Nonlinear least-squares modeling of 3D interaction position in a monolithic scintillator block

Abstract

This paper presents a study of possible models to describe the relation between the scintillation light point-of-origin and the measured photo detector pixel signals in monolithic scintillation crystals. From these models the X, Y and depth of interaction (DOI) coordinates can be estimated simultaneously by nonlinear least-square fitting. The method depends only on the information embedded in the signals of individual events, and therefore does not need any prior position training or calibration. Three possible distributions of the light sources were evaluated: an exact solid-angle-based distribution, an approximate solid-angle distribution and an extended approximate solid-angle-based distribution which includes internal reflection at side and bottom surfaces. The performance of the general model using these three distributions was studied using Monte Carlo simulated data of a 20 x 20 x 10 mm lutetium oxyorthosilicate (Lu₂SiO₅ or LSO) block read out by 2 Hamamatsu S8550 avalanche photo diode arrays. The approximate solid-angle-based model had the best compromise between resolution and simplicity. This model was also evaluated using experimental data by positioning a narrow 1.2 mm full width at half maximum (FWHM) beam of 511 keV photons at known positions on the 20 x 20 x 10 mm LSO block. An average intrinsic resolution in the X-direction of 1.4 mm FWHM was obtained for positions covering the complete block. The intrinsic DOI resolution was estimated at 2.6 mm FWHM.

High resolution detectors based on continuous crystals and SiPMs for small animal PET

“…However, Fig. 1(b) shows that the DoI is visibly biased towards the side where the SiPM array is located in agreement with the original work [9]. In comparison, Fig.…”

“…The model is based on the solid angle subtended by the estimated position of interaction and every SiPM pixel, considering reflections in every side of the crystal [9]. …”

“…The 3D positions of g-ray interactions are estimated using an analytical model [9] with no previous training. Monte Carlo simulations and experimental data are compared to investigate the DoI estimation.…”

Detector characterization and first coincidence tests of a Compton telescope based on LaBr3 crystals and SiPMs

“…We are testing a method [7] that estimates the interaction position in ðx,y,zÞ using an analytical model based on the angle subtended by the interaction position with the photodetector elements. This method has the advantage that no previous calibration is required.…”

Position reconstruction in monolithic block detectors

“…The readout electronics detect coincident events between this detector and the PMT for electronic collimation. A diode matrix sums the 64 PMT channels to eight row and eight column signals and a chargeto-time converter [8] translates them into pulse lengths. After conversion by a time-to-digital converter (TDC) the 16 values are transmitted to a pc for recording in case that a coincidence was detected.…”