Film Cassette

FILM CASSETTE

FILM CASSETTES

This is a container for exposed & unexposed film They are used to hold x-ray film and intensifying screen in close contact and uniformity with one another

FILM CASSETTE

A cassette is a light proof rigid holder that contains screens and film Cassettes are usually hinged (latches) on one side and can be opened from the other side. The side which is having the latches is the back side and other side facing the patient is called front side.

The front side is made of material of low atomic number, like plastic or carbon fiber. This is to maximize the transmission with low attenuation. Carbon fiber (Z = 6) absorbs only 50% of X-rays compared to aluminum.

Cassette with carbon fiber can be operated with low radiographic techniques, resulting in lesser patient dose.

The back side is usually made of heavy metals (lead), having high atomic number, to minimize back scatter.

CASSETTE

X-RAY CASSETTES

FUNCTIONS

• Protect film from exposure to light
• Protect film from bending and scratching during use.
• Contain intensifying screens, keeps film in close contact to screen during exposure.

Exclude dust and dirt from the sensitive screen

FEATURE OF THE IDEAL CASSETTE

• Strong and rigid to withstand daily wear and tear
• Lightweight to facilitate easy handling and carrying

Easy to open and close, under low light conditions The cassette front must provide minimal beam attenuation be of uniform thickness and hence on irregularities which might be visible on radiograph No sharp edges and corners which might injure patients or staff Have a strong aperture for use in patient’s identification system

Cassette design and construction should include

• feature contributing to close contact between film and
• screen e.g. Foam sponges
• Some similar materials covered front providing
• warmth to touch
• Should be available in range of film size

Be sold with same guarantee of quality

CONSTRUCTION

Consist of a FRONT and BACK hinge at one long edge Attached to the inside back of the cassette is a thin sheet of lead foil and attached to a plastic foam pressure pad and an intensifying screen Front of the cassette :

Cassette well containing the front intensifying screen and short lead blocker for patient identification May incorporate an additional foam pressure pad underneath the front intensifying screen

Back of the cassette :

May incorporate, in one corner, a recess and sliding aperture for with patient identification camera Locking methods e.g. spring clips, sliding locking bars, all serves to exclude all light when in locked position The foam pressure pad maintain close and uniform contact between the film and screen All internal metal or plastic surface are given a black coating in order to prevent the possibility of internal light reflection

A large number of synthetic materials are used in the construction of the cassette to make them lightweight

Cassette front

Should be uniform in thickness and density and have no irregularities which might be made visible on the be made visible on the radiograph In order to minimize beam attenuation cassette front should confront the British standard (Bs 4302 1968) states that the cassette front, if metal, should have an Al equivalent of no more than 1.6 mm when used at 60 kVp or, if plastic, no more than 0.2mm Al equivalent.

Materials used in cassette construction

Metal (e.g. aluminium), plastic laminate or carbon fibre are material commonly used in cassette front construction

• All these material have the following advantages
• Light in weight
• Low beam absorption

Strength and stiffness

N/B The use of carbon fibre cassettes reduce patient dose significantly due to their lower beam attenuation

Cassette front

Materials used in cassette construction

Cassette back:

May be made of metal or plastic construction and lined with lead foil in order to protect film from radiation scattered backwards from a buck tray or other surface The BS recommendation states that it should have a lead equivalent of at least 0.12 mm when used with equipment operating at 150kV constant potential

Cassette back

Materials used in cassette construction

• Cassette fitting
• Clip or fastener – usually stainless steel
• Hinge metal or Plastic

Pressure pad plastic foam sponge

TYPES OF X-RAY CASSETTE

• (i) Single screen cassette :

Have single intensifying screen and are designed to be used with single – sided emulsion film Their principal application is in mammography

ii) Double screen cassettes:

Have screen on both sides have intensifying screen on both sides and are designed to be used with double– sided emulsion film Used in general radiography

TYPES OF X-RAY CASSETTE

• CURVED CASSETTE:

There are of two types

The first used when the necessary close object / cassette contact cannot be achieved with a conventional flat cassette e.g. intercondylar projections of the knee with the joint flexed The second used to obtain panoramic views of the mandible and maxilla in orthodontic radiography ( orthopantomography)

Film Cassette

(a) is used where the necessary close contact between object and cassette cannot be achieved with a conventional flat cassette, e.g. intcrcondylar views of the flexed knee joint;

(b) is used to obtain panoramic views of the mandible (orthopantomography).

CURVED CASSETTE

TYPES OF X-RAY CASSETTE

• GRIDDED CASSETTE:

Have stationary secondary radiation grid incorporated in the front wall of the cassette, between the front intensifying screen and the front of the cassette.

The cassette is used for radiography where a conventional buck system is unavailable e.g. in ward mobile work Details of the grid, such as its grid ratio, should be identifiable on the outside of the cassette

TYPES OF X-RAY CASSETTE

• MULTISECTION CASSETTES:

Most common use is in tomography where they are used to produce, with one radiographic exposure, a set of films each bearing an image of a different layer height within the body. Moreover, the layer images so produced will be representative of body sections equal distances apart These cassettes may hold 3-7 films, with their respective intensifying and spacers. The spacers may be 5 or 10 mm in thickness and made of radiolucent foam sponge.

Films which are separated by 5 mm spacers will produce images of the body sections 5 mm apart.

Similarly, films which are separated by 10mm of spacing materials will bear images of separate body layers 10 mm apart.

Multisection cassette have another application in a technique known as multiple radiography . In this procedure the cassette is loaded with a set of films and varying speed intensifying screens, but no spacers.

Thus, with one exposure a set of films is produced each a different density range and contrast due to the variation in intensifying screen speeds used.

The intensifying screen film combinations can thus be chosen in order to give the desired range of image densities, e.g. from bone to soft tissue

MULTISECTION CASSETTE

CASSETTES AND AUTOMATIC EXPOSURE DEVICES

Where cassette are to be used with a phototiming device placed behind the cassette, the back of the cassette must have no lead present and be as radiolucent as front This is in contradistinction to the situation where ionization chamber devices are being used, when , because of their placement between the source and the film, they may be used with any conventional x-ray cassette

CARE OF X-RAY CASSETTE

Treated with care, x-ray cassettes will survive many years of hard work.

Careless handling lead to cassette damage and problems such as poor film/ screen contact or light leakage

CARE OF X-RAY CASSETTE

• Point to note:

Treat cassette gently

Limit the number of cassette carried to any one time. Carry securely between body and arm, with the fingers holding their bottom edges If store on edges ensure that cassette are as near vertical as possible. Damage can ensure if cassette are stored at an angle, with other more weighty ones leaning against them.

Where cassette need to placed directly under a patient cassette tunnel should be consider to reduce pressure on the cassette itself Avoid contact with fluid, protect the cassette with some sort of plastic water proof cover where necessary

CASSETTE MAINTANANCE

In order to provide both a check on a cassette’s lifespan and contribute to the efficiency of maintenance, the following Procedures should be carried out Record on the cassette the date it was introduced in the department Identify each cassette with a letter or numerical placed on one edge of intensifying screen and the same on the outside of the cassette Keep a record of cassette maintenance N/B cassettes and screens should be inspected regularly for signs of damage and withdraw from the service if necessary

LOADING AND UNLOADING CASSETTE

The normal, useful life of intensifying screens depends on a large extent on the care taken during film loading and unloading, for it is at this time that the sensitive screen surfaces are exposed to the possibility of dust contamination and the danger of insensitive handling

LOADING AND UNLOADING CASSETTE

UNLOADING CASSETTE:-

• Under safelight
• Cassette face downward on the bench

Locked clip released

Turn over the cassette and the front of the cassette tripped so that film falls from the cassette well Remove film with free dry hand and cassette closed

LOADING AND UNLOADING CASSETTE

LOADING CASSETTE

• Under safe light
• Cassette face downward on the bench
• Unexposed cassette slightly gripped at its edge and lowered gently into the cassette well

Cassette is closed by bringing over the back and engaging the locking clip

OTHER TYPES OF CASSETTE

• VACUUM CASSETTE:

Supplied with vacuum pump are made from flexible vinyl material and have a valve attached at one edge Inside is a removable plastic folder containing a single intensifying screen.

To prepare the cassette for use, a single –sided emulsion film is inserted inside the folder, with its emulsion surface facing the intensifying screen The entire folder is placed inside the cassette and the cassette scaled by applying pressure along the edges of the opening. A sliding clamp is then drawn over the scaled edges

Film Cassette

The vacuum pump is attached to the valve and air expelled thus bringing the intensifying screen and film into very close contact. In this position they are held by uniform distribution of atmospheric pressure Although primary developed for use in mammography, vacuum cassettes have other applications in radiography where their inherent flexibility can be used to advantage in positioning , e.g. under a flexed joint.

The cassette are available in a range of sizes, 18 x 24cm and 24 x30cm being the most popular

Vacuum cassette

OTHER TYPES OF CASSETTE

• FORMATTER CASSETTE

Used for imaging from cathode ray tube (CRT) and TV monitors in Ultrasound , Nuclear Medicine, Computerized Tomography (CT), Digital subtraction Angiography (DSA) and Magnetic resonance imaging (MRI). It is used in conjunction with a formatter or video imager.

The cassette consist of a frame designed to hold two single – sided emulsion film by their edges, and two removable slides which protect the film from light exposure when not in use. They do not contain intensifying screens

Film Cassette

The cassette is loaded under safelight condition by removing the two slides and sliding the individual films, emulsion side facing outwards, into either side of the frame, carefully ensuring that they are securely held in the side channels of the frame by their long edges. This is very important, otherwise when the side is removed the film will sag when in the imager . Finally, the slides are inserted When required for use, the cassette is inserted into the multiformat imager and the slide nearest the film to be exposed is removed . The film is now ready for exposure.

Film Cassette

Once imaging is complete, the side is returned to the cassette, the cassette withdrawn from the imager, turned over and reinserted.

The second slide is removed, thus making the second film available for exposure

Formatter cassette

OTHER TYPES OF CASSETTE

• ANGIOGRAPHY CASSETTES

Siemens Elema AOT system: the film feed or supply cassette will hold up to 30 sheets of unexposed films, size 35x35cm, each positioned between metal spacers After loading and sliding shut the two panels under safelight conditions, the cassette can be inserted in the AOT equipment . The take – up cassette with its sliding lid open, is also inserted in the AOT On completion of an imaging sequence, the exposed films will have been transferred via the exposure area of the AOT apparatus to the take –up cassette

Film Cassette

A button on the front of this cassette is pressed, closing the sliding lid. The take – up cassette can then be withdrawn and conveyed to the darkroom, where the exposed films are removed and processed

The AOT film take-up cassette

Film Cassette

Puck system: basic principles are the some as AOT, during an angiographic procedure 35x35cm films are rapidly conveyed from supply to take – up cassette

The puck rapid film changer

OTHER TYPES OF CASSETTE

PHOTOFLUOROGRAPHY CASSETTES:

Photofluorography, or the recording of images from the output phosphor of an image intensifier tube, is usually carried out on 70 mm or 105 mm roll film, or on 100 mm sheet film.