Flowcell Autofocus Using Fixed Contrast Targets for Blood Cell Imaging
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Solution Overview
Problem
Existing particle analysis systems, particularly in hematology, face challenges in achieving high-quality imaging and accurate classification of blood cells due to issues like temperature fluctuations affecting focus, and the need for user intervention or focusing liquids, leading to out-of-focus images.
Innovation Solution
Implementing autofocus systems that automatically focus on a fixed target within the flowcell, using geometric hydrofocusing and viscosity differences to maintain image clarity without user intervention, and adjusting focus based on temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If autofocus systems automatically focus on a fixed target within the flowcell, then image quality and focus consistency are improved, but device complexity increases due to additional autofocus components and control mechanisms
Solution Approach 1:
An autofocus target is introduced as an intermediary element within the flowcell to enable automatic focusing. The target serves as a reference object that the imaging system can lock onto, eliminating the need for manual focusing while maintaining image quality. The target acts as a mediator between the imaging system and the sample, providing a stable reference point for focus determination.
Solution Approach 2:
The system performs self-focusing by automatically detecting the autofocus target and adjusting the focus mechanism without user intervention. The imaging system continuously monitors the target position and maintains optimal focus automatically, enabling the system to service itself regarding focus maintenance throughout the analysis process.
2Reliability
If geometric hydrofocusing and viscosity differences are used to maintain image clarity, then focusing reliability is improved without user intervention, but device complexity increases due to additional flowcontrol mechanisms
Solution Approach 1:
Geometric hydrofocusing utilizes fluid dynamics principles where the sheath fluid flow geometry and viscosity differences create hydrodynamic forces that automatically position and focus the sample stream. The hydraulic flow patterns and pressure distributions within the flowcell enable reliable focusing without mechanical adjustment mechanisms, using fluid physics to achieve the focusing function.
Solution Approach 2:
The system exploits viscosity differences between the sheath fluid and sample fluid as a controllable parameter to achieve focusing. By carefully selecting and maintaining specific viscosity ratios and flow rate parameters, the system creates stable hydrodynamic conditions that reliably focus the sample stream, using parameter optimization rather than mechanical complexity.
3Adaptability or versatility
If focus adjustment is made based on temperature changes, then adaptability to environmental conditions is improved, but device complexity increases due to temperature sensing and control mechanisms
Solution Approach 1:
Temperature sensors provide continuous feedback about the thermal state of the flowcell and imaging system. This feedback is used by the control system to automatically adjust focus parameters or compensate for thermal expansion effects, enabling the system to adapt to temperature changes. The feedback loop maintains focus accuracy despite environmental temperature variations without requiring manual intervention.
Solution Approach 2:
The system accounts for and compensates for thermal expansion effects on the flowcell dimensions and optical path. By understanding the thermal characteristics of the materials and geometry, the system can predict and correct for focus shifts caused by temperature changes, either through active compensation mechanisms or by designing thermally stable structures.
4Device complexity
If manual focusing or focusing liquids are used, then device complexity is reduced, but measurement precision deteriorates due to out-of-focus images and user intervention requirements
Solution Approach 1:
An autofocus target serves as an intermediary reference object that enables precise automatic focusing. This target provides a known, stable feature that the imaging system can use to determine the optimal focus position, eliminating the imprecision of manual focusing while avoiding the need for complex focusing liquids. The target mediates between the simple imaging system and the requirement for high image quality.
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
Ensures high-quality, focused images of blood cells are consistently produced, enabling accurate classification and counting, even in the presence of temperature fluctuations, without the need for focusing liquids or user interaction.
Implementation Method 1
Implementing autofocus systems that automatically focus on a fixed target within the flowcell, using geometric hydrofocusing and viscosity differences to maintain image clarity
Implementation Method 2
using geometric hydrofocusing and viscosity differences to maintain image clarity
Data Source
AI summary
Particles such as blood cells can be categorized and counted by a digital image processor. A digital microscope camera can be directed into a flowcell defining a symmetrically narrowing flowpath in which the sample stream flows in a ribbon flattened by flow and viscosity parameters between layers of sheath fluid. A contrast pattern for autofocusing is provided on the flowcell, for example at an edge of a rear illumination opening. The image processor assesses focus accuracy from pixel data contrast. A positioning motor moves the microscope and/or flowcell along the optical axis for autofocusing on the contrast pattern target. The processor then displaces microscope and flowcell by a known distance between the contrast pattern and the sample stream, thus focusing on the sample stream. Blood cell images are collected from that position until autofocus is reinitiated, periodically, by input signal, or when detecting temperature changes or focus inaccuracy in the image data.