  A PET scanner based on silicon photomultipliers (SiPMs) has been widely used
as an advanced nuclear medicine imaging technique that yields quantitative
images of regional in vivo biology and biochemistry. The compact size of the
SiPM allows direct one to one coupling between the scintillation crystal and
the photosensor, yielding better timing and energy resolutions than the light
sharing methods that have to be used in photomultiplier tube (PMT) PET systems.
To decrease the volume of readout electronics, a front end multiplexer with
position decoder is a common choice for the one to one system without a highly
integrated application specific integrated circuit (ASIC). However, in this
case we cannot measure each crystal's deposited energy inspired by an
annihilation photon, so the inter-crystal scatter (ICS) events will lead to the
crystal mispositioning and then deteriorate the detector intrinsic resolution.
Besides, considering the events rejection within the energy window resulting
from the gain dispersion and nonlinear outputs of the SiPMs, an energy
correction mechanism is needed. Yet, lack of the information of each crystal's
energy will introduce large energy correction error for the ICS events. For
this issue, an online energy correction mechanism implemented on a Kintext-7
Field Programmable Gate Array (FPGA) device is presented in this paper.
Experiments in the laboratory were performed using an 8 x 8 segmented LYSO
crystals coupled with an 8 x 8 SiPM (J-series, from ON Semiconductor) array
which is under 22Na point source excitation. Test results indicate that both
the energy of the non-ICS and ICS events can be precisely corrected and the
energy resolution is better than 12 %. We also applied this method to an actual
clinical PET scanner under a 68Ge line source to verify its multi-channel
reliability.
