Distortion

Size distortion

magnification, present in any radiographic image and can be calculated

• you always have this

Shape distortion

misrepresentation by unequal magnification of the actual shape of the structure being examined

cephalad

toward head

caudal

toward feet

mag factor = (image and object)

image width/ object width

mag factor = (SID and SOD)

SID-OID

Advanced magnification formula

Image/Object = SID/SOD

more blurry means

less spatial resolution

• larger number means more blurry which means the image is worse

image contrast is decided by

the look up table (picking oblique ankle for an ankle and not a spine)

Digital image resolution is determined by

• matrix size

• pixel size

• gray bit depth

Digital imaging requires that spatial resolution frequency signal be sampled __ from each cycle

twice

• the image is run 2 times the machine before you see the image

shape distortion

misrepresentation by unequal magnification of the actual shape of the object being examined

unit of resolution

line pairs per millimeters

poor resolution names

• blur

• penumbra

resolution improved

• decrease in OID

• increase in SID

slow film screen

• increases resolution

• increase patient dose

size distortion in radiography

only magnification

• controlled by

  • SID

  • OID

  • radiographic distances

part is improperly aligned

foreshortening

• part is closer to tube

tube or image receptor is not properly aligned

elongation

• part is farther from tube

What is spatial resolution?

the ability to distinctly define one object from another

SID and spatial resolution

more SID = more spatial resolution

OID and spatial resolution

more OID = less spatial resolution

focal spot size and spatial resolution

increase in focal spot size = decrease spatial resolution