Shape distortion in Radiography (Foreshortening and Elongation)

Foreshortening and elongation are shape distortions which occur in projection radiography. In foreshortening the anatomy of interest is not perpendicular to the iso-ray and appears shorter on the image receptor. In addition the changes in magnification leads to different shape distortion between the different sides of a bone.
Elongation occurs when the image receptor is not perpendicular to the iso-ray. Elongation results in an elongation or stretching of the projection of the anatomy on the image receptor.
For more information on the physics of x-ray and CT imaging see our site:
howradiologyworks.com .
Chapters:
00:00 Intro are these the same bone?
00:30. Correct x-ray positioning to avoid shape distortion.
01:42. Foreshortening in radiography.
03:15. Comparison of foreshortening and correct x-ray images.
04:00. Elongation in radiography
05:15 Is there foreshortening or elongation in Computed Tomography?

[@talkingtreeswithprofessort8372]

Halloween shirt? 🎃 Another great video, I really learned a lot. We don't have these issues in CT!

[@TheNettforce]

Thanks Prof Tim. Yeah CT takes off some of the pressure on positioning for ideal angles.

[@HowRadiologyWorks]

And yes that is a thrift store shirt

[@DamienMearns]

In your "ideal situation" there is still distortion, not just magnification - if you put notches evenly along the actual bone then the X-ray would show those notches being further away from each other, the further away from the centre of the bone they are

[@HowRadiologyWorks]

Thanks Damien that is right when things are magnified with a divergent beam, ie one that spreads out the magnification is more towards the outside

[@raihannordin1070]

what happens if the beam is rotated but the anatomy of interest is perpendicular to the image receptor? E.g Long view Radiography using rotation method.

[@HowRadiologyWorks]

Yes there is an effect of the angle difference between two neighboring acquisitions on a Longview system that uses rotation of the X-ray beam. There is typically overlap and blending at the seam on those systems . You can see this if you scan an X-ray ruler.www.shimadzu.com/med/sites/shimadzu.com.med/files/literature/fluoro/k25cur0000003yfx-att/od0gjn0000001qnm.pdf

[@neodemo7465]

Yes, but does beam angulation foreshorten or elongate the part?

[@raihannordin1070]

@@neodemo7465 That’s exactly what I was thinking!