WO1989006377A1

WO1989006377A1 - System for recording data on an x-ray film fitted in a cassette

Info

Publication number: WO1989006377A1
Application number: PCT/EP1988/001205
Authority: WO
Inventors: Ronald Jan Geluk
Original assignee: B.V. Optische Industrie 'de Oude Delft'
Priority date: 1987-12-29
Filing date: 1988-12-23
Publication date: 1989-07-13
Also published as: NL8703156A

Abstract

A system for recording data on an x-ray film fitted in a cassette, which cassette is provided with an exposure window. An optical system images a column of light-emitting components in the space defined by the window. The recording system comprising the light-emitting components and the optical system can be brought into relative motion with respect to the window, whereby the data are recorded column by column on the x-ray film.

Description

System for recording data on an x-ray film fitted in a cassette The invention relates to a system for recording data on an x-ray film fitted in a cassette, which cassette is provided with an exposure window.

In mammographic radiographs, in particular, use is at present made of a cassette with an x-ray film therein, it being possible for the material of the cassette to transmit the x-ray radiation. Such a cassette is provided with a window via which a portion of the xray film can be exposed to visible light in order to provide data relating to the patient directly on the film. Up to now, this recording of the patient data on the film was carried out beforehand by means of a separate exposure. This involves the risk that a cassette with a film in it with the data of a particular patient is inadvertently used for radiographing another patient. It is obvious that such errors can in general be inconvenient and in certain cases even extremely painful for the patient concerned.

The object of the invention is to offer a solution to this problem by providing a system in which a patient's data are recorded on the x-ray film only when the cassette is placed in the x-ray machine with which the radiograph of the patient is to be made. This makes it possible to eliminate the risk that incorrect patient data are recorded on the x-ray film because when the data are recorded, the patient concerned is already present at the x-ray machine. A problem in developing a system of the abovementioned type is that the exposure windows for the patient data have different dimensions and are fitted at different positions in the cassette housing in cassettes of different makes. Another problem is that, in the case of a mammography cassette placed in the x-ray machine, there is only a very small space having a height of approximately 20 mm between the cassette wall fitted with the window and a lead plate which serves to absorb the x-ray radiation transmitted through the cassette so that the space for exposing the window of the cassette placed in the x-ray machine is extremely limited.

The invention offers a solution to this problem by providing a system of the abovementioned type provided with at least one column of light-emitting components and an imaging optical system comprising at least one lens for imaging the column of light-emitting components in the space defined by the window, and with means for bringing about relative displacement between the cassette and the recording system. Preferably, the light-emitting components are light-emitting diodes, hereinafter termed LED's, which offer the advantage of a small dimension accompanied by a relatively high light yield, each LED in a column being coupled to the optical system via an associated light guide and the end of the light guide situated nearest each LED being attached to the LED.

Although this preferred embodiment is provided with a column of LED's in which the successive lines to be imaged in the window of the cassette are imaged consecutively, it is also possible to give the column of LED's a length such that only one column section always provides for the exposure of one line so that, by driving all the column sections simultaneously, all the lines can be imaged simultaneously by causing the LED's and the optical system to move across the window.

It is also possible, if required, to provide a matrix composed of light-emitting components, preferably also LED's, in which each matrix is driven in a manner such that it exposes the window character-by-character, it being possible in the case of a matrix having a sufficiently large column length, that a number of lines can again be exposed s imultaneously.

The invention will be explained below in more detail on the basis of an exemplary embodiment with reference to the drawing, in which:

Fig. 1 shows a bottom view of a film cassette;

Fig. 2 is a section of the cassette according to Fig. 1 along the line II - II, said cassette being placed in a radiographing device which is provided with the system according to the invention which is shown diagrammatically;

Fig. 3a shows a first possible way of exposing the x-ray film;

Fig. 3b shows a second possible way of exposing the x-ray film; Fig. 3c shows a third possible way of exposing the x-ray film;

Fig. 4a shows a detail of the system according to Fig. 3a;

Fig. 4b shows a front view of the free ends of the light guides, the other ends of which are coupled to the LED's; and

Fig. 4c shows a more specific detail of the way of coupling a light guide to a LED in the embodiment according to Fig. 4a; Fig. 5 shows a variant of the system according to the invention. Figures 1 and 2 show, in bottom view and in section respectively, one of the diverse known types of xray film cassettes, comprising a housing 1 having a window 2 in the bottom face thereof, via which window patient data can be provided on the f ilm 3, which is present in the cassette and is also sensitive to x-ray radiation, with the aid of visible light. In practice, the dimensions of the window may be approximately 16 x 35 mm². With a character size approximately 2.5 mm high, and approximately 2 mm wide, which is still legible with the naked eye, a maximum of 4 to 5 lines of approximately 31 characters can therefore be imaged in the window. The housing 1 is provided with a hinge 4 to enable it to be opened and the film to be taken out of the housing. Some type of removable or slide-aside cover may be provided in front of the window 2 to prevent premature exposure via the window. Although only one type of housing is shown, it will be obvious from what follows that the invention can be applied to any type of cassette provided only that it is provided with an exposure window.

As shown in Figure 2, when used in an x-ray machine intended for mammography, there is situated beneath the cassette 1 a lead plate 5 which serves to absorb any radiation still transmitted through the x-ray film. Between the bottom 1' of the cassette and the plate 5, a space is available which has a height of only 20 mm, in which space the imaging system 6 according to the invention is placed. The system comprises a light source 7, to be discussed in more detail below, a lens 8 and a mirror 9. The lens 8 has a focal length such that it sharply images the light source 7 on the film 3 via the mirror 9. The light source 7, the lens 8 and the mirror 9 are mounted on a common frame or carrier, which is not shown, means being provided, which are also not shown, for causing said frame or the carrier to move in the longitudinal direction, ie. in the plane of the drawing, over the window in order to be able to expose successive film regions. Diverse solutions which will be known to those skilled in the art and are therefore not explained in more detail are available for constructing the frame or the carrier and for the means for the advance thereof.

To expose the film in the cassette, use is preferably made of green LED's. These have the advantage that the light produced is well matched to the spectral sensitivity of the x-ray film, while further advantages are the low cost price, the small dimensions and the possibility of short light pulses.

The required alphanumerical information can be imaged on the film in diverse ways, viz. by:

- exposure per complete character, - exposure per column of a character, both of which possibilities can be combined with:

- one line per movement across the window,

- several or all the lines per movement across the window. Figure 3a shows how the film region to be exposed via the window can be exposed with the aid of a column 10 composed of LED's 7. The LED's are driven in a manner such that the required imaging of alphanumerical symbols is obtained; it being possible to cause the column to move continuously with respect to the window, in which process the LED's image different parts of a symbol in the window at successive instants. An advantage of this solution is the low cost price because few LED's are necessary and the electronic circuit for driving the LED's can be simple.

Figure 3b shows how the film region to be exposed via the window can be exposed with the aid of a matrix 11 composed of LED's 7. Although this solution is more expensive than that according to Figure 3a, it has the advantage that, if all the columns are driven simultaneously, a short exposure time per character is possible.

If all the columns are driven at the same time, the matrix can be moved continuously across the window, but it is also possible to drive the successive columns by means of multiplexing so that they light up consecutively. In this case, the drive of the LED's is simple but it is necessary to cause the matrix to stop with respect to the window for each exposure so that the mechanism for causing the matrix to move across the window is more complicated. However, this embodiment has the further advantage that the amount of light used for the exposure can be regulated by regulating the time that the matrix stands still.

As shown diagramatically in Figure 3c, it is possible to place a number of matrices 11, but in the same way also a number of columns 10, in a line above each other in order to expose a number of lines in the window simultaneously in this way. This has the advantage that no mechanical displacement of the exposure system perpendicular to the longitudinal direction of the window is necessary to constantly image the next line and that the total exposure time can be short. The imaging of the text in the window has preferably to be carried out within one to two sec. If a window Length of 75 mm is assumed, it has been found in practice that a speed of movement of the exposure system with respect to the window of 100 mm/sec is quite satisfactory. This speed is high enough to move to and fro across the entire window within the stated time. If an image blur S of 0.1 mm due to movement is assumed to be acceptable, the maximum exposure time T_m for a constant speed is :

T_m = V/S = 1.0 ms. If the width of one character B_k is 2 mm and the exposure takes place simultaneously per character by means of a matrix of LED's, the repetition frequency F_h of the light pulse is given by:

F_h = V/B_k = 50 Hz. If a character is made up of eight columns which are driven consecutively, the pulse repetition frequency is given by : F_h = 8 V/B_k = 400 Hz.

As already stated above, exposure with the aid of a column of LED's has been chosen for an exemplary embodiment. However, with a single column of LED's, a fairly Large power dissipation per LED is necessary for an adequate light yield. This power dissipation is, however, so high that, in practice, it can result in problems unless measures are taken to reduce dissipation without this being at the expense of the quantity of Light which can reach the window from an LED. This quantity of light is determined in the first place by the diameter of the lens 8, but this is associated with a maximum as a result of the small distance between the bottom of the housing 1 and the lead plate 5. The quantity of light is further determined by the properties of the LED's. An LED has a relatively small actual light-emitting surface with respect to the housing thereof because the housing of the LED functions as a lens and diffuser. Relatively large LED's would therefore have to be used for an adequately high light yield. To expose the x-ray film, an as intense light as possible from preferably adjacent, small punctiform sources is required so that a good letter quality can be obtained. The light source should also preferably be kept small in order to keep the optical reduction small (maximum 8 to 9 times) in order to ensure an adequately large depth of focus. It is obvious that this produces conflicting requirements.

According to the embodiment of the invention, a solution to this is offered by providing a number of light guides situated next to each other which are coupled, on the one hand, to relatively large LED's, which therefore have a high light yield, and, on the other hand, the free ends of which have a small diameter and can easily be placed in an unbroken row . All this is shown in Figures 4a and b. 4a shows, diagrammatically, a column 11 composed of LED's 7 in which a light guide 12 is connected to each LED. The free ends of the light guides are, as shown in Figure 4b, accommodated in a holder 13 which ensures that said free ends are able to position themselves close to each other in one line. The way of coupling a light guide to an LED is shown in more detail in Figure 4c, from which it is evident that a small hole through which the preferably polished core 12' of the light guide 12 projects into the vicinity of the actual light-emitting surface 7" of the LED is drilled in the housing 7' of each LED 7. The light transfer between the light-emitting surface 7" and the core 12' may possibly be improved still further by introducing a quantity of optical fluid beforehand into the drilled hole. In this manner, an optimum light transfer between the LED and the light guide is obtained. To fix the core 12' in the housing 7', use can be made, for example, of glue. The other ends of the light guides 12, which are fitted in the holder 13 and provide the exposure of the x-ray film are placed, as shown in Figure 4b, close to each other in one line, in order to ensure as good a letter quality as possible. These free fibre ends are preferably directed more or less towards the centre of the lens 8, as a result of which the light loss in the light emerging from the outermost light guides as a consequence of the decrease in light at the edge of the lens is prevented. It is also possible to place the light guides parallel and to place a field lens between the free ends thereof and the lens 8 to converge the light coming from the light guides towards the centre of the lens 8. In the embodiment of the invention according to

Figure 4, an adequate number of light guides 12 can be placed next to each other to image one column of one character, but preferably enough light guides are placed next to each other for it to be possible to expose simultaneously the character columns of all the lines to be imaged above each other in the window.

Although an exemplary embodiment of the recording system according to the invention has been discussed above for application in an x-ray film cassette for mammography, the recording system according to the invention can also be used advantageously in x-ray film cassettes which are intended for radiographing other sections of the body, for example radiographing the thorax or the abdomen. In such applications, a larger space is often available between the bottom wall of the cassette and the lead plate than in mammography and the recording system may possibly be constructed without reflecting surface, the light-emitting components being placed at a distance below the cassette and the lens being located between said components and the bottom wall of the cassette so that the light-emitting components are imaged directly on the cassette. An exemplary embodiment of such a system is shown in Figure 5 which shows a side view of the system and the cassette seen along the line V-V in Figure 1 and in which light-emitting components 7 and a lens 8 are again provided in a column or a matrix. The lens 8 is positioned between the column of components 7 and the window 2 in the cassette housing 2 in a manner such that the Scheimpflug condition is satisfied, as a result of which the imaging of the column in the window is sharp.

Claims

C L A I M S

1. System for recording data on an x-ray film fitted in a cassette, which cassette is provided with an exposure window, characterized in that the system is provided with at least one column of light-emitting components and an imaging optical system comprising at least one lens for imaging the column of light-emitting components in the space defined by the window, and with means for bringing about a relative displacement between the cassette and the recording system.

2. System according to Claim 1, characterized in that the imaging optical system comprises at least one reflecting surface.

3. System according to Claim 1 or 2, characterized in that a number of columns of light-emitting components are provided next to each other for simultaneously imaging a complete character in the window.

4. System according to Claim 3, characterized in that the light-emitting components in the column are all simultaneously driven for each character.

5. System according to Claim 1, 2 or 4, characterized in that the means for bringing about a relative displacement between the cassette and the recording system provide a continuous movement.

6. System according to Claim 3, characterized in that the light-emitting components in the columns are driven column-by-column by means of multiplexing and in that the means for bringing about a relative displacement between the cassette and the recording system are equipped for providing a step-wise movement.

7. System according to Claim 1, 2 or 3, characterized in that the column or columns have a length such that a number of lines can be exposed simultaneously in the window.

8. System according to Claim 1 or 2, characterized in that the light-emitting components are composed of the first ends of a number of light guides placed next to each other, the other ends of which are always coupled to an associated light-emitting diode.

9. System according to Claim 8, characterized in that the other end of each light guide is coupled to the associated light-emitting diode by fixing the end of the light guide in a longitudinal drilled hole which is formed in the end face of the LED and which extends to the vicinity of the actual light-emitting surface of the LED.

10. System according to Claim 8 or 9, characterized in that the first ends of the light guides are directed towards the centre of the lens.

11. System according to Claim 8 or 9, characterized in that the first ends of the light guides are placed parallel to each other and in that a field lens is positioned between said ends and the lens.