X-ray beam divergence (diagram)

Case contributed by Andrew Murphy

Original artwork by Andrew Murphy.

Forearm radiograph centered at the midshaft of the radius, great for demonstrating the entirety of the forearm yet not ideal for the wrist or the elbow as seen by the beam divergence.

Correctly centered wrist radiograph with no potential elongation/foreshortening from beam divergence.

Case Discussion

These diagrams demonstrate the impact of the divergent beam on peripheral anatomy. It is occasionally proposed that two forearm projections can be used to exhibit the wrist and elbow joints and hence cancel out any further imaging, yet beam divergence can obscure occult fractures at either end.

When looking for large forearm fractures, two forearm projections are adequate, yet when searching for the subtle pathology of the wrist and/or elbow separate imaging should be requested. 

These diagrams are not to scale, they are a basic portrayal of beam divergence. Pure beam divergence angle can be calculated if you know the diameter of the beam at two points and the distance between those two points.

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Case information

rID: 47215
Published: 4th Aug 2016
Last edited: 14th Aug 2019
Inclusion in quiz mode: Excluded

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