{HEAD ~ The grid} of {TAIL ~ this invention} is of an air core type, eliminating the x ray transparent material of the prior known grids 
of
{ HEAD ~ The grid } of { TAIL ~ this invention } is of an air core type , eliminating the x ray transparent material of the prior known grids
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH