Basically, plot the values obtained from something like:
mrstats dwi.mif -mask brain_mask.mif -output mean
But also, the scaling parameters did differ in the mrinfo output…
Basically because there is no clinical drive for it… The scaling parameters are there to store values that are quantitative (e.g. FA values, ADC values, T2 / T1 maps, etc), but the expectation is that these have been computed on the scanner, and will invariably have been derived from a single series, using the manufacturer-supplied sequence.
But in general, there are many factors that influence the signal: coil loading, coil tuning, frequency drift, transmit power calibration, the receive coils used, as well as all the different steps in the image recon. On a Siemens scanner, these differences can be avoided (as far as I know) by making sure that the scanner adjustments are performed for the first scan only, and turned off for subsequent scans - this ensures the same transmit power, etc, is used. But otherwise, yes you do need to worry about this.
I don’t think there’s a standard DICOM tag for that. On Siemens, you might be able to find this info in the CSA fields. Try dcminfo -a -csa dcm_file, see if you can see anything interesting in there…