken with and without the object, but without searched features to be imaged (e.g. source of an illness, instruments, foreign bodies), and the features to be searched and their physical properties are recorded separately and are taken into consideration numerically during evaluation and image representation.  
           [0033]    In an advantageous embodiment of the invention, an auxiliary means casts defined shadows (in the relevant spectral range of the recording) onto the converter. In a simple embodiment, identical round short rods of a suitable material, e.g. aluminum, are used, which are perpendicular to the converter. The rods have a similar effect as a sun-dial. The angle of impingement can be determined numerically or in a different fashion and can be displayed. In an embodiment, the auxiliary means can be easily aligned towards the source because the shadows thereby become minimal in size, reflecting maximum absorption. In a similar manner, alignment towards secondary sources is also possible. One or several primary or secondary sources can be represented as an image or in a different manner following numerical processing. In principle, one rod is sufficient, however, a grid, mesh or another formation can also be used instead of rods. The length of e.g. the rods or the distance from the recording plane is determined i.a. by the required angular resolution and the resolution of the converter.  
           [0034]    In an embodiment, the plastic material of the membrane is polarized during production to always permit subsequent build-up of an electric voltage. Methods known from microphone technology can be modified for the inventive application in the carrier, to facilitate or omit charging before irradiation.  
           [0035]    Further advantages and advantageous embodiments of the invention can be extracted from the following description, the drawing and the claims.  
           [0036]    The drawing shows an embodiment of the invention which is described in more detail below. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0037]    [0037]FIG. 1 shows a schematic representation of an arrangement of an X-ray source, a person to be examined and an X-ray image converter;  
         [0038]    [0038]FIG. 2 shows an first embodiment of the X-ray image converter in accordance with the invention; and  
         [0039]    [0039]FIG. 3 shows an a second embodiment of the X-ray image converter in accordance with the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0040]    [0040]FIG. 1 shows an arrangement of X-ray source  1  and X-ray image converter  2  for recording X-ray images of a person  3 . The X-ray converter comprises a plastic sheet  4  carrier which is disposed on two rollers  5  which can support and transport the sheet. The plastic sheet  4  can have a thickness of fractions of to tens of centimeters. After impingement of the X-rays on the plastic sheet  4 , the sheet  4  is rolled over the rollers and moved past a detector device  6 . The detector device  6  is not subjected to X-ray radiation and can therefore not be damaged thereby. The sheet and rollers may comprise a precise guidance, e.g. a pin feed system and have synchronization markings. In the present example, the sheet is an endless belt.  
         [0041]    The detector device has a longitudinal extension parallel to the rollers (not visible in the drawing) and must therefore not be moved over the plastic sheet since the sheet itself moves over the detector device along its entire width. The detector device may be connected to a computer via appropriate leads for evaluation of the scanned voltage differences.  
         [0042]    Depending on the intensity of the radiation and on the properties of the plastic sheet, a charge difference may occur not only on the side of the plastic sheet facing the X-ray source  1  but also in the area of the plastic sheet  4  facing away from the X-ray source. For evaluation, both regions of the plastic sheet can be used.  
         [0043]    [0043]FIG. 2 shows an embodiment of an X-ray converter  2  in accordance with the invention. A partial section of the entire converter of FIG. 1 is illustrated, including the lower roller  5 . The plastic sheet  4  is illustrated with exaggerated thickness for reasons of clarity. Referring to the rear portion of the converter  2  at the right hand part of FIG. 2, the plastic sheet  4  is seen to be lined on one side thereof with an array of mutually separated electrically conducting pads  10 . The pads  10  are electrically insulated from each other via the plastic sheet  4 . A charger  12  is disposed proximate the converter  2  and contacts the pads  10  to apply electrical charge thereto. The charger  12  is connected to an appropriate power supply  14 . As can be seen on the left portion of FIG. 2, the side of the plastic sheet  4  opposite to the pads  10  is covered with a uniform electrically conducting sheet  16 . The sheet  16  can be maintained at ground potential through contact with an electrically grounded and conducting surface  18  of the lower roller  5 . A detector device  6  is located at the lower rear portion of the converter  2  and comprises a linear array of detection units  20 . The detection units communicate with an analysis unit  22  via suitable cable connection  24 .  
         [0044]    The embodiment of FIG. 2 operates as follows. In an initial step the rollers  5  of FIG. 1 (only the lower one of which is illustrated in FIG. 2) are set into rotation by a suitable drive motor in the direction indicated by arrow  26 . The pads  10  located at the rear of the converter  2  thereby pass by charger  12  and are thereby charged to a suitable voltage which is typically in the range of 50 to 100 volts. As the lower roller  5  continues to rotate, the plastic sheet with its associated charged pads  10  travels over the top roller  5  (see FIG. 1) and proceeds in a downward direction at the front, left portion of the converter  2 . At this point in time, rotation of the lower roller  5  is interrupted and the converter is exposed to X-ray radiation  28 . The X-ray radiation passes through the thin layer of pads  10  and penetrates into the plastic sheet  4  to ionize materials in the plastic sheet  4 . As a result of these ionization processes, a voltage decrease between a given pad  10  and the oppositely disposed conducting sheet  16  occurs which is proportional to the X-ray dose absorbed by that portion of the sheet  4  proximate a given pad  10  and therefore to the X-ray intensity incident on that pad  10 . Following exposure, the X-ray source  1  (see FIG. 1) is switched off and the rollers  5  are once more set into rotation in the direction of arrow  26 . Exposed pads  10  are thereby caused to pass by detector array  6  which detects the residual voltage in the respective pad  10  by means of detection units  20  and passes this information on to analysis unit  22  for image construction.  
         [0045]    [0045]FIG. 3 illustrates aspects of a further embodiment of the invention. In this embodiment, the detector  40  has associated mechanics  44  for displacement thereof in one or two dimensions relative to the converter  38 . The detector  40  incorporates an FET/operational  48  amplifier for detecting the image recorded on the converter  38 . An additional second converter  36 , can be used to construct a cooperative image of the target  34  in conjunction with irradiation thereof by a first  30  and/or a second  32  X-ray source. At least one X-ray source  30  may have associated means  44  for mechanical displacement thereof to provide one X-ray source radiating at two anode regions  30 ,  32 . A shadow casting arrangement  46  may also be deployed. The first converter  36  has associated detection means  50 .  
         [0046]    All the features shown in the description, the following claims and the drawing may be essential to the invention either individually or collectively in any arbitrary combination.  
       LIST OF REFERENCE NUMERALS  
       [0047]    [0047] 1  X-ray source  
         [0048]    [0048] 2  X-ray image converter  
         [0049]    [0049] 3  person  
         [0050]    [0050] 4  plastic sheet  
         [0051]    [0051] 5  roller  
         [0052]    [0052] 6  detector device  
         [0053]    [0053] 10  pads  
         [0054]    [0054] 12  charger  
         [0055]    [0055] 14  charger power supply  
         [0056]    [0056] 16  conducting sheet  
         [0057]    [0057] 18  roller ground surface  
         [0058]    [0058] 20  detection units  
         [0059]    [0059] 22  analysis unit  
         [0060]    [0060] 24  cables  
         [0061]    [0061] 26  rotation direction  
         [0062]    [0062] 28  impinging X-rays  
         [0063]    [0063] 30  first X-ray source  
         [0064]    [0064] 32  second X-ray source  
         [0065]    [0065] 34  target  
         [0066]    [0066] 36  first converter  
         [0067]    [0067] 38  second converter  
         [0068]    [0068] 40  detection unit  
         [0069]    [0069] 42  detection unit displacement means  
         [0070]    [0070] 44  X-ray source displacement means  
         [0071]    [0071] 46  shadow casting means  
         [0072]    [0072] 48  Fet/operational amplifier  
         [0073]    [0073] 50  detection unit