GB1578746A

GB1578746A - Radiographic film cassette

Info

Publication number: GB1578746A
Application number: GB25949/76A
Authority: GB
Original assignee: Agfa Gevaert NV; Agfa Gevaert AG
Current assignee: Agfa Gevaert NV; Agfa Gevaert AG
Priority date: 1976-06-22
Filing date: 1976-06-22
Publication date: 1980-11-12
Also published as: SE430928B; JPS5392A; DE2727005B2; DE2727005C3; SE7707120L; NL7706399A; BE855415A; FR2356182B1; IT1079054B; CA1086124A; FR2356182A1; DE2727005A1

Description

(54) RADIOGRAPHIC FILM CASSETTE (71) We, AGFA-GEVAERT, a naamloze vennootschap organised under the laws of Belgium, of Septestraat 27, B 2510 Mortsel, Belgium, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to radiographic film cassettes and more particularly to radiographic film cassettes having improved sharpness characteristics.

Present day radiographic techniques in which great importance is attached to high resolving power of the recording cycle, require the use of so-called "soft" X-rays, which means that a relatively low voltage is applied to the X-ray source so that a radiation is obtained which is of a rather long wave-length.

In contrast to the use of a radiation of shorter wave-length (or harder X-radiation), the radiation adsorption is more pronounced. The choice of the soft range in the radiographic spectrum results in that even small or thin irregularities produce such a decrease in radiation intensity that a clearly discernable contrast upon the radiographic recording material is obtained after processing the latter.

An inconvenience of "soft" X-rays, however, resides in the fact that they are very liable to become scattered and that, therefore, extreme care must be taken in order to guarantee an intimate contaot between the radiographic film and the fluorescent screen(s). Moreover, the distance between the film/screen sandwich and the object to be radiographed should be as small as possible.

In order to, at least partially, fulfil these requirements generally use is made of radiographic film cassettes of rather conventional design which, prior to exposure, are connected to a suitable source of vacuum so that an intimate contact between the film and fluorescent screen(s) is established as a result of the atmospheric pressure acting upon the cassette bottom and cover.

The design of this type of cassettes has the drawback that the coyer, facing the source of radiation and which is usually made of metal, absorbs already a substantial part of the soft radiation, which results in the need for increasing the radiation dose. It must also be noted that the distance between the film/screen combination and the object to be radiographed is still considerable due to the thickness of the cassette cover.

Another method for locating the radiographic film during exposure consists in placing the recording material, whether or not accompanied by one or two fluorescent screens, in a light-tight bag of polymeric material and heat-sealing the bag while applying vacuum to the interior of it. By this means a thin radiographic recording unit is obtained which does not show a significant absorption in respect of the incident rays, and which at the same time, because the bag wall may be very thin, permits the set formed by the film/screen combination to be located very close to the object to be radiographed.

Unfortunately, when the bag is opened by means of a cutting tool, such as a pair of scissors, part of the useful space always gets lost, so that the number of times such a bag may be used is rather limited. After two or three exposures, the dimensions of the bag may have diminished to such an extent that it will no longer hold a film of a given format. The unavoidable flexure of the film/screen set may also lead to difficulties with respect to a correct positioning. An analogous drawback may be noticed when employing radiographic film cassettes of classical design but which are made of a flexible material, such as polymer ma terial.

It is therefore an object of the invention to provide a radiographic film cassette which does not show the inconveniences of the above mentioned prior art devices.

According to the invention, there is provided: A radiographic film cassette wherein there is a bottom and a cover hingewise connected to each other and fastening means, said bottom and said cover when closed and fastened forming a light-tight enclosure in which a radiographic film sheet can be accommodated; wherein the cover is formed in part by a flexible foil which is transparent to penetrating radiation and extends over part of the plan area of the cassette, and in part by a less flexible marginal portion to which said foil is connected, and which has a thickness that is greater than that of the flexible foil; and wherein there is at least one exhaust opening via which air can be aspirated from the interior of the closed and fastened cassette to cause the said foil to become pressed towards the interior of the cassette.

In the foregoing, the "plan area" of the cassette must be interpreted as the area occupied by the closed cassette viewed normally to the plane in which it holds a film sheet.

The "cover" means that member which is turned towards the X-ray source and upon which the object to be radiographed is positioned.

A radiographic cassette of this design can combine the advantages of a classical radiographic film cassette and the polymeric bag in that on the one hand it can have an overall rigidity, imparted by the bottom and the marginal part of the cover as they are locked together, and on the other hand the object to be radiographed can be located very close to a film/screen set in the cassette because only the thickness of the flexible foil has to intervene.

A preferred field of application of the cassette according to the invention are mammography techniques.

The cassette may be designed so that it can be fastened or unfastened automatically by mechanisms forming part of an automatic cassette loading and/or unloading apparatus, e.g. an apparatus which can operate in a well-lit room.

The latter possibility may be of importance when radiographic examinations are carried out by ambulance teams which do not dispose of the classical hospital facilities.

Preferably, the bottom of the cassette is provided with an intensifying screen.

In order to increase the efficiency of the vacuum, supplementary sealing expedients may be provided in the cassette, so that it is not necessary to maintain the source of vacuum in operation after a sufficiently low pressure has been established in the cassette. It will also be clear that the aspirating means may be equipped with means which provide or at least facilitate the atmospheric pressure restoration once the exposure has taken place. In fact the exposure cycle which comprises the loading of the cassette, the application of vacuum, the exposure itself, the release of the vacuum and the unloading of the cassette in a magazine or directly into a processing apparatus may be carried out fully automatically.

In a preferred embodiment, the flexible foil occupies at least 60% of the plan area of the cassette. Preferably the foil itself has a thickness of not more than 0.5 millimeter and advantageously it is composed of a polymer material, preferably polyethylene, in which carbon black is dispersed as opaci- fying agent.

The cassette according to the invention may be designed in such a manner that it may cooperate with a gripping element located at the exposure station of a mammographic X-ray table, in which element also means are provided for automatically connecting the vacuum means with the vacuum valve of the cassette. In this way a reproducible positioning of the cassette is possible and in the meantime excessive time losses due to occasional bad connections are avoided.

The scope and spirit of the invention will be understood in a clearer way at the hand of a detailed description of a prefer rod embodiment and in the light of the accompanying drawings in which: Fig. 1 is a longitudinal cross-sectional view according to the line 1-1' in fig. 3 and 3-3' in fig. 4 of a radiographic film cassette according to the invention, Fig. 2 is a longitudinal cross-sectional view according to the line 2-2' in fig. 3 and 3-3' in fig. 4 of a radiographic film cassette as illustrated in fig. 1 (showing small structural differences) when the cassette is partly opened, Fig. 3 is an under-plan view of the cover, Fig. 4 is an under-plan view of the bottom, Fig. 5 is a top view of another embodiment of a cassette according to the invention and Fig. 6 is a cross-sectional view of an alternative embodiment of the cassette according to the invention.

As illustrated in figs. 1 and 2, the radiographic film cassette 10 according to the invention comprises a bottom 11 and a cover 12 which are hingingly connected to each other with the help of hinges 13 (only one being shown). The cover 12 and the bottom 11 represented in the form of a sandwich structure in fig. 1 may be made of a metal such as aluminium or of a,' poly- meric material having a high degree of stiffness, and is so designed that its dimensions enable the use of current format radiographic- film and their incorporation in exposure apparatus. The bottom 11 bears an intensifying screen 17 which may be resiliently supported and which is intended to increase the yield of the conversion of penetrating radiation into a latent image builtup in the radiographic film contained in the cassette.

Part of the surface area of the cover 12 consists of a flexible foil 16 which is opaque to visible light but which transmits the penetrating radiation creating a latent image.

The' purpose of this foil 16 is to guarantee an optimum contact with the film 28 and the intensifying screen 17 so that scattering or, other quality decreasing phenomena may b ' avoided to a large extent. This intimate coatac't -is made possible by the application of a vacuum in the inner space of the cassette 10 after locking the latter with the help of locking mechanism 14, 15, so that the atmospheric pressure tends to flex the flexible foil 16, and that as a consequence a firm contact between the latter and the fifm 28 is established. In order to evacuate the inner space a usual vacuum valve 18 is provided in one of the corners of the cover frame 12 which valve may be connected to a suitable source of vacuum (not shown). If the flexible foil 16 is connected only with the cover 12, the vacuum source is kept in communication with the interior of, the cassette during the exposure. If however the foil 15 of about twice the length of the foil shown in Fig. 1 and extends not only over the film but also under the whole area of the intensifying screen 17 (as illustrated in Fig. 2), or if supplementary sealing means as for example a strip of silicone rubber 27 (see" again Fig. 1) is provided, the connection to the vacuum source may be terminated once a sufficiently low pressure has been est blished in the cassette.

A good contact between the film and the screen is usually ensured once the pressure within the cassette has fallen to 30 kPa below atmospheric pressure.

Fig. 3 is an under plan view of the cover 12 of the cassette. It comprises a rigid Ushaped member 19 which is provided with an upstanding ridge 20 which is capable of entering in a corresponding groove (see Fig.

4) provided in the bottom 11 of the cassette.

The flexible foil 16 of rectangular shape is secured to the U-shaped member 19 by known means such as adhesive, heat sealing, etc., over ,about 'three quarters of its, periphery. The residual part 24 partly extends under the intensifying screen 17,' and by closing the cassette a relatively airtight unit is obtained.

The space 21 defined by the upstanding ridge 20 and the upstanding wall 22 of the cover may be provided with supplementary sealing means 27 of resilient nature (only parts of said means have been illustrated for the sake of clearness). The area occupied by the flexible foil 16 is of such shape and dimensions that it is ample for covering an bbject (for example a breast) to be radiographed, even after possible partial compression of such object.

At the end of the legs of the U-shaped member 19, there are provided small recesses 25 and 26, which serve to house one element of the hinges 13 (see also fig. 1).

The flexible foil 16 is made from a flexible polymeric foil such as polyethylene in which carbon black has been previously dispersed as opacifying agent.

Fig. 4 illustrates an under-plan view of the bottom 11.

It comprises a rigid plate 30 in which a groove 31 is provided, extending over about three quarters of its periphery and which serves for receiving the upstanding ridge 20 of the cover 12 (see preceding fig. 3). At the inside of the bottom 12, an intensifying screen 17 is provided which is mounted onto the inner surface of the plate 30 and the dimensions of said screen are about the same as the format of the radiographic film (not shown) which is to be exposed. If desired, a portion 24 of the flexible foil may, as shown, extend under said intensifying screen 17 in order to increase the 'airtightness of the whole arrangement.

It will be dear that when prpviding a flexible foil (which in figs. 3 and 4 is denoted by 16) of a width exceeding the distance between opposite edges of the groove 31, as shown by dotted lines 16', the airtightness reaches a very -high accuracy as part of the flexible foil is urged into the space defined by the groove 31 of the bottom 11 and the ridge 20 of the cover 12, so forming a kind of air-tight bag when closing the cassette.

In the bottom 11 are also provided recesses 32 and 33 in which the second element of hinges 13 may be located.

As may be derived from the foregoing, when closing the cassette, the flexible foil 16 (or 16f) folds itself about its edge 23.

A mernber 34 which partly projects from the bottom 11 and fixedly connected therewith enables the ,bottom 11 to, be taken hold of by means of an appropriate mechanism and to further open the cassette, once the locking/unlocking 14, 15 mechanism (fig. 1) is in its unlocking position.

This feature makes possible to incorporate the cassette according to the invention into already existing daylight loading/unipading systems or into daylight loading/unloading systems, especially adapted or designed for this type of cassette.

Each of the cassettes which are shown in Figs. 5 and 6 has a cover foil 16 which is the same as that in the cassette shown in the earlier figures, and they likewise have an exhaust opening with a vacuum valve corresponding with valve 19 in such earlier figures but this is not shown in the case of the Fig. 6 embodiment. The cassettes shown in Figs. 5 and 6 also have sup elementary features which will now be described, for improving the ergonomic properties of the cassette or decreasing the radiation dosage to which a subject is exposed. Referring firstly to Fig. 5, the cassette shown in this figure comprises a bottom 11 (of which only the side edges may be seen) and a cover 12 which are hingingly connected with each other. Suitable locking means 14 are provided. In contrast to the cassette of fig. 1, the locking means are located in the side walls of the cassette and may comprise a pin fixedly connected to the cover 12 and a yieldingly biased slot which is located on a rail or in a groove fixedly connected with the bottom 11 wherein the pin and slot are capable of en gaging each other when exerting a pressure on the cover 12. As this locking / unlocking means is no part of the invention it has not been represented in detail. The cover 12 of which a part is formed by a flexible foil 16 is provided with means which permit the film to be provided with supplementary data related to the person or to the object to be radiographed.

So are provided first identification means 40, 41, 42 which enable to print additional information related to the person to be radiographed upon the film (not shown).

The said identification means comprise a small chamber 40 in which a slide 41 is located and which slide 41, -by pushing the knob 42 in downward direction, may per form a translational movement into the chamber 40, so providing a small rectan gular opening in the cover 12. At that moment data carrying means (not shown) such as a small typewritten card may be placed into a special exposure unit (not shown) which, by means of a small light source, prints the data upon the film via the above mentioned opening in the cover.

The slide 41 may be resiliently biased in the chamber 40, so that upon withdrawing the cassette 10 from the special exposure unit the slide 41 automatically closes again in a light-tight manner.

There are also provided second identifi cation means for printing supplementary data upon the film during its exposure to penetrating radiation.

Especially in mammography in which generally two practically identical objects are radiographed, it is desirable to dispose of identification upon the film which positively indicates whether it is the left or the right breast which is represented on the radiographic record.

As such, symbols 45 or 46 provided on a slide 43 and associated with respectively the left or right side of the patient are fixedly located in the cover 12 of the cassette. The slide 43 made of a material opaque to penetrating radiation and having an opening 44 may take a dual position in that the opening 44 may be positioned either over the symbol 45 or over the symbol 46.

The said symbols 45 and 46, which are made of a penetrating radiation absorbing material, such as lead, intercept the radiation during exposure, so that after processing the film a white area in the form of the symbol is obtained thereon. The circles 50 and 51 represent the areas on which cover lifting means (such as sucker cups) may be located for opening the cassette when the latter is incorporated into or forms part of a daylight loading / unloading system.

The cassette 10 shown in Fig. 6 incor porates a second intensifying screen 29 which is connected to the flexible foil 16 on the cover 12. This second intensifying screen 29 contributes positively to a sub stantial decrease of the radiation dose by the fact that the radiographic film 28, hav ing in general a penetrating radiation sen sitive coating on either side, will be ex posed to the light emitted by both inten sifying screens 17 and 29, which means that the radiation dose may practically be halved.

The second intensifying screen 29 may be secured to the flexible foil 16 by known means such as pressure adhesive tape. If desired, the side of the flexible foil 16 facing the inner space of the cassette itself may be provided with a fluorescent coating, so that the use of a separate support for this coat ing may be dispensed with.

WHAT WE CLAIM IS: 1. A radiographic film cassette wherein there is a bottom and a cover hingewise connected to each other and fastening means, said bottom and said cover when closed and fastened forming a light-tight enclosure in which a radiographic film sheet can be accommodated; wherein the cover is formed in part by a flexible foil which is transparent to penetrating radiation and extends over part of the plan area of the cassette, and in part by a less flexible marginal portion to which said foil is connected and which has a thickness that is greater than that of the flexible foil; and wherein there is at least one exhaust opening via which air can be aspirated from the interior of the closed and fastened cassette to cause the said foil to become pressed towards the interior of the cassette.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

this type of cassette.

Each of the cassettes which are shown in Figs. 5 and 6 has a cover foil 16 which is the same as that in the cassette shown in the earlier figures, and they likewise have an exhaust opening with a vacuum valve corresponding with valve 19 in such earlier figures but this is not shown in the case of the Fig. 6 embodiment. The cassettes shown in Figs. 5 and 6 also have sup elementary features which will now be described, for improving the ergonomic properties of the cassette or decreasing the radiation dosage to which a subject is exposed. Referring firstly to Fig. 5, the cassette shown in this figure comprises a bottom 11 (of which only the side edges may be seen) and a cover 12 which are hingingly connected with each other. Suitable locking means 14 are provided. In contrast to the cassette of fig. 1, the locking means are located in the side walls of the cassette and may comprise a pin fixedly connected to the cover 12 and a yieldingly biased slot which is located on a rail or in a groove fixedly connected with the bottom 11 wherein the pin and slot are capable of en gaging each other when exerting a pressure on the cover 12. As this locking / unlocking means is no part of the invention it has not been represented in detail. The cover 12 of which a part is formed by a flexible foil

16 is provided with means which permit the film to be provided with supplementary data related to the person or to the object to be radiographed.

So are provided first identification means 40, 41, 42 which enable to print additional information related to the person to be radiographed upon the film (not shown).

The said identification means comprise a small chamber 40 in which a slide 41 is located and which slide 41, -by pushing the knob 42 in downward direction, may per form a translational movement into the chamber 40, so providing a small rectan gular opening in the cover 12. At that moment data carrying means (not shown) such as a small typewritten card may be placed into a special exposure unit (not shown) which, by means of a small light source, prints the data upon the film via the above mentioned opening in the cover.

The slide 41 may be resiliently biased in the chamber 40, so that upon withdrawing the cassette 10 from the special exposure unit the slide 41 automatically closes again in a light-tight manner.

There are also provided second identifi cation means for printing supplementary data upon the film during its exposure to penetrating radiation.

Especially in mammography in which generally two practically identical objects are radiographed, it is desirable to dispose of identification upon the film which positively indicates whether it is the left or the right breast which is represented on the radiographic record.

As such, symbols 45 or 46 provided on a slide 43 and associated with respectively the left or right side of the patient are fixedly located in the cover 12 of the cassette. The slide 43 made of a material opaque to penetrating radiation and having an opening 44 may take a dual position in that the opening 44 may be positioned either over the symbol 45 or over the symbol 46.

The said symbols 45 and 46, which are made of a penetrating radiation absorbing material, such as lead, intercept the radiation during exposure, so that after processing the film a white area in the form of the symbol is obtained thereon. The circles 50 and 51 represent the areas on which cover lifting means (such as sucker cups) may be located for opening the cassette when the latter is incorporated into or forms part of a daylight loading / unloading system.

The cassette 10 shown in Fig. 6 incor porates a second intensifying screen 29 which is connected to the flexible foil 16 on the cover 12. This second intensifying screen 29 contributes positively to a sub stantial decrease of the radiation dose by the fact that the radiographic film 28, hav ing in general a penetrating radiation sen sitive coating on either side, will be ex posed to the light emitted by both inten sifying screens 17 and 29, which means that the radiation dose may practically be halved.

The second intensifying screen 29 may be secured to the flexible foil 16 by known means such as pressure adhesive tape. If desired, the side of the flexible foil 16 facing the inner space of the cassette itself may be provided with a fluorescent coating, so that the use of a separate support for this coat ing may be dispensed with.

WHAT WE CLAIM IS: 1. A radiographic film cassette wherein there is a bottom and a cover hingewise connected to each other and fastening means, said bottom and said cover when closed and fastened forming a light-tight enclosure in which a radiographic film sheet can be accommodated; wherein the cover is formed in part by a flexible foil which is transparent to penetrating radiation and extends over part of the plan area of the cassette, and in part by a less flexible marginal portion to which said foil is connected and which has a thickness that is greater than that of the flexible foil; and wherein there is at least one exhaust opening via which air can be aspirated from the interior of the closed and fastened cassette to cause the said foil to become pressed towards the interior of the cassette.
2. A radiographic cassette according to

claim 1, in which the bottom bears an intensifying screen.
3. A radiographic film cassette according to claim 1 or 2, in which said cover and said bottom at the surfaces facing each other are provided with a ndge-like, re spectively a groove-like structure which inter-engage when the cassette is in closed condition.
4. A radiographic film cassette according to claim 3, in which between the edge of the cover and the ridge-like structure thereon there is resilient, material for forming an air-tight seal.
5. A radiographic film cassette according to claim 4, in which said material is a silicone rubber.
6. A radiographic film cassette according to any preceding claim, in which the flexible foil has a rectangular form.
7. A radiographic film cassette according to any preceding claim, in which the flexible foil is a polymeric material.
8. A radiographic film cassette according to claim 7, in which said polymeric material is polyethylene containing carbon black.
9. A radiographic film. cassette according to any preceding claim, wherein said foil occupies at least 60% of the plan area of the cassette.
10. A radiographic film cassette according to any preceding claim, wherein said foil has a thickness of not more than 0.5 millimeter.
11. A radiographic film cassette according to claim 1 or 2, in which the said marginal portion of the cover is of U-shaped form and said flexible foil is folded near the hinge joint between the bottom and cover and extends over said bottom.
12. A radiographic film cassette according to claim 3 or 4, in which said flexible foil has a width exceeding the width between the overlying parts of said ridge-like or groove-like structure.
13. A radiographic film cassette according to any of the preceding claims, which contains an intensifying screen which contacts that side of said flexible foil which faces the interior of said cassette.
14. A radiographic film cassette according to claim 13, in which said intensifying screen is in the form of a coating on said flexible foil.
15. A radiographic film cassette according to claim 13, in which said intensifying screen is in the form of a coating on a support which is secured to said flexible foil.
16. A radiographic film cassette according to any of the preceding claims which has means permitting the printing of additional information on a film contained in the closed cassette.
17. A radiographic film cassette according to claim 16, in which said means comprise an opening of generally rectangular form in the cover which can be screened off from ambient light by means of a slide, and via which opening data from outside the cassette . may be projected onto a radiogranhic film contained in the latter.
18. A radiographic film cassette according to claim 16 or 17, in which there are also provided second identification means in order to permit additional information to be printed on the film.
19. A radiographic film cassette according to claim 18, in which said second identification means comprise at least one significant symbol in penetrating radiation opaque material, said significant symbol being capable of being screened off from or to be put into the beam of penetrating radiation during exposure, so preventing or enabling the formation of a latent image in or on said radiographic film.
20. A radiographic cassette substantially as herein described with reference to the accompanying drawings.