Design and Evaluation of an FPGA-ADC Prototype for the PET Detector Based on LYSO Crystals and SiPM Arrays
C. Ma, Xue Dong, Li Yu, Wubin Wang, Xiao-Kun Zhao, Xing Li, Zhenqing Huang, Guocheng Wu, Lei Lu, Hansheng Chen
Abstract
The aim of this study is to design and evaluate a simple free running analog–digital converter (ADC) based on the field-programmable gate array (FPGA) device to accomplish the energy and position readout of the silicon photomultiplier (SiPM) array for application as positron emission computed tomography scanners. This simple FPGA-ADC based on a carry chain time-digital converter (TDC) implemented on a Kintex-7 FPGA consists of only one off-chip resistor so it has greater advantages in improving system integration and reducing cost than commercial chips. In this article, an FPGA-ADC-based front-end electronics prototype is presented, and both the design principle and implementation considerations are discussed. Experiments were performed using an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8 \times 8$ </tex-math></inline-formula> (crystal size: 4 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 4 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 15 mm) and a 12 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 12 (crystal size: 2.65 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2.65 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 15 mm) segmented LYSO crystals coupled with an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8 \times 8$ </tex-math></inline-formula> SiPM (J-series, from ON Semiconductor) array which is under <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22</sup> Na point source excitation. Initial test results indicate that the energy resolution of the two detectors after correction is around 13.2% and 13.5% at 511 keV, and the profiles of the flood histograms show a clear visualization of the discrete scintillator element. All measurements were carried out at room temperature (~ 25°C), without additional cooling.