Banding Artifacts

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. Built-in Features for Minimizing Beam Hardening.—Manufacturers minimize beam hardening by using filtration, calibration correction,
and beam hardening correction software.
Filtration: 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. Calibration correction: 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 reconstructed. This helps minimize blurring of the bone–soft tissue interface in brain scans and also reduces the appearance of dark bands in nonhomogeneous cross sections (Fig a-b)
Banding artifact:

Cause
Effective energy is shifted to higher value as the X-rays pass through an object
Correction
• Prefilter the X-ray beam near the focus
• Avoid highly absorbing bony regions
• Algorithms