docs: def getnii_descr(fim):
      '''
      Extracts the custom description header field to dictionary
      '''
      nim = nib.load(fim)
      hdr = nim.header
      rcnlst = hdr['descrip'].item().split(';')
      rcndic = {}
      
      if rcnlst[0]=='':
          # print 'w> no description in the NIfTI header'
          return rcndic
      
      for ci in range(len(rcnlst)):
          tmp = rcnlst[ci].split('=')
          rcndic[tmp[0]] = tmp[1]
      return rcndic