Maximum-likelihood calibration of small gamma cameras for 511 keV positron annihilation radiation

The feasibility of employing maximum-likelihood (ML) position estimation in small scintillation cameras for use in FDG coincidence imaging was investigated. A small camera consisting of a Hamamatsu R-2487 position-sensitive photomultiplier tube (PSPMT) coupled to a single 8 mm thick NaI(Tl) crystal was calibrated with a tungsten and lead shielded 511 keV ¹⁸F source. The same calibration method has been previously employed at 140 keV using ^99mTc. The source was positioned at each location of the image space to determine detector-signal distributions used in look-up table (LUT) generation. Corrected 511 keV point-array and flood images were obtained using the resulting 511 keV calibration LUT. Resolution was 2.0 mm-2.5 mm full-width at half maximum (FWHM). This demonstrates that it may be feasible to use ML estimation to obtain accurate event positioning in similar imaging detectors employing more suitable scintillators