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GATE a simulation platform for nuclear medicine based on GEANT4

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1 GATE a simulation platform for nuclear medicine based on GEANT4
Application for Tomographic Emission GATE a simulation platform for nuclear medicine based on GEANT4 D. Lazaro, V. Breton For the OpenGATE Collaboration

2 Imaging in nuclear medicine
Two imaging modalities: morphological imaging (MRI, scanner, X-rays…) detailed informations about the patient anatomy Functional imaging (scintigraphic imaging: SPECT, PET) non-invasive method: a radioactive drug is injected to the patient and naturally evacuated from the organism spatial distribution of the radiopharmaceutical in the body  study of the functional activity of an organ or a specific tissue (e.g tumor) SPECT Single photon emitters (99mTc  6 h) Resolution down to 7 mm Poor sensitivity PET Positron emitters (18FDG  2 h) Resolution down to 2 mm Multimodality Combined imaging modalities (e.g PET/CT) Resolution improved

3 Why simulations in Nuclear Medicine?
Scanner design Image Reconstruction Simulation Protocol optimization Data analysis Algorithm testing Scatter correction Quantification recovery

4 Two approaches… General purpose simulation codes (GEANT4, EGS4, MCNP…)
 wide range of physics  wide community of developers and users  documentation, maintenance and support  complexity  speed Dedicated simulation codes (PETsim, SimSET, Eidolon,…)  optimized for nuclear medical imaging applications (geometry, physics...)  ease of use and fast development  maintenance, upgrades

5 Simulation requirements
PET/SPECT dedicated tools GATE GEANT4 core potentialities Realistic modelisation of PET/SPECT experiments modelisation of detectors, sources, patient movement (detector, patient) time-dependent processes (radioactive decay, movement management, biological kinetics) Ease-of-use Fast Long-term availability, support and training

6 A generic simulation platform for PET/SPECT applications
GATE A generic simulation platform for PET/SPECT applications Based on GEANT4 object Oriented Analysis & Design wide range of physics models long term availability upgrades, documentation & support Specific developments regarding to Nuclear medical imaging needs material database, sources, readout time and movement management Ease-of-use for non C++ programmers scripting commands to define all paramaters of the simulation (construction of the geometry, specification of the physical processes involved, of the sources...)

7 GATE structure 3 different levels GEANT4 core Developer level
framework and application classes C++ programming User level sequence of scripting commands geometry construction physical processes involved sources (geometry, activity) movement (type, speed…) duration of the acquisition User interface Application classes Framework Geant4

8 Geometry construction by scripting commands
world A specific mechanism has been developed to help the user construct easily a geometry scripting commands geometry = combination of geometric volumes, like ‘russian dolls’ Source Scanner Body Head Rsector Crystal LSO BGO D.Strul Uni Lausanne

9 Geometry examples of GATE applications
Multi-ring PET D. Strul IPHE Lausanne Triple-head gamma camera S. Staelens Uni Ghent

10 Source management 15O 11C Multiple sources
controlled by source manager inserted via scripting complex geometries: customized GPS Optimized decay customized G4 Radioactive Decay Module (RDM) PET-specific sources 15O 11C

11 Timing Simulation time Time-dependant objects
a clock models the passing of time during experiments the user defines the experiment timing Time-dependant objects updated when time changes allows programming of movement, tracer kinetics...

12 Physical processes PHOTONS ELECTRONS
Choices of processes via scripting commands: low energy, standard or inactive Cut settings LE photoelectric effect Standard photoelectric effect LE Compton scattering Standard Compton scattering LE Rayleigh scattering PHOTONS ELECTRONS Standard Gamma conversion LE Gamma conversion Standard Ionisation LE Ionisation Standard Bremsstrahlung LE Bremsstrahlung

13 Photons: Standard or low energy processes ?
NaI(Tl) crystal sensitivity : comparison between values computed with different versions of GEANT4 and NIST values sensitivity (%) crystal thickness (mm) crystal thickness (mm) Relative difference (%)

14 Electrons: Standard or low energy processes ?
energy (keV) Relative difference (%) Stopping power in NaI(Tl) in GEANT4 and NIST values energy (keV) Relative difference (%) Stopping power in water in GEANT4 and NIST values

15 Sensitive detector / Digitizer
Hits Digis Energy response Spatial response Centroid readout Threshold Electronics Pre-programmed components Sensitive detectors Trajectory analyser Digitizer Linear signal processing chain Modular: set-up via scripting

16 Data output Multiple parallel output channels:
 ROOT (real-time display, storage in ROOT files for further analysis)  ASCII files Binary files Specific scanner formats (e.g Crystal Clear LMF…) GATE simulation Sinogram Reconstructed image

17 The OpenGATE Collaboration
GATE under development since Autumn 2001 Objectives of the collaboration Develop a reliable generic simulation platform for nuclear medicine shared development share results and know-how allow multiple work axes: development, validation… Current status: 10 groups Fields: planar scintigraphy, SPECT, PET, microPET Organization Steering committee (one representative / group) Technical meeting every two months

18 Current efforts of development
Improvement of the detection models Use of voxelised geometries (sources): under development Validation work, against experimental data Small animal imaging gamma camera (LPC – IASA Athens) Dual-headed gamma camera (University of Ghent) Strategies to improve computation speed Parallel computation Use of computing grids

19 Validation of GATE against experiment
Simulation of a small animal imaging gamma camera CsI(Tl) crystal array coupled to a PSPMT Small animal imaging (study of new radiopharmaceuticals) Lead shielding PSPMT LEHR collimator source CsI(Tl) crystal array crystal array

20 GATE deployment on DataGRID
Computation speed becomes (too!) large in case of voxelised geometry huge number of events Potential solution under study at LPC: deployment of GATE on DataGRID (first tests successful in July 2001) Input file Database Input file exploding Output file merging GRID-GATE output file GATE output result file GATE on the GRID

21 For more informations…
GATE web site Technical Coordinator: Daniel Strul, IPHE Lausanne Spokesman: Christian Morel, IPHE Lausanne

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