Catphan 504 HU tolerance CTP486, CTP404

I was wondering if there was a way to change the HU tolerance for the Uniformity (CTP486) and Linearity (CTP404) separately. I saw that both can be changed using hu_tolerance which changes both the HU uniformity and linearity.

However I just want the uniformity tolerance to be ±30 HU from the center ROI and the linearity tolerances to be ±50. I was wondering where I could find the HU value analyzed for the center ROI for the uniformity module.

Unfortunately, there isn’t a way to decouple these currently out of the box. However, the data is there under the hood. Here is a gist to compare the center uniformity ROI to the surrounding ones within 30 HU. Center Unif ROI (
The same approach can be taken for the linearity module using the ctp404.hu_rois attribute. See this section and related class for what data is available CatPhan — pylinac 3.8.0 documentation CatPhan — pylinac 3.8.0 documentation