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Kirov A S, MSKCCKirov A S, MSKCC
Overview of Geant4 Use and Issues in Imaging:
Emission Tomography (PET and SPECT)
Assen S. KirovDepartment of Medical Physics
Memorial Sloan-Kettering Cancer Center New York
Assen S. KirovDepartment of Medical Physics
Memorial Sloan-Kettering Cancer Center New York
Kirov A S, MSKCCKirov A S, MSKCC
Why simulate imaging systems and scans ?
• Better understand and model phenomena affecting image quality and accuracy
• Optimize scan imaging and processing parameters
• Calculate parameters needed for improved image reconstruction
Kirov A S, MSKCCKirov A S, MSKCC
Basis of this talk
Membership in the
OpenGATE collaboration
( www.opengatecollaboration.org )
Whose goal is
- the creation of an elaborate and flexible Monte Carlo program that allows realistic simulation of the physical processes, detector geometry and all factors affecting emission tomography applications
- realistic modeling of patient and small animal anatomy
- based on GEANT4
Kirov A S, MSKCCKirov A S, MSKCC
Basis of this talk
• Product of OpenGATE : GATE (GEANT4 Application for Tomographic Emission)
• Widely used for
– PET
– SPECT
• Potential for CT (why not ?)
• Potential for Radioimmunotherapy and Nuclide Therapy dosimetry
Jan et al, PMB 49 (2004) 4543Jan et al, PMB 49 (2004) 4543
Kirov A S, MSKCCKirov A S, MSKCC
Use of GEANT4 prior to GATE for imaging
• GEANT3 and GEANT4 based codes
– example Jan S (Thesis) : GePETos
• Summary of other codes:
– Buvat and Castiglioni (Q J Nuc Med, 46, p 48-61, 2002)
Kirov A S, MSKCCKirov A S, MSKCC
GATE architecture
GEANT 4GEANT 4
Core LayerCore Layer
Application LayerApplication Layer
User LayerUser Layer
Jan et al, PMB 49 (2004) 4543Jan et al, PMB 49 (2004) 4543
Kirov A S, MSKCCKirov A S, MSKCC
User Layer
…/gate/block/daughters/name crystal/gate/block/daughters/insert box/gate/crystal/placement/setTranslation 0.0 0.0 0.0 mm/gate/crystal/geometry/setXLength 30.0 mm/gate/crystal/geometry/setYLength 4.4 mm/gate/crystal/geometry/setZLength 4.75 mm/gate/crystal/setMaterial BGO…
…/gate/block/daughters/name crystal/gate/block/daughters/insert box/gate/crystal/placement/setTranslation 0.0 0.0 0.0 mm/gate/crystal/geometry/setXLength 30.0 mm/gate/crystal/geometry/setYLength 4.4 mm/gate/crystal/geometry/setZLength 4.75 mm/gate/crystal/setMaterial BGO…
-Verbosity and visualization-Geometry-Digitizer-Physics-Sources-Outputs-Experiment
-Verbosity and visualization-Geometry-Digitizer-Physics-Sources-Outputs-Experiment
Kirov A S, MSKCCKirov A S, MSKCC
GATE systems
• Geometry organization: Hierarchical structures
– For realistic signal processing organization
– Simplifies geometry input
GATE system:
{Hierarchically organized geometry + corresponding LMF output}
5 GATE systems
SPECT - 1PET – 3 (2 block based, 1 pixelated)
Generic -1
GATE system:
{Hierarchically organized geometry + corresponding LMF output}
5 GATE systems
SPECT - 1PET – 3 (2 block based, 1 pixelated)
Generic -1
Jan et al, PMB 49 (2004) 4543Jan et al, PMB 49 (2004) 4543
Kirov A S, MSKCCKirov A S, MSKCC
GATE time and movements
Needed for: - Patient and organ motion - Scanner rotation - Activity distribution changes
GEANT4 limitations: - geometry: static during simulation - no source movements
Needed for: - Patient and organ motion - Scanner rotation - Activity distribution changes
GEANT4 limitations: - geometry: static during simulation - no source movements
Solutions in GATE: - Geometry updated between simulation time steps - The source is confined to a smaller volume moving inside a larger emission volume
Santin et al, 2003 Strul et al, 2003
Solutions in GATE: - Geometry updated between simulation time steps - The source is confined to a smaller volume moving inside a larger emission volume
Santin et al, 2003 Strul et al, 2003
Jan et al, PMB 49 (2004) 4543Jan et al, PMB 49 (2004) 4543
Kirov A S, MSKCCKirov A S, MSKCC
GATE physics
• Sources
– Particle type, position (volume), direction (solid angle), energy (spectrum), activity
– Modified GEANT4’s RDM – virtual clock defines absolute time used to initialize GEANT4’s internal tracking time
– Multiple, voxelized sources
– e+ emission (Jan 2002):
» + spectra parametrization - faster
» annihilation photon noncolinearity
• GEANT4’s interaction processes and cuts
Jan et al, PMB 49 (2004) 4543Jan et al, PMB 49 (2004) 4543
Kirov A S, MSKCCKirov A S, MSKCC
GATE digitization
- Resolution blurring, spatial blurring, crosstalk
- Parallelizable and non-parallelizable dead times
- Coincidence processing
- Post simulation processing of output files stored before digitization
- Resolution blurring, spatial blurring, crosstalk
- Parallelizable and non-parallelizable dead times
- Coincidence processing
- Post simulation processing of output files stored before digitization
Kirov A S, MSKCCKirov A S, MSKCC
GATE validation
• PET at least 5 patient and microPET scanners
energy spectra, sensitivity, resolution, scatter faction, count rates, image quality,
contrast recovery
• SPECT at least 5 systems
energy spectra, sensitivity, resolution,…
• Prototype at least 4 systems
energy spectra, sensitivity, resolution…
More than 15 references in Jan et al, PMB 49 (2004) 4543 and at www.opengatecollaboration.org
Kirov A S, MSKCCKirov A S, MSKCC
GE Advance/ DLS PET scanner
Kirov A S, MSKCCKirov A S, MSKCC
MC based coincidence count rates for IQ phantom
See Schmidtlein et al, SU-EE-A4-03 Mod. Poster at this meeting See Schmidtlein et al, SU-EE-A4-03 Mod. Poster at this meeting
0
50
100
150
200
0 5 10 15 20 25 30 35 40Activity (kBq/cc)
Co
un
t R
ate
s (
kc
ps
)SF Trues SF Scatters
SF Randoms SF NECR
IQ Trues IQ Scatters
IQ Randoms IQ NECR
NECRNECR
ScatteredScattered
TruesTrues
RandomsRandoms
Kirov A S, MSKCCKirov A S, MSKCC
Other issues
• CT simulations – GATE could handle the geometry, not tested yet
• Optical imaging – very promising field for GEANT4 : small animal; 3D dosimetry (see Kirov et al, SU-FF-T-229 at this meeting), etc.
• Worst GATE/GEANT4 problem for imaging
» Very time consuming simulations
35 CPU days on 2 GHz !!
Kirov A S, MSKCCKirov A S, MSKCC
Conclusions
• GEANT4 with GATE - powerful, flexible, convenient for use and accurate tool for nuclear medicine imaging applications
• GEANT4 without GATE: worth pursuing only if a new approach can drastically improve performance
• Efficiency: work needed