# Normalization on CASToR **URL:** \ **Category:** General Discussions\ **Tags:** pet\ **Created:** [February 11, 2025, 3:50pm UTC](https://castor-project.discourse.group/t/normalization-on-castor/979 "2025-02-11T15:50:32Z")\ **Posts on this page:** 1\ **Showing post:** 2
**Author:** ![s\_mousavi](https://avatars.discourse-cdn.com/v4/letter/s/8edcca/32.png) [@s\_mousavi](https://castor-project.discourse.group/u/s_mousavi)\ **Post date:** [February 11, 2025, 5:08pm UTC](https://castor-project.discourse.group/t/normalization-on-castor/979/2 "2025-02-11T17:08:38Z")
Hello Beatriz, First note that castor-norm is for direct normalization and in addition your data should be in the histogram format rather than list-mode. Answering your question, as far as I understand, you need to feed castor-norm the true image and not the reconstructed one by castor-recon. I think you are referring to the following post on the forum. > [@Normalization file preparation and normalization factor computation](https://castor-project.discourse.group/t/normalization-file-preparation-and-normalization-factor-computation/966/5): > > Hi Seyyed, To my understanding, castor-norm is based on a direct normalization, unlike the paper from Pepin et al. which is based on a component-based normalization. The principle of a direct normalization is simple : the normalization factor is given by the ratio between the expected projection and the measured projection. The expected projection is the forward projection of the normalization phantom. This is why you have to provide the true image of the normalization phantom to castor-norm,… If you look at this post, it is stated clearly. > [@Normalization file preparation and normalization factor computation](https://castor-project.discourse.group/t/normalization-file-preparation-and-normalization-factor-computation/966/5): > > The expected projection is the forward projection of the normalization phantom. This is why you have to provide the true image of the normalization phantom to castor-norm, rather than the reconstructed (hence, approximative) image of the normalization phantom. > > Experimentally, it is better to use an annular phantom to neglect attenuation and scattered coincidences. If not, you have first to correct the measured data for attenuation and scattered coincidences. You shall also remove the random coincidences. It depends on you, whether you want to correct for the attenuation effect or not. Providing atten factors with the normalization is optional and not mandatory. As you can see in the quoted post, if you choose an annular phantom you can probably ignore the effect of attenuation. To conclude, I think it depends on your specific needs and goal. The more corrections, the better the quality of the reconstructed image. Best, Seyyed --- _[View the full topic](https://castor-project.discourse.group/t/normalization-on-castor/979)._