Rescale voxel values of CBCT to MDCT HU

I have a CBCT and MDCT of the same specimen and I want to “convert” the grey values in CBCT accordingly the ones in MDCT and consequently be able to measure “HU” values in the CBCT volume?

I have a CBCT and MDCT of the same specimen and I want to “convert” the grey values in CBCT accordingly the ones in MDCT and consequently be able to measure “HU” values in the CBCT volume?

If you know the correspondence between original values and HU then applying that transformation to voxel intensities should be trivial. If you need don’t know it then you need to do a few measurements.

These topics should help:

Note that for many operations, such as visualization, registration, segmentation, a calibrated CT is useful, but not essential. What is your application? What would you like to achieve overall?

i need the HU units for the treatment planning system and monte carlo simulation

For radiation therapy treatment planning you indeed need voxels in HU, so you need to calibrate the intensity as described in the topics linked above.