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Department of Radiology UNIVERSITY OF PENNSYLVANIA
Image Reconstruction inPositron Emission Tomography
Robert M. Lewitt Samuel Matej
Ivan G. Kazantsev Lucretiu Popescu
PET Reconstruction TeamMedical Image Processing Group
2
Department of Radiology UNIVERSITY OF PENNSYLVANIA
Examples of clinical PET images
S.H.
P1309
clf2716
M.B.
P1310
clf2717
M.G.
P1311
clf2720
Female82 years
1.70 m (5’7”)101 kg
Lung carcinoma
Male81 years
1.90 m (6’3”)105 kg
Lymphoma + Lung carcinoma
Female24 years
1.55 m (5’1”)45 kg
Lymphoma
Advantages: high sensitivity to cancer Problems: resolution, noise, attenuation, scatter, randoms
(Illustrated images lack proper treatment of those effects)
3
Department of Radiology UNIVERSITY OF PENNSYLVANIA
Whole-bodyPET study –Fully 3D reconstruction
4
Department of Radiology UNIVERSITY OF PENNSYLVANIA
PET data - classification of events
false coincidence lines
1) True event
2) Scatter event
3’, 3”) Single events
3’+3”) Random event
detector crystal
detector crystal
3”3’ 2
2
Side shield
Patient shield
1
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Department of Radiology UNIVERSITY OF PENNSYLVANIA
PET data - 2D vs. 3D scanner geometry
“2D” detector crystal
detector crystal
“3D”
⇒ The larger the acceptance angle, the more (good and bad) events are accepted.
6
Department of Radiology UNIVERSITY OF PENNSYLVANIA
Fully 3D reconstruction
Fully 3D PET reconstruction flowchart
4DAC, Scatter, Randoms,…
Forward-projection
Fully 3D dataEmision data
x
x
x
x
3D image
Emission image
Attenuation imageTransmission data Transmission reconstruction
Scatter, randomsestimation
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Department of Radiology UNIVERSITY OF PENNSYLVANIA
Fast Fully 3D Reconstruction – WHY?
Modern emission tomography systems:
Fast increase of data sizes (exceeding Moore’s law)→ needed – reduction of computation demands of reconstruction
Low counts per data bin – noisy dataData attenuation, scatter and contamination
→ needed – reconstruction techniques with better modeling
Conflicting demands→ needed – very fast reconstruction approaches
8
Department of Radiology UNIVERSITY OF PENNSYLVANIA
Studied 3D PET reconstruction approaches
3D non-iterative analytical techniques (3DRP, 3D-FRP)
3D iterative techniques (3D RAMLA, ...)
Rebinning (into non-oblique data) followed by multislice2D or 2.5D iterative reconstruction
List mode reconstruction
Time-of-flight reconstruction
Dynamic list mode reconstruction
9
Department of Radiology UNIVERSITY OF PENNSYLVANIA
Favorite tools
Fourier-based approachesAnalytical reconstructionForward and back-projectors for attenuation correction and iterative reconstruction
Kaiser-Bessel window functionsImage basis functionInterpolatorsDisplay 0
0.25
0.5
0.75
1
0 1 2 3
Radius
αα
m
Efficient gridsReconstruction Display
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Department of Radiology UNIVERSITY OF PENNSYLVANIA
Analytical 3D/2.5D reconstructions
3D-FRP
3DRP
FORE reconstruction
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Department of Radiology UNIVERSITY OF PENNSYLVANIA
AllegroIterative
approaches
3D recon2.5D recon
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Department of Radiology UNIVERSITY OF PENNSYLVANIA
Fourier-based projection
Projection Difference No zeropadding 100% zeropadding
1% scale 0.5% scale
58 ms/view 96 ms/view
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Department of Radiology UNIVERSITY OF PENNSYLVANIA
Fourier-based iterative reconstruction
14Department of Radiology UNIVERSITY OF PENNSYLVANIA
The End
Image Reconstruction inPositron Emission TomographyWhole-bodyPET study – Fully 3D reconstructionFully 3D PET reconstruction flowchartFast Fully 3D Reconstruction – WHY?Studied 3D PET reconstruction approachesFavorite toolsAnalytical 3D/2.5D reconstructionsAllegroFourier-based projectionFourier-based iterative reconstructionThe End