Multi-Threshold Coincidence Resolving Time Readout Circuit
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Solution Overview
Problem
Traditional CRT readout circuits using single-threshold comparators for SiPMs in medical imaging systems, such as PET, suffer from loss of information at high photon rates due to fixed threshold settings, leading to suboptimal coincidence resolving time and image quality.
Innovation Solution
A multi-threshold CRT readout circuit employing a flash ADC with a configurable voltage range based on parameters like scintillator characteristics, amplifier bandwidth, and system jitter, which allows for simultaneous operation of multiple thresholds, eliminating the need for threshold tuning and enhancing timestamp resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-threshold comparator is used to digitize the SiPM output, then the circuit complexity is reduced and ease of manufacture is improved, but information is lost at high photon rates when multiple photons are registered as single photon events
Solution Approach 1:
The patent segments the single digitization function into multiple parallel threshold comparators, each operating at a different threshold level. This allows simultaneous detection of single-photon and multi-photon events without information loss, while maintaining manufacturing simplicity by using identical comparator circuits operating in parallel.
Solution Approach 2:
The patent makes the digitization system multi-functional by having multiple comparators with different threshold values process the same SiPM output signal simultaneously. Each comparator serves a specific function (detecting different photon multiplicities), and their combined output provides comprehensive photon event information without requiring different types of circuitry.
2Device complexity
If a single-threshold comparator is used, then the device complexity is reduced, but measurement precision of coincidence resolving time deteriorates due to loss of intensity information
Solution Approach 1:
The patent divides the measurement function into multiple parallel threshold comparators that simultaneously detect different photon event intensities. This segmentation preserves intensity information crucial for accurate coincidence resolving time measurement while keeping each individual comparator simple and identical to the others.
Solution Approach 2:
The patent adds a threshold dimension to the detection system by operating multiple comparators at different threshold levels simultaneously. This transforms the single-dimensional detection into a multi-dimensional measurement space, enabling precise CRT measurement by capturing both timing and intensity information.
3Measurement precision
If multiple threshold values are implemented for converting SiPM output to digital values, then information loss is eliminated and measurement precision is improved, but device complexity increases due to multiple comparators or configurable ADC
Solution Approach 1:
The patent segments the threshold comparison function into multiple identical, simple comparator circuits operating in parallel, each handling a specific threshold level. This approach achieves multi-threshold measurement precision while keeping individual circuit elements simple and manufacturable, reducing the complexity burden compared to a single complex configurable ADC.
Solution Approach 2:
The patent uses identical copies of simple comparator circuits with different fixed threshold values instead of a single complex configurable comparator or ADC. This copying strategy simplifies the overall system by repeating a basic, well-understood circuit element rather than implementing a more complex but less proven single-circuit solution.
4Ease of operation
If a configurable single-threshold comparator is used, then ease of operation is improved through single parameter control, but productivity is reduced due to inability to capture high photon rate events accurately
Solution Approach 1:
The patent segments the photon detection capability into multiple parallel threshold comparators that simultaneously capture single-photon and multi-photon events. This segmentation enables accurate processing of high photon rate events (improving productivity) while maintaining ease of operation through fixed, pre-optimized threshold values that require no runtime configuration.
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 approach improves the coincidence resolving time measurement quality by enabling multiple timestamping without additional digitization circuitry on the SiPM, reducing standard deviation and enhancing the ability to detect photon events accurately, thus improving image resolution in medical imaging applications.
Implementation Method 1
an analog SiPM sensor for detecting photons and generating an SIPM output signal
Implementation Method 2
an amplifier is provided for amplifying the SiPM output signal in advance of the SiPM signal being received by the ADC
Data Source
AI summary
A coincidence resolving time readout circuit is described. An analog SiPM sensor for detecting photons and generating an SIPM output signal is provided. An ADC is configured to provide multiple threshold values for converting the analogue SiPM output signal to digital values. A time to digital converter configured to receive multiple digital values from the ADC and timestamp the digital values.