Beam hardening phenomenon refers to the effect of changing the energy of the x-ray beam has on imaging.
An x-ray beam is composed of individual photons with a range of energies. As the beam passes through an object, it becomes "harder" (mean energy increases) because the lower-energy photons are absorbed more rapidly, leaving behind only the high energy photons.
Two types of artifact can result from this effect :
- cupping artifacts
- dark bands or streaks between dense objects in the image.
X rays passing through the middle portion of a uniform cylindrical phantom are hardened more than those passing though the edges because they are passing though more material.
As the beam becomes harder, the rate at which it is attenuated decreases, so the beam is more intense when it reaches the detectors than would be expected if it had not been hardened.
Streaks and dark bands
In very heterogeneous cross sections, dark bands or streaks can appear between two dense objects in an image.
They occur because the portion of the beam that passes through one of the objects at certain tube positions is hardened less than when it passes through both objects at other tube positions.
This type of artifact can occur both in bony regions of the body and in scans where a contrast medium has been used.
Minimising beam hardening
A number of techniques can be used to minimize this effect, including:
- calibration correction
- beam hardening correction software
A flat piece of attenuating, usually metallic material is used to "pre-harden" the beam by filtering out the lower-energy components before it passes through the patient.
An additional "bowtie" filter further hardens the edges of the beam, which will pass through the thinner parts of the patient.
Manufacturers calibrate their scanners using phantoms in a range of sizes. This allows the detectors to be calibrated with compensation tailored for the beam hardening effects of different parts of the patient.
Beam hardening correction software
An iterative correction algorithm may be applied when images of bony regions are being reconstructe (i.e. minimize blurring of the bone–soft tissue interface in brain scans)2,3.
This article is in need of some more references!
You can make a difference to Radiopaedia.org by adding some relevant ones.
- 1. Barrett JF, Keat N. Artifacts in CT: recognition and avoidance. Radiographics. 24 (6): 1679-91. doi:10.1148/rg.246045065 - Pubmed citation
- 2. Van Gompel G, Van Slambrouck K , Defrise M , Batenburg KJ , Sijbers J , Nuyts J (2011). "Iterative correction of beam hardening artifacts in CT". Medical Physics 38 (1): 36-49 doi:10.1118/1.3577758
- 3. Van de Casteele E , Van Dyck D , Sijbers J , Raman E (2004). "A model-based correction method for beam hardening artefacts in X-ray microtomography". Journal of X-ray Science and Technology 12 (1): 43-57
Synonyms & Alternative Spellings
|Synonyms or Alternative Spelling||Include in Listings?|
|Beam hardening artifact||✗|
|Beam hardening phenomena||✗|
|Beam hardening artefact||✗|
|Beam hardening artefacts||✗|
|Beam hardening artifacts||✗|