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Metal artifact reduction
1. Automated Segmentation and Interpolation in Sinograms for Metal Artifact Suppression in CT Wouter JH Veldkamp, PhD Raoul MS Joemai, BSc Aart J. van der Molen, MD Jacob Geleijns, PhD Department of Radiology, Leiden University Medical Center, The Netherlands
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4. Traditional image based approach For instance: W.A.Kalender, R.Hebel, and J.Ebersberger, "Reduction of Ct Artifacts Caused by Metallic Implants," Radiology 164, 576-577 (1987). original sinogram segmented sinogram interpol . sinogram back-projection uncorrected corrected Exclusion by interpolation segmented back-projection forward-projection
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7. Raw data based approach Original sinogram mask Interpol. sinogram Back-projection Back-projection uncorrected corrected High pass filter & thresholding MRF Canny filter Interpolation Selecting ROI
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10. The following empirically determined parameter values are used in the MRF model for segmentation of metal implants. Raw data based approach Parameter values 900 150 7 0 Background ( l=0 ) 300 0 0 0 Foreground ( l=1 ) δ γ β α
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13. Signal addition a pragmatic method was applied Original signal Interpolated signal Interpolated signal + fraction of original signal
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15. a b c d e 3 1 2 4 5 Metal artifact reduction in phantom images. Fig. a shows the uncorrected scan and the ROIs. Among other things the effect of different interpolation methods is shown. Fig. b shows a detail of the corrected image using the per view interpolation, Fig. c shows the same detail corresponding to the smooth interpolation and Fig. d corresponds to the shortest distance interpolation method. Finally, in Fig. e a result without adding the scaled projections to the interpolated values is shown (using smooth interpolation). Note that the streaking pattern is no longer evident in the images, but the region of reduced density between the objects is still present in the images and more evident in Fig. b (per view interpolation). Results
16. Results Mean CT number and the standard deviation, both measured in HU, for pixels belonging to different inserts (ROIs) in the phantom are determined as a measure of distortion. Values are based on measurements in 40 consecutive reconstructed slices. 88 +/- 56 117 +/- 33 -53 +/- 27 -52 +/- 36 862 +/- 48 Smooth interpolation without signal 90 +/- 56 119 +/- 34 -54 +/- 28 -52 +/- 36 865 +/- 48 Smooth interpolation 99 +/- 51 118 +/- 34 -52 +/- 28 -53 +/- 37 867 +/- 48 Shortest distance interpolation 76 +/- 57 118 +/- 34 -67 +/- 28 -49 +/- 36 841 +/- 47 Per view interpolation 101 +/- 98 116 +/- 72 -64 +/- 85 -52 +/- 63 889 +/- 82 No artifact suppression With titanium 117 +/- 36 117 +/- 36 -62 +/- 30 -59 +/- 36 902 +/- 49 Without titanium Original raw data 5: PMMA 4: PMMA 3: PVC 2: PVC 1: Teflon Phantom configuration / Correction method Raw data type Region of interest
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18. Results Patient with hip implant. At the left slices of the original scan data are shown. At the right corresponding slices are shown that correspond to corrected raw data (smooth interpolation). The window center and window width were respectively 150 and 700 HU for all slices. Four different slices are shown consecutively.
19. Results Results of four other patients with different implants. At left original slices are shown and at the right slices from corrected raw data are shown (smooth interpolation). For left and right images identical window center and window width was chosen.
20. Results Results of four other patients with different implants. At left original slices are shown and at the right slices from corrected raw data are shown (smooth interpolation). For left and right images identical window center and window width was chosen.
21. Results Results of four other patients with different implants. At left original slices are shown and at the right slices from corrected raw data are shown (smooth interpolation). For left and right images identical window center and window width was chosen.
22. Results Results of four other patients with different implants. At left original slices are shown and at the right slices from corrected raw data are shown (smooth interpolation). For left and right images identical window center and window width was chosen.
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