High-resolution monolithic detector design for clinical Positron emission tomography systems

INTRODUCTION State-of-the-art clinical positron emission tomography (PET) scanners utilize detector blocks consisting of many pixelated scintillation crystals. First systems in the preclinical domain are now based on monolithic crystal blocks showing a remarkable performance which also makes it potentially interesting for clinical PET [1][2]. The advantages are better spatial resolution with intrinsic depth-of-interaction (DOI) information, improved light output and better timing properties. In this study, we use optical simulation to design such a clinical detector. The challenge is to optimize design parameters, (such as crystal aspect-ratio, surface finish and read-out schemes), to balance performance, calibration procedures and cost. Monte Carlo simulations are a common tool to test different design parameters. MATERIALS AND METHODS The detector consists of a 50 x 50 x 16 mm3 LYSO scintillation block coupled to a 3 x 3 mm2 pixel 16 x 16 SiPM array. The photon detection efficiency is 50%. The detector is calibrated with a pencil beam in 1 mm steps. The acquired events are grouped in 6 DOI layers by their standard deviation. The mean signal is then calculated for each layer and saved in look-up-tables. Positioning is done with a k-nearest neighbors’ algorithm. The spatial resolution is evaluated in the central region of the detector by means of FWHM. RESULTS AND DISCUSSION 40.000 γ - events are positioned in a 11 x 11 grid in the central area of the detector. The determined spatial resolution is 0.65 mm. The balance between thickness of the detector, pixel size and degree of multiplexing should be carefully chosen to find appropriate positioning accuracy and sensitivity. This monolithic detector is promising for clinical PET systems due to its high spatial resolution and intrinsic DOI information. Future studies include the experimental validation of the simulation set-up and implementing machine learning algorithms to find the γ - interaction position in the detector block. References [1] R. Marcinkowski, P. Mollet, R. Van Holen, and S. Vandenberghe, “Sub-millimetre DOI detector based on monolithic LYSO and digital SiPM for a dedicated small-animal PET system,” Phys. Med. Biol., vol. 61, no. 5, pp. 2196–2212, 2016. [2] E. Berg and S. R. Cherry, “Innovations in Instrumentation for Positron Emission Tomography,” Semin. Nucl. Med., 2018