Note: Descriptions are shown in the official language in which they were submitted.
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~ his invention relates to radiographic film cassettes
and more particularly to radiographic film cassettes having
improved sharpness characteristics.
Present day radiographic techniques in which great im~
portance is attached to high resolving power of the recording
cycle, require the use of so-called "sof-t" 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 ra-ther long
wave-length.
In contrast to -the use of a radiation of shorter wave-
length (or harder X-radiation), the radiation absorption is
more pronounced. ~he choice of the soft range in the radio-
graphic spectrum results in that even small or thin irregu-
larities produce such a decrease in radiation intensity
that a clearly discerneable contrast upon the radiographic
recording material is obtained after processing the latter.
An inconvenience o~ "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 con-tact 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 requiremcn-ts
generally use is made of radiographic film cassettes of rather
conventional design which, prior to exposure, are connec-ted
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to a suitable source of vacuum so that an intimate contact
be-tween the film and fluorescent screen(s) is established as
a result of the atmospheric pressure acting upon the casse-tte
bottom and cover.
~ he design of this -type of cassettes has the drawback
that the cover, facing the source of radia-tion and which is
usually made of metal, absorbs already a substantial part of
` the soft radiation, which resul-ts in the need for increasing
the radiation dose. It must also be noted -that the distance
between -the film/screen combina-tion and the object to be
radiographed is still considerable due to the thickness of
the cassette cover.
Another method for locating the radiographic film durin~
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 in-
2~ cident 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.
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Unfortunately, when the bag is opened by means of acutting tool, such as a pair of scissors, part of the useful
space always ~ets lost, so that the number of times such a
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bag may be used is ra-ther 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 correc-t
positioning. An analogous drawback may be noticed when
employing radiographic film casset-tes of classical design
but which are made of a flexible material, such as polymer
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I-t is therefore an obaect of the invention to provide
a radiographic film cassette which does not show the inconve- -
nierces of the above mentioned prior art devices.
l According to the invention, there is provided :
A radiographic film cassette comprising a bottom and a cover
hingc~l~c connected~to each other and fatening means, said
bottom and said cover when closed and fastened form a light-
tight enclosure in which a radiographic film sheet can be
accommodated,the cover being 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 connec-ted
and that has a thickness that is greater than that of the
flexible foil,and comprising at least one exhaust opening
via which air can be aspirated from the interlor of the closed
and fastened cassette to cause atmospheric pressure to be
- exerted on said screen and film system via said foil.
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In the foregoing, -the "plan area" of the cassette must
be in-terpreted as the area occupied by the clos~d cassette
viewed normally to -the plane in which it holds a film sheet.
The "cover" means tha-t ~ler~ber which is turned towards
the X-ray source and upon which the object to be radiographed
is positioned.
A radiographic casse-tte of this design combines the
advantages of a classical radiographic film casse-t-te and -the
polymeric bag in that on the one hand it is undeformable
~ 10 due -to the combined rigidity of the bo-ttom and the cover as
; they are locked -together and on the other hand by the fact
that the distance between the objec-t to be radiographed and
the set of film/screen is limited -to the thickness of the
flexible foll only.
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 automa-tically 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.
~ he latter possibility may be of importance when radio-
graphic examinations are carried out by ambulant teams which
do not dispose of the classical hospital facilities.
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,',7 Preferably, the bottom of the cassette is provided with
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an intensifying screen.
In order to increase the efficiency of the vacuum,
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supplementary sealing expedients may be provided in the
cassette, so that it is not necessary to maintain the source
of vacuum in operà-tion after a sufficiently low pressure
has been established in the cassette. It will also be clear
that the aspira~ing means may be equipped wi-th means which
provide or at leas-t ~acilitate the a-tmospheric pressure
restoration once the exposure has taken place. In ~act the
~i exposure cycle which comprises -the loading of the casse~tte,
the application of vacuu~, the exposure i-tself, the release
of the vacuum and the unloading of ~the cassette in a magazine
or direc-tly 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. ~he foil
itself has a thickness o~ not more than 0.5 millimeter and
, is advantageously composed of a polymer material, preferably
polyethylene, in which carbon black is dispersed as opaci-
~ fying agent.
', ~he cassette according to the invention may be designed
in such a manner that it may coopera-te 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.
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~ he scope and spirit of the inven-tion will be understood
in a clearer way at -the hand of a detailed description of a
preferred embodimen-t and in -the light of -the accompanying
drawings in which :
~ig. 1 is a longitudinal cross-sectional view according to
the line 1-1' in l'ig. 3 and 3-3' in fig. 4 of` a r~dio-
graphic 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 radio-
graphic film casse-tte as illustrated in fig. 1 (showing
small structural differences) when the cassette is partl~-
opened,
Fig. 3 is an under-plan view of the cover,
~ig. 4 is an under-plan view of the bo-t-tom,
~ig. 5 is a top view of another embodiment of a cassette
according to the invention and
~ig. 6 is a cross-sec-tional 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~. ~he 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 polymeric material having a high degree of stiffness~
and is so designed that its dimensions enable the use of
current format radiographic films and their incorporation
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in exposure apparatus. The bo-t-tom 11 bears an intensifying
screen 17 which may be resilien-tly sup~orted and which is
intended to increase the yield of the conversion of pene-trating
radiation into a latent image built-up in the radiographic
film contained in the cassette.
Par-t o~ the sur~ace area of -the cover 12 consists o~
a flexible foil 16 which is opaque to visible light but
which transmits the penetra-ting radia-tion creating a latent
image. The purpose of this foil 16 is to ~uarantee àn
optimum contact with -the film 28 and the intensifying screen
17 so that sca-ttering or other quality decreasing phenomena
may be avoided to a large extent. ~his in-timate contact 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 a-tmospheric
pressure tends to flex the flexible foil 16, and that as a
consequence a firm contact between the latter and the film
28 is establishedO In order to evacuate the inner spaGe a
usual vacuum valve 18 is provided in one o~ the corners of
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the cover frame 12 which valve may be connected to a suitable
source of vacuum (not shown). In case the flexible foil 16
is connected with only the cover 12, the vacuum is malntained
i during the exposure. When however the flexible foil has
twice its original length (as especially illustrated in fig.2)
< and continues under the whole area of the intensifying screen
'i 17, or when supplementary sealing means as for example a
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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 established in the
cassette. ~he good working of the cassette is already
guaranteed when the vacuum within -the inner space
of the cassette attains 7000 mm of water column or less.
Fig. 3 is an under plan view of -the cover 12 of -the
cassette. It comprises a rigid U-shaped member 19 which is
provided with an upstanding ridge 20 which is capable to
disappear in a correspo~ding groove (see fig. 4) provided
in the bottom 11 of the casse-tteO ~he flexible foil ~6 of
rectangular shape is secured to -the U-shaped member 19 by
known mea~s 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 air-tight unit is obtained.
The space 21 defined by the upstanding ridge 20 and the
, upstanding wall 22 of the cover may be provided with supple-
mentary 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 -there is ample space in order to locate
the objects (for example a breast) to be radiographed in an
easy manner9 even after partly compressing the latters.
`~ At the end of the legs of the U-shaped member ~9, there
i are provided small recesses 25 and 26, which serve to house
one element of the hinges 13 (see also fig. 1).
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r~he flexible foil 16 is made from a flexible polymeric
foil such as polye-thylene in which carbon black has been
previously dispersed as opacifying agent.
~ ig. 4 illustra-tes an under-plan view of the bottom 11.
It cornprises a rigid plate 30 in which a groove 31 is
provided, extending over abou-t three quarter60f i-ts periphery
and ~rhich serves for receiving the upstanding ridge 20 of the
cover ~2 (see preceding fig~ 3). At -the inside of the bottom
12, an intensifying screen 17 is provided w~ich is mounted onto
the inner surface of -the pla-te 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 air-tightness
of the whole arrangement.
It will be clear that when providing 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 sho~m
by dotted lines 16', the air-tightness reaches a very
high accura~ as part of the flexible foil is urged into the
space defined by the groove 31 o~ the bottom 11 and the ridge
20 of the cover 12, so forming a kind of alr-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
-l cassette, the flexible ~oil 16 (or 16') folds itself about
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its edge ~3.
A member 34 which par-tly projects from the bottom 11
and fixedly connected therewi-th enables the bottom 1~ to be
taken hold of by means of an appropriate mechanism and to
further open the cassette, once the locking/unlocking 14, 15
mechanism (~ig. 1) is in i-ts unlocking position. ~his
feature makes possible to incorporate -the casse-tte according
to the invention in-to already existing daylight loading/
unloading systems or into daylight loading/unloading ~ys-tems,
especially adapted or designed for this -type of cassette.
In fig. 5 is illustra-ted a top view of another preferred
embodimen-t of a cassette 10, according to the invention which
~` is provided with supplementary expedients in order to increase
its ergonomic properties. ~he casset-te 10 comprises a bottom
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11 (of which only the side edges may be seen) and a cover 12
'1 which are hingingly connected with each other. Suitable
locking means 14 are provided. In contrast to the cassette ~t
of fig. 1, the locking means are located in the side walls
of -the cassette and may comprise a pin fixedly connected to
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the cover 12 and a yieldi~gly biased slot which is located
on a rail or in a groove fixedly connected with -the bottom 11
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` wherein the pin and slot are capable of engaging each other
~; when exerting a pressure on the cover ~2. As this locking/
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unlocking means is no part of the invention i-t has not been
represented in detail. ~he cover 12 of which a part is formed
by a flexible foil 16 is provided wi-th means which permit
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-the film to be provided with supplementary data related to
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-the person or to -the objec-t to be radiographed.
So are provided first identification means 40,41,42
which enable to print additional informa-tion related -to -the
person to be radiographed upon the film (not shown). ~he
said identification means comprise a small chamber ~0 in which
a slide 41 is located and which slide 41, by pushing -the
knob 42 in downward direction, may perform a transla-tional
movement into -the chamber 40, so providing a small rec-tangular
opening in the cover ~2. At -tha-t moment data carrying
means (not shown) such as a smal:L 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. ~he slide 41
may be resilien-tly biased in the chamber 40, so that upon
withdrawing the casse-tte ~0 from the special exposure unit
the slide 41 automatically closes again in a light-tight
manner.
~here are also provided second identification means
for printing supplementary data upon the film during its
exposure to penetrating radiation.
. Especially in mammography in which generally two practi-
cally 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 4~ and
associated with respectively the left or right side of the
GV.893 PC~ - 11 _
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pa-tien-t are flxedly loca-ted in the cover 12 of t~e cassette.
~he slide ~3 made of a material opaque to pene-trating radia-
tion 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 pene-
trating radiation absorbing ma-terial, such as lead, intercep-
~-the radiation during exposure, so -that after processing the
film a white area in the form of the symbol is obtained there-
on. ~he circles 50 and 51 represen-t -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.
~ inally, fig. 6 shows an alternative embodiment of -the
cassette 10 of fig. 1, in which a second intensifying screen
29 is connected to the flexible foil 16 on the cover 12.
~his second intensifying screen 29 contributes positively to
a substantial decrease of the radiation dose by the fact that
the radiographic film 28, having in general a penetra-ting
radiation sensitive coating on either side, will be exposed
to the light emitted by both intensifying screens 17 and 29,
which means that the radiation dose may practically be halved.
~he 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
,7 a fluorescent coating, so that the use of a separate support
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. for this coating may be dispensed wi-th.
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