GB2125989A - X-ray film cassette - Google Patents

Abstract

A first intensifying screen 15 is secured to a flexible magnetic plate 14 provided on a top part 9 of a cassette, while a second intensifying screen 18 is rigidly secured to a counterfoil 17 which is flexibly attached to a cassette bottom part 1 by means of securing elements 16. The parts 1 and 9 of the cassette are interconnected by a hinge 13 so that they may be opened and closed to permit an X-ray film (not shown) to be inserted between the intensifying screens 15 and 18. Each of the securing elements 16 comprises a foil strip 16a secured to the cassette bottom part 1 by an adhesive strip 16b and secured to the counterfoil 17 by an adhesive strip 16c, these two adhesive strips being mutually offset. The assembly of the counterfoil 17 and the intensifying screen 18 can thus move relative to the cassette bottom part 1 in directions both parallel and perpendicular to a base wall 2 of that cassette part. To increase the freedom of movement the strips may be weakened e.g. by providing oblique, arcuate or V- shaped cuts. <IMAGE>

Description

SPECIFICATION X-ray film cassette This invention relates to a cassette for radiation-sensitive film, particularly X-ray film.

Typically, such a cassette comprises first and second parts which can be opened and closed relative to one another, a flexible magnetic plate which is attached to the first cassette part and which is substantially the same size as the film, and a ferromagnetic counterfoil flexibly connected to the second cassette part by means of at least one securing element, whereby intensifying screens and said film can be inserted between the magnetic plate and the counterfoil. An example of this type of cassette is disclosed in German OS 2917547, wherein the securing element which flexibly connects the counterfoil to the second cassette part (the cassette bottom) comprises a circumferentially continuous foam strip.This foam strip enables the counterfoil to execute a certain amount of lifting movement perpendicularly to the cassette bottom as well as small lateral sliding movements in directions parallel to the cassette bottom. Such a slight amount of movability is necessary for the magnetic plate or for the counterfoil in a pressure application sandwich system of this kind, in order that one or the other of these parts may "give" under the tension which exists when the two cassette parts are closed. This so-called "floating suspension" also allows for differential thermal expansion between the cassette material, the counterfoil or magnetic plate and the intensifying screen.

This connection has, however, been found to allow too little freedom of movement for the counterfoil and/or the magnetic plate in a direction perpendicular to the cassette bottom, and entails a risk that the movable component (the counterfoil or the magnetic plate) will be damaged or destroyed. It is an object of the present invention to provide a cassette of the abovedescribed general type in which this freedom of movement is increased to a suitable level.

According to the invention, a cassette for radiation-sensitive film, particularly X-ray film, comprises first and second cassette parts which can be opened and closed relative to one another, a flexible magnetic plate attached to the first cassette part, a magnetic or magnetisable counterfoil flexibly connected to the second cassette part by means of at least one securing element, and an intensifying screen rigidly secured to the counterfoil, the or each securing element being composed of a flexible foil strip having a first part thereof attached to the second cassette part and a second part thereof attached to the counterfoil, the first and second parts being offset from one another.

In this way, a comparatively large degree of movability can be achieved for the counterfoil/intensifying screen assembly in a direction perpendicular to the second cassette part (the cassette bottom) which allows the overall height of the cassette to be made less than is the case when a conventional foam strip securing element is used. Furthermore, by making the or each securing element in the form of a foil strip, the invention enables compensation to be achieved for a relative length variation between the counterfoil/intensifying screen assembly and the first and second cassette parts (which will usually be made of ABS plastics material), since mobility is provided in directions both parallel and perpendicular to the cassette bottom.

Preferably, the or each foil strip is of elongated configuration, and said first and second parts thereof are constituted respectively by opposite edge portions of the elongate strip. At least two such foil strips can be provided, being arranged in mutually parallel relationship.

Conveniently, the first and second parts of the or each foil strip are provided with strips of adhesive respectively on opposite surfaces of the foil strip. Where a plurality of such foil strips are provided, these are advantageously oriented uniformly relative to the arrangement of their adhesive strips.

Desirably, the or each foil strip has regions of weakness between said first.and second parts thereof, which may be formed by incisions or punched-out perforations, for example.

The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a sectional perspective view of a cassette according to the invention, the cassette being shown in a partly open condition; Figure 2 is a cross-section through a bottom part of the cassette shown in Figure 1; Figure 3 is a top view of the bottom part of the cassette, illustrating in particular securing elements thereof; and Figures 4a to 4e illustrate different embodiments of the securing elements.

The cassette shown in Figure 1 comprises a first, bottom part 1 which includes a cassette wall 2, a frame 3 bordering the wall 2 and a flange 4 formed on three sides of the bottom part 1. On the fourth side of the bottom part 1, a flange 4a of inferior height is onmoulded and carries a Tsection member 5 on its outwardly directed side.

The bottom part 1 also includes a circumferentially continuous rib moulding 6 which is slightly spaced away from the flanges 4 and the flange 4a, and which forms part of a light-exclusion device substantially surrounding the space in which a radiation-sensitive film will be received. On the opposite side of the bottom part 1 to that on which the flange 4a is provided, a locking bolt 7 is arranged between the flange 4 and the rib 6, and co-acts with a hook 8 provided on a second top part 9 of the cassette. A hinge 13 connects the top and bottom parts of the cassette together.

The top part 9 is constructed substantially as a sandwich assembly, and comprises a cassette wall 10 to the hinge side of which is onmoulded a flange 1 2 which also carries a T-section member 11. On the inwardly directed side of the top part 9, there is provided a flexible magnetic plate 14 on which an intensifying screen 1 5 is mounted by means of an adhesive or the like. A further intensifying screen 1 8 faces the screen 1 5 and has a ferromagnetic counterfoil 17 rigidly secured to a surface thereof opposite its fluorescence layer, the counterfoil 17 being itself flexibly connected to an inwardly directed side of the wall 2 of the bottom part 1 of the cassette by a plurality of securing elements 16.The arrangement of the securing elements 1 6, the counterfoil 1 7 and the intensifying screen 1 8 is particularly clearly shown in Figures 2 and 3. In use, an X-ray film (not shown) is received between the intensifying screens 1 5 and 18, and the magnetic plate 14 acts to attract the counterfoil 1 7 when the cassette is closed, thereby urging the intensifying screens 1 5 and 1 8 into close contact with opposite sides of the film, respectively.

Figures 2 and 3 in each case show three securing elements 1 6 arranged parallel to one another and parallel to the longitudinal direction of the cassette. Each securing element 1 6 consists essentially of a foil strip 1 6a provided in the longitudinal direction on one outwardly facing side thereof with an adhesive coating 1 6b. On the other side of the foil strip 1 6a there is also provided a strip of adhesive 1 6c which extends parallel to the longitudinal side of the foil strip but is offset relative to the strip of adhesive coating 1 6b. Conveniently, the two adhesive strips 1 6b and 1 6c are arranged in respective outer marginal zones of the foil strip 1 6a.

In the assembled cassette, the downwardly directed adhesive strip 1 6b on the left-hand side of the foil strip 1 6a (as viewed in Figures 2 and 3) is attached to the cassette wall 2 of the bottom part 1, whereas the upwardly facing adhesive strip 1 6c on the right-hand edge of the foil strip 1 6a is attached to the counterfoil 1 7. On the other side of the counterfoil 17, the intensifying screen 18 is secured by a double-sided adhesive tape 1 9 extending continuously around a marginal edge thereof.

In a cassette of the above-described construction, the counterfoil 1 7 together with the intensifying screen 1 8 fitted thereon has a relatively large amount of freedom of movement in a vertical direction relative to the cassette wall 2, namely by substantially the full width of each foil strip 1 6a less the widths of the two adhesive strips 1 6b and 1 6c.

The freedom of movement in directions parallel to the cassette wall 2 depends essentially on the flexibility of the foil strips 1 6a. In order to improve such freedom of movement in these directions, the foil strip 1 6a may be provided with regions of weakened material between the adhesive strips 1 6b and 1 6c, as shown in Figures 4a to 4e. Such weakening of the material may be obtained, for example, by making oblique incisions 20 (Figure 4a), V-shaped cuts 21 (Figure 4b) or arcuate incisions 23 (Figure 4d). Such cuts or incisions extend for a substantial part of the area between the two adhesive strips 1 6b and 1 6c. However, it is equally feasible to provide the foil strips 1 6a with punched-out perforations, such as V-shaped holes 24 as shown in Figure 4c, or S-shaped perforations 25 as shown in Figure 4e.

The foil strips 1 6a are preferably made of polyester. Moreover, the counterfoil 1 7 may be coated, conveniently on both sides thereof, with a polyester foil which serves as a protection against corrosion. As a result of these provisions, the thermal expansion coefficients of the securing elements 1 6 and the envelope of the counterfoil 1 7 are made equal to one another.

Claims (8)

1. A cassette for radiation-sensitive film, particularly X-ray film, comprising first and second cassette parts which can be opened and closed relative to one another, a flexible magnetic plate attached to the first cassette part, a magnetic or magnetisable counterfoil flexibly connected to the second cassette part by means of at least one securing element, and an intensifying screen rigidly secured to the counterfoil, the or each securing element being composed of a flexible foil strip having a first part thereof attached to the second cassette part and a second part thereof attached to the counterfoil, the first and second parts being offset from one another.

2. A cassette as claimed in Claim 1, wherein the or each foil strip is of elongated configuration, and said first and second parts thereof are constituted respectively by opposite edge portions of the elongate strip.

3. A cassette as claimed in Claim 1 or 2, wherein at least two such foil strips are provided and are arranged in mutually parallel relationship.

4. A cassette as claimed in Claim 1, 2 or 3, wherein the first and second parts of the or each foil strip are provided with strips of adhesive respectively on opposite surfaces of the foil strip.

5. A cassette as claimed in Claim 4, wherein a plurality of such foil strips are provided and are oriented uniformly relative to the arrangement of their adhesive strips.

6. A cassette as claimed in any preceding claim, wherein the or each foil strip has regions of weakness between said first and second parts thereof.

7. A cassette as claimed in Claim 6, wherein said regions of weakness are formed by incisions or punched-out perforations.

8. A cassette for radiation-sensitive film, substantially as hereinbefore described with reference to Figures 1 to 3 and any one of Figures 4a to 4e of the accompanying drawings.