Annular Aperture Phase Microimaging for Resolution and Noise
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Solution Overview
Problem
Existing phase retrieval methods using light intensity transfer equations face challenges with low-frequency noise and high-frequency information loss, leading to poor spatial resolution and accuracy in phase reconstruction, particularly due to the trade-off in choosing defocus distance, which affects the signal-to-noise ratio and imaging speed.
Innovation Solution
An annular-irradiation high-resolution quantitative phase method is introduced, utilizing an annular aperture and weak object optical transfer function to improve frequency response, collecting three intensity images, and applying a deconvolution algorithm to resolve the light intensity transfer equation, thereby enhancing phase reconstruction resolution and robustness against noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If defocus distance is increased to obtain axial differential of light intensity, then phase retrieval can be achieved, but high-frequency information is lost and fine features become fuzzy
Solution Approach 1:
The illumination aperture is segmented into multiple discrete annular zones (inner annular zone and outer annular zone) rather than using a single circular aperture. This segmentation allows different spatial frequency components to be captured and processed separately, enabling recovery of high-frequency information that would otherwise be lost with large defocus distances.
Solution Approach 2:
Different regions of the aperture are assigned different functions: the inner annular zone captures low-frequency information with reduced noise, while the outer annular zone captures high-frequency information. This local differentiation of aperture regions enables simultaneous optimization for both noise reduction and high-frequency preservation.
2Loss of information
If defocus distance is decreased to preserve high-frequency information, then fine features are maintained, but low-frequency noise increases and phase contrast decreases
Solution Approach 1:
The aperture is divided into inner and outer annular zones that can be independently controlled. The inner zone is optimized for capturing low-frequency information with minimal noise, while the outer zone captures high-frequency information. This segmentation allows the system to operate at small defocus distances without suffering from low-frequency noise contamination.
Solution Approach 2:
The deconvolution algorithm acts as an intermediary processing step that separates and reconstructs different frequency components from the captured intensity images. It processes the data from both annular zones to produce a final phase image with both low-frequency noise removed and high-frequency details preserved.
3Measurement precision
If multi-plane intensity measurement methods are used to estimate axial differentials, then phase retrieval accuracy improves, but data acquisition time and system complexity increase
Solution Approach 1:
Instead of requiring multiple defocus planes, the method uses a single plane with partial coherence illumination through the annular aperture. This provides sufficient frequency information for accurate phase retrieval without the time penalty of acquiring multiple planes, achieving a balance between accuracy and speed.
Solution Approach 2:
The illumination coherence parameter is changed from fully coherent to partially coherent with specific annular aperture geometry. This parameter change enables the system to achieve multi-plane equivalent frequency information from a single plane measurement, reducing acquisition time while maintaining accuracy.
4Device complexity
If conventional circular illumination is used, then the optical system remains simple, but spatial resolution is limited by the diffraction cutoff frequency
Solution Approach 1:
The circular aperture is segmented into concentric annular zones with different transmission characteristics. This simple geometric modification to the illumination aperture enables super-resolution beyond the conventional diffraction limit without requiring complex optical components or multiple lenses.
Solution Approach 2:
The numerical aperture distribution parameter is changed from uniform (circular aperture) to annular distribution. This parameter change in the illumination profile enables the system to achieve higher spatial resolution by utilizing higher spatial frequency components that are blocked in conventional circular illumination.
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 method significantly improves spatial resolution, addressing both low-frequency noise and high-frequency fuzziness, achieving a cut-off frequency twice that of coherent imaging systems, with improved phase contrast and robustness against noise, while maintaining the simplicity of traditional bright field microscopy.
Implementation Method 1
By invoking the weak object approximation, the parameters of annular irradiation aperture and bright field microscopy are used to calculate a weak object optical transfer function (WOTF) on the basis of a partially coherent imaging theory
Implementation Method 2
The imaging space cut-off frequency can be remarkably improved to twice the diffraction limit of a coherent imaging system
Implementation Method 3
three intensity images are collected by a camera and the quantitative phase image of object is obtained by resolving the light intensity transfer equation with a deconvolution algorithm
Data Source
AI summary
An annular-irradiation high-resolution quantitative phase microimaging based on light intensity transfer equation is proposed here includes designing an annular aperture for the imaging system illumination; invoking the weak object approximation by using the parameters of annular illumination aperture and bright field microscopy to calculate a weak object optical transfer function (WOTF) on the basis of a partially coherent imaging theory; and collecting three intensity images by a camera and obtaining the quantitative phase image of object by resolving the light intensity transfer equation with a deconvolution algorithm.