Film-Based Dental Radiographic Imaging Flashcards
what are two factors affecting X-ray attenuation?
A. ENERGY OF X RAYS
More energetic photons are more likely to be scattered, or penetrate the matter completely without interacting.
B. IRRADIATED MATTER
- Thickness
- Atomic number
- Density
The thicker the matter, the more x rays are likely to be absorbed or scattered. The greater the atomic number of the matter, the more likely x rays will be absorbed (remember – photoelectric effect). The denser the matter is, the more likely that x rays will be scattered (remember – Compton effect, the MOST COMMON interaction of x rays with matter in the diagnostic energy range).
why are some areas radiolucent and some are radiopaque on xray film?
The remnant x ray beam (i.e. the x ray beam left after interacting with the patient) interacts with the film or image receptor to result in creation of the image. The remnant beam consists of x ray photons that have penetrated the tissues without interacting, and scattered photons.
The portions of the image where a large number of x rays have struck the film/image receptor will be dark, and are called radiolucent– they represent areas where the tissues have attenuated relatively little of the primary x ray beam (the x ray beam leaving the x ray machine, before interaction with the patient’s tissues). The portions of the image where a small number of, or no, x rays have struck the film/image receptor will be white, and are called radiopaque – they represent areas where tissues have attenuated all, or a great deal, of the primary x ray beam. Remember, there are different degrees of radiolucent and radiopaque, due to differences in x ray attenuation.
The xray film packet is light-tight for what? what else is in there?
The x ray film packet is light-tight to prevent inadvertent exposure of the film emulsion to light. The packet contains 1 or 2 films. The films are wrapped in opaque black paper. The packet also contains a sheet of lead foil (we will discuss the reason for this later). For “extraoral” radiographs, the film is enclosed in a light-tight cassette.
Most of the thickness of the x ray film is the plastic base (the base is blue tinted – apparently better for viewing). The emulsion is green in colour. The emulsion is the photosensitive area – it is placed on both sides of the film (this allows an acceptable image to be produced with less radiation than if a film with a single-sided emulsion is used), and is made up of crystals/grains of primarily silver bromide, with small amounts of silver iodide, suspended in a special gelatin. The silver bromide and silver iodide form a three-dimensional “latticework”. Several free silver ions (interstitial silver ions) are present in the space between the crystalline lattice ions. The crystals/grains are chemically sensitized by the addition of trace amount of sulfur compounds that bind to their surfaces, and create what can be termed “sensitivity sites”.
how is the latent image produced?
Note that creation of the latent image sites on the surface of exposed crystals/grains renders the crystals/grains more sensitive to the action of the developer chemical. Also, note that the more silver atoms that are present at the latent image site (i.e. the larger the latent image site), and/or the more latent image sites the crystal/grain has, the more quickly and effectively the developer is able to act on that crystal/grain. Also, the developer chemical will act first on those crystals that have a latent image site.
1 - exposure to x rays; photoelectric and Compton interactions occur
2 - liberated electrons migrate to, and are trapped at, the sensitivity site
3 - silver ions migrate to combine with the electrons at sensitivity site to become
neutral silver atoms
4 - the collection of several silver atoms at the sensitivity site forms what is now the latent image
• hidden or unobservable image in the
emulsion of the exposed film
• formed by the pattern of silver bromide
grains that have a latent image site (small collection of silver atoms) on their surfaces
ONLY grains that were exposed to x rays
will have such latent image sites.
PROCESSING is required to make the latent image a VISIBLE IMAGE.
The silver bromide grains (crystals) that have latent image sites will be MORE SENSITIVE to the action
of the developer than those without latent image sites.
What are the five steps in processing and what is it?
Processing is the series of operations that collectively produce the visible image on the film after the latent image is produced following exposure. Processing may be accomplished by manual or automatic methods. Manual processing is not commonly used any more, but reference to it will be made several times for the purposes of teaching.
The five steps in processing are:
(1) Developing
(2) Rinsing (not done in automatic processing)
(3) Fixing
(4) Washing
(5) Drying
what is the action of the developer?
The action of the developer is reduction of all silver ions in the exposed silver bromide crystals to metallic silver.
Ag+ + e- = Ag (metallic)
what is the ideal development? what are the significant factors in developing?
Ideally, development occurs such that only the crystals that have been exposed to x rays will have their silver ions reduced to silver. Overdevelopment of a correctly exposed film will affect unexposed silver bromide crystals, but only very slowly (see figure 6-3 in White and Pharoah). In such a case, the quality of the final radiograph will definitely be less than optimal, since contrast will be reduced and overall density will be increased, but it may still be clinically acceptable.
The significant factors in developing are time, temperature, and concentration of the developer. An increase in any one of these beyond what is recommended by the manufacturer will result in overdevelopment.
what are the 4 developer solution components?
(all components dissolved in water)
- DEVELOPER
- Activator
- Preservative
- Restrainer
what does the developer do in the developer solution?
Converts exposed silver bromide crystals into metallic silver grains
what does the activator do in the developer solution?
Maintains required alkalinity *Causes swelling of gelatin
what does the preservative do in the developer solution/
- Protects the developing chemicals from oxidation by atmospheric oxygen
- Combines with brown oxidized developer
what does the restrainer do in the developer solution?
Restrains development of unexposed silver bromide crystals
what are the 2 ways that depletion of the developer occurs?
A. By Exhaustion (Weakening) 1. Oxidation 2. Number of films processed 3. Contaminants 4. Accumulation of by- products (O2, H+, Br-)
DEPLETION OF DEVELOPER
B. By Decrease in Volume
Some solution is removed from the tank with each film.
what does replenishment do?
REPLENISHMENT
1. Maintains level of liquid in tank.
.2. Maintains chemical activity of developer.
Should be done before noticeable reduction in quality is noticed - need to have a simple quality control program.
Developer replenisher is a more concentrated developer solution that is used to “top off” the developer tank each day. This maintains the proper level of liquid in the tank, and also maintains the chemical activity of the developer.
Replacement must be done on a regular basis to prevent loss of quality. Under average conditions, solutions should be changed every few weeks. The frequency of change, however, should be determined for each individual office. The office must have some type of quality control program to monitor the quality of the processing. Both developer and fixer should be changed at the same time.
what happens after developing?
rinsing
Rinsing is required to remove or dilute the developer present in the emulsion before the film enters the fixer. Rinsing thus slows the development process, and reduces the amount of developer solution that may be transferred to the fixer tank. Rinsing is generally only a step in manual processing, and is not done in most automatic processors.
