[Gate-users] RE: about attenuation and sensitivity in GATE

[Hongwei Ye]

Somehow my message was treated as spam and deleted!! So I repost it here.

Dear Susana and GATE users,

Thank you very much for your solutions.

I have tested Susana's ideas by following 5 quick simulations:
1. air + back-to-back(object+source): 3409/2/20/20 
(true/scatter/random/delay)
2. vacuum + back-to-back: 3483/0/20/23
3. water + back-to-back: 2208/383/17/18
4. no object + back-to-back: 29472/0/11/16
5. no object + F-18: 5818/0/19/28

All simulations are applied on ECAT 962, the object (if have one) is same 
shape to the source (cylinder with 4 cm radius and 3.88 cm long). Activity 
is 0.01 mCi and scan time is 1 second. (see the attached .mac)

Obviously, simulation 4 is definitely wrong!! By using the absolute 
sensitivity of this system (about 9 cps/kBq according to 
Daube-Witherspoon, J Nucl Med 2002, 43: 1398-1409 ), the recorded true 
counts should be around 3300. Does this mean that we cannot use this 
combination for simulations?

Simulation 5 is also questionable. When there is no medium around the 
source, how can Gate simulate annihilations without electrons? And the 
total counts is also too high. Simulation 1 & 2 are reasonable from my 
point of view.

Did I do something wrong, or miss something here ? Any comments are very 
welcome. Thank you very much.

Sincerely,
Hongwei




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