Initially, {TAIL ~ a set} of {HEAD ~ focus points} are identified that were used in the scan of a virtual slide image 
Initially , { TAIL ~ a set } of { HEAD ~ focus points } are identified that were used in the scan of a virtual slide image
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH