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Distortion
geometric property that affects the quality of the image.
Misrepresentation of the size/shape of the structures being examined.
Shape distortion
misrepresentation by unequal magnification of the actual shape of the structure being examined.
Size Distortion
can only be magnification in x-ray
what is size distortion controlled by?
OID and SID
Controlled by positioning the body part and the tube to maximize SID and minimize OID
Reduced magnification size distortion __________ spatial resolution
increases
SID =
SOD + OID
What kinda relationship does SID and magnification have?
inverse relationship
What kinda relationship does OID and magnification have?
direct
As OID __________, magnification _____________
increases, increases
Ways to decrease size distortion
increase SID
decrease OID
decrease patient thickness
ways to increase size distortion
decrease SID
increase OID
increase patient thickness
shape distortion increases when
Improper CR alignment
Improper anatomical part alignment
Improper receptor alignment
Improper direction of CR angle
Improper degree of CR angle
What is elongation?
It projects the object so it appears to be longer than it really is.
When does elongation occur?
When the TUBE or CR is at an angle.
What is foreshortening?
Foreshortening projects the object so it appears shorter than it really is.
When does foreshortening occur?
Foreshortening occurs when the object is at an angle and the CR is perpendicular to the IR.
Magnification factor =
SID / SOD
Object Size
Image size / magnification factor
Shape distortion can be caused or avoided by:
Careful alignment of the CR with the anatomical part and the IR
Part and IR must be parallel
Whenever the CR is not perpendicular, some degree of shape distortion will occur.
Spatial Distortion happens when
happens when CR is at an angle but the object and IR are parallel to each other
Angulation
refers to the direction and degree the tube is moved from its normal position perpendicular to the IR
most common tube angle
longitudinal
direction of tube angle must be __________ when patient position is reversed
reversed