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

daniel.strul@iphe.unil.ch

Spokesman: Christian Morel, IPHE Lausanne

christian.morel@iphe.unil.ch