docs: def list_dcm_datain(datain):
      ''' List all DICOM file paths in the datain dictionary of input data.
      '''
  
      if not isinstance(datain, dict):
          raise ValueError('The input is not a dictionary!')
  
      dcmlst = []
      # list of mu-map DICOM files
      if 'mumapDCM' in datain:
          dcmump = os.listdir(datain['mumapDCM'])
          # accept only *.dcm extensions
          dcmump = [os.path.join(datain['mumapDCM'],d) for d in dcmump if d.endswith(dcmext)]
          dcmlst += dcmump
  
      if 'T1DCM' in datain:
          dcmt1 = os.listdir(datain['T1DCM'])
          # accept only *.dcm extensions
          dcmt1 = [os.path.join(datain['T1DCM'],d) for d in dcmt1 if d.endswith(dcmext)]
          dcmlst += dcmt1
  
      if 'T2DCM' in datain:
          dcmt2 = os.listdir(datain['T2DCM'])
          # accept only *.dcm extensions
          dcmt2 = [os.path.join(datain['T2DCM'],d) for d in dcmt2 if d.endswith(dcmext)]
          dcmlst += dcmt2
  
      if 'UTE1' in datain:
          dcmute1 = os.listdir(datain['UTE1'])
          # accept only *.dcm extensions
          dcmute1 = [os.path.join(datain['UTE1'],d) for d in dcmute1 if d.endswith(dcmext)]
          dcmlst += dcmute1
  
      if 'UTE2' in datain:
          dcmute2 = os.listdir(datain['UTE2'])
          # accept only *.dcm extensions
          dcmute2 = [os.path.join(datain['UTE2'],d) for d in dcmute2 if d.endswith(dcmext)]
          dcmlst += dcmute2
  
      #-list-mode data dcm
      if 'lm_dcm' in datain:
          dcmlst += [datain['lm_dcm']]
  
      if 'lm_ima' in datain:
          dcmlst += [datain['lm_ima']]
  
      #-norm
      if 'nrm_dcm' in datain:
          dcmlst += [datain['nrm_dcm']]
  
      if 'nrm_ima' in datain:
          dcmlst += [datain['nrm_ima']]
  
      return dcmlst