Fabricating high-resolution and high-sensitivity scintillator arrays using Laser Induced Optical Barriers

High-resolution positron emission tomography (PET) requires pixelated scintillators - however, if the pixelation process leaves inter-pixel gaps, the loss of material results in loss of sensitivity. PET sensitivity also requires scintillators such as LSO and LYSO to be thicker than 2 cm, due to the high penetrating power of 511 keV gamma rays. Fine pixelation of LYSO is difficult, since it is very hard material and is known to crack under thermal and mechanical stress. We have developed a method to introduce optical barriers within monolithic LYSO crystals to form pixelated arrays with small pixel size and large thickness. Arrays were fabricated using a high-frequency solid-state laser to form optical barriers (inter-pixel gaps), which can be as thin as 13 mu m without affecting the transparency of the crystals. Our method yields near-perfect, extremely high aspect ratio pixels. By controlling parameters such as laser pulse repetition rate and energy density, LYSO crystals can be effectively pixelated with virtually no material loss. We have laser processed LYSO crystals ranging from 5 to 20 mm thick and 0.8x0.8 to 1.5x1.5 mm(2) in pixel cross section. When a collimated beam (0.5 mm) of 70 kVp X-rays was incident on one pixel of a 10x10x20 mm(3) scintillator array with 0.8x0.8 mm(2) pixel size, an average optical crosstalk ratio was measured at 6.5:1, which shows excellent pixel separation. Our technique is ideal for fabricating scintillator arrays for clinical/pre-clinical PET and SPECT systems as well as photon counting CT detectors. Our technique is automated, and is cost-effective.