How to calibrate the reconstruction output to Hounsfield Units?
Regarding parameters that have to be used for calibrating a scanner: a) PARTAG_SCALEFACTOR in general does not make any impact; it is canceled out. COBRA pipeline is the following: input signal (16-bit integers) –> preprocessed signal (64 bit floats) preprocessed signal (16 bit integers) = preprocessed signal (64 bit floats) * PARTAG_SCALEFACTOR. Internal output (32 bit integers) = backprojecting / accumulating N projections, each = preprocessed signal (16 bit integers). Final output = Internal output (32 bit integers) / N projections / PARTAG_SCALEFACTOR * const * OPTTAG_SLICESCALE; So if PARTAG_SCALEFACTOR does not cause over- or under-flow the output slice values do not depend on it. b) PARTAG_SCALEFACTOR is needed for converting 64-bit double result of FFT into integers for accumulation. For biological objects the good value is 1000 (-1 in that case means the same 1000 as the result of automatic scaling). However since dental scans usually contain metal I recommend to apply 500. c
