RAD 350 Chapter 12 Screen-Film
After interacting with the patient, the beam is said to be attenuated – the amount depends on
the atomic number and mass density/volume of the varied anatomical parts inside the patient.
The remnant beam is what strikes the intensifying screen and/or film and consists of noninteracting photons and scattered photons. The “VOID” created by totally absorbed photons
also contributes to the radiographic image but IS NOT remnant radiation as it no longer exists.
The remnant beam interacts with the intensifying screen crystals (where it is converted from
x-rays to light) and strikes the active portions of the film (emulsion) to form the invisible, yet
there, LATENT image. Remember that in “screen film” it is LIGHT from the intensifying screen
crystals that is responsible for the majority of the emulsion’s exposure.
The light given off by the intensifying crystals MUST match the color sensitivity of the film.
This is called SPECTRAL MATCHINIG!
See Figure 12-1 Radiographic double emulsion film
-supercoating/overcoating – sometimes used to protect the emulsion layer
-emulsion layer – made of gelatin and silver halide/bromide crystals (the sensitivity spec
is an “imperfection” in the emulsion where during processing, the silver atoms are attracted to
and concentrate).
-base – usually made of polyester and gives support to the emulsion layer(s)
-adhesive layer bonds the emulsion to the base
LATENT IMAGE – the invisible image on the film after exposure BUT prior to developing
MANIFEST IMAGE – the visible image after exposure and processing
See figure 12-2 Silver halide crystal – silver bromide and silver iodine are in “ion form” (+ and –
charges) and form the CHEMICAL LATTICE. When the silver halide crystal is formed, the silver
atoms release an outer shell electron (atom becomes positively charged). The bromine and
iodine atoms each have one additional electron (negative charge). The crystal therefore has a
negative total charge.
See Figure 12-5: As secondary photoelectric or scattered Compton electron interacts with the
lattice, it can dislodge electrons from the exposure lattice. The silver ions now and an ADDED
electron are converted to “atomic silver” (latent image) and when processed (developed)
become BLACK METALLIC SILVER.
Types of film: direct exposure (cardboard holders/bite wings), screen film, matrix film, video
recording (tape, DVD/CD), subtraction, cine (usually 16 or 35 mm), laser, spot film (70/105
mm), mammo and duplication film.
SPECTAL RESPONSE = the film’s response to the color emission of the light emitted (from the
intensifying screen). The color the FILM is sensitive to MUST MATCH the color light given off
by the intensifying screen crystals – SPECTRAL MATCHING.
-calcium tugstate crystals emit blue/blue-violet light. So they need film sensitive to BLUE
-“rare earth” (rare earth elements with atomic numbers 57-71) crystals emit blue-green
light – so these need blue-green sensitive film (ORTHOCHROMATIC FILM).
PANCHROMATIC film is used in photography and is sensitive to ALL colors of light.
Film speed: LARGE emulsion crystals (silver halide/bromide as well as/OR a THICKER emulsion
layer will INCREASE the speed of the film, but will LOWER radiographic detail. Another
IMPORTANT consideration: the thickness of the automatic processing or laser film MUST be
constant to enable it to pass through the processor.
CROSS OVER can occur in a variety of ways : double emulsion film can have image
“differences” on EACH side of the emulsions AND/OR also in a cassette/receptor with TWO
intensifying screens – as light from one screen can “cross over” onto the other side causing
loss of detail. “Anti-cross over” (anti-halation) layers can be used to prevent this.
EXPOSURE LATITUDE of a film is the response of the film to build up OD (and shades of gray) to
a given amount of radiation or light. This is INHERENT in “that given film” and will not change
unless one switches to another speed/type of film. The “WIDER THE EXPOSURE LATITUDE”
THE WIDER range of mAs can be used and still get the same (crappy) looking film.
LAW OF RECIPROCITY = exposure equals amount of photoms X time (i.e. 2 X mAs should give
2X OD.
SAFE LIGHT: 15 watt bulb NO CLOSER than 5 feet from the film tray. Blue sensitive film uses an
amber colored filter (will fog green sensitive film). A red filter (“Wratten 6-B”) may be used
with blue sensitive film
Laser film is sensitive to RED light, so must be loaded in total darkness of with a grenn/yellow
safelight.
ARTIFACTS: creases in the film, dirt, scratches, lotion, grease-oil, and gelatin from the
processor as well as static (“tree static” is most common*****) can detract from the
radiographic appearance of the image and should be avoided.
Storage of radiographic film:
-Store on END; NEVER lay flat (could cause “PRESSURE mark artifacts”)
-68 degrees or less F (20 C)
-between 40-60% humidity
-protect from light, radiation, chemicals and heat (EXPOSED, undeveloped film is MUCH
more SENSITIVE to all the items than UNEXPOSED, undeveloped film!)
-Shelf life date is very important as the film starts to develop as SOON as it is made!
PROCESSING THE LATENT IMAGE:
-Important dates: 1942 Pako came out with the first “automatic processor” (10 feet long
and all films were placed on “wire hangers” to be transported and dipped into each chemical)
1956 – Kodak – first roller film transporting processor (5 minutes)
1965 – Kodak – first 90 sec, processor
Important KEY chemical information:
-DEVELOPMENT converts the latent image to visible, MANIFEST IMAGE (black METALLIC
SILVER) ALKALINE chemistry
-FIXER – TWO IMPORTANT items and TIMES: CLEARING TIME – TIME REQUIRED TO
“clear” the unexposed/non-developed silver halide – removes/dissolved from the
emulsion. FIXINT TIME = total time to stop development and stabilize the film imageACIDIC chemistry
Table 12-8 Key developer chemicals (alkaline)
-“reducing agents”/developing agents
Hydroquinone – SLOW build up of blacks
Phenedine/metol/elon – TAST build up of grays
-“Buffering agents” (enable the developing agents to enter emulsion and maintains ph)
Sodium carbonate/sodium hydroxide
-“Restrainer” prevents the developing agents from developing the UNEXPOSED silver
halide/bromide crystals
“POT ASS”ium bromide “POT ASS”ium iodide
-“Preservative” helps control oxidation
Sodium sulfite
-“Hardener” (lack of hardener is the cause for MANY processor problems
Gluteraldehyde
***Key topics for developer are: Time, temperature/chemical concentration
See figure 12-9 FIXING AGENTS – ACIDIC
-“Activator” NEUTRALIZES the developer and STOPS development action
Acidic acid
-“Fixing agent” removes UNEXPOSED silver halide/bromide from emulsion (sometimes
called “clearing agent”
Ammonium thiosulfate (also called hypothiosulfate)
-“Hardener” maintains hard emulsion
Viagra (just kidding) potassium alum/aluminum choride or chrome alum
-Preservative” maintains chemical balance
Sodium sulfite
See figure 12-31 Automatic processor (be able to draw one and list the SYSTEMS and parts)
-Feed tray/micro switch
-Roller racks/drive motor/crossover racks
-rollers are either transport or squeegee
-pi lines (what is the circumference of a circle with a one inch diameter?)
-guide shoes
SYSTEMS:
-transport
-temperature (really several areas – developer, was water and dryer)
Discuss difference between wet and sticky film
-circulation
-replenishment (how to place a film on feed tray!!! Always short dimension against feed
tray wall
-dryer
-electrical
Visit the lab (room two) and play with the Kodak M-6 processor for DEMONSTRATION use (not
the one we process film with). Take out the rollers, racks, crossovers and put back together.
90 second processing keys:
-developer temp = 95 degrees F (35 C) + or – 5 degrees
- about 22 seconds for the film to spend in EACH the developer and fixer
Rapid processing (45 sec) ER/OR pros/cons
Extended processing – mammo (advantages)
Daylight systems pros/cons