ch 19 20 21. physics. 2 semester Flashcards
what are the five characteristics of the base in film?
flexible, tough, stable , rigid and Lucent
film is often coated with a substance to prevent light from one screen crossing over to the other which causes blurring. what is this effect called?
crossover effect
what can a manufacturer do to decreased the crossover effect?
use ultraviolet emission from an intensifying screen
The effect caused by light being reflected from the air interface on the back of the base material is called?
halation
what can be done to prevent halation?
anti-halation coating may be applied to the back of single emulsion film to absorb light and prevent backscatter, visible light or reflected light from degrading the image
note that this coating is removed by the processing chemicals to permit light to be transmitted through the film for viewing
what are the four stages of construction of diagnostic radiographic film?
base
adhesive
emulsion with crystals
supercoat
base
modern day made from polyester
adhesive:
thin coat is applied to the basement material before it’s coated with emulsion to glue the emulsion to the base
what is the purpose of the adhesive?
glue the emulsion to the base, prevents bubbles and distortion when film is bent during processing handling , when wet ,and heated during development
emulsion:
A gelatin which photosensitive silver halide crystals are suspended
what is the purpose of the gelatin emulsion?
it must be clear. Gelatin acts as a neutral lucent suspension medium for silver halide crystals that must be separated from one another to allow processing chemicals to reach them
it distributes crystals evenly over the film and prevents clumping of silver halide so that certain areas of the film are not more photosensitive than another
what are the three types of silver halide used in radiographic film
Silver bromide 95-98%
silver Iodide
silver chloride
supercoat:
A layer of hard Protective gelatin that prevents the soft emulsion underneath from being physically or chemically abused from scratches, abrasions from stacking, and skin oils. it is also anti static and very strong
define photosensitive:
materials capable of responding to exposure by photons
important facts to know about crystal production:
Silver bromide crystals are produced in total darkness
Silver nitrate and potassium bromide are combined in the presence of gelatin
Silver bromide will precipitate out and the potassium nitrate can be washed away as a waste product
The gelatin must be present as a medium to permit the crystals to form. It limits oxidation and reduces Crystal surface energy tension and facilitates chemical reactions
each Crystal is a matrix of silver, bromine, and iodine Atoms found by strong ionic bonds
what is the most important key to the formation of the latent image
The crystal structure allows free silver and electrons to drift through the lattice
The silver halide crystals must have an impurity added: what is it and why ?
Gold silver sulfide ….forms sensitivity specs which provide film sensitivity. During latent image formation the specs serve as electrodes
to attract the free silver Ions
what is the ripening period?
during this period the Silver halides are allowed to grow. The size of the crystals determines their total photosensitivity. The longer the ripening. The larger the crystals and the more sensitive they are
at the proper time the emulsion is cooled shredded and washed to remove potassium nitrate
mixing:
occurs after ripening
The shredded emulsion is melted to sensitize the crystals and additives such as colored dyes , hardeners, anti fogging agents and Bactericides and fungicides are mixed into the emulsion
pandromatic
sensitive to all colors
orthochromatic
not sensitive to red
coating:
requires extremely precise and expensive coating equipment
A three-step process
- adhesive layer is applied to base
- emulsion
- supercoat
all manufacturing, packaging transport , exposure and processing is done in ______ ________
total darkness
latent image formation
formed by the light photons and X Ray photons which come from the intensifying screens that are in contact with the film
define latent image
The unseen change in the atomic structure of the crystal lattice which causes the production of a visible image due to sensitivity specs
describe the process of latent image
incident photons either light or x-ray interact with one of the halides either bromine or iodine. The ejected electron is free to wander and may be trapped by a sensitivity spec causing a negative charge. the negative charged spec attracts a free silver ion. The silver ion neutralizes the spec and resets the trap
describe the ionic stage of latent image formation
This stage is repeated several times till a clump of silver rests on the spec. At least three silver Atoms are needed to see a visible black metallic silver to be formed by chemical development. More silver equals more black. less silver equals white
what are the two main types of film
Direct exposure/non screen film and intensifying screen film
some important facts about direct exposure/nonscreen film
it is used on exams that require fine detail
it increases dose to patient
used in mammography
Single emulsion
find grain silver halide crystals
high silver content
requires a thick emulsion layer 2 to 3 times thicker than medical screen film
important facts about intensifying screen film
it is available in many speeds, contrast ranges, latitudes and resolutions
The contrast, latitude and resolution in this film is linked to speed. note that large crystals and thick emulsion cause low contrast, wide latitude, and decreased resolution
screens are faster via:
double emulsion
how do you achieve a lower silver content
More efficient distribution of silver
what is the primary purpose of radiographic processing?
to deposit enough black metallic silver at the latent image sites in film to allow the formation of a permanent visible image
what is the most sensitive and variable factor when producing a radiograph?
processing
what are the four primary steps to processing a radiograph?
developing
fixing
washing
drying
washing and drying are the two archiving steps
what is the first step in the wet processing of the film
developing
Silver is deposited at the latent image sites and an image becomes visible in this step:
developing
The depositing of ________ amplifies the density of the image
silver
True or false?
Silver ions of the latent image are stabilized and More silver is added causing a visible clump
true
what are the two primary agents of developer?
phenidone and hydroquinone
what are the five automatic developer solutions?
activator, restrainer, preservative, hardener, solvent
what three things control the action of the developer?
immersion time, solution temperature, chemical activity
what is the purpose of activator?
it keeps the solution alkaline. Between 10.0 and 10.5 pH
what is a another action of activator?
to assist reducers in reaching the silver halide’s by causing gelatin to swell and become permeable
what does the restrainer do and what is its name
potassium bromide
it is added to the developer to stop reduction action to the crystals
what is the preservative?
sodium sulfite
decreases the oxidation of reducing agents when combined with air. After mixing the developer with this is only good for a few weeks
what is the purpose and the name of hardener?
Glutaraldehyde
it controls swelling of the gelatin to prevent scratches and abrasions to the emulsion during processing. This hardener maintains uniform thickness. Too much causes hardening too soon, too little and the film leaves the processor moist and soft
what is the purpose of the solvent?
suspends chemicals it is usually water and should be filtered to remove impurities
if the film is developed in a tank that was contaminated with 0.1% of fixer or more what would it look like
it would appear gray having decreased contrast. Because of this one cleaning the tanks the fixer should be filled first
if a film does not go through the fixings stage what happens?
there will be a slow blackening of the film and the image will become obscured
what chemical process must be done in order for the image to be fixed for viewing
underdeveloped silver halides must be removed from the emulsion
this is done by using a clearing agent that binds with the unexposed silver halides and removes them from the emulsion. the clearing agent is a fixer agent
what is the name of the clearing or fixing agent
ammonium Thiosulfate
this clearing agent uses silver in the emulsion to form ammoniumthiosilver sulfate. It takes 5 to 10 seconds. If not cleared the film will have a milky appearance
what is the name and purpose of the activator?
acetic acid.
maintains the acidic pH of 4.02 4.5 to enhance the functioning of the clearing agent. It serves as a stop bath because it’s acidic. It stops reduction of silver halide
what is the name and function of the preservative
sodium sulfite
dissolves silver from the ammoniumthiosilver sulfate and allows it to continue to remove silver from the emulsion
what is the name and purpose of the hardener
aluminum chloride, chromium aluminum, potassium aluminum. These prevent scratches and abrasions to the emulsion
what will happen to a film if it does not have enough time washing or if there is not enough agitation
Silver stains or a yellowing of the emulsion after a few years will occur
what is the purpose of drying a developed film
drying seals the supercoat
what is the appropriate storage temperature and humidity for films
68degrees F at 30-60% humidity
if a film exits the processor and it is damp what is usually the cause?
depletion or lack of hardener in the fixer or a contaminated wash tank
when starting a fresh tank of developer what is the special starter solution must be added to the replenisher
acetic acid and potassium bromide
if this is not added the images are dark and the sensitometry is not correct
what occurs if the hardener is added to a fixer to quickly
it precipitates sulfur and aluminum causing an insufficient hardener
what is the purpose of agitation
it ensures that the chemicals enter and exit the emulsion
what are the 4 film characteristics that we can measure on a sensitometric curve?
resolution, speed, contrast, latitude
The measurement of the characteristic responses of film to exposure. It is used to evaluate film, exposure systems and processing equipment
sensitometry
what type of relationship exists between the resolution and Crystal size?
inverse
define speed
The amount of density a film produces per exposure
define resolution
the ability to accurately image an object. faster film speeds produce lower resolution
define contrast
The difference between adjacent densities
what relationship exists between contrast and latitude
inverse
what instrument is used to read an exposed and developed film
densitometer
what are the 4 film characteristics that we can measure on a sensitometric curve?
resolution, speed, contrast, latitude
The measurement of the characteristic responses of film to exposure. It is used to evaluate film, exposure systems and processing equipment
sensitometry
what type of relationship exists between the resolution and Crystal size?
inverse
define speed
The amount of density a film produces per exposure
define resolution
the ability to accurately image an object. faster film speeds produce lower resolution
define contrast
The difference between adjacent densities
what relationship exists between contrast and latitude
inverse
what instrument is used to read an exposed and developed film
densitometer
