title: 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.
authors.affiliation: Department of Experimental Diagnostic Imaging, University of Texas M.D. Anderson Cancer Center, Houston, TX 77030 USA.
authors.forename: Hongdi
authors.initials: H
authors.lastname: Li
authors.forename: Chao
authors.initials: C
authors.lastname: Wang
authors.forename: Hossain
authors.initials: H
authors.lastname: Baghaei
authors.forename: Yuxuan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Rocio
authors.initials: R
authors.lastname: Ramirez
authors.forename: Shitao
authors.initials: S
authors.lastname: Liu
authors.forename: Shaohui
authors.initials: S
authors.lastname: An
authors.forename: Wai-Hoi
authors.initials: WH
authors.lastname: Wong