This document discusses factors that cause geometric distortion in medical imaging. It explains that minimizing magnification improves detail visibility and reduces penumbra effect. Thicker objects and those farther from the image receptor experience more object image distance and distortion. Position distortion occurs when overlapping objects have different distances. Keeping the object and image planes parallel prevents distortion. Anatomy imaged off-center is most distorted due to increased beam angle. Foreshortening results when objects are angled toward the central ray, while elongation occurs when the image receptor or object is angled away. To avoid distortion of inclined anatomy, the beam should be angled halfway to the raised side.

1. FUNDAMENTAL
S OF IMAGING
RAD 206
Geometric factors

2. PRACTICE
QUESTIONS
Two erect chest x-ray were
done using AP and PA
techniques,
Estimate distance between
the heart and the back
surface of the patient..
Note:
Direct exposure on film, No
Bucky was used,
SID for erect CXR is 180cm

4. SIZE AND
DISTORTION

6. Umbra
 Minimizing Magnification also improves Detail
Penumbra

10. DISTORTION

11. DISTORTION

12. SHAPE DISTORTION
Depends on
Objects
ThicknessThickness
PositionPosition
ShapeShape

13. OBJECTOBJECT THICKNESSTHICKNESS
Thicker objects
have more OID and
are more distorted
than thinner objects

15. POSITION
DISTORTION
OBJECT POSITIONOBJECT POSITION

16. POSITION
DISTORTION
When we have two
separate objects with
different OID’s ,
when they are
superimposed they
show as one object ,
which produces a
position distortion

17. • If the object plane and the
image plane are Parallel, than
the image is not distorted,
(hence if one of them is not parallel to the
other than the image will be distorted)
• If the CR if Perpendicular the
object plane than the image
should not be distorted

18. Anatomy or objects can cause
considerable distortion when
imaged off central axis ( i.e.
away from the center of the
image)
The further the distance from
the center of the image, the
more is the beam angle, and
the more the distortion,
specially for non-linear or
irregular anatomy

20. Foreshortening :
when the object is
inclined to the Beam
(CR) near the CR axis
, its image looks
shorter

21. Elongation:
a)when the Image
Receptor is inclined to the
CR (object is not
inclined ), or
b)When the Object is
inclined lateral (away)
from the CR axis,
Note: If you continue increasing inclination of the object than foreshortening will occur

22. SHAPE DISTORTION
Foreshortening and elongation of the image

25. How to avoid distortion when the anatomical
body part is inclined such as
The beam should be angled
half the parts angle with IR,
directed towards the raised
side of the part

28. ACTIVITY