CatPhan Uniformity index and Integral Non Uniformity

Hi all,

I am working the catphan CBCT image analysis using Pylinac. I have doubts on Uniformity index and Integral non uniformity

Uniformity index

Can any explain me why the 1000 is added in denominator as given below in uniformity index

uis = [100*((roi.pixel_value-center.pixel_value)/(center.pixel_value+1000)) for roi in self.rois.values()]

As for I understand, 1000 is to eliminate the infinity value when center.pixel is 0

Integral non uniformity

Can any explain me why the 2000 is added in denominator as given below in Integral non uniformity

(maxhu - minhu)/(maxhu + minhu + 2000)

Sorry It may be simple I can’t get it.

Please explain


I can’t recall off the top of my head. I tried searching for it but can’t find that reference. let me look into it; it may need to be removed. Thanks

Hi James,
Thanks for the effort
I got the reference for that

Ulrik V. Elstrøm, Ludvig P. Muren, Jørgen B. B. Petersen & Cai Grau (2011) Evaluation of image quality for different kV cone-beam CT acquisition and reconstruction methods in the head and neck region, Acta Oncologica, 50:6, 908-917, DOI: 10.3109/0284186X.2011.590525

They have used it. Thanks

Also see AAPM report 39 page 37-38.