Geometry Flashcards
Name the 3 types of Unsharpness
Geometric Unsharpness (Ug) Movement Unsharpness (Um) Photographic Unsharpness (Up)
Name the 3 causes of Geometric unsharpness
Focal spot size
Object – Image Receptor distance
Source (focus) – Image Receptor distance
What is Penumbra?
A region of partial shadow around the image where the image is not sharp
What is the Real / Actual focus?
The electron beam from the source
What is the Apparent / Effective focus?
The main x-ray beam coming off the anode
What focal spot size does the Fine focus have?
0.6mm^2
What focal spot size does the Broad focus have?
1.2mm^2
What focal spot size has the largest penumbra?
Broad focus / 1.2mm^2
What 3 things increases Geometric unsharpness?
Larger focal spot size
Larger Object – Image Recepter (film) distance
Smaller Source – Image Recepter (film) distance
Name the 3 causes of Movement Unsharpness
Patient movement
Tube movement
Image receptor movement
What 3 things minimise Movement unsharpness?
Minimise patient movement
Use shortest exposure time to reduce tube movement
Ensure no movement of tube or receptor
Name the 4 causes of Photographic Unsharpness
The size of silver halide crystals in any film media
The size of phosphor crystals in intensifying screens
The resolution of the computerised image recording
system
The size of pixels on a TV monitor
How is Total Unsharpness calculated?
Ug + Um + Up = Total unsharpness
Name the 2 types of Image distortion
Size distortion (magnification) Shape distortion
What is Foreshortening?
The image is shorter than the original on the recpetor due to object changing position
