Geometry of imaging Flashcards
Magnification is based off what two distances?
Target to film - keep as large as possible Object to film - keep as small as possible
Distortion is defined as
Unequal magnification
Penumbra is also known as
Edge gradient or geometric unsharpness
Penumbra is the lease on what side of the x-ray tube?
Width is smallest on the ANODE side
Types of unsharpness?
Geometric
Motion
Absorption
Inverse Square Law
Intensityold/Intensitynew= (Distanceold)2/(Distancenew)2
What size focal spot does magnification radiology need?
Small to reduce geometric unsharpness
Method of measuring Focal spot size?
Slit camera
Method of measuring MTF?
Slit camera
Method of measuring Blooming?
Slit camera
Method of measuring Orientation?
Pinhole
Method of measuring intesity distribution?
Pinhole
Method of measuring resolution?
Star test
Most common type of distribution of focal spot?
Edge band
Three type of intensity distribution for focal spots?
Edge band
Homogeneous
Centerally peaked (Gaussian)
Blooming is?
Changes in focal spot size with variation of technique
Blooming occurs under what conditions?
Focal spot enlarges when mAs (current) is increased
- Way more apparent parallel to tube axis
Focal spot decrease when increasing kVp
Projected focal spot length is shorter on the cathode or anode side?
Anode (heel side)
Area of failure of resolution is when?
cannot distinquish the areas of the star
MTF of focal spot is affected by magnification how?
FS MTF DECREASES with magnification
Intensifying screen MTF is affect by magnification how?
MTF of intensifying screens increase with mag
Motion unsharpness depends on what?
Velocity of motion
Exposure time
Quantum mottle is affect how by magnification?
IT IS NOT AFFECTED!
How to decrease magnification?
Small object to film distance
Large focus to film distance
How to decrease penumbra?
small focal spot
large focus to film distance
small object to film distance
How to decrease motion unsharpness?
short exposure
restraint
