This document discusses two types of distortion that can occur in radiography: size distortion and shape distortion. Size distortion refers to unequal magnification and is influenced by the object-to-film distance and film-to-focus distance. Shape distortion occurs when there is elongation or foreshortening due to the central ray-part-film alignment. Magnification radiography can be used intentionally to visualize small structures and comes at the cost of increased patient dose. Proper technique such as parallel part-film alignment and perpendicular central ray direction can minimize distortion.

1. Distortion

2. Distortion
 Unequal magnification of different portions
of the same object.
 Two types of distortion:
1.Size distortion
2.Shape distortion

3. Size Distortion
 Refers mispresentation of actual size of the structure as
recorded on the film. Another term for size distortion is
magnification.
 Size distortion influenced by :
a) OFD
b) FFD
 Formula to calculate size distortion

image width
FFD

---------------- = -------
Object width
FOD

4. Example of calculation of the amount
of magnification of an image width,
object width.

5. Magnification resulting from different
OFD

6. Magnification resulting from different
FFD.

7. Minimal Distortion Radiography
 Size Distortion:
 Always place the structure to be examined
as close to the film as possible.
 Use a standardize FFD for all radiographic
procedures. This should be the greatest
distance consistent with the x-ray tube
output and demands of the procedure with
regard to motion control.

8. Size Distortion Used to Advantage
 In angiography to visualize small blood
vessel.
 In macroradiography to visualize early bone
destruction .

9. How is magnification achieved?
 By increasing the distance between the
anatomy to be radiographed and the image
receptor (OID)

10. Magnification Radiography
 Can be intentional or unintentional
 Unintentional:
– Occurs when the film cannot be placed near the body part being
radiographed
 Intentional Uses
–
–
–
–
Vascular imaging
Neuroradiology
Orthopedics
Mammography

11. The Magnification Factor
 The means of determining how much the
image will be magnified
 Magnification = SID/SOD or SID/SID - OID

12. Technical Requirements for
Magnification
 A small focal spot must be used
– App. 0.3mm or less
 Grids are not necessary as the increased
OID utilizes the air gap technique
 Low mA must be used

13. Disadvantages of Magnification
Radiography
 Patient dose is increased
 To obtain a magnification factor of 2, the
patient must be placed halfway between the
film and tube
 A magnification factor of 2 increases patient
dose by a factor of 4

14. Macroradiograph of hand-wrist phantom: magnification factor of 2; angle of 10°;
long axis of trabecular pattern at 90° to cathode–anode axis (fingers pointing at
90° to cathode–anode axis); measured positional-dependent effective focal spot
size of
0.14 mm.

15. Macroradiograph of hand-wrist phantom: magnification factor of 2; angle of 0°;
measured positional-dependent effective focal spot size of 0.76 mm.

16. Macroradiograph of hand-wrist phantom: magnification factor of 2;
angle of -10°; long axis of trabecular pattern at 90° to cathode–anode
axis (fingers pointing at 90° to cathode–anode axis); measured
positional-dependent effective focal spot size of 0.14 mm.

17. Shape Distortion
 Often referred to a true distortion, caused
by elongation or foreshortening in
radiographic image.
 Shape distortion influenced by:
 (a) Part- film relationship.
 (b) Central ray- part-film alignment.
 (c) Central ray direction.

18. Examples of incorrect (non-parallel) and correct
(parallel) relationship of structure/ plane of the
interest to the of the film.

19. Examples of good (centered) and poor (off-center)
alignment of the central ray, the body part, and the
film.

20. Examples of proper (left) and improper (right)
direction of the central ray alignment to the structure/
plane of interest.

21. Scapular images (a) free from distortion, (b)
with elongation, (c) with shorten
(a)
(b)
(c)

22. Shape Distortion Used to advantage
 To avoid superimposition.
 To demonstrate anatomy.

23. Examples of arrangement of central ray-part-film relationship
to produce distortion that (a) avoid superimposition and (b)
demonstrates anatomy.

24. Minimal Shape Distortion
 Place the body part to be examined in a
parallel relationship with the film surface
whenever possible.
 The central ray should passed through the
midpoint of structure to be examined.
 The central ray must be directed at right
angles (perpendicular) to the long axis of
the structure.

25. THANKS