Acoustic-Optical Imaging System for Light Absorption Measurement
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Solution Overview
Problem
Current acoustic-optical imaging systems face challenges in accurately acquiring images of biological tissues due to the diffusion of visible light, which complicates the measurement of local absorption within the medium.
Innovation Solution
An imaging system that employs a coherent light source, a modulation device for applying pseudo-random sequences of phase, frequency, or amplitude jumps to the object beam, and a demodulation device for non-correlated sequences, allowing for the reconstruction of light absorption profiles at multiple positions along the optical path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If visible light is used to illuminate biological tissue, then the medium can be illuminated, but the light propagates according to a diffusion regime causing photons to follow multiple optical paths and their relative arrangements are modified, making it impossible to acquire a faithful image with a standard image sensor
Solution Approach 1:
The patent segments the optical signal into marked photons (that crossed the acoustic marking area) and unmarked photons (that did not cross), using acoustic modulation to tag specific photon paths. This segmentation allows selective measurement of photons that traversed the region of interest, overcoming the diffusion problem by identifying and isolating specific photon trajectories within the diffuse field.
Solution Approach 2:
The patent introduces an acoustic wave as an intermediary medium to modulate the optical signal. The acoustic wave creates a time-varying refractive index pattern that marks photons passing through the marking area, serving as a mediator between the light source and the image sensor to encode spatial information within the diffuse photon field.
2Measurement precision
If acoustic-optical imaging techniques are used with acoustic marking, then local absorption information can be obtained, but the system complexity increases with multiple beams and demodulation requirements
Solution Approach 1:
The patent merges the reference beam and object beam paths to a common detection point, using a single image sensor to detect both beams. The reference beam carries the acoustic modulation signature, and by combining it with the object beam at the sensor, the system achieves demodulation capability without requiring separate detection paths, thereby reducing overall system complexity.
Solution Approach 2:
The image sensor serves multiple functions: it detects both the reference beam and the object beam, performs the interference measurement, and enables demodulation of the acoustic signal. This multi-functional use of a single component reduces the number of specialized devices needed, simplifying the system architecture while maintaining measurement precision.
3Measurement precision
If pseudo-random sequences are applied to modulate the object beam and reference beam with non-correlated sequences, then the signal-to-noise ratio is improved and axial resolution is enhanced, but the processing complexity increases
Solution Approach 1:
The patent applies pseudo-random modulation sequences to both the reference beam and object beam in advance, before the actual measurement and reconstruction process. This preliminary encoding of the signals with known non-correlated sequences enables subsequent correlation processing to extract the absorbed signal with enhanced signal-to-noise ratio, as the pre-applied codes facilitate noise rejection during reconstruction.
Solution Approach 2:
The system uses the known pseudo-random sequences as reference codes for correlation processing during image reconstruction. By comparing the detected signal with the pre-applied non-correlated sequences, the system performs feedback-based noise filtering and signal enhancement, improving axial resolution and signal-to-noise ratio through computational correlation rather than hardware complexity.
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 system enhances the accuracy of light absorption measurements by improving the signal-to-noise ratio and enabling the determination of absorption profiles with higher axial resolution, overcoming the limitations of standard imaging techniques.
Implementation Method 1
An interference between the light beam originating from the medium, called object beam, and a reference beam originating from the same light source but which has not crossed the diffusing medium, is then caused
Implementation Method 2
a portion of the observed medium is submitted to an acoustic wave, typically an ultrasound acoustic wave. The vibration of the diffusers along the propagation path of the acoustic wave
Implementation Method 3
The vibration of the diffusers along the propagation path of the acoustic wave, also called acoustic marking area or also acoustic marking column, and then modulates the phase of the diffused photons
Implementation Method 4
An interference between the light beam originating from the medium, called object beam, and a reference beam originating from the same light source but which has not crossed the diffusing medium, is then caused. This enables to demodulate the object beam and to take the pulse of the marked photons down to the frequency of the acoustic wave. An image sensor is then used to measure the optical signal modulated at the acoustic frequency
Data Source
AI summary
The present invention relates to an imaging system, including: a coherent light source delivering an object beam and a reference beam; a device of modulation of the object beam with a modulation signal; an image sensor arranged to receive an interference pattern resulting from a combination of the object beam and of the reference beam; and a demodulation device, the system being configured to, during a measurement phase: apply to the modulation signal a first pseudo-random sequence of jumps of a parameter selected among the phase, the frequency, and the amplitude; and simultaneously apply to the modulated portion of the object beam a second pseudo-random sequence of jumps of said parameter, wherein the first and second sequences of jumps of said parameter are non-correlated.