1
GATEGATEa simulation platform for a simulation platform for
nuclear medicine based on nuclear medicine based on GEANT4GEANT4
D. Lazaro, V. Breton
For the OpenGATE Collaboration
GGeant4 AApplication forTTomographic EEmission
2
Imaging in nuclear medicineImaging 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)PET PET
Positron emitters (18FDG 2 h)
Resolution down to 2 mm
SPECT SPECT Single photon emitters (99mTc
6 h) Resolution down to 7 mm
Poor sensitivityMultimodalityMultimodality Combined imaging modalities (e.g PET/CT)
Resolution improved
3
Why simulations in Nuclear Why simulations in Nuclear Medicine?Medicine?
Scannerdesign
Protocoloptimization
Algorithmtesting
Scattercorrection
Quantificationrecovery
Dataanalysis
ImageReconstruction
Simulation
4
Two approaches…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 requirementsSimulation requirements
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-useFastLong-term availability, support and training
PET/SPECT dedicated tools
GEANT4 core potentialities
GATEGATE
6
GATEGATEA generic simulation platform for PET/SPECT applicationsA 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 structureGATE structure
3 different levelsGEANT4 coreDeveloper 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 Geometry construction by scripting commandsscripting commands
A specific mechanism has been developed to help the user construct easily a geometry scripting commands geometry = combination of
geometric volumes, like ‘russian dolls’
world
Source
Body Head
Scanner
Rsector
Crystal
LSO BGO
D.Strul Uni Lausanne
9
Geometry examples of GATE Geometry examples of GATE applicationsapplications
Multi-ring PET
D. StrulIPHE Lausanne
Triple-head gamma camera
S. StaelensUni Ghent
10
Source managementSource management
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
TimingTiming
Simulation time– 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 processesPhysical processes
PHOTONSELECTRO
NS
Standard photoelectric effectLE Compton scattering
Standard Gamma conversion
Standard Ionisation
Standard Bremsstrahlung
LE photoelectric effect
Standard Compton scatteringLE Rayleigh scattering
LE Gamma conversion
LE Ionisation
LE Bremsstrahlung
Choices of processes via scripting commands:low energy, standard or inactive
Cut settings
13
Photons: Photons: Standard or low energy processes ?Standard or low energy processes ?
NaI(Tl) crystal sensitivity : comparison between values computed with different versions of GEANT4 and NIST
values
0
2
4
6
8
10
12
14
0 1 2 3 4 5 6 7 8 9 10 11
(NIST - G4.2.0 std)/NIST
(NIST - G4.2.0 low)/NIST
(NIST - G4.4.0 std)/NIST(NIST - G4.4.0 low)/NIST
(NIST - GEANT3)/NIST
crystal thickness (mm)
Rel
ati
ve
dif
fere
nce
(%
)30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8 9 10 11
GEANT4.2.0 stdGEANT4.2.0 low EGEANT4.4.0 stdGEANT4.4.0 low EGEANT3XCOM (NIST)
sen
siti
vity
(%
)
crystal thickness (mm)
14
Electrons: Electrons: Standard or low energy processes ?Standard or low energy processes ?
0
2
4
6
8
10
12
14
16
18
20
0 20 40 60 80 100 120 140 160
(NIST-Geant4.2.0 Std)/NIST
(NIST-Geant4.2.0 LowE)/NIST
(NIST-Geant4.4.0 Std)/NIST
(NIST-Geant4.4.0 LowE)/NIST
energy (keV)
Rel
ativ
e d
iffe
ren
ce (
%)
Stopping power in NaI(Tl) in GEANT4 and NIST values
0
2
4
6
8
10
12
14
0 20 40 60 80 100 120 140 160
(NIST-Geant4.2.0 Std)/NIST(NIST-Geant4.2.0 LowE)/NIST(NIST-Geant4.4.0 Std)/NIST(NIST-Geant4.4.0 LowE)/NIST
energy (keV)
Rel
ativ
e d
iffe
ren
ce (
%)
Stopping power in water in GEANT4 and NIST values
15
Sensitive detector / DigitizerSensitive detector / Digitizer
Hits
Digis
Energyresponse
Spatialresponse
Centroidreadout
ThresholdElectronic
s Pre-programmed components
– Sensitive detectors– Trajectory analyser
Digitizer– Linear signal processing
chain– Modular: set-up via scripting
16
Data outputData 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 CollaborationThe OpenGATE Collaboration
GATE under development since Autumn 2001
Objectives of the collaborationDevelop 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 developmentCurrent 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 Validation of GATE against experimentagainst 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 GATE deployment on DataGRIDon DataGRID
Inputfile
Database
file
Input file exploding
Output file merging
GRID-GATE
output file
GATE output
result file
GATE on the GRID
Database
file
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)
21
For more informations…For more informations…
GATE web sitehttp://www-iphe.unil.ch/~PET/research/gate/
Technical Coordinator: Daniel Strul, IPHE Lausanne
Spokesman: Christian Morel, IPHE Lausanne