A New Statistics-Based Online Baseline Restorer for a High Count-Rate Fully Digital System

Abstract

The goal of this work is to develop a novel, accurate, real-time digital baseline restorer using online statistical processing for a high count-rate digital system such as positron emission tomography (PET). In high count-rate nuclear instrumentation applications, analog signals are DC-coupled for better performance. However, the detectors, pre-amplifiers and other front-end electronics would cause a signal baseline drift in a DC-coupling system, which will degrade the performance of energy resolution and positioning accuracy. Event pileups normally exist in a high-count rate system and the baseline drift will create errors in the event pileup-correction. Hence, a baseline restorer (BLR) is required in a high count-rate system to remove the DC drift ahead of the pileup correction. Many methods have been reported for BLR from classic analog methods to digital filter solutions. However a single channel BLR with analog method can only work under 500 kcps count-rate, and normally an analog front-end application-specific integrated circuits (ASIC) is required for the application involved hundreds BLR such as a PET camera. We have developed a simple statistics-based online baseline restorer (SOBLR) for a high count-rate fully digital system. In this method, we acquire additional samples, excluding the real gamma pulses, from the existing free-running ADC in the digital system, and perform online statistical processing to generate a baseline value. This baseline value will be subtracted from the digitized waveform to retrieve its original pulse with zero-baseline drift. This method can self-track the baseline without a micro-controller involved. The circuit consists of two digital counter/timers, one comparator, one register and one subtraction unit. Simulation shows a single channel works at 30 Mcps count-rate with pileup condition. 336 baseline restorer circuits have been implemented into 12 field-programmable-gate-arrays (FPGA) for our new fully digital PET system.

Performance of a high-resolution depth-encoding PET detector module using linearly-graded SiPM arrays

“…This is sufficient for preclinical PET applications where the standard injected dose for a mouse is ~100 u Ci. However, if needed, higher event rates can likely be handled by restoring the baseline of the signal (Li et al 2010), a method which was not implemented in our current readout electronics.…”

Computationally Efficient Hybrid Interpolation and Baseline Restoration of the Brain-PET Pulses

“…It allows a solution to be realized using regular ADCs and Field Programmable Gate Arrays (FPGAs). Comparing the amplitude of digitized versions of PET pulses to established thresholds, they measure timestamps [23,24,35]. The time is stamped by using the instants of the threshold crossing.…”

Positron Emission Tomography: Current Challenges and Opportunities for Technological Advances in Clinical and Preclinical Imaging Systems

“…They can be used to implement waveform digitization of the detector pulses, and from that, researchers can derive additional information that can be used by the binning and image-reconstruction algorithms. This extra information can also be used, for example, to remove pulse pileups in situations with a high count rate (29), in TOF imaging (30), and to implement DOI correction (31). …”