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A pragmatic approach to metal artifact reduction in CT: merging of metal artifact reduced images

Abstract

The purpose of this study was to improve metal artifact reduction (MAR) in X-ray computed tomography (CT) by the combination of two artifact reduction methods. The presented method constitutes an image-based weighted superposition of images processed with two known methods for MAR: linear interpolation of reprojected metal traces (LI) and multi-dimensional adaptive filtering of the raw data (MAF). Two weighting concepts were realized that take into account mean distances of image points from metal objects or additional directional components. Artifact reduction on patient data from the jaw and the hip region shows that although the application of only one of the MAR algorithms can already improve image quality, these methods have specific drawbacks. While MAF does not correct corrupted CT values, LI often introduces secondary artifacts. The corrective impact of the merging algorithm is almost always superior to the application of only one of the methods. The results obtained with directional weighting are equal to or in many cases better than those of the distance weighting scheme. Merging combines the advantages of two fundamentally different approaches to artifact reduction and can improve the quality of images that are affected by metal artifacts.

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Abbreviations

LI:

linear interpolation algorithm

MAF:

multi-dimensional adaptive filtering algorithm

MAR:

metal artifact reduction

f(x, y):

object function at (x, y)

F(ϑ), F(ξ):

normalized filter function in the direction of the coordinates ϑ and ξ

I :

primary X-ray intensity

I 0 :

transmitted X-ray intensity

N D :

number of detectors per detector row

p :

attenuation

p(β,α), p(ϑ,ξ):

projection data (fan and parallel geometry)

p th :

lower threshold of the attenuation of adaptive filtering

p max :

maximum value of the attenuation of adaptive filtering

(x, y):

image point

α :

projection angle in fan geometry

β :

angle within the fan relative to the central ray

Δα, Δβ, Δz, Δϑ, Δξ :

minimum functions for adaptive filtering

ϑ :

projection angle in parallel geometry

ξ :

orthogonal distance of a ray to the center of rotation in parallel geometry

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Acknowledgment

This work was supported by Grant no. AZ 286/98 of the Bayerische Forschungsstiftung, Munich, Germany.

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Correspondence to Oliver Watzke.

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Watzke, O., Kalender, W.A. A pragmatic approach to metal artifact reduction in CT: merging of metal artifact reduced images. Eur Radiol 14, 849–856 (2004). https://doi.org/10.1007/s00330-004-2263-y

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  • DOI: https://doi.org/10.1007/s00330-004-2263-y

Keywords

  • Computed tomography
  • Artifacts
  • Image manipulation
  • Correction