# Parameters that allow to reuse sensitivity image

**URL:** <https://castor-project.discourse.group/t/parameters-that-allow-to-reuse-sensitivity-image/760>\
**Category:** General Discussions\
**Created:** [April 15, 2024, 5:57pm UTC](https://castor-project.discourse.group/t/parameters-that-allow-to-reuse-sensitivity-image/760 "2024-04-15T17:57:51Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![miguelleaolopes](https://avatars.discourse-cdn.com/v4/letter/m/85e7bf/32.png) [@miguelleaolopes](https://castor-project.discourse.group/u/miguelleaolopes)\
**Post date:** [April 15, 2024, 5:57pm UTC](https://castor-project.discourse.group/t/parameters-that-allow-to-reuse-sensitivity-image/760/1 "2024-04-15T17:57:51Z")

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Dear CASToR users and developers,

I have a system with a large number of elements, which leads to a large sensitivity image generation time. (I am using list-mode/emission data - aka data with format t,id1,id2)

Thus I want to know, after a calculation of one sensitivity image, which reconstruction parameters can I change to reuse the previous sensitivity image.

There are someone more obvious, like FOV size, voxel size, offset and projector, data, convolutions?  
But the ones like the optimizer, (e.g. MLEM vs OSL), penalties and its strength. I am particular curious about changing the beta value, the strength, if I can reuse it. I also assume that changing the iterations is indiferent.

Thank you very much in advance for the help,  
Miguel

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**Author:** ![tmerlin](https://yyz2.discourse-cdn.com/free1/user_avatar/castor-project.discourse.group/tmerlin/32/216_2.png) [@tmerlin](https://castor-project.discourse.group/u/tmerlin)\
**Post date:** [April 16, 2024, 10:44am UTC](https://castor-project.discourse.group/t/parameters-that-allow-to-reuse-sensitivity-image/760/2 "2024-04-16T10:44:27Z")

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Hi Miguel,  
For list-mode compatible optimizers, the sensitivity image generation is independent of the selected optimizer. You can reuse it with different penalties parameters.  
Changing the number of iterations or subsets is not an issue either. The same sensitivity image is used for each iteration, and corrected with the number of subsets.

Best,  
Thibaut