Computed tomography

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== Introduction ==
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== <span style="color:#000080"> Introduction </span> ==
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This tutorial will based on the DICOM GEANT4 example originally developed by Louis Archambault, Luc Beaulieu and Vincent Hubert-Tremblay. In this example a list of DICOM files (.dcm) are converted to ASCII files (.g4dcm) and binary (.g4bin) that can be read by GEANT4. Then, these files are used by GEANT4 to construct patient geometry. The geometry is constructed by voxelizing computed tomography data. Four navigation algorithms are available to create the voxel geometry: G4SmartVoxel, G4VNestedParameterisation, G4RegularNavigation and G4Replica. In this tutorial we investigate the different geometry implementations.
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This tutorial is based on the GEANT4 DICOM example originally developed by Louis Archambault, Luc Beaulieu and Vincent Hubert-Tremblay. In this example a list of DICOM files (.dcm) are converted to ASCII files (.g4dcm) and binary files (.g4bin) that can be read by GEANT4. Each of these files corresponds to a Z Computed tomography (CT) slice. Then, the .g4dcm (.g4bin) files are merged into one volume.  
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Hounsfield Unit in DICOM is converted to density according to the [http://www.hep.ucl.ac.uk/pbt/RadiotherapyWorkbook/skins/common/images/DICOM/CT2Density.dat Hounsfield scale].  
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The geometry is constructed by voxelizing this volume. There are four navigation algorithms used to create the voxel geometry: '''G4RegularNavigation''', '''G4VNestedParameterisation''', '''G4SmartVoxel'''/'''G4VoxelNavigation''' and '''G4PVReplica'''.  
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A simple monenergetic electron beam is simulated inside the patient. The output of the example is a text file with dose deposited in several voxels.
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The material for this volume is constructed by converting the pixel values (Hounsfield numbers) from the DICOM images to densities using the [http://www.hep.ucl.ac.uk/pbt/RadiotherapyWorkbook/skins/common/images/DICOM/CT2Density.dat Hounsfield scale]. Then, the densities are converted to material types according to this [http://www.hep.ucl.ac.uk/pbt/RadiotherapyWorkbook/skins/common/images/DICOM/Materials.txt table].
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A simple monenergetic electron beam is simulated using '''G4ParticleGun''' class. The output of the tutorial is a text file with dose deposition in several voxels. The dose is scored using classes '''G4MutiFunctionalDetector''', '''G4VPrimitiveScorer''', '''G4PSDoseDeposit3D''' and '''G4THitsMap'''.  
http://www.hep.ucl.ac.uk/pbt/RadiotherapyWorkbook/skins/common/images/DICOM/dicom.png
http://www.hep.ucl.ac.uk/pbt/RadiotherapyWorkbook/skins/common/images/DICOM/dicom.png
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This is one of the DICOM files that will be used in this tutorial.
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This is one of the DICOM files used in the tutorial.
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== Setting up the environment ==
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== <span style="color:#000080"> How to run the tutorial </span> ==
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; Connect to HEP cluster and create folder DICOMFolder in your area
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; Connect to the HEP cluster and create folder DICOMFolder in your area
<pre style="color: #800000; background-color: #dcdcdc">
<pre style="color: #800000; background-color: #dcdcdc">
ssh -X username@plus1.hep.ucl.ac.uk  
ssh -X username@plus1.hep.ucl.ac.uk  
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password: type your password here
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username@plus1.hep.ucl.ac.uk's password: type your password here
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cd /home/username/
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[username@plus1 ~]$ mkdir DICOMFolder
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mkdir DICOMFolder
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[username@plus1 ~]$ cd DICOMFolder   
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cd DICOMFolder   
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</pre>
</pre>
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<pre style="color: #800000; background-color: #dcdcdc">
<pre style="color: #800000; background-color: #dcdcdc">
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source /unix/pbt/software/dev/bin/pbt-dev.sh   
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[username@plus1 DICOMFolder]$ source /unix/pbt/software/dev/bin/pbt-dev.sh   
</pre>
</pre>
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== <span style="color:#000080"> How to get the code </span> ==
 
; Copy the code to your working directory and rename it
; Copy the code to your working directory and rename it
<pre style="color: #800000; background-color: #dcdcdc">
<pre style="color: #800000; background-color: #dcdcdc">
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cp -r /unix/pbt/tutorials/basic/DICOM .
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[username@plus1 DICOMFolder]$ cp -r /unix/pbt/tutorials/advanced/DICOM .
    
    
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mv DICOM DICOM_source
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[username@plus1 DICOMFolder]$ mv DICOM DICOM_source
</pre>
</pre>
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== <span style="color:#000080"> How to run the code </span> ==
 
; Inside /home/username/DICOMFolder/ create a directory
; Inside /home/username/DICOMFolder/ create a directory
<pre style="color: #800000; background-color: #dcdcdc">
<pre style="color: #800000; background-color: #dcdcdc">
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mkdir DICOM_build   
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[username@plus1 DICOMFolder]$ mkdir DICOM_build   
</pre>
</pre>
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<pre style="color: #800000; background-color: #dcdcdc">
<pre style="color: #800000; background-color: #dcdcdc">
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cd DICOM_build  
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[username@plus1 DICOMFolder]$ cd DICOM_build  
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cmake -DGeant4_DIR=/unix/pbt/software/dev /home/username/DICOMFolder/DICOM_source  
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[username@plus1 DICOM_build]$ cmake -DGeant4_DIR=/unix/pbt/software/dev /home/username/DICOMFolder/DICOM_source  
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make   
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[username@plus1 DICOM_build]$ make   
</pre>
</pre>
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; Run macro run.mac.
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; Run macro run.mac
<pre style="color: #800000; background-color: #dcdcdc">
<pre style="color: #800000; background-color: #dcdcdc">
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./DICOM run.mac
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[username@plus1 DICOM_build]$ ./DICOM run.mac
</pre>
</pre>
== <span style="color:#000080"> How to analyze data </span> ==
== <span style="color:#000080"> How to analyze data </span> ==
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This is a [http://geant4.web.cern.ch/geant4/UserDocumentation/Doxygen/examples_doc/html/ExampleDICOM.html link] to the official DICOM explanation notes. We recommend to read it before proceeding with this tutorial.
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This is a [http://geant4.web.cern.ch/geant4/UserDocumentation/Doxygen/examples_doc/html/ExampleDICOM.html link] to the official DICOM tutorial explanation notes. We recommend to read it before proceeding with this tutorial.
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=== <span style="color:#000080"> Text files </span> ===
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The macro run.mac produces a text file '''dicom.out''' which includes the dose deposition in several voxels.
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=== <span style="color:#000080"> Run with different settings </span> ===
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; Chose among several voxelization algorithms
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* <span style="color:#ff0000"> G4RegularNavigation </span>:
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'''G4RegularNavigation''' class is the default class for this tutorial. This algorithm skips frontiers between voxels when they have the same material i.e. "replacing group of voxels with a smaller number of larger voxels". 
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* <span style="color:#ff0000"> G4NestedParameterization </span>:
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To run with this voxelization algorithm you need to set the variable '''DICOM_NESTED_PARAM'''
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<pre style="color: #800000; background-color: #dcdcdc">
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[username@plus1 DICOM_build]$ export DICOM_NESTED_PARAM=1
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</pre>
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You can check if it is set correctly by typing in the command line
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<pre style="color: #800000; background-color: #dcdcdc">
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[username@plus1 DICOM_build]$ env
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</pre>
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Then, compile and run the code:
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<pre style="color: #800000; background-color: #dcdcdc">
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[username@plus1 DICOM_build]$ make
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[username@plus1 DICOM_build]$ ./DICOM run.mac
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</pre>
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* <span style="color:#ff0000"> G4SmartVoxel / G4VoxelNavigation </span>:
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Using smart voxels required a huge amount of memory. At /home/username/DICOMFolder/DICOM_source/src/DicomRegularDetectorConstruction.cc set
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<pre style="color: #800000; background-color: #dcdcdc">
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patient_phys->SetRegularStructureId(0);
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</pre>
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compile and run the code:
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<pre style="color: #800000; background-color: #dcdcdc">
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[username@plus1 DICOM_build]$ make
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[username@plus1 DICOM_build]$ ./DICOM run.mac
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</pre>
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; Change the type, energy and position of the incident particle
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At /home/username/DICOMFolder/DICOM_source/src/DicomPrimaryGeneratorAction.cc change the following lines:
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<pre style="color: #800000; background-color: #dcdcdc">
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G4ParticleDefinition* particle = particleTable->FindParticle(particleName="e-");
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fParticleGun->SetParticleEnergy(100.*MeV);
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fParticleGun->SetParticlePosition(G4ThreeVector(0.,0.,0.));
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</pre> 
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You can chose among several particles like "gamma", "e+", "alpha" and "He3". Then, compile and run the code
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<pre style="color: #800000; background-color: #dcdcdc">
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[username@plus1 DICOM_build]$ make
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[username@plus1 DICOM_build]$ ./DICOM run.mac
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</pre>
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=== <span style="color:#000080"> Visualisation </span> ===
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Run the visualisation macro vis.mac
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<pre style="color: #800000; background-color: #dcdcdc">
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[username@plus1 DICOM_build]$ ./DICOM vis.mac
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</pre>
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which will produce .prim file. You can open this file in DAWN
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<pre style="color: #800000; background-color: #dcdcdc">
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[username@plus1 DICOM_build]$ dawn g4_00.prim
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</pre>
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This will create 3D image showing the patient geometry and the incident electron beam. The image is big and it takes time to open:
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http://www.hep.ucl.ac.uk/pbt/RadiotherapyWorkbook/skins/common/images/DICOM/g4_03.eps
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== <span style="color:#000080"> Files </span> ==
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[[List of computed tomography files with brief description]]

Latest revision as of 15:40, 2 September 2014

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