Optimization of fiber-optic readout of LSO scintillation crystals with acid etching

Optimizing the collection of scintillation light is essential for good positron emission tomography scanner performance, and even more so when the crystals are read out through optical fibers. Acid etching has been proposed as a cost-effective alternative to mechanical polishing, but there are discrepancies between the results published so far. The aim of this paper is to gain a better understanding of acid etching and its effects on the light yield, and to assess its application to fiber-optic-based configurations. We have examined the surface state of LSO crystals etched for various times and measured their light output in different configurations, with both direct and fiber-optic readout. Our results indicate that crystal etching is a complex process, where different crystal faces may be etched in different ways. Acid etching always resulted in an improved light yield and energy resolution of the crystals, and was as efficient as, or in many cases superior to, mechanical polishing. While this improvement was somewhat limited for the configurations with direct readout of the crystals we tested, it was much larger for the fiber-optic-based configuration.