Parameters for applying materials to CT

Dear FLUKA experts,
I am trying to simulate a simple CT calibration phantom in FLUKA.
I have implemented the relevant DICOM files through FLAIR, using the provided body.mat file. However, I should update the file, to my understanding.
I have the HU to electron density from the CT scan, and the electron density of the calibration phantom.

  1. How should I update the file? Should I create a new file, based on the my HU ranges?
  2. What is the meaning of the Crho_min/Chro_max and CdEdx_rel_min/CdEdx_rel_max parametes? I saw that in the provided file the CdEdx_rel_min/CdEdx_rel_max parameters were set to 1. Should I change it? if so, how to?

Thank you in advance,
Hen Shukrun

Hi @rachel.hen.shukrun

Giving one material for each HU would require the definition of thousands of materials, and the MC will not be able to handle. So you need to split into HU ranges, with each range having a given material.

However giving a certain material to a HU range would result in a step-like density variation. To make it smooth, we use the correction factors.

  1. The head.mat and body.mat are provided as an example for a specific machine. The HU → MATERIALS correspond to the Schneider parametrisation, but for your CT you might need some adjustments. You can copy the body.mat or head.mat (which ever fits better to your case) and modify it, either with a text editor or inside flair.
    The condition is that the each given range of HU units should correspond to a certain MATERIAL/composition with a given density ρ.
    Τhe density variation from the lower HU to the higher HU in each given range, should be in the range [2/3\timesρ, 3/2\timesρ).

  2. You can adjust the Crho_min and Crho_max to make a smooth variation of the density (linearly interpolated in the given HU range) and to ensure continuation with the range before and after.
    Normally you don’t need to modify the CdEdx_rel_min/max, unless if you want to fine tune the conversion with respect some calibrated data with a phantom in your facility.