Usage of long axially oriented crystals in PET applications: the AX-PET demonstrator and beyond

par Chiara Casella (CERN)

jeudi 21 nov. 2013, 14:00 → 15:00 Europe/Paris

Amphiteatre (CPPM)

In PET (Positron Emission Tomography) detectors, a radial arrangement of short crystals is normally employed for the detection of the two coincident 511 keV photons from the annihilation of the positrons. An alternative approach is to use long and axially-oriented crystals, stacked in several layers. Such an axial concept is proposed by the AX-PET experiment as a viable solution towards a high sensitivity and high resolution, parallax free detector. The AX-PET is a fully operational PET demonstrator, based on matrices of LYSO crystals (3x3x100 mm3 each) and wavelength shifting strips, individually readout by SiPM. After extensive characterization measurements, the AX-PET has been used for the reconstruction of images of several phantoms and a few small animals, filled and injected with F-18 based solutions. The recent advent of digital SiPM (dSiPM) from Philips - with their compactness, high level of integration and excellent timing performance - opened interesting possibilities for future PET detectors with Time of Flight capabilities, and motivated the study of small scale prototypes modules of long crystals coupled to dSiPM. Excellent coincidence timing resolution of ~ 210 ps have been achieved from dSiPM dual-sided readout 100 mm long LYSO bare crystals. In parallel, possibilities to reconstruct the axial coordinate from the dual-sided readout, by light sharing techniques, have been explored. Spatial resolutions around 4 mm FWHM, constant all along the length of the crystal, are obtained, with 100 mm long crystals with etched surfaces. The AX-PET concept and results will be presented, as well as the results of the study of long crystals coupled with dSiPM, both in terms of timing and spatial resolution.

Transparents Casella_Nov2013_pdf