What Is Fog In Radiographic Film ?
Fog in radiographic film is a term used to describe the appearance of radiograph (x-ray image ) that has a hazy or diffuse appearance, rather than being sharp and clear. The fog is grayness of film of varying grades from grey colour to complete blackness of density. If the fog level is very high, the film have less contrast and the low density areas in the image will merge with fog. This may be general mature involving the entire film surface on one side or may be both side. Fog May occur some particular area of film.
The cause of fog In Radiographic Film are:-
1) Chemical fog.
2) Age fog.
3) Safe light fog.
4) Radiation fog.
5) Oxidation fog.
6) Backscatter fog.
7) Colour fog.
8) Edge fog
1) Chemical fog:- The chemical fog occurs during developing time at following conditions.
– Fault mixed of developing solution.
– High temperature of developing solution.
– Contaminated developing solution.
– Dirty film hangers.
– Maximum time take for film developer.
2) Age fog:- The age fog occurs when the film are to old.
3) Safe light fog:-
– The film exposed too long time in safe light.
– The safe light with cracks or peeling or bleaching of filter glass colour if present.
– if the safelight bulb more than 15 watts.
4) Radiation fog:- Films are fogged by exposure to x-ray or gamma rays due to inadequate protection of film in the x-ray room.
5) Oxidation fog:-The oxidation fog occurs, the emulsion is affected by air, through inspecting the film too frequently and too long during development.
6) Backscatter fog:- The Backscatter fog occurs when the scattered radiation through the under layer when using non screen film.
7) Colour fog:-The colour fog occurs when interaction of developer and fixer due to insufficient rinsing and or old fixer.
8) Edge fog:- Edge fog occurs when the cassette are not closing properly. The light leaks into cassette.
FAQs
Q. What causes fog on a radiograph?
Fog can be caused by chemical reactions forming catalytic development centers in the emulsion layer, by unwanted exposure to radiation, or by the attack of the developer on silver halide crystals lacking catalytic development centers.
Q. What factor causes film fog?
Fogging may be due to many factors, including improper film storage conditions, accidental exposure to ionizing radiation, improper processing, or using film kept past its expiration date
Q. How can we prevent fog in radiography?
Fog can prevent by overcome by identifying and eliminating sources of fog, such as incorrect safelight filters, excessive safelight wattage, using too many safelights or placing them too close to the work area, light leaks, and indicator lights on telephones, silver recovery units, timers, or other electrical devices.
Q. What is fog density in film?
The optical density of a processed film caused by anything other than the direct action of image – forming radiation. It can be aging fog, chemical fog, dichroic fog, exposure fog or inherent fog.
Q. What is the effect of fog on image contrast?
The effect of fog is decrease the image contrast.
Book link:- Textbook of Radiology for X-ray, CT, MRI, BSc, BRIT and MSc Technicians