[Gate-users] what does each detector pixel record?

[Howard]

Hi GATE users,

I have been using GATE to simulate CBCT. One question I have been thinking
to ask is: what does each detector pixel (set as the crystal sensitive
detector) record, photon energy or photo number?

Let's say the output of each run (one projection angle) is set as:

# Specific CT Image output
/gate/output/imageCT/enable
/gate/output/imageCT/setFileName output_dir/proj

What if I use ROOT output format?

# Generic ROOT output
#/gate/output/root/enable
#/gate/output/root/setFileName output_dir/results

My detector macro is set as follows for your reference.

####  General informations about the scanner
# CT scanner for small animal imaging
# 150 x 200 pixels in one module
# Size of pixels : 0.4 x 0.3 x 3.0 mm3
# Pixels are made up of silicon (no dead space between pixels)
# This scanner is designed to be fixed (the phantom will rotate instead).
# Let's position it perpendicular to the Z axis at a radial distance of 80
mm.


## CTscanner system (this is the encompassing volume)
# This first volume containing the scanner should have the same hard-coded
name
# as the one predefined in GATE (here CTscanner)
# Create it as a box that can contain all pixels
# Set it 80 mm away from the center of the world along the Z axis
# Set material Air, and visualize it as a white wire frame
/gate/world/daughters/name CTscanner
/gate/world/daughters/insert box
/gate/CTscanner/geometry/setXLength  60. mm
/gate/CTscanner/geometry/setYLength  60. mm
/gate/CTscanner/geometry/setZLength   3. mm

/gate/CTscanner/placement/setTranslation 0. 0. 80. mm # original position

#/gate/CTscanner/placement/setTranslation 0. -80. 0. mm # for parallel
computing, 6/10/2022
#/gate/CTscanner/placement/setRotationAxis 1 0 0 # for parallel computing,
6/10/2022
#/gate/CTscanner/placement/setRotationAngle -90. deg # for parallel
computing, 6/10/2022


/gate/CTscanner/setMaterial Air
/gate/CTscanner/vis/forceWireframe
/gate/CTscanner/vis/setColor white

## The first component of the CTscanner is the module
# CTSCANNER #   ---->   #  MODULE  #
# Here we will use only one module, so just create it identical to the
encompassing volume
/gate/CTscanner/daughters/name module
/gate/CTscanner/daughters/insert box
/gate/module/geometry/setXLength  60. mm
/gate/module/geometry/setYLength  60. mm
/gate/module/geometry/setZLength   3. mm
/gate/module/setMaterial Air
/gate/module/vis/forceWireframe
/gate/module/vis/setColor white

## The second component of the CTscanner is the cluster (located inside the
module)
# There are 3 possible clusters: cluster_0, cluster_1 and cluster_2
#  MODULE  #   ---->   # CLUSTER_0 #
# Here we will use only one type of clusters, so again just create it
identical to the mother volume
/gate/module/daughters/name cluster
/gate/module/daughters/insert box
/gate/cluster/geometry/setXLength  60. mm
/gate/cluster/geometry/setYLength  60. mm
/gate/cluster/geometry/setZLength   3. mm
/gate/cluster/setMaterial Air
/gate/cluster/vis/forceWireframe
/gate/cluster/vis/setColor white

## The third component of the CTscanner is the pixel (located inside the
cluster)
# There are 3 possible pixels, one by cluster: pixel_0 (in cluster_0),
pixel_1 (in cluster_1) and pixel_2 (in cluster_2)
#  MODULE  #   ---->     # CLUSTER_0 #   ---->   # PIXEL_0 #
# Here we will use only one type of pixels
# The pixel size is 0.4 x 0.3 x 3 mm3
# Visualize it as a solid object, color of your choice
/gate/cluster/daughters/name pixel
/gate/cluster/daughters/insert box
/gate/pixel/geometry/setXLength 0.4  mm
/gate/pixel/geometry/setYLength 0.3 mm
/gate/pixel/geometry/setZLength 3. mm
/gate/pixel/setMaterial Silicon
/gate/pixel/vis/forceSolid
/gate/pixel/vis/setColor red

# Now we can repeat the pixel inside the cluster
# We want 150 x 200 pixels
# Note: the repeated objects will be automatically centered on the original
position of the single volume
# Set the correct number of repeated volumes and the repeat vector
/gate/pixel/repeaters/insert cubicArray
/gate/pixel/cubicArray/setRepeatNumberX 150
/gate/pixel/cubicArray/setRepeatNumberY 200
/gate/pixel/cubicArray/setRepeatNumberZ   1
/gate/pixel/cubicArray/setRepeatVector 0.4 0.3 0. mm
## Attach to hard-coded CTscanner system (here only cluster_0 and pixel_0
are used)
# These commands allow GATE to make a link between the arbitrary volumes
you defined and the predefined components of
# the system in use (here the CTscanner). It is used to make a link with
the output modules associated to the system

/gate/systems/CTscanner/module/attach module
/gate/systems/CTscanner/cluster_0/attach cluster
/gate/systems/CTscanner/pixel_0/attach pixel

## Attach the pixel as the crystal sensitive detector
# This command is used to specify which arbitrary volume is used as the
sensitive volume.
# All interactions occuring in this volume can be recorded and analyzed.
/gate/pixel/attachCrystalSD

Any feedback is greatly appreciated!
Howard
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