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  The problem of metal 

  and high-density objects 

Metallic materials such as protheses, dental fillings, surgical clips, and electrodes produce streak and star pattern artifacts in the CT image. In medical applications they usually appear together. Streaks across the image are typically caused by patient motion and/or small errors of scanner geometry parameters. Streaking may be absent for stationary objects.

 

Streak And Metal Artifact Reduction Algorithm. The metal coil on the blood vessel. Input radiograph.

Metal coil, aneurysma and blood vessel. Input radiograph. 

Streak And Metal Artifact Reduction Algorithm.The metal coil on the blood vessel. Reconstructed slice

CT reconstruction. Note star pattern and streaks.

Streak And Metal Artifact Reduction Algorithm.Star-patterns artifacts

Slice image of metal screws in cadaver. Note star-pattern artifacts without high spatial frequency streaks.

  SAMARA: Streak And Metal  

  Artifact Reduction Algorithm  

Exxim has developed and implemented an iterative  algorithm for 3D reconstruction, which is more tolerant against input data imperfections than the standard Feldkamp method. Such data imperfections can have any nature, e.g. absorption non-linearities or scanner geometry misalignment. One possible field of application for the method is metal artifact reduction.  

SAMARA technology is available as an option 

in COBRA starting version 4 

Exxim's  Streak And Metal Artifact Reduction Algorithm (SAMARA) preserves image details close to the metal and compensates high-density non-linearities 

Several methods have been invented to remove the artifacts coming from metal. The most popular and well known technique is based on threshold values to define (and replace by interpolation) erroneous pixels before image reconstruction. In practice, because of  object motion (blood pulse, breathing, etc.) such an approach subjects too much area to interpolation. Additionally, in many cases (like in the "coil" case we use for illustrating  SAMARA technology) the metal or high-density objects do not block the signal completely. In spite of the non-linearities, the high frequency and low/medium contrast details are still observable in the SAMARA reconstructed slices (blood vessel close to the coil ). In contrast, the interpolation technique typically is "smoothing out" everything close to the metal. SAMARA technology (available as an option in COBRA starting version 4) provides significant reduction in non-linear image distortion preserving image details close to the metal.

 

Streak And Metal Artifact Reduction Algorithm.Reconstructed slice

Metal coil and blood vessel. Reconstructed CT slice.

Streak And Metal Artifact Reduction Algorithm.Using typical MAR interpolation technique

Metal coil and blood vessel, using a typical MAR interpolation technique. The details close to the metal coil are lost.

Streak And Metal Artifact Reduction Algorithm.SAMARA (Streak And Metal Artifact Reduction Algorithm) preserves image  details.

Metal coil and blood vessel. SAMARA (Streak And Metal Artifact Reduction Algorithm) preserves image  details close to the metal and compensates high-density non-linearities (star-pattern artifacts). 

 

 Visit the GALLERY to see more examples

 

 

 

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