beam geometry Flashcards
what is magnification caused by
the duverging beam (form isotropic emission)
what is magnification affected by
SID, SOD/OID
what is the magnification factor
how much larger the object appears in the image
what is the formula for magnification factor
SID/SOD
how can you reduce magnification
increase SID
decrease OID (better)
when is magnification helpful
sometimes can be used to increase object size
what is distortion
unequal magnification of an object
what are the 2 types of distortion
elongation
foreshortening
what affects distortion
SIDm OID, object position, object thickness
how does foreshortening happen
IR is flat, but the object is angled
how does elongation happen
object is parallel to IR, CR is angled
CR is perpendicular, but the IR is angled
how is distortion used to our advantage
bisecting angle method and superimposition reduction
what is the bisecting angle method
reduces the distortion on naturally angled bones
what angle is used for the bisecting angle method
angle of CR to IR = 1/2 angle of object to IR
what causes focal spot blur
diverging beam and multiple point sources