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Metal artifact reduction in computed
tomography at head and neck region
Sornjarod Oonsiri, MSc
Anchali Krisanachinda, PhD
David Sutton, PhD
Chulalongkorn University, Thailand
University of Dundee, United Kingdom
Content
• Introduction
• Material and method
• Result
• Conclusion
2
CT for radiation therapy
• Organ delineation
• Dose calculation
3
Artifact
• Artifacts are significant problem in CT • Streak artifact• Motion artifact• Ring artifact
Sprawls P. 1995Popilock R et al. 2008 4
Artifact
• Artifacts are significant problem in CT • Streak artifact• Motion artifact• Ring artifact
5Sprawls P. 1995
Popilock R et al. 2008
Metal artifact
• Source: Metal implant• Dental implant• Surgical clip• Coils, wires• Orthopedic hardware
• Metal streak artifacts occur because filtered back projection
Miller‐Thomas MM et al. 2005Rutherford EE et al. 2007
Boas EF et al. 2011 6
OMAR
• O‐MAR = Metal Artifact Reduction for Orthopedic Implants
• O‐MAR is a commercial product available from Philips Healthcare which implements a robust and efficient algorithm to mitigate artifact caused by metal objects in CT images
Philips Healthcare, 2012 7
OMAR in radiation therapy
RegionImage quality (%Noise) Dosimetric evaluationFBP OMAR Dose difference (%) 1%,1mm
Oral cavity 61.5 44.4 3.7 100%
8Oonsiri S. et al. 2014
Filter back projection OMAR
Research objective
• To develop the method for metal artifact reduction in oral cavity computed tomography image using MATLAB
9
Material and method
10
Material and method
• Philips Brilliance CT• Big Bore Oncology• OMAR
• MATLAB• New algorithm
• Phantom• CTDI head phantom• Alderson‐Rando phantom
11
Segment of streak artifact
Remove the streak artifact
CorrectedCT image
Fill the blank region by• Interpolation
• Linear interpolation• Non‐linear interpolation
• Average value• Weighted average value• Substitution
12
Phantom test
• With and without metalic inserts• 120 kVp• 3 mm slice thickness• Vary mA over clinical range (100‐250)
13
Result
14
Homogeneous phantom without metallic
FBP New algorithmOMAR15
Homogeneous phantom with metallic
FBP New algorithmOMAR16
Noise of homogeneous phantom (HU)
Without metallic With metallic
FBP OMAR New algorithm FBP OMAR New
algorithm
100 mAs
150 mAs
200 mAs
250 mAs
10.2
7.6
6.3
6.3
9.7
7.6
6.4
6.5
10.0
7.5
6.4
6.4
52.6
30.9
17.6
17.6
23.8
17.3
16.2
10.2
35.8
22.4
17.4
12.3
17
Alderson‐Rando phantom without metallic
FBP New algorithmOMAR18
Alderson‐Rando phantom with metallic
FBP New algorithmOMAR19
Noise of Alderson‐Rando phantom (HU)
Without metallic With metallic
FBP OMAR New algorithm FBP OMAR New
algorithm
100 mAs
150 mAs
200 mAs
250 mAs
11.9
8.6
7.6
7.3
10.2
8.0
7.9
6.9
10.6
8.0
7.5
6.7
73.2
51.2
48.5
47.9
41.2
38.9
38.1
37.8
52.3
43.7
42.6
40.2
20
Discussion
• Metal artifact reduction techniques cannot eliminate metal artifacts totally but it can suppress the metal artifact and improve the image quality in the CT images
• The overall dose distribution difference in the clinical application was within 2%
Oonsiri S. et al. 2014
21
Conclusion
• Metal artifact reduction techniques reduce metal artifacts 20‐40% in CT images of the treatment planning system
22
Future work
• Further analysis with phantom
• Implement to the patient CT image
• Improve performance of new algorithm
23
FBP
New algorithm
Thank youfor your attention
24