# Reconstruction of pet data with attenuation correction factor **URL:** \ **Category:** General Discussions\ **Tags:** pet\ **Created:** [November 29, 2023, 10:14am UTC](https://castor-project.discourse.group/t/reconstruction-of-pet-data-with-attenuation-correction-factor/660 "2023-11-29T10:14:12Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![seanlam](https://avatars.discourse-cdn.com/v4/letter/s/ac91a4/32.png) [@seanlam](https://castor-project.discourse.group/u/seanlam)\ **Post date:** [November 29, 2023, 10:14am UTC](https://castor-project.discourse.group/t/reconstruction-of-pet-data-with-attenuation-correction-factor/660/1 "2023-11-29T10:14:12Z")
Dear CASToR users and developers, I’m trying to reconstruct GATE simulation data with attenuation correction factors in data file, but it ended with an error as shown below: ![image-20231129175959542](https://global.discourse-cdn.com/free1/uploads/castor_project/original/1X/653746d6307be1e711670bcdfc4fbfc46c666367.jpeg) by the way, i’m trying to reconstruct emission image with attenuation corrected by transmission PET, so the attenuation correction factors is the ratio of the blank transmission sinogram to transmission with object one’s. and here is my code for castor-recon: castor-recon -df ./xxx.Cdh -opti MLEM -it 5:4 -proj joseph -fout ./xxx/xxx -th 0 -dim 170,170,71 -vox 1,1,1.98 Thank you very much in advance for your help. seanlam ---
**Author:** ![COMTAT\_Claude](https://avatars.discourse-cdn.com/v4/letter/c/9e8a1a/32.png) [@COMTAT\_Claude](https://castor-project.discourse.group/u/COMTAT_Claude)\ **Post date:** [November 29, 2023, 12:56pm UTC](https://castor-project.discourse.group/t/reconstruction-of-pet-data-with-attenuation-correction-factor/660/2 "2023-11-29T12:56:38Z")
Dear Seanlam, According to my understanding, the answer is in the first line of CASToR output : « Attenuation correction is included in the data file while it is not in the sensitivity computation ! ». Apparently, you are reconstructing list-mode data. To compute the sensitivity image, you need to provide CASToR either a normalization datafile with attenuation correction factor (see section 6.1 and Table 4 in the general documentation, option -norm) or an attenuation image (option -atn). Regards, **Claude COMTAT** BioMaps Service Hospitalier Frédéric Joliot 91401 Orsay, France [www.biomaps.universite-paris-saclay.fr](http://www.biomaps.universite-paris-saclay.fr/) **Claude COMTAT** BioMaps Service Hospitalier Frédéric Joliot 91401 Orsay, France [www.biomaps.universite-paris-saclay.fr](http://www.biomaps.universite-paris-saclay.fr/) ---
**Author:** ![seanlam](https://avatars.discourse-cdn.com/v4/letter/s/ac91a4/32.png) [@seanlam](https://castor-project.discourse.group/u/seanlam)\ **Post date:** [November 30, 2023, 2:21am UTC](https://castor-project.discourse.group/t/reconstruction-of-pet-data-with-attenuation-correction-factor/660/3 "2023-11-30T02:21:29Z")
Hi Claude, First of all, thank you very much for your reply. I’ve try your advice by providing an attenuation image and it did solved the error. But the reconstruction image seems to be the same img of no acf datafile reconstructed with the attenuation image. The acf contained in the datafile doesn’t seem to have any effect. Could you further explain the role of attenuation correction factor in datafile? and I will try providing a normalization datafile with acf also, to see any difference. thank you for your kindly help. Best wishes sean ---
**Author:** ![seanlam](https://avatars.discourse-cdn.com/v4/letter/s/ac91a4/32.png) [@seanlam](https://castor-project.discourse.group/u/seanlam)\ **Post date:** [December 1, 2023, 6:59am UTC](https://castor-project.discourse.group/t/reconstruction-of-pet-data-with-attenuation-correction-factor/660/4 "2023-12-01T06:59:27Z")
Hi Claude it worked, by reconstructing with the normalization datafile with attenuation factor. thanks for you help! Regards sean ---
**Author:** ![claude.comtat](https://avatars.discourse-cdn.com/v4/letter/c/ce7236/32.png) [@claude.comtat](https://castor-project.discourse.group/u/claude.comtat)\ **Post date:** [December 1, 2023, 8:43am UTC](https://castor-project.discourse.group/t/reconstruction-of-pet-data-with-attenuation-correction-factor/660/5 "2023-12-01T08:43:54Z")
Great ! **Claude COMTAT** BioMaps Service Hospitalier Frédéric Joliot 91401 Orsay, France [www.biomaps.universite-paris-saclay.fr](http://www.biomaps.universite-paris-saclay.fr/)