Flow Cytometer Particle Detection Using Dynamic Thresholds
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Solution Overview
Problem
Flow cytometers face challenges in accurately distinguishing between large and small particles due to the presence of laser lobes and optical reflections, which can lead to incorrect particle sizing and counting, especially when particles pass through minor lobes of the laser beam.
Innovation Solution
Implementing an analog or digital deconvolution filter to process light intensity data and a particle detection trigger mechanism that re-evaluates signals based on thresholds and time differences to differentiate between signals from main and side lobes, allowing for accurate classification of particle sizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a focused laser beam is used to illuminate particles in a flow channel, then measurement precision is improved, but laser lobes and optical reflections create false signals that worsen measurement accuracy
Solution Approach 1:
The patent segments the particle detection process into multiple threshold levels (first threshold for small particles, second threshold for large particles) and uses time-based segmentation to distinguish between particles passing through different lobes. This segmentation allows the system to differentiate between genuine large particles and false signals from laser lobes.
Solution Approach 2:
The patent introduces an intermediary trigger mechanism that mediates between the raw optical signals and final particle classification. This trigger system uses intermediate threshold comparisons and time-difference calculations to filter out false signals before they reach the final detection output.
2Device complexity
If a single threshold is used for particle detection, then device complexity is reduced, but the ability to distinguish between large and small particles deteriorates
Solution Approach 1:
The patent implements dynamic threshold selection based on the detection context. The system automatically switches between a first threshold (for small particles) and a second threshold (for large particles) depending on which threshold is exceeded first and the time difference between triggers. This dynamic approach maintains measurement precision without requiring complex manual configuration.
Solution Approach 2:
The patent changes the detection parameter (threshold level) dynamically based on the signal characteristics. By adjusting which threshold is active based on the sequence and timing of signal exceedances, the system achieves accurate particle size classification while keeping the underlying detection mechanism relatively simple.
3Measurement precision
If laser power is increased to detect smaller particles, then detection sensitivity is improved, but the relative signal from side lobes increases causing more false positives
Solution Approach 1:
The patent uses feedback from the trigger timing and threshold comparison results to adjust particle classification decisions. When a first trigger occurs followed by a second trigger within a specific time window, the system uses this feedback pattern to identify false positives from side lobes and correct the classification, thereby maintaining detection sensitivity while reducing false positives.
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 effectively mitigates the effects of laser lobes and optical imperfections, enabling precise detection and sizing of particles across a wide dynamic range (50 nm to 50 μm) with minimal measurement errors, ensuring accurate classification of particles as either small or large.
Implementation Method 1
The particles scatter the light and also cause fluorescent light of a different wavelength than the incident beam to be emitted
Implementation Method 2
The particles scatter the light and also cause fluorescent light of a different wavelength than the incident beam to be emitted
Implementation Method 3
The beam shaping optical elements may also have small reflections from various surfaces
Data Source
AI summary
Light from a light source is directed at a flow path of particles of a flow cytometer. The directed light results in a light pattern having a plurality of lobes. A first signal is detected exceeding a first threshold. A second signal exceeding a second threshold is detected, wherein the second threshold is greater than the first threshold. Based on detecting the second trigger after detecting the first trigger, is determined that the first and second signals were created by a relatively large particle.