PET Photodetector Digitizer Using Level-Crossing ADCs for Fast Pulse Timing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current PET imaging systems face challenges in achieving high sensitivity and efficient data processing, particularly in accurately measuring the fast rise time of PET signal pulses, which affects image quality and scan time, due to limitations in existing analog-to-digital conversion methods.
Innovation Solution
The integration of differential transimpedance amplifiers and level crossing analog-to-digital converters with differential comparators and programmable gain amplifiers, along with a clock for time stamping, allows for precise noise reduction and adjustable gain settings, enabling accurate measurement of both the fast rise and trailing edges of PET signal pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional analog-to-digital conversion methods are used, then device complexity is reduced, but timing resolution and measurement precision deteriorate
Solution Approach 1:
The patent segments the analog-to-digital conversion process into multiple parallel comparator circuits, each handling a specific voltage threshold level. This segmentation allows simultaneous measurement of multiple signal parameters (timing, energy, rise time) without requiring a single complex sequential converter, thereby achieving high timing resolution while managing system complexity through parallel modular architecture.
Solution Approach 2:
The patent introduces an intermediary discriminator circuit that converts photodetector signals into standardized TAC (Time-to-Amplitude Converter) signals before further processing. This intermediary stage acts as a mediator that prepares signals for subsequent analysis, enabling precise timing measurements by converting fast rising edges into measurable voltage pulses that can be processed by the multi-level comparator system.
2Measurement precision
If high sensitivity detection is implemented, then measurement precision improves, but loss of time increases due to complex signal processing
Solution Approach 1:
The patent performs preliminary signal processing by immediately converting incoming photodetector signals into TAC signals and simultaneously feeding them to multiple comparator levels. This preliminary action captures timing and energy information in parallel before the signal decays, eliminating the need for sequential processing steps and preventing time loss while maintaining high energy resolution through the multi-level comparison architecture.
Solution Approach 2:
The patent employs periodic sampling of the signal at multiple predetermined voltage thresholds through the comparator circuitry. This periodic action occurs at fixed time intervals determined by the signal's own characteristics rather than external timing, allowing continuous monitoring of signal evolution and accurate energy measurement without introducing additional processing delays.
3Adaptability or versatility
If adjustable gain settings are added, then adaptability improves, but device complexity increases
Solution Approach 1:
The patent implements a universal signal processing architecture where the same core circuitry (photodetector, TAC converter, multi-level comparator system) serves multiple detector types including SiPMs, APDs, and photomultiplier tubes. The adjustable gain settings provide versatility without requiring separate processing chains for different detectors, as the system can be configured through software or hardware switches to match the characteristics of various photodetector types, thereby achieving adaptability without proportionally increasing complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances the timing resolution to 25 ps and energy resolution of 8%-15%, improving image quality and reducing scan time while optimizing the use of photodetectors, such as SiPMs, by efficiently processing PET signals with adjustable settings for different detector types.
Implementation Method 1
An example of a high energy photon detector is a scintillation crystal that is connected to an optical photodetector such as a photomultiplier tube. The blue optical photons then hit a photodetector which converts the light into an electrical signal.
Data Source
AI summary
An integrated circuit in a PET imaging system with a plurality of photo detectors is provided. A plurality of differential transimpedance amplifiers with differential inputs and differential outputs is provided, wherein differential inputs for each differential transimpedance amplifier of the plurality of differential transimpedance amplifiers are electrically connected to a photodetector. A plurality of level crossing analog-to-digital converters is provided wherein differential inputs for each level crossing analog-to-digital converter of the plurality of level crossing analog-to-digital converters are electrically connected to differential outputs of a differential transimpedance amplifier, wherein each level crossing analog-to-digital converter of the plurality of level crossing analog-to-digital converters, comprises a plurality of differential comparators with differential inputs and differential threshold inputs, wherein the differential inputs are electrically connected to the output of the differential outputs of the differential transimpedance amplifier electrically connected to the level crossing analog-to-digital converter and a clock.