Lesson 6 Distortion Flashcards

Magnification (minification is not possible in x-ray due to beam divergence)

Misrepresentation of the shape of an object by either foreshortening or elongation

Magnification is controlled by radiographic distances:  SID and OID.  Increasing OID = Increase in magnification while increasing SID = decrease in magnification.  Exams with natural OID (i.e. lat c-spine) can use longer SID to compensate.  Lowest magnification = highest SID, lowest OID

An increase in OID = Increase in magnification due to beam divergence

An increase in SID = Decrease in magnification due to beam divergence.  You use less of the divergent beam to image with higher SID

Occurs when beam is angled or the plate is angled out of the plane of alignment

Occurs when the part is out of the plane of alignment

The x-ray tube should be perpendicular to the part and IR.  The part and IR should be parallel

Angles must be switched when moving from AP to PA to preserve them.  For example, AP oblique cspine uses a cephalic angle, PA obliques use a caudal angle.  This preserves the angle and creates the same image.

Found by dividing:  SID/SOD

Due to beam divergence, objects will always appear larger to some degree.  We minimize this by putting the part of interest closest to the IR (i.e. heart in a PA chest).