Film-Based Dental Radiographic Imaging Flashcards Preview

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Flashcards in Film-Based Dental Radiographic Imaging Deck (30):

what are two factors affecting X-ray attenuation?

More energetic photons are more likely to be scattered, or penetrate the matter completely without interacting.

1. Thickness
2. Atomic number
3. 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)

2. Activator
3. Preservative
4. 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-
(O2, H+, Br-)

B. By Decrease in Volume
Some solution is removed from the tank with each film.


what does replenishment do?

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 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.


what occurs after rinsing?

The fixer removes (dissolves) undeveloped silver halide crystals from the emulsion. Its secondary function is to harden or fix the emulsion that became swollen and softened when it was immersed into the developer.
silver bromide + ammonium thiosulfate = silver thiosulfate complex (water soluble) + sodium bromide
In manual processing, fixing should be done for twice the developing time.
Replenishment of the fixer solution maintains its chemical activity and prolongs its life. Replacement should be performed at the same time the developer is changed.


what is the fixer solution components (4)?

FIXER SOLUTION COMPONENTS (all components dissolved in water)
2. Acidifier
3. Preservative
4. Hardener


what does the clearing agent do in the fixer solution?

*Dissolves and removes unexposed silver bromide grains*
- ammonium thiosulfate


what does the acidifier do in the fixer solution?

*Maintains required acidity to keep fixer pH constant
*Inactivates developing agents remaining in the emulsion*
- acetic acid


what does the preservative do in the fixer solution?

*Prevents oxidation of the thiosulfate clearing agent
*Binds with any remaining coloured oxidized developer*
- sodium (or ammonium) sulfite


what does the hardener do in the fixer solution?

*Complexes with gelatin and prevents damage during handling
*Reduces swelling of emulsion during washing
•Prevents mechanical damage (e.g. scratching) •Limits water absorption to reduce drying time


what does replenishment of the fixer solution do?

Replenishment of the fixer solution maintains its chemical activity and prolongs its life. Replacement should be performed at the same time the developer is changed.

•Should be done before noticeable
reduction in quality is noticed
•Need to have a simple quality control program
•Replace both developer and fixer
at same time


what happens if a film is inadequately fixed?

there may be:
1. Inadequate hardening of emulsion (greater possibility of physical damage e.g. scratching).
2. Slower drying of the emulsion (emulsion not shrunk adequately)
3. Possible loss of permanence of image. (unexposed crystals may slowly be reduced)
4. Obscuring/”clouding” of the image (due to presence of unexposed crystals)

if there is fixer chemical remaining in the emulsion then the image can get washed away


what if the film is in the fixer for an unusually long period of time?

Prolonged fixing (not a common problem) may result in:
1. Loss of density of the image (silver grains will slowly be dissolved by the acetic acid in the fixing solution)
2. Brown staining (if thiosulfate becomes bound to the emulsion, it may ultimately react with silver to produce silver sulfide which is brown)

NOTE: Exposed film, once removed from its covering or cassette, MUST remain in the dark or in proper “safelight” conditions until FIXING is completed. WHY?
because the silver has been exposed and converted to silver bromide and so it would end up black on the image.


what happens after fixing?


This is done to assure removal of all processing chemicals remaining on or in the emulsion. Inadequate washing will lead to staining of the final radiograph; silver compounds may stain the radiopaque (white) areas, and residual thiosulfate may ultimately lead to formation of silver sulfide (brownish stain


what happens after washing?


Ideally, the radiographs should be dry before they are interpreted. The emulsion in dry films is thinner, and there is less distortion in the image. As well, a wet emulsion is soft and easy to damage, so handling and transferring wet films may result in scratches, gouges, dust and hair adherence, etc. if they are dropped or otherwise mishandled.


what are then the 5 steps of manual processing?

1. Developing (approx. 5 minutes)
2. Rinsing (20 - 30 seconds)
3. Fixing (approx. 10 minutes)
4. Washing (15-30 minutes)
5. Drying (??)

you could look at the film once the fixing was completed but it still needed to be washed and dried but you could at least look at it to see how it was.


what were automatic processing solutions for?

• modified to operate more rapidly, and at higher
• fixer has an additional hardener

these rollers operate at a specified speed so that the film will be in contact with the solution for a certain amount of time, so the solution level or amount needs to be kept constant. The temperature also had to be very constant.


what are four advantages of automatic processing?

1. The overall processing time is greatly shortened
2. More constant end results are obtained (assuming the machine is maintained properly and the solutions are at optimal strength)
3. The need for a sink with developer and fixer tanks in a darkroom is eliminated
4. If a daylight loader is used with the processor, the need for a separate darkroom to process films is also eliminated


what are the 4 disadvantages of automatic processing?

1. Greater cost than manual processing equipment
2. Need for regular and stringent maintenance procedures to maintain quality
3. Improper maintenance may reduce quality
4. No "back-up" if mechanical problems occur

As with manual solutions, automatic processor solutions must be replenished on a regular basis. In automatic processing, replenishment of the developer (and fixer) chemicals will usually occur automatically (a small amount of chemical is pumped into the tank when a film is placed into the machine). Also, as with manual processing, automatic processing chemicals must be replaced before a reduction in radiographic quality is evident. Again, a quality control program is essential.