OpenKBP - 2020 AAPM Grand Challenge Forum

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> CT images - grey level to HU

Hello, is it possible to know the transformation from grey level to HU for the given CT images? Is it 1000, 1024 or something like that? Is it the same for all or it depends on the patient?


Posted by: ana_barragan @ May 18, 2020, 2:14 p.m.

Hi Ana,

I believe all CT images should be in HU already. However, these scans were taken at several institutions so there may be some variability.


Posted by: OpenKBP @ May 20, 2020, 3:19 p.m.

Thanks for your answer Aaron!

In the pdf you have in git it says: ct.csv - grey-scale images of the patients prior to treatment. Moreover, when I look at the minimum it is zero for all patients. Given that HU=0 corresponds to water, it cannot be HU. In that case, the minimum of images should be around -1000 (HU of air).


Posted by: ana_barragan @ May 20, 2020, 7:25 p.m.

Thanks for bringing this up! The CT images were rescaled so that air = 0 and water ≈ 1000. I say "≈ 1000" only because there may be some variation introduced by the variety of machines that would have been used to acquire the CT images. In hindsight, I recognize that this may be a little unorthodox, but it really helped us keep the CT files sparse (and with a small file size). Maybe we could have made this more clear in the documentation... perhaps in v2 :)


Posted by: OpenKBP @ May 20, 2020, 8:03 p.m.

Perfect! Ok, I got it now :)


Posted by: ana_barragan @ May 20, 2020, 8:12 p.m.
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