Next generation of the Albira small animal PET based on high density SiPM arrays

A new design of the small animal PET Albira system which detectors are based on arrays of SiPMs and monolithic LYSO scintillator is presented here. The system is made out of 3 rings of 8 detectors each, resulting on an axial and transaxial FOVs of 148 and 80 mm, respectively. The scanner is thermally stabilized using air-cooling. Working temperatures around 22-25°C are reached with individual detector variations around 0.2°C minimizing dark count rates and gain drifts. One of the most significant improvements of the current system is the accurate photon impact determination within the crystal volume, specially its depth of interaction. This allows the calculation of the true line of response and, therefore, minimizes the parallax error at the image FOV edges. As a result, the system returns a homogeneous volumetric spatial resolution FWHM for the entire FOV, of about 1 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> (MLEM algorithm). Applying the NEMA protocol, this prototype reaches a Noise Equivalent Count Rate of 576 kcps at 986 uCi using the mouse-like phantom and 330 kcps at 1275 uCi using the rat-like phantom. The current geometry, similar to the former design based on PSPMTs but with higher active detection area, shows a NEMA sensitivity of 9% using a 50% energy window.