There are {HEAD ~ a number} of {TAIL ~ methods} for producing images of internal structures of a body 
There are { HEAD ~ a number } of { TAIL ~ methods } for producing images of internal structures of a body
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH