Kirov A S, MSKCC
Overview of Geant4 Use
and Issues in Imaging:
Emission Tomography (PET and SPECT)
Assen S. Kirov
Departme...
Kirov A S, MSKCC
Why simulate imaging systems and scans ?
• Better understand and model phenomena
affecting image quality ...
Kirov A S, MSKCC
Basis of this talk
Membership in the
OpenGATE collaboration
( www.opengatecollaboration.org )
Whose goal ...
Kirov A S, MSKCC
Basis of this talk
• Product of OpenGATE : GATE
(GEANT4 Application for Tomographic Emission)
• Widely us...
Kirov A S, MSKCC
Use of GEANT4 prior to GATE for imaging
• GEANT3 and GEANT4 based codes
– example Jan S (Thesis) : GePETo...
Kirov A S, MSKCC
GATE architecture
GEANT 4GEANT 4
Core LayerCore Layer
Application LayerApplication Layer
User LayerUser L...
Kirov A S, MSKCC
User Layer
…
/gate/block/daughters/name crystal
/gate/block/daughters/insert box
/gate/crystal/placement/...
Kirov A S, MSKCC
GATE systems
• Geometry organization: Hierarchical structures
– For realistic signal processing organizat...
Kirov A S, MSKCC
GATE time and movements
Needed for:
- Patient and organ motion
- Scanner rotation
- Activity distribution...
Kirov A S, MSKCC
GATE physics
• Sources
– Particle type, position (volume), direction (solid angle),
energy (spectrum), ac...
Kirov A S, MSKCC
GATE digitization
- Resolution blurring, spatial blurring, crosstalk
- Parallelizable and non-paralleliza...
Kirov A S, MSKCC
GATE validation
• PET at least 5 patient and microPET scanners
energy spectra, sensitivity, resolution,
s...
Kirov A S, MSKCC
GE Advance/ DLS PET scanner
Kirov A S, MSKCC
MC based coincidence count rates for IQ phantom
See Schmidtlein et al, SU-EE-A4-03 Mod. Poster at this me...
Kirov A S, MSKCC
Other issues
• CT simulations – GATE could handle the
geometry, not tested yet
• Optical imaging – very p...
Kirov A S, MSKCC
Conclusions
• GEANT4 with GATE - powerful,
flexible, convenient for use and accurate
tool for nuclear med...
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  1. 1. Kirov A S, MSKCC Overview of Geant4 Use and Issues in Imaging: Emission Tomography (PET and SPECT) Assen S. Kirov Department of Medical Physics Memorial Sloan-Kettering Cancer Center New York
  2. 2. Kirov 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
  3. 3. Kirov 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
  4. 4. Kirov 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) 4543
  5. 5. Kirov 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)
  6. 6. Kirov A S, MSKCC GATE architecture GEANT 4GEANT 4 Core LayerCore Layer Application LayerApplication Layer User LayerUser Layer Jan et al, PMB 49 (2004) 4543
  7. 7. Kirov 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 … -Verbosity and visualization -Geometry -Digitizer -Physics -Sources -Outputs -Experiment
  8. 8. Kirov 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 - 1 PET – 3 (2 block based, 1 pixelated) Generic -1 Jan et al, PMB 49 (2004) 4543
  9. 9. Kirov 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 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) 4543
  10. 10. Kirov 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): » β+ spectra parametrization - faster » annihilation photon noncolinearity • GEANT4’s interaction processes and cuts Jan et al, PMB 49 (2004) 4543
  11. 11. Kirov 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
  12. 12. Kirov 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
  13. 13. Kirov A S, MSKCC GE Advance/ DLS PET scanner
  14. 14. Kirov A S, MSKCC MC based coincidence count rates for IQ phantom See Schmidtlein et al, SU-EE-A4-03 Mod. Poster at this meetingSee 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 40 Activity (kBq/cc) CountRates(kcps) SF Trues SF Scatters SF Randoms SF NECR IQ Trues IQ Scatters IQ Randoms IQ NECR NECR Scattered Trues Randoms
  15. 15. Kirov 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 !!
  16. 16. Kirov 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

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