[Gate-users] Simulation problems with time-activity curves (TAC)

[Benoît Presles]

Dear gate users,

I am reaching out to you to ask for your help concerning a GATE 
simulation that I am working on at the moment. I am trying to perform a 
dynamic simulation by integrating time-activity curves (TAC) to a 
voxelized NEMA phantom geometry. I use a CT image as the phantom 
(/CT.mha)/ and a labeled image (/CTMuliLabel.mha), /of the same size as 
the phantom image, as my activity image. In order to perform the TAC 
implementation I followed the example provided on the GateContrib on 
github: https://github.com/OpenGATE/GateContrib/tree/master/imaging/TimeActivityCurve 
<https://github.com/OpenGATE/GateContrib/tree/master/imaging/TimeActivityCurve>

However, I noticed that GATE doesn't seem to be taking into account my 
TAC even though I believe to have correctly followed the example. In my 
experience, Gate only seems to consider the /activityRange.dat /file 
when defining the activity and not the /acti.range/ which indexes the 
TAC to be used. What is weird is that while compiling the simulation, 
the verbose I get in the terminal shows that the TAC file has been read 
but the activity values contained in the file are not given to the 
corresponding voxels. In order to verify this, I did a simulation with 
and without the TAC integration while keeping an identical seed and the 
generated results are identical. Therefore, I concluded that my 
simulation only takes into account the activities entered in the 
/activityRange.dat/ file and completely ignores the TAC indexed in the 
/acti.range /file.

Linked below in the email you can find a link 
<https://drive.google.com/drive/folders/1NeWu2e1eojkL03pUZKUqq_-9IKmK8MUN?usp=sharing>to 
a simplified version of my simulations with and without TAC along with 
the necessary data (in the data folder). To run the simulation you 
simply need to run one of the main macros:
   - for the simulation with TAC: /Gate mac/main_with_TAC.mac/
   - for the simulation without TAC: /Gate mac/main_with_NO_TAC.mac/

Pay attention to the fact that "total activity (Bq)" provided by the 
Voxel reader verbose only takes into account the value provided in the 
/activityRange.dat /(the value in this field is obtained by multiplying 
the activity provided in the /activityRange.dat /file, which is 8 Bq for 
voxels with an intensity of 8, and the number of pixels which have an 
intensity of 8, which are 13939 in my example):
image.png

Other than wanting to know why the simulation doesn't take into account 
the TACs, I have some other questions as well:

1) Why do we still need the activityRange.dat file in a dynamic setting? 
Since we use TACs, I do not understand the use of using a 
rangeTranslator and the activityRange.dat

2) Is there a better or newer method to attribute TACs to a voxelized 
geometry?

Thank you for your time.

Best regards,
Ben


https://drive.google.com/drive/folders/1NeWu2e1eojkL03pUZKUqq_-9IKmK8MUN?usp=sharing 
<https://drive.google.com/drive/folders/1NeWu2e1eojkL03pUZKUqq_-9IKmK8MUN?usp=sharing>
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