SiPM Digital Discriminator for Dark Pulse Rejection
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Solution Overview
Problem
Silicon Photomultipliers (SiPMs) in nuclear medicine imaging systems face performance limitations due to dark-current pulses, which resemble true events and lead to false triggers, degrading system performance and requiring cumbersome look-up tables to deactivate noisy microcells.
Innovation Solution
A digital discriminator method that generates a time-mark from the first photo-electron of a gamma-event, ignoring dark-current pulses by counting primary and secondary pixels within a fixed time frame, and using thresholds to differentiate between true events and dark pulses, thereby preventing false triggers without deactivating pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dark-current pulses are filtered using traditional threshold-based discriminators, then false triggers are reduced, but true gamma-events with low amplitude may be missed, reducing detection sensitivity
Solution Approach 1:
The discriminator processes pixels in segments by dividing the SiPM array into blocks and processing primary pixels and their associated secondary pixels in groups. This segmentation allows the system to apply coincidence logic efficiently while maintaining the ability to detect low-amplitude events through the spatial distribution pattern of triggered pixels.
Solution Approach 2:
The invention transitions from amplitude-based discrimination to a spatio-temporal dimension by detecting coincident pixel triggers within a defined time window. Instead of relying solely on signal amplitude thresholds, the system uses the spatial coincidence of multiple pixel triggers and their temporal correlation to distinguish true gamma-events from dark-current pulses, thereby maintaining sensitivity to low-amplitude events while reducing false triggers.
2Reliability
If pixels are deactivated using look-up tables to reduce dark pulse effects, then false triggers are minimized, but device complexity and operational burden increase
Solution Approach 1:
The system dynamically identifies and processes primary pixels and their associated secondary pixels in real-time based on trigger coincidence logic. Instead of statically deactivating pixels through look-up tables, the discriminator adaptively determines which pixels to process based on the spatial-temporal pattern of triggers, eliminating the need for cumbersome pixel deactivation management while maintaining reliability.
3Measurement precision
If all pixels are processed for every trigger event, then detection accuracy is maintained, but system throughput decreases due to processing overhead
Solution Approach 1:
The discriminator segments the pixel array into blocks and processes only primary pixels and their associated secondary pixels for each trigger event. This segmentation strategy reduces the number of pixels that need to be processed while maintaining detection accuracy through the coincidence logic that identifies true gamma-events based on spatial-temporal correlations among triggered pixels.
Solution Approach 2:
The system processes a subset of pixels (primary and secondary pixels) rather than all pixels for each trigger event. This partial processing approach is sufficient to maintain detection accuracy because true gamma-events produce characteristic spatial-temporal patterns that can be identified through coincidence logic applied to the relevant pixel subset, thereby improving throughput without sacrificing accuracy.
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 system throughput by reducing false triggers, allowing efficient detection of true gamma-events and minimizing noise, while maintaining high sensitivity and accuracy in imaging systems like PET/MR, PET/CT, and standalone PET systems.
Implementation Method 1
When a photon is absorbed in the junction, it can cause a photo-electron to be released
Implementation Method 2
The photo-electron drifts to a region of high electric field where it accelerates and causes additional electrons to be released by impact ionization
Implementation Method 3
A scintillator (not shown) attached to the SiPM sensor 108 converts a high energy gamma-ray to many photons
Data Source
AI summary
Apparatuses and methods are provided that minimize the effects of dark-current pulses. For example, in one embodiment of the invention, a method is provided where a first pixel is struck (i.e., a primary pixel). Pixels struck within a fixed time frame after the primary pixel is struck are referred to as secondary pixels. After a short fixed time frame has expired, the number of primary and secondary pixels is added. If the count exceeds a threshold, the primary pixel was activated by the first (or early) photon from a true gamma event. If the threshold is not met then it is likely the primary pixel generated a dark pulse that should be ignored.