{HEAD ~ Active groups} are any of various pharmacologically or therapeutically active moieties, including moieties useful for {TAIL ~ magnetic resonance contrast enhancement} 
{ HEAD ~ Active groups } are any of various pharmacologically or therapeutically active moieties , including moieties useful for { TAIL ~ magnetic resonance contrast enhancement }
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL