| Geant4 Cross Reference |
1 ------------------------------------------------------------------- 2 3 ========================================================= 4 Geant4 - an Object-Oriented Toolkit for Simulation in HEP 5 ========================================================= 6 7 Example B3 8 ---------- 9 10 This example simulates schematically a Positron Emitted Tomography system. 11 12 1- GEOMETRY DEFINITION 13 14 The support of gamma detection are scintillating crystals. A small number 15 of such crystals are optically grouped in a matrix of crystals. In 16 this example, individual crystals are not described; only the matrix of 17 crystals is and it is still called 'Crystal' hereafter. 18 19 Crystals are circularly arranged to form a ring. Few rings make up the full 20 detector (gamma camera). This is done by positionning Crystals in 21 Ring with an appropriate rotation matrix. Several copies of Ring are 22 then placed in the full detector. 23 24 The head of a patient is schematised as a homogeneous cylinder of brain 25 tissue, placed at the center of full detector. 26 27 The Crystal material, Lu2SiO5, is not included in the G4Nist database. 28 Therefore, it is explicitly built in DefineMaterials(). 29 30 2- PHYSICS LIST 31 32 The physics list contains standard electromagnetic processes and the 33 radioactiveDecay module for GenericIon. It is defined in the B3::PhysicsList 34 class as a Geant4 modular physics list with registered physics builders 35 provided in Geant4: 36 - G4DecayPhysics - defines all particles and their decay processes 37 - G4RadioactiveDecayPhysics - defines radioactiveDecay for GenericIon 38 - G4EmStandardPhysics - defines all EM standard processes 39 40 This physics list requires data files for: 41 - low energy electromagnetic processes which path is defined via 42 the G4LEDATA envirnoment variable 43 - nuclides properties which path is defined via 44 the G4ENSDFSTATEDATA envirnoment variable 45 - radioactive decay hadronic processes which path is defined via 46 the G4RADIOACTIVEDATA envirnoment variable. 47 48 See more on installation of the datasets in Geant4 Installation Guide, 49 Chapter 3.3: Note On Geant4 Datasets: 50 http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides 51 /InstallationGuide/html/ch03s03.html 52 3- ACTION INITALIZATION 53 54 B3[a,b]::ActionInitialization class instantiates and registers to Geant4 kernel 55 all user action classes. 56 57 While in sequential mode the action classes are instatiated just once, 58 via invoking the method: 59 B3[a,b]::ActionInitialization::Build() 60 in multi-threading mode the same method is invoked for each thread worker 61 and so all user action classes are defined thread-local. 62 63 A run action class is instantiated both thread-local 64 and global that's why its instance is created also in the method 65 B3[a,b]::ActionInitialization::BuildForMaster() 66 which is invoked only in multi-threading mode. 67 68 4- PRIMARY GENERATOR 69 70 The default particle beam is an ion (F18), at rest, randomly distributed 71 within a zone inside a patient and is defined in 72 B3::PrimaryGeneratorAction::GeneratePrimaries(). 73 The type of a primary particle can be changed with G4ParticleGun commands 74 (see run2.mac). 75 76 5- DETECTOR RESPONSE: scorers 77 78 A 'good' event is an event in which an identical energy of 511 keV is 79 deposited in two separate Crystals. A count of the number of such events 80 corresponds to a measure of the efficiency of the PET system. 81 The total dose deposited in a patient during a run is also computed. 82 83 Scorers are defined in B3::DetectorConstruction::ConstructSDandField(). There are 84 two G4MultiFunctionalDetector objects: one for the Crystal (EnergyDeposit), 85 and one for the Patient (DoseDeposit) 86 87 The scorers hits are saved in form of ntuples in a Root file using Geant4 88 analysis tools. This feature is activated in the main () function with instantiating 89 G4TScoreNtupleWriter. 90 91 Two variants of accumulation event statistics in a run are demonstrated 92 in this example: 93 94 B3a: 95 96 At the end of event, the values acummulated in B3a::EventAction are passed 97 in B3a::RunAction and summed over the whole run (see B3a::EventAction::EndOfevent()). 98 In multi-threading mode the data accumulated in G4Accumulable objects per 99 workers is merged to the master in B3a::RunAction::EndOfRunAction() and the final 100 result is printed on the screen. 101 102 G4Accumulable<> type instead of G4double and G4int types is used for the B3a::RunAction 103 data members in order to facilitate merging of the values accumulated on workers 104 to the master. Currently the accumulables have to be registered to G4AccumulablesManager 105 and G4AccumulablesManager::Merge() has to be called from the users code. This is planned 106 to be further simplified with a closer integration of G4Accumulable classes in 107 the Geant4 kernel next year. 108 109 B3b: 110 111 B3b::Run::RecordEvent(), called at end of event, collects informations 112 event per event from the hits collections, and accumulates statistic for 113 B3b::RunAction::EndOfRunAction(). 114 In addition, results for dose are accumulated in a 115 standard floating-point summation and using a new lightweight statistical 116 class called G4StatAnalysis. The G4StatAnalysis class records four values: 117 (1) the sum, (2) sum^2, (3) number of entries, and (4) the number of entries 118 less than mean * machine-epsilon (the machine epsilon is the difference 119 between 1.0 and the next value representable by the floating-point type). 120 From these 4 values, G4StatAnalysis provides the mean, FOM, relative error, 121 standard deviation, variance, coefficient of variation, efficiency, r2int, 122 and r2eff. 123 124 In multi-threading mode the statistics accumulated per workers is merged 125 to the master in B3b::Run::Merge(). 126 127 6- STACKING ACTION 128 129 Beta decay of Fluor generates a neutrino. One wishes not to track this 130 neutrino; therefore one kills it immediately, before created particles 131 are put in a stack. 132 The function B3::StackingAction::ClassifyNewTrack() is invoked by G4 kernel 133 each time a new particle is created. 134 135 The following paragraphs are common to all basic examples 136 137 A- VISUALISATION 138 139 The visualization manager is set via the G4VisExecutive class 140 in the main() function in exampleB3.cc. 141 The initialisation of the drawing is done via a set of /vis/ commands 142 in the macro vis.mac. This macro is automatically read from 143 the main function when the example is used in interactive running mode. 144 145 By default, vis.mac opens an OpenGL viewer (/vis/open OGL). 146 The user can change the initial viewer by commenting out this line 147 and instead uncommenting one of the other /vis/open statements, such as 148 HepRepFile or DAWNFILE (which produce files that can be viewed with the 149 HepRApp and DAWN viewers, respectively). Note that one can always 150 open new viewers at any time from the command line. For example, if 151 you already have a view in, say, an OpenGL window with a name 152 "viewer-0", then 153 /vis/open DAWNFILE 154 then to get the same view 155 /vis/viewer/copyView viewer-0 156 or to get the same view *plus* scene-modifications 157 /vis/viewer/set/all viewer-0 158 then to see the result 159 /vis/viewer/flush 160 161 The DAWNFILE, HepRepFile drivers are always available 162 (since they require no external libraries), but the OGL driver requires 163 that the Geant4 libraries have been built with the OpenGL option. 164 165 Since 11.1, the TSG visualization driver can also produce the "offscrean" 166 file output in png, jpeg, gl2ps formats without drawing on the screen. 167 It can be controlled via UI commands provided in '/vis/tsg' which are 168 demonstrated in the tsg_offscreen.mac macro in example B5. 169 170 For more information on visualization, including information on how to 171 install and run DAWN, OpenGL and HepRApp, see the visualization tutorials, 172 for example, 173 http://geant4.slac.stanford.edu/Presentations/vis/G4[VIS]Tutorial/G4[VIS]Tutorial.html 174 (where [VIS] can be replaced by DAWN, OpenGL and HepRApp) 175 176 The tracks are automatically drawn at the end of each event, accumulated 177 for all events and erased at the beginning of the next run. 178 179 B- USER INTERFACES 180 181 The user command interface is set via the G4UIExecutive class 182 in the main() function in exampleB3.cc 183 184 The selection of the user command interface is then done automatically 185 according to the Geant4 configuration or it can be done explicitly via 186 the third argument of the G4UIExecutive constructor (see exampleB4a.cc). 187 188 The gui.mac macros are provided in examples B2, B4 and B5. This macro 189 is automatically executed if Geant4 is built with any GUI session. 190 It is also possible to customise the icons menu bar which is 191 demonstrated in the icons.mac macro in example B5. 192 193 C- HOW TO RUN 194 195 - Execute exampleB3a in the 'interactive mode' with visualization 196 % ./exampleB3a 197 and type in the commands from run1.mac line by line: 198 Idle> /control/verbose 2 199 Idle> /tracking/verbose 2 200 Idle> /run/beamOn 1 201 Idle> ... 202 Idle> exit 203 or 204 Idle> /control/execute run1.mac 205 .... 206 Idle> exit 207 208 - Execute exampleB3a in the 'batch' mode from macro files 209 (without visualization) 210 % ./exampleB3a run2.mac 211 % ./exampleB3a exampleB3.in > exampleB3.out 212 213