Post on 31-Dec-2015
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European Instituteof Molecular Imaging
Generation of multiple respiratory phases in PET/CT
A phantom study
Mohammad Dawood, F Büther, O Schober, M Schäfers, KP Schäfers
European Institute for Molecular ImagingUniversity of Münster, Germany
European Institutefor Molecular Imaging
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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases
PET, Minutes
CT, Seconds
Motivation
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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases
CT based attenuation of PET data at inspiration
CT based attenuation of PET data at expiration
Problem
Myocardial Uptake: NCAT phantom data
Corresponding PET and CT Non-Corresponding PET and CT Difference
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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases
1. Use PET data to estimate motion with optical flow methods
2. Apply motion vectors to the given CT to generate 4D-CT respiratory phases
Proposed solution
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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases
Generating FDG PET data using NCAT
Emission map
Attenuation map
Emission sinogram
Attenuation sinogram
Attenuated emission sinogram
Simulation of 10 respiratory gates @ 30 mm diaphragm motion10 emission and 10 attenuation maps
Noisy emission sinogram
→ EM reconstruction(20 iterations):
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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases
Optical flow
As a voxel at position 1 moves to position 2 its gray value remains the same:
I : Gray value (Activity)x,y,z,t : Position
Brightness consistency constraint
V : Flow (Motion)
Motion estimation
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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases
Discontinuity Preserving Algorithm
Local Consistency + Global smoothness + Organ boundaries
Motion estimation
Dawood, Büther, Jiang, Schäfers: Motion correction in 3d PET/CT with advanced optical flow algorithms. IEEE Trans Med Imaging, 2008; 27(8):1164-75.
Global smoothnessLocal consistency
PET patient data without ACCoronal slice from 3D volume
FDG, 1 h p.i.
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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases
Application to the given CT respiratory phase
Ground truth NCAT phantom data
Generated respiratory phases by the proposed method
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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases
Ground truth Generated
Results: Position of the diaphragm
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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases
Respiratory phase No Ground truth data Generated data
1 2.9 2.9
2 3.1 3.1
3 3.4 3.4
4 3.7 3.7
5 4.0 3.9
6 4.1 4.0
7 3.9 3.8
8 3.6 3.6
9 3.3 3.3
10 3.0 3.1
Average 3.50 3.48
Lung volume analysis
(volume in liters)
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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases
Results: Myocardial uptake in LV on NCAT phantom data
PET : Insp. GeneratedCT : Insp.
100
90
80
70
60
50
40
30
20
10
0
-
PET : Insp. Ground TruthCT : Insp.
=
PET : Exp. Ground TruthCT : Exp.
100
90
80
70
60
50
40
30
20
10
0
Artifacts are removed if corresponding PET/CT phases are used for attenuation correction
Difference between generated and ground truth: Average 0.5%, Maximum = 4.3%
Difference
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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases
Results: Myocardial uptake on patient data
PET : Insp.CT : Insp.
PET : Exp.CT : Insp.
PET : Exp.CT : Exp. (generated)
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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases
Conclusions
- Respiratory motion leads to artifacts during attenuation correction
- up to 20% in this case
- Corresponding respiratory phases are required
- An optical flow based method is proposed to solve this problem
- Studies on NCAT phantom data showed encouraging results
- uptake error reduced to 0.5% on average, 4.3% max- correlation with ground truth 98.6%- lung volumes corresponded 99.4% with ground truth data- position of diaphragm same
- Further studies on patient data to be conducted soon
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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases
Thank you !
EIMI - Technology team
Torsten BudumluFlorian BütherKatharina BüscherBjörn CzekallaMohammad DawoodMichael FieselerFabian GigengackThomas KöstersKlaus SchäfersSönke SchmidDaniel TenbrinckSusanne Zeglin