What causes the streaks in a CT scan when a metal object is present?

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SUMMARY

The presence of a metal object near a CT scanner causes streak artifacts due to x-ray scattering and reflection. This phenomenon is a result of the mathematical reconstruction process, where multiple projection x-rays are taken around a circle to separate overlapping anatomical structures. However, due to the finite number of projections and resolution, a point spread function emerges, leading to visible streaks, particularly pronounced with bright objects like metal. Understanding this effect is crucial for accurate image interpretation in medical imaging.

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  • Understanding of CT imaging principles
  • Familiarity with x-ray physics and scattering
  • Knowledge of mathematical reconstruction techniques in imaging
  • Awareness of point spread function concepts
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  • Research the effects of metal artifacts in CT imaging
  • Study mathematical reconstruction algorithms used in CT scans
  • Explore techniques to mitigate streak artifacts in medical imaging
  • Learn about the role of point spread function in image quality
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Radiologists, medical imaging technicians, and researchers in the field of diagnostic imaging will benefit from this discussion, particularly those focused on improving image quality and understanding artifact causes in CT scans.

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What exactly causes it when a metal object is placed near the scanner?
 
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Perhaps the x-rays are reflecting/scattering off of the metal?
See 'scatter" on page 7: http://www.glidewelldental.com/downloads/dentist/services/nobel-guide-glossary.pdf
 
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It is part of the math of the reconstruction. When you take an x-ray you get everything on top of each other in a single projection, so in a chest x-ray you see the spine and the ribs and the lungs all on top of each other. A CT works by taking a bunch of projection x-rays all around a circle and then mathematically untangling them so that the ribs are separate from the spine and the lung etc.

If you acquired an infinite number of projections, each with infinite resolution, then you could reconstruct the image exactly, but since it is finite you get what is called a point spread function. The point spread function has "streaks" in it which become visible for very bright objects, like metal.
 

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