Radiographic distortion can be size-based or shape-based. Size distortion relates to magnification and is affected by object-to-image distance (OID) and source-to-image distance (SID), with shorter OID and longer SID reducing magnification. Shape distortion alters the true shape and can involve elongation from non-perpendicular alignment of the central ray, anatomical part, and image receptor, or foreshortening from non-parallel alignment of the part and receptor. Proper alignment minimizes shape distortion.

1. Radiographic DistortionRadiographic Distortion
Principles of Radiographic Imaging

2. ObjectivesObjectives
• Define Radiographic Distortion
• Differentiate between Size and Shape Distortion
• Summarize and analyze the relationship of factors that
control and affect distortion.
• Perform calculations to determine image magnification
and percent magnification.
• Explain the effects SID and OID have on image
distortion
• Discuss various methods of minimizing distortion
• Explain elongation and foreshortening
• Describe the routine relationships between central ray,
anatomical part, and image receptor
•

3. Geometric Properties
Sharpness
Recorded Detail Distortion
Size Shape
Receptor
Unsharpness
Geometric
Unsharpness
Motion
Unsharpness

4. Assessing Radiographic DistortionAssessing Radiographic Distortion
• Radiographic misrepresentation of either
the size or shape of the anatomic part is
called distortion
• 2 Types of Distortion
DISTORTION
SIZE SHAPE

5. Factors Affecting Distortion

6. Size Distortion - Magnification
• An increase in the object’s image size
compared with its true, or actual size
• There is a percentage of magnificationmagnification in
every radiographic image
• As the percentage of magnificationmagnification
increasesincreases, the level of geometric
unsharpnessunsharpness also increasesincreases

7. Influences of Size DistortionInfluences of Size Distortion
• Size distortion is influenced by
• OID and SIDOID and SID
– Object-to-Image DistanceObject-to-Image Distance
– Source-to-Image DistanceSource-to-Image Distance

8. OIDOID
Shadow
OID has aOID has a direct relationshipdirect relationship with size distortionwith size distortion
As OID increases, size distortion/magnification increases
As OID decreases, size distortion/magnification decreases

10. A
B
• SID has anSID has an inverse relationshipinverse relationship withwith
size distortionsize distortion
• A long SID produces less size
distortion
• A short SID produces more size
distortion
With a long SID the beam is more
perpendicular creating less of a
divergence
SIDSID

11. Lab DemonstrationsLab Demonstrations

12. Interactive ReviewInteractive Review
• Interactive Online Reviews
– Plickers
– Quizstar
– Qzzr
• Group/Team Work

13. Calculating Size Distortion
• Magnification Factor
– indicates how much size distortion is
demonstrated on a radiograph
• MF = SID / SOD
Source-to-Image Distance
----------------------------------------
Source-to-Object Distance
• If SOD is unknown
–SID - OID
M
SID
SOD

14. Calculating MF
• Examples

15. Calculating Size Distortion
•MF = I / O
•If Object Size is unknown
•Object Size = Image size / MF
O
I
M

16. Calculating MF
• Examples

17. If….Then…
M
SID
SOD
O
I
M
• If…
• MF = SID / SODMF = SID / SOD
• And…
• MF = Image Size / Object SizMF = Image Size / Object Siz
• Then…
• SID / SOD = IS / OSSID / SOD = IS / OS

18. Calculating MF
• Examples

19. Assessing Radiographic DistortionAssessing Radiographic Distortion
• 2 Types of Distortion
DISTORTION
SIZE SHAPE

20. Shape Distortion
• True Distortion
• Produces a true perversion of the structures
of interest that can make the recorded image
unrecognizable from the original structures
of interest

21. Shape Distortion
• Two Types:
– ElongationElongation
– ForeshorteningForeshortening
• Due to:
– AlignmentAlignment
• Central rayCentral ray
• Anatomical partAnatomical part
• Image receptorImage receptor
– AngulationAngulation
• DegreeDegree
• DirectionDirection

22. Shape Distortion
• ElongationElongation refers to
images of objects that
appear longer than the
true object
• ForeshorteningForeshortening refers to
images that appear shorter
than the true objects

23. ElongationElongation
Shape distortion resulting from improper
alignment of the Image Receptor

24. ElongationElongation
Shape distortion resulting from
improper alignment of the x-ray
tube (CR)

25. ForeshorteningForeshortening
Shape distortion resulting from improper
alignment of the part

26. The Affects of Distortion
Take a close look at this
illustration. Do you see
how the bone ends at the
fracture site look a little
different in each
radiograph? These
different views result from
differences in the
alignment of the CR, bone,
and IR.

27. A simple fracture may
go undetected due to
shape distortion

28. Lab DemonstrationsLab Demonstrations

29. Minimizing Shape Distortion
• X-ray tube alignment (CR)
– Perpendicular to Part and IR
– *Elongation
• Image Receptor alignment
– Parallel to Part
– *If the IR is the piece un-aligned
– (CR and part still perpendicular)
– *Elongation
• Part alignment
– Parallel to IR
– *If the Part is the piece un-aligned
– (CR and IR still perpendicular)
– *Foreshortening

30. Interactive ReviewInteractive Review
• Interactive Online Reviews
– Plickers
– Quizstar
– Qzzr
• Group/Team Work

31. SUMMARY
• Size Distortion
– OID
• Shortest OID
– SID
• Longest SID
• Shape Distortion
– Alignment and Angulation
• Elongation
– CR, IR, and Part Perpendicular
• Foreshortening
– Part and IR Parallel