Ultra-dense lutetium oxide ceramic scintillators for positron emission tomography

<i>Objective.</i>Lutetium oxide (Lu₂O₃), with its high density (9.4 g cm^-3), presents a compelling scintillation host for detecting 511 keV annihilation photons in positron emission tomography (PET). Despite its favorable density, the practical deployment of Lu₂O₃-based scintillators for PET has faced limitations due to difficulties in crystal growth and inappropriate decay time. Recent progress in ceramic processing has facilitated the development of transparent Lu₂O₃ceramics, while targeted doping strategies have significantly improved their luminescence performance. This study evaluates the performance of Lu₂O₃:Yb and a newly developed ceramic scintillator of (Lu,Y)₂O₃:La, a modified Lu₂O₃-based compound incorporating yttrium (Y) and doped with lanthanum (La).<i>Approach.</i>Various ceramic disks were fabricated and cut into 3 × 3 × 5 mm³samples. The performance of both Lu₂O₃:Yb and (Lu,Y)₂O₃:La ceramic samples in terms of decay time, energy resolution, and coincidence timing resolution (CTR) was assessed. Decay time measurements were conducted using waveform data collected from samples mounted on an H10580 photomultiplier tube (PMT) and irradiated with 511 keV photons from a²²Na source. Energy and CTRs were evaluated using both PMT and silicon photomultiplier setups, arranged in coincidence with a reference lutetium-yttrium oxyorthosilicate (LYSO) detector of the same size.<i>Main results.</i>All three (Lu,Y)₂O₃:La ceramic scintillator samples exhibited a triple exponential decay profile and were dominated by a slow component ranging from 1379.3 to 1515.6 ns. The best energy resolution of 15.4% at 511 keV and the best CTR of 237.9 ps full width at half maximum (FWHM) were observed for the same sample. In contrast, a fast decay time of 1.6 ns was observed for the Lu₂O₃:Yb samples, which exhibited CTR values ranging from 237.9 ps to 261.4 ps FWHM, while the photopeak at 511 keV was difficult to distinguish. These CTR values were estimated between two identical ceramic samples, derived from coincidence measurements of each ceramic sample against the LYSO reference detector. The (Lu,Y)₂O₃:La samples achieved CTR values comparable to those of the Lu₂O₃:Yb samples, as their much higher light yield offsets the disadvantage associated with their slower decay time.<i>Significance.</i>These results highlight the promising potential of the (Lu,Y)₂O₃:La ceramic scintillators for PET applications, especially for time-of-flight PET.