The line source image is maintained in focus during scanning by {HEAD ~ synchronous refocussing} of {TAIL ~ the imaging system} 
The line source image is maintained in focus during scanning by { HEAD ~ synchronous refocussing } of { TAIL ~ the imaging system }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL