Performance comparison of finely pixelated LYSO- and GAGG-based Si-PM gamma cameras for high resolution SPECT

Although Lu-based scintillators, including Ce-doped Lu1.8Y0.2SiO5 (LYSO) scintillators, are often used for positron emission tomography (PET) detectors, they are not commonly used in gamma cameras for single-photon emission computed tomography (SPECT) because background counts due to contamination of the natural radioisotope in Lu are detected. However, several studies report that deterioration in image contrast due to background counts of the natural radioisotope is not critical and thus LYSO is promising for use in SPECT detectors. Meanwhile, a new scintillator, the Ce-doped Gd3Al2Ga3O12 (GAGG) with a high light yield and no natural radioisotope, has been developed and is also thought to be a promising scintillator. Thus, we compared the performance of LYSO with that of GAGG to determine which is more appropriate for a silicon photomultiplier (Si-PM)-based high-resolution small field-of-view (FOV) gamma camera for SPECT. We used finely pixelated LYSO and GAGG plates that were optically coupled to Si-PM arrays to form gamma cameras and measured the basic performance for 122-keV gamma photons. The energy resolutions of the LYSO- and GAGG-based Si-PM gamma cameras were 30% and 23% full width at half maximum (FWHM), respectively. The intrinsic spatial resolution of the GAGG (∼0.5mm FWHM) based gamma camera was better than that of the LYSO (∼0.6mm FWHM). The background counts of the LYSO-based gamma camera were 28 times larger than that of the GAGG. Based on these results, we conclude that GAGG is more appropriate than LYSO for the development of a Si-PM based gamma camera for high resolution SPECT.