Interferometric NIR Spectroscopy With Lock-In Detection for Neuroimaging
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Solution Overview
Problem
Near infrared spectroscopy systems face challenges in digitizer bandwidth demands, which are expensive and constrain system size, necessitating a more efficient signal processing approach.
Innovation Solution
An interferometric near infrared spectroscopy system using wavelength-swept emission and a lock-in amplifier to simplify signal processing, reducing digitizer bandwidth requirements by performing Fast Fourier Transform in the analogue domain and utilizing a dual phase lock-in amplifier for signal analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional NIRS systems use direct digitization of optical signals, then signal processing is straightforward, but digitizer bandwidth demands increase significantly, leading to higher costs and larger system size
Solution Approach 1:
The patent replaces the conventional direct digitization approach with an interferometric optical processing system. The detector combines reference light with sample light to generate beat frequency signals, and a lock-in amplifier performs frequency-selective detection in the analog domain. This substitution of mechanical/electronic digitization with optical interference and analog signal processing resolves the contradiction by reducing digitizer bandwidth requirements while maintaining signal processing effectiveness.
Solution Approach 2:
The system transforms the detection approach by changing the frequency domain parameters. Instead of directly digitizing the optical signal at high frequencies, the system uses wavelength-swept emission and interferometric mixing to down-convert the signal to lower beat frequencies. The lock-in amplifier then selectively detects specific frequency components, effectively performing Fourier transformation in the analog domain. This parameter transformation reduces the bandwidth requirements for subsequent digitization.
2Measurement precision
If digitizer bandwidth is increased to handle full signal spectrum, then measurement precision improves, but system cost and size increase
Solution Approach 1:
The lock-in amplifier extracts only the specific frequency components of interest from the broad spectral signal. By using frequency-selective detection, the system isolates the beat frequency signals corresponding to the wavelengths of interest, discarding the rest of the spectrum. This extraction approach maintains measurement precision for the target wavelengths while avoiding the need to digitize and process the entire broad bandwidth, thereby reducing system size and cost.
Solution Approach 2:
Instead of processing the complete spectral signal across all frequencies, the system applies partial action by focusing detection resources only on the specific frequency ranges that contain the relevant information. The lock-in amplifier is tuned to detect only the beat frequencies corresponding to the wavelengths being measured, performing sufficient processing to achieve the required precision without the excessive action of processing the entire spectrum.
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
The system simplifies signal processing, reduces digitizer bandwidth needs, and enables efficient neuroimaging and analysis of brain tissue with lower costs and smaller system size.
Implementation Method 1
the detector is arranged to combine the received sample light with the reference light to provide a combined light signal comprising one or more components at a beat frequency between sample light and reference light
Implementation Method 2
a lock-in amplifier arranged to: (i) receive a detection signal based on the combined light signal and formed of one or more components at different frequencies, (ii) receive a selection signal at a selection frequency, and (iii) to provide one or more output signals indicative of a component of the detection signal at the selection frequency
Data Source
AI summary
An imaging system comprising: a light source configured to provide wavelength-swept emission of light; a sample delivery channel coupled to the light source and arranged to be coupled to an object to be imaged to direct light from the light source towards said object; a reference channel coupled to the light source for receiving light therefrom; a sample receiving channel arranged to be coupled to the object to be imaged for receiving sample light from the object; a detector coupled to the sample receiving channel for receiving sample light, and coupled to the reference channel for receiving reference light, wherein the detector is arranged to combine the received sample light with the reference light to provide a combined light signal comprising one or more components at a beat frequency between sample light and reference light; and a lock-in amplifier arranged to: (i) receive a detection signal based on the combined light signal and formed of one or more components at different frequencies, (ii) receive a selection signal at a selection frequency, and (iii) to provide one or more output signals indicative of a component of the detection signal at the selection frequency.