Integral Transformed Optical Measurement System for Diffuse Tomography
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Solution Overview
Problem
Time-domain optical measurement systems, particularly diffuse optical tomography systems, face limitations in data acquisition speed and signal-to-noise ratio due to slow data collection and high computational complexity, with existing methods like TCSPC being slow and streak cameras having low dynamic range and temporal nonlinearity.
Innovation Solution
A method involving the generation of broadband signals and modulation/reference signals using a circuit network, where a first-order low pass filter determines the Laplace transform parameter, allowing for direct generation of integral transformed measurements through cross-correlation, reducing the need for point-by-point time spectrum recording and numerical transformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If TCSPC is used to record TPSF, then sensitivity and dynamic range are improved, but data acquisition speed becomes very slow
Solution Approach 1:
The patent replaces the mechanical photon-counting process of TCSPC with an all-optical measurement system using intensity-modulated continuous wave (IM-CW) light sources and photodetectors. This substitution eliminates the need for slow sequential photon accumulation while maintaining measurement capability through optical interference and correlation techniques.
Solution Approach 2:
The patent transforms the measurement approach by changing from time-resolved photon counting to frequency-domain intensity modulation. By modulating the light source intensity at specific frequencies and analyzing the modulated reflected light, the system achieves fast acquisition without sacrificing sensitivity, as the modulation frequency serves as the distinguishing parameter instead of time-of-flight.
2Manufacturing precision
If streak camera is used to record TPSF, then time resolution is improved to around 1 picosecond, but dynamic range becomes low and temporal nonlinearity occurs
Solution Approach 1:
The patent replaces the streak camera's electron-based time-to-space conversion mechanism with an all-optical intensity modulation and detection system. This substitution eliminates the inherent limitations of streak cameras including low dynamic range and temporal nonlinearity, while achieving comparable or sufficient time resolution through frequency-domain measurements and correlation analysis.
3Measurement precision
If TPSFs are directly used as input to reconstruction algorithms, then image quality is maintained, but computation time becomes huge
Solution Approach 1:
The patent applies preliminary mathematical transformation (Laplace transform) to the measured signal before it is used in image reconstruction. By transforming the time-domain TPSF into the Laplace domain using a pair of transform parameters, the system pre-processes the data to reduce its dimensionality and complexity, making subsequent reconstruction computations much faster while preserving essential image quality information.
4Productivity
If spread spectrum time-resolve measurement method is used, then data acquisition speed is improved compared to TCSPC, but system complexity increases due to hardware devices required
Solution Approach 1:
The patent replaces the complex hardware correlation devices (mixers, low-pass filters, programmable delay lines) required by spread spectrum methods with a simpler intensity-modulation-based system. By using directly modulated laser diodes and standard photodetectors with frequency-domain analysis, the system achieves fast acquisition without requiring specialized correlation hardware, thereby reducing overall system 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 approach enhances data acquisition speed and signal-to-noise ratio while reducing system complexity, cost, and size by enabling faster data collection and improved image reconstruction with simplified mathematical models and reduced noise sensitivity.
Implementation Method 1
A first order low pass filter is used to generate either a modulation signal or a reference signal, the time domain measurement is Laplace transformed. The time constant of the filter determines the transform parameter.
Implementation Method 2
illuminating a sample with a light source modulated by the modulation signal
Implementation Method 3
The detected diffusive photon density at a given distance is a function of time
Implementation Method 4
cross-correlating the detected signal from the sample with the reference signal
Data Source
AI summary
An optical measurement method for high-speed acquisition of integral transformed time domain optical signals is presented. A circuit network is used to generate a modulation signal and a reference signal from a broadband signal such as a pseudo random bit sequence. The integral transformed measurements are obtained by cross correlating the time dependent response to the modulated illumination with the reference signal.