- Unsharpness (penumbra)
- Magnification
- Distortion
X-rays travel in diverging lines, which projects edges of objects farther away from each other. This results in magnification.
Structures have 3 dimensions, but are projected onto a 2 dimensional film/sensor. Different parts of the structure are varying distances, hence magnification is different at each distance distorting image.
Unsharpness (Penumbra)
Unsharpness is minimized by:
- Long source-object distance --longer PID
- Short object-flim distance --place film closer to tooth surface
- Small focal spot --done by manufacturer
- Limiting patient motion
Magnification
Equal Enlargement of all parts of the image.
Magnification is reduced by:
- Long source-object distance --longer PID
- Short object-flim distance --place film closer to tooth surface
- Small focal spot
Distortion
Unequal enlargement of parts of the image. Normal crown to root ratio is 1:2. Distortion appears across all teeth. If patient has naturally long roots then it will appear in only a few teeth.
Reduced by:
- Parallel alignment of teeth and film --film parallel to long axis of tooth
- Perpendicular alignment of beam and teeth/ x-ray is at right angle to film
Summary: Accurate Image Formation
- Long source-object distance --longer PID
- Short object-film distance --place film closer to tooth surface
- Small focal spot
- Perpendicular alignment of beam and teeth/ x-ray is at right angle to film