midterms Flashcards
(49 cards)
Cassettes may vary because of screens of different manufacture, age, or front panel materials. If there is any doubt or question as to the equality of radiographic speeds among cassettes or screens, the following simple test should be performed.
Test for Assessing the Speed of Film and Film-Screen Combination
Equipment: Speed of Film and Film-Screen Combination
- cassettes (of the same size)
- Unexposed films
- Densitometer
Procedure
- Procedure: Place no more than four cassettes, preferably all the same size, on the x-ray table with the corners touching.
- One of the four should be a known standard cassette/screen combination.
- All cassettes should be loaded with film from the same box.
- The x-ray tube is centered perpendicular to the intersection of the four cassettes and an exposure made which will produce a film density between ____
0.8 to 1.5
Evaluation
- For the speed test, compare the resulting densities on the four processed test films close to the central ray.
- Visual densities should be the same.
- If a densitometer is used to compare densities the maximum density variation should be ____
plus or minus 0.2
The light-tightness of the darkroom is important because a non-insulated darkroom can ruin all the films in a department or significantly degrade their quality.
Test for DR Fog and Safelight
Possible Sources of DR fog
- Safelight filters (old or compromised)
- Safelight housing
- Safelight too close to work area
- Light bulb of incorrect wattage or type
- Ancillary indicator lights on processor
- Timers
- Radios
- Fluorescent light afterglow
- Light leaks
- Suspended ceilings
- Any place there is a hole cut in the wall
- Excessive ambient light through the tinted viewing windows of daylight loading systems
Frequency: Test for DR Fog and Safelight
- Semi-annually
- When a fault in the light-tightness of the darkroom is suspected.
- After a bulb or filter replacement
- After changing or adding types of film
Equipment: Test for DR Fog and Safelight
- most sensitive film available (the film with the highest speed)
- Cardboard box
- Six coins
- Watch
- Lead sheet
Visual inspection:
- Step into the darkroom.
- Shade the windows, if any, and make the darkroom light-tight as usual.
- Turn off all the lights in the darkroom, including the safelight.
- Allow sufficient time (approximately ____) for your eyes to adjust to the low light conditions.
- Check for any spots letting white light into the room through the doors, processor, film exchange boxes, extractors or ceiling.
5 min
Qualitative Measurement
- Load a film into a cassette.
- Always use a new package of films because a package opened earlier may be already foggy.
- Expose half of the film to x-rays, choosing exposure settings to obtain an optical density of ___
- The other half of the film may either be covered by a lead sheet or the film could be cut into half to observe the differences.
- Place the sensitized film on a workbench in the darkroom.
1 (sensitization exposure)
Next Procedure
- Place the six coins at approximately the same distance from each other along the longer side of the film.
- Use cardboard to cover the area of the film containing five of the coins. Wait for ___ and move the cardboard to reveal one more coin.
- Repeat until the film and all coins are completely uncovered.
- When the last ___ have elapsed and none of the coins is covered, process the film.
- Repeat steps (1 to 6) to test with any safelight illumination used.
30 s
Baseline Tolerances: Test for DR Fog and Safelight
No coins should be visible on the film
Corrective Actions: Test for DR Fog and Safelight
- The darkroom should be insulated against stray light and the safelight should be checked to ensure that it is not leaking white light.
- If needed, replace the filter of the safelight and check the power rating of the bulbs
Film should only be handled in correct safelight conditions. White light should not be allowed to leak into the darkroom.
White Light Fogging Test
Frequency of White Light Fogging Test
- Semi-annually
- As needed
Equipment: White Light Fogging Test
- 1 unexposed film
- 1 cardboard (same size with the film)
Procedure White Light Fogging
- Turn on all the lights in areas adjacent to darkroom.
- Switch off darkroom lights including safelights.
- Ensure that any doors are closed.
- Place the sheet of film on the workbench.
- Cover half of the film with the sheet of card.
- Leave for ___. Process the film.
3 minutes
Evaluation: White Light Fogging Test
- If the density of the uncovered part of the film is greater than the covered part, then some fogging has occurred.
Action: White Light Fogging Test
- Seal any areas of light leakage.
- Repeat the white light leakage test. File a report.
A darkroom should be fitted with appropriate safelighting.
Safelight Efficiency Test
Frequency: Safelight Efficiency Test
Semi-annually or annually
Equipment: Safelight Efficiency Test
- 1 unexposed film
- 2 cardboards (same size with the film)
- Timer
- 1 sheet of lead or lead rubber (same size)
Procedure: Safelight Efficiency Test
- Place cassette face up on the X-ray
table.
- Set a FFD (SID) of ___. Cover one third of the cassette with lead rubber, lengthways (area C).
- Collimate to the uncovered area of the cassette.
- Expose the film using a minimum exposure (suggested exposure ____.)
100 cm
45 kV 2 mAs
Procedure: Safelight Efficiency Test
- Unload the cassette in the darkroom in total darkness.
- Place the film on the workbench.
- Cover one third of the exposed side of the film with the sheet of card, lengthways (area A).
- Cover areas B and C of the film, horizontally, with the second sheet of card, except for a ___ strip at the top.
3cm
