A NEW TWO-DIMENSIONAL POSITION ENCODER IS PROPOSED FOR PET WITH POSITION RESOLUTION BETTER THAN 3 MILLIMETERS.

A NEW TWO-DIMENSIONAL POSITION ENCODER IS PROPOSED FOR PET WITH POSITION RESOLUTION BETTER THAN 3 MILLIMETERS. THE NEW DETECTOR INCLUDES 32 BISMUTH GERMANATE (BGO) SCINTILLATION CRYSTALS MOUNTED ON A LIGHT GUIDE. THE LIGHT GUIDE PROVIDES A SQUARE ROOT SEPARATION OF THE LIGHT DISTRIBUTION FROM EACH CRYSTAL. THE LIGHT FROM THE LIGHT GUIDE IS DETECTED BY TWO DUAL HAMAMATSU PHOTOMULTIPLIER TUBES (R1548) THAT ARE ONE INCH SQUARE. THE SIGNAL FROM EACH PHOTOMULTIPLIER IS PROCESSED THROUGH THE ENCODING ELECTRONICS TO PRODUCE A DIGITAL SIGNAL INDICATING A SIGNAL POSITION (1 OUT OF 32) FOR EACH 511 KEV GAMMA RAY IMPINGING ON THE DETECTOR. THE DIMENSION OF EACH OF THE 32 CRYSTALS IS NOMINALLY 3 MILLIMETERS 12 30 MILLIMETERS. IT IS ANTICIPATED THAT THE DETECTOR, INCLUDING CRYSTALS, LIGHT GUIDE, PHOTOMULTIPLIER AND ELECTRONICS FOR THE 32-CRYSTAL ARRAY, WILL COST $2,500 COMPARED TO THE ACTUAL COST OF $15,000 FOR 32 INDIVIDUAL CRYSTALS, PHOTOMULTIPLIERS, AND SETS OF ELECTRONICS. THE IMPROVED POSITION RESOLUTION ( 3 MM) WILL ALLOW PET TOMOGRAPHS TO OBTAIN THE THEORETICAL LIMIT IMPOSED BY THE MOMENTUM OF THE POSITRON. IT ALSO OFFERS A REDUCTION IN FRONT END COST FROM APPROXIMATELY $2,000,000 TO $320,000 FOR A FOUR-RING TOMOGRAPH USING 3-MM WIDE CRYSTALS.