[Gate-users] Defining an activity distribution with background

[Cassandra Miller]

Hi Satyajit,

Have you tried defining a cold source? You can use the "forbid" command, 
for example:

/gate/world/daughters/name cold_area
/gate/world/daughters/insert cylinder
/gate/cold_area/vis/forceWireframe
/gate/cold_area/vis/setColor green
/gate/cold_area/geometry/setRmax 3.0 cm
/gate/cold_area/geometry/setHeight 1. cm

/gate/source/addSource number1
/gate/source/number1/setActivity 100000. becquerel
/gate/source/number1/gps/particle gamma
/gate/source/number1/setType backtoback
/gate/source/number1/gps/type Volume
/gate/source/number1/gps/shape Cylinder
/gate/source/number1/gps/radius 5. cm
/gate/source/number1/gps/halfz 0.5 cm
/gate/source/number1/gps/centre 0. 0. 0. cm
/gate/source/number1/gps/monoenergy 511. keV
/gate/source/number1/gps/angtype iso
*/gate/source/number1/gps/Forbid cold_area *
/gate/source/number1/dump 1

It might work if when you define your background, you forbid the area 
where the hot rods are, and then you define your hot rods separately as 
you are already doing. I'm not sure if it will fix your problem but it's 
worth a shot. Then you also can define the rods with whatever activity 
you want, without having to take into account the background.

Best,
Cassandra Miller
PhD Student
Quantitative Tomography Lab & Medical Imaging Research Group
Department of Physics & Astronomy, University of British Columbia


On 2019-11-13 8:54 a.m., Satyajit Ghosh wrote:
> Dear GATE users,
>
>                I am trying to define an activity distribution of four 
> circular hot rods with a backgrodeund (of ratio 1:2 wrt hot region) 
> using analytic definition of source (not voxelized definition). I know 
> that the 'setActivity' command basically assigns a certain amount of 
> activity inside a the defined volume. Naturally the background volume 
> is needed to be defined as universal volume containing four volumes 
> for hot rods. After assigning the appropriate activity values in 5 
> volumes (4 hot rods and one background), I am not getting desired hot 
> to background ratio in STIR reconstructed image of GATE data. Please 
> note that I have set the activity of individual hot rods considering 
> contribution from background activity. *I believe the reason of not 
> getting desired result can be the fact that one can't define 
> overlapping source volumes. Is this correct?* If not then how do I 
> define an activity distribution with a background using analytic 
> definition of source.
>
> Satyajit Ghosh
> Phd student
> Physics Department
> IIT Bombay, Mumbai
> 13-Nov.2019
> -- 
> *Satyajit Ghosh*
> *PhD Student*
> *Nuclear Spectroscopy and Molecular Imaging Lab,
> *
> *Physics Department, IIT Bombay,*
> *Mumbai-400076, INDIA*
>
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