System for recording information on a medium sensitive to X-rays

A system for recording information on a film medium sensitive to X-rays, without disturbing the radiographic image previously recorded on the same film. The system includes a set of adjacent X-rays sources and a source control which sequentially controls the X-rays emitted by each source. Different printing levels on the medium are obtained by controlling X-ray output dosage by each source.

TECHNICAL DOMAIN
 This invention relates to a system for recording information on a medium
 sensitive to X-rays. Applications of the invention are particularly in the
 medical fields of radiology and tomography, to add information such as
 data about the patient, information about conditions under which the
 radiology examination is carried out, or radiography instrument
 identification numbers, onto the radiographs of patients. The invention
 may also be used in other fields of application such as X-ray grating
 spectrography and fluorescence, for example to add data concerning the
 samples being treated to the records.
 STATE OF PRIOR ART
 Archiving and analysis of X-ray media, and particularly radiology films, is
 made very much easier if the film is accompanied by a certain number of
 data, for example such as the patient's name. These data may be entered on
 a label which can be glued onto the film, or may be written on the film
 directly by means of special inks developed with the film. Very simple
 data can also be recorded on the film using a code based on small
 perforations made in the film.
 However, manipulating labels or film can be the source of human errors.
 Labels could be glued on a film to which they do not correspond, and text
 written on the film directly using special inks could become illegible if
 the film is overexposed.
 Thus, techniques have been developed for recording information directly on
 the film, to avoid analysis or archiving errors. These techniques are
 described below.
 Radiography films usually used for medical applications are films sensitive
 to visible light and are placed in an envelope of a luminescent material
 capable of converting X-radiation into visible radiation. This material
 can also make the film sensitive to X-rays in order to record radiographic
 images of patients.
 To facilitate its manipulation, the film is placed inside an envelope
 opaque to visible light but transparent to X-rays.
 There are several known techniques for adding patient identification
 information to the sensitive film.
 According to a first technique, the film envelope is opened in safe light
 (in a dark room) and the film is placed under a device which will print on
 the undeveloped film and add information. Information is marked on the
 film by illuminating part of this film with visible light that passes
 through a label containing the information to be recorded.
 One of the main difficulties when using this type of device is to avoid
 concealing the complementary part of the film on which the radiographic
 record has been or will be received.
 Consequently, the film envelope may be a cassette containing a system of
 removable optical caches. These caches may be moved to expose a window so
 that only a portion of the film is illuminated, when transferring
 information.
 According to a second technique, the information may be transferred onto
 the film by exposing it to a very fine light beam from a laser. This laser
 is moved parallel to the film surface to write characters or codes on the
 film. This operation is also carried out in a dark room, or by using a
 specially adapted opaque cassette.
 According to one variant, the recording on the undeveloped film may also be
 made by applying an illuminated liquid crystal display (LCD) screen, or a
 vacuum fluorescent display (VFD) screen, to it.
 In all these applications, it is observed that it is important to very
 carefully isolate the part of the film that will receive information from
 the part of the film that will receive the radiographic image. Light
 produced by information recording equipment and particularly ambient light
 can "pollute" or conceal all or part of the film.
 According to a third technique, transfer elements in the form of letters
 and containing a material absorbing X-rays are used to write information
 on the film. Transfer elements are placed on the film envelope (opaque to
 visible light) and are subjected to X-radiation. This radiation may
 originate from the X-ray tube used for the radiography of the patient or
 another type of secondary X-ray tube.
 In this case also, the transfer elements are used with a system of
 removable caches.
 Document EP-A-0 238 464 also illustrates other processes using similar
 techniques for marking films sensitive to X-rays.
 There are implementation difficulties with all the techniques mentioned
 above, related particularly to the need to optically isolate the part of
 the film on which the information will be received.
 Parasite reflections of visible or infrared light could disturb the
 radiographic image on the film.
 Furthermore, the processes described above are only suitable for simple
 reproduction of alphabetic or numeric characters, but cannot be used for
 the fine reproduction of various shades of gray. Therefore these processes
 are not suitable for transferring other information such as images or
 personalized icons onto the film.
 DESCRIPTION OF THE INVENTION
 The purpose of this invention is to propose a system for recording
 information on a sensitive medium that does not have the difficulties or
 limitations mentioned above.
 One particular purpose of the invention is to propose such a system for
 recording information on a film without disturbing the radiographic image
 already recorded on the film, or that will be recorded later.
 Another purpose is to be able to directly record data previously input to
 the computer, or stored on the computer, onto the film.
 Another purpose of the invention is to record images or logos displayed in
 different shades of gray.
 Finally, another purpose is to provide a device capable of guaranteeing
 good contrast of information marked on the film.
 In order to achieve these purposes, the purpose of the invention is more
 precisely a system for recording information on a medium sensitive to
 X-rays, comprising a set of adjacent X-ray sources and selective source
 control means, to print a selected pattern on the said sensitive medium.
 Sources are controlled concomitantly or sequentially to selectively provoke
 or not provoke emission of X-rays by each source. The intensity or the
 X-ray dose output by each source can also be varied to obtain different
 printing levels on the medium. These levels correspond to shades of gray
 in the case of a radiographic film.
 According to a particular embodiment of the system, the system may comprise
 a single dimensional or a two-dimensional network of point X-ray sources.
 A point source is a source that emits on a very small surface on an image,
 that can be treated like a point. A network of point sources can thus be
 used to reproduce a text or an image by placing points or image elements
 called pixels adjacent to each other.
 For example, X-ray sources may be made in the form of microtip sources.
 These sources can form miniaturized inscription matrices with a large
 number of sources.
 This type of matrix can be used to reproduce images with a good resolution
 and a large number of pixels.
 More precisely, each X-ray source may comprise at least one source of
 electrons with microtips. Electron sources are associated with one or
 several anodes capable of emitting X-rays in response to electron impacts.
 Each electron source may be associated with a particular anode. However, a
 set of sources may also share a common anode.
 According to a first means of polarizing X-ray sources, the anode may be
 connected to a ground potential and control means may comprise switches
 associated with electron sources to selectively connect the microtips from
 the selected electron sources to a high negative voltage, and/or to power
 supplies designed to generate electron beams.
 According to this polarization method, the switches are at a high voltage.
 Control means may also comprise a control unit such as a computer to
 control the switches and/or power supplies.
 The switches and/or power supplies may be connected to the computer through
 a galvanic isolation device in order to make it impossible for the
 computer to be at the same potential as the switches and/or power
 supplies.
 According to another polarization option, the anode may be connected to a
 high positive voltage and the control means switches and/or the power
 supplies may be controlled so as to selectively connect the microtips on
 the selected sources to a ground potential, and/or to generate more or
 less intense electron beams starting from the selected cathodes.
 According to another advantageous aspect of the invention, the system may
 comprise an envelope opaque to visible light, capable of containing the
 radiography film, and a cache opaque to X-rays that can be adapted to the
 box to cover a region of the envelope. This region corresponds to an area
 on which information is recorded on the film.
 The cache opaque to X-rays is held in place on the envelope while the
 sensitive medium, for example a film contained in the envelope, is exposed
 to the X-rays in a radiography instrument. Thus, X-rays from the
 radiography do not expose the area set aside for recording of information.
 The cache can then be removed from the envelope later to print on the film
 in the said information recording area, using the X-ray sources described
 above. This gives an improved contrast for the recording.
 Other characteristics and advantages of this invention will become clearer
 from the following description with reference to the figures in the
 attached drawings. This description is given for illustrative purposes
 only and it is in no way restrictive.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
 FIG. 1 shows a very much enlarged view of a information recording device on
 a medium sensitive to X-rays such as a radiographic film 10.
 The film 10 comprises a coating sensitive to X-radiation and is covered by
 a conversion material capable of transforming received X-rays into visible
 light that can make an impression on the coating.
 The film 10, only part of which is visible, may be contained in a
 protective envelope 50 which, for simplification reasons, is shown very
 diagrammatically in chain-dotted lines. This type of envelope, preferably
 opaque to visible light and transparent to X-rays, will be described in
 more detail in the rest of this text.
 The film 10 is placed under an X-ray tube 20 in a vacuum containing several
 point X-ray sources 22 laid out in a two-dimensional network. For example,
 the miniaturized sources 22 may be laid out in rows and columns to form a
 matrix of point sources.
 For simplification reasons, FIG. 1 shows a tube with only three sources 22
 laid out in line. However, this type of tube may contain a large number of
 miniaturized sources placed adjacent to each other to form a matrix of
 sources capable of printing an image formed of image elements, or pixels
 on a sensitive surface. Each source will be used to supply X-rays to print
 a corresponding pixel.
 Each X-ray source 22 comprises a field emission cathode 24 equipped with
 one or several microtips 26 and an anode 28.
 According to one variant, a common anode may be provided for several
 sources or for all sources.
 The anode(s) 28 is (are) connected to a reference potential (0 volts) which
 in this case is the potential of the ground 30.
 Cathodes 24 may be selectively connected to a negative high voltage source
 32 through switches 34. Each cathode is equipped with a particular switch
 34, for example made in the form of a transistor, which may be controlled
 by external control means consisting of a personal computer 36.
 Switches are connected to the computer through galvanic isolation means 38,
 for example comprising optocouplers. The galvanic isolation means isolate
 the computer from the negative high voltage source 32. For example, the
 high voltage in source 32 may output a negative voltage -HT of the order
 of -10 kV to -30 kV.
 FIG. 1 shows that the X-ray tube 20 also comprises grids 40 located between
 each cathode 24 and the corresponding anode. Each grid is polarized with
 respect to the high voltage potential with a positive voltage output by a
 corresponding controlled power supply 35.
 Therefore, the potential of a grid polarized with a positive potential Vg
 is equal to -HT+Vg. The values of the grid polarization voltage may be
 continuous values or discrete values taken within a determined range to
 print on the film in different shades of gray. For example, the range may
 be between 40 volts and 100 volts. FIG. 1 shows that the controlled power
 supplies 35 are also controlled by the computer 36 to which they are
 connected through galvanic isolation means 38.
 According to one variant, selective addressing in X-ray sources may consist
 of row and column addressing. In this case, the cross-addressed rows and
 columns may be associated with the cathodes and grids of the X-ray sources
 respectively. Switches placed at the top of rows and columns are used to
 selectively apply power supply voltages to the rows and columns at the
 intersection of which the X-ray sources to be activated are located.
 According to one simplified variant, the sources may also be controlled by
 acting only on the corresponding grids which are then polarized according
 to two values of Vg corresponding to a state in which a source emits
 (Vg=+100V) and a state in which it does not emit (Vg&lt;40V). Switches 34 are
 then superfluous.
 An additional grid may be inserted between the electron sources and the
 anodes. The function of this grid is to prevent ions returning onto
 electron sources originating from the anode while the X-ray tube is in
 operation.
 Application of a high voltage to a cathode causes the emission of electrons
 through microtips in the cathode. The electrons are accelerated under the
 effect of the electric field existing between the cathode and the anode,
 and bombard the anode material.
 A vacuum is created inside tube 20 in order to enable a long free passage
 of electrons between the cathode and the anode. The tube may comprise a
 getter type element (not shown) to maintain a very low inside pressure.
 For example, anodes may comprise a thin layer of tungsten (W), or possibly
 lightweight materials such as magnesium or aluminum capable of emitting
 X-rays in response to electron impacts.
 Anodes 28 are placed on a window 42 in a material transparent to X-rays,
 for example such as beryllium.
 The dimensions of anodes, and therefore of X-ray sources, is of the order
 of 10 .mu.m in the plane of the window 42, and their thickness is a few
 micrometers.
 Furthermore, the anodes and the window 42 are separated from the cathodes
 by a distance of the order of a few millimeters to about one centimeter
 and, as described above, are at a ground potential (0 volts).
 Thus, particular electrical isolation measurements of the window 42 are not
 necessary.
 The reference 44 denotes a magnet in the air gap in which the X-ray tube 20
 and the film 10 are located. The magnet 44 creates a magnetic field
 denoted B, perpendicular to the plane of the cathodes (i.e. perpendicular
 to the plane of the film) and ensures that the impact of electrons on the
 anodes is limited to an area located facing the cathode from which the
 electrons are emitted. The magnetic field is chosen with a sufficient
 amplitude (for example from 10.sup.-2 to 10.sup.-1 Tesla) to prevent
 dispersion of electrons such that the area of the anode receiving the
 electrons and emitting X-rays is no larger than the cathode of the
 corresponding source.
 FIG. 2 shows an embodiment of a device comprising a variant of the device
 in FIG. 1. For simplification reasons, parts in FIG. 2 that are identical,
 similar or equivalent to parts in FIG. 1 are marked with the same
 references. Therefore, the above description is applicable to these parts.
 The main difference between the device in FIGS. 1 and 2 is in the
 polarization of the cathodes and anodes.
 In the device in FIG. 2, anodes 28 are connected to a high positive
 potential 32. The anodes 28 are not formed on the output window 42 as in
 FIG. 1, but are separated and electrically isolated to prevent the high
 positive voltage from appearing on window 42.
 In this embodiment, as in the previous embodiment, all individual anodes 28
 can be replaced by an anode common to all X-ray sources.
 To generate electrons, grids 40 are polarized to be positive with respect
 to the cathodes by voltages Vg that may be varied continuously, or
 according to fixed values. These voltages are output by controlled power
 supplies 35.
 If a voltage Vg is less than a given threshold, the emission from the
 corresponding cathode will be zero. This means that a cathode may be made
 to operate or not (in On/Off) in the same way as opening or closing a
 switch.
 If Vg exceeds this threshold, the emission from the cathode, which is more
 or less intense (depending on the value of Vg) will lead to a more or less
 intense emission of X-rays and consequently a more or less pronounced
 insolation of the film.
 Advantageously according to this embodiment, the controlled power supplies
 35 do not need to be brought to a high potential. Consequently they can be
 connected directly to the computer 36 which operates at low voltage
 without the need for particular galvanic isolation means.
 As for the previous embodiment described above, the sources may be
 addressed simultaneously or in sequence source after source, row after row
 or column after column to reproduce an image dot by dot (pixel by pixel)
 on the film. Image data or the information to be recorded may be stored in
 a computer memory.
 The insolation time, in other words the X-ray emission time from each
 source, may be adjusted as a function of the transparency of the beryllium
 film that forms the window 42 of the X-ray tube, and as a function of the
 sensitivity of the film used.
 In particular, the insolation time may be adjusted depending on whether the
 sensitive film is or is not equipped with a layer of light intensifying
 material.
 FIG. 3 shows a particular embodiment of an envelope that enables easy
 manipulation of the sensitive medium and capable of writing information
 with an excellent contrast. The use of this type of envelope is
 particularly suitable for applications of the invention to radiology.
 The envelope is formed by a box 50 made of a material opaque to visible
 light and transparent to X-rays, for example such as a carbon sheet.
 The envelope contains a sensitive medium that in the case shown in FIG. 3
 is a radiographic film 10. The film comprises a first area 10a designed to
 record an radiography image and a second area 10b on which information
 contained in the computer file will be recorded.
 It is observed that the housing is equipped with a removable cache 52
 opaque to X-rays which can be put into position on the box 50 to cover
 part of a region corresponding to the second area 10b of the film. In the
 example shown, the cache 52 made of lead may be engaged sideways on box
 50.
 The envelope formed of the box 50 and possibly the cache 52 makes it
 possible to manipulate the film in complete safety without any risk of
 exposing it to visible light.
 Furthermore the film, with the envelope, may be put into place in a typical
 radiography instrument to form a radiographic image on the first area 10a
 of the film. When the film is exposed to X-rays to form the radiography
 image, part 10b is protected by the cache and will not be printed.
 When information has been recorded on the film, which may take place before
 or after radiography, cache 52 is removed. A two-dimensional X-ray tube
 like that described above, is then placed adjacent to the housing 50 in
 the region corresponding to the area 10b of the film.
 Since this area of the film is protected when the radiographic image is
 formed, information may be recorded with an improved contrast.
 As described above, the system according to the invention can be used to
 enter information such as alphabetic or numeric characters, bar codes,
 icons or logos, or previously memorized images, in area 10b of the film.