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Overview of Geant4 Use and Issues in Imaging: Emission Tomography (PET and SPECT)

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. Why simulate imaging systems and scans ?.

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Overview of Geant4 Use and Issues in Imaging: Emission Tomography (PET and SPECT)

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  1. 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. 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. 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. 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. 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. GATE architecture User Layer Application Layer Core Layer GEANT 4 Jan et al, PMB 49 (2004) 4543

  7. User Layer • -Verbosity and visualization • Geometry • Digitizer • Physics • Sources • Outputs • Experiment … /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 …

  8. 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. 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. 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): • b+ spectra parametrization - faster • annihilation photon noncolinearity • GEANT4’s interaction processes and cuts Jan et al, PMB 49 (2004) 4543

  11. 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. 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. GE Advance/ DLS PET scanner

  14. MC based coincidence count rates for IQ phantom Randoms Trues Scattered NECR See Schmidtlein et al, SU-EE-A4-03 Mod. Poster at this meeting

  15. 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. 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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