RT210 - Cassettes

Radiographer error in selecting the correct speed

Problems encountered with cassettes

ill defined (unsharp)

The radiographic image of the wire mesh will appear ___________ in areas where screen-film contact is poor.

wire mesh

Cassettes may be tested for poor screen-film contact using a

3/16, Plexiglas

wire mesh is usually ______ in. squares enclosed in a thin sheet of ------.

transient

Bending of the cassette under a heavy patient is -------because once the cassette is removed, it will return to its normal shape.

Air

\------- may be trapped between a screen & the film as a radiographer hurriedly loads a film & slams the cassette shut.

transient

Some causes of poor screen-film contact are

transient

air trapped between the film and a screen & the temporary bending of the cassette under the weight of heavy patients.

poor screen-film contact

which presents on the finished radiograph as an area of poor detail or a blurred area.

misuse or dropping of the cassette, resulting in either a sprung frame or in loosened or broken hinges or latches.

The cause in poor screen-film contact is usually

warped front panel

warped screens due to excessive moisture

worn screen backing

foreign particulate matter between the screens & film.

Other causes of poor screen-film contact

radiographic cassette

is any type of holder used to protect and transport the radiographic film as it travels through the medical imaging department & other parts of the medical facility.

conventional

computed

2 types of cassettes

Conventional cassettes

cassettes that use standard radiographic film

Computed Radiography cassettes

cassettes that use no film.

projection radiography

(or sometimes as conventional radiography)

With conventional cassettes, an image is projected onto a sheet of film, and for this reason the process is referred to as

grid or nongrid

Conventional cassettes can be either

scattered & secondary radiation emitted from the patient.

A grid in the front panel of the cassette absorbs

Conventional cassettes

are the most common type found in medical imaging departments

very large exposure and radiation dose

Since the sensitivity of radiographic film to direct x-ray exposure is very low, a ---------------------- to the patient is necessary to produce an adequate image.

light energy or directly expose the film.

The x-rays coming from the x-ray tube, carrying anatomical information from the patient, either are converted into ------------- or ------------.

90-99% , 1-10%

Approximately ------ of the image is produced from light exposure, and less than ----- is produced by direct x-ray exposure.

Keep the intensifying screens and film in close contact with one another.

Protect the screens and film from physical damage.

Protect the film from being exposed externally

Cassettes have 3 main purposes

aluminum

steel

heavy plastic.

In a typical radiographic cassette, the frame is made of

plastic

carbon fiber

bakelite

aluminum

magnesium.

Common front panel materials include

aluminum

stainless steel

plastic.

The back panel of the cassette is commonly made of

Poor processing conditions

improper film handling

patient clothing and jewelry

dirt or other foreign matter on cassette screens and film.

Causes (artifacts):

Dual-screen cassettes

Single-screen cassettes

2 types of conventional radiographic cassettes

Dual-screen cassettes

are designed for use with radiographic film having 2 emulsions, or dual-emulsion film.

Single-screen cassettes

are designed for use with film having 1 emulsion, or single-emulsion film.

felt, plastic foam, or rubber material

In a dual-screen cassette, the front and back panels are lined with a ----------------- that serves as a backing to which the screens are attached

is to exert a gentle, even pressure on the screens as they touch the film.

Another function of the backing material

screen speed

the speed at which the screens or screens convert x-rays to visible light

the size of the cassette and an identification number to produce a radiographic image

Other labeling includes

Lightweight, durable

Lightproof

Not easily bent

Smooth, washable surfaces

Smooth, rounded edges and corners

Capable of maintaining good screen-film contact

Can be opened and closed easily

Characteristics of a Good Cassette

Curved Cassettes

Are designed to decrease the distance between a body part and the film when the body-part plane & film plane are not parallel.

convexly curved , concavely curved

A curved cassette includes a -------- front panel and a -------- back panel.

Flexible Cassettes

Are used with rotational dental units to provide a panoramic view of the entire mandible and teeth.

Daylight Cassettes

Are those that are used with daylight film systems.

are generally used with a daylight film-loading unit attached to a wall inside or directly outside a radiographic room.

Mammography Cassettes

cassettes that have only 1 screen.

polycarbonate-polystyrene

Some mammography cassettes have a -------------- front panel to minimize absorption of the xray beam.

vacuum cassette

Another less commonly used type of Mammography cassette is called a

vacuum cassette

a cassette that the air is drawn out of the cassette after the film has been inserted to provide optimal screen-film contact.

It has a built-in vacuum valve and an internal envelope that holds the film.

is polyethylene bag that can be loaded with a film, evacuated, and heat-seated.

2 types of vacuum cassettes:

linearly or crosshatched

A grid of lead strips, arranged either ----------- or --------- in the front panel is used to absorb wideangle scattered and secondary radiation coming from the patient.

ratio, frequency, & focal range

Grids are classified according to their

Slip-on grids

These grids have a slotted frame into which a cassette is inserted.

Computed Radiography Cassettes

Is a relatively new technology that has been adopted by many health care facilities throughout the world.

photostimulable-phosphor image plate

In Computed Radiography Cassette, A cassette is used, but there are no screens or radiographic film. Instead, a ______________ is used.

aluminum, plastic or steel

The frame of the computed radiography cassette is made of