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

Area of Science:

• Nuclear Instrumentation
• Digital Signal Processing
• Medical Imaging Technology

Background:

• High count-rate nuclear instrumentation, such as Positron Emission Tomography (PET), often uses DC-coupled analog signals for optimal performance.
• Signal baseline drift in DC-coupled systems degrades energy resolution and positioning accuracy, and complicates pileup correction.
• Existing baseline restorer (BLR) methods have limitations in count-rate capability or require complex analog front-end application-specific integrated circuits (ASICs).

Purpose of the Study:

• To develop a novel, accurate, real-time digital baseline restorer (BLR) for high count-rate digital systems.
• To address the performance degradation caused by signal baseline drift in systems like PET.
• To provide a self-tracking BLR solution that operates effectively under high count-rate and pileup conditions.

Main Methods:

• Developed a simple statistics-based online baseline restorer (SOBLR) utilizing existing free-running Analog-to-Digital Converters (ADCs).
• Acquired additional signal samples, excluding actual pulses, for online statistical processing to determine baseline values.
• Implemented a digital circuit comprising counter/timers, a comparator, a register, and a subtraction unit for real-time baseline correction.

Main Results:

• The SOBLR method effectively removes DC baseline drift from digitized waveforms, retrieving original pulses.
• Simulations demonstrate a single channel's capability to operate at a 30 Mcps count-rate, even with signal pileup.
• 336 SOBLR circuits were successfully integrated into 12 Field-Programmable Gate Arrays (FPGAs) for a fully digital PET system.

Conclusions:

• The developed SOBLR offers a high-performance, real-time solution for baseline restoration in high count-rate digital systems.
• This statistical approach self-tracks baseline drift, eliminating the need for micro-controller intervention.
• The successful implementation in a digital PET system validates its effectiveness and scalability for demanding nuclear instrumentation applications.