Optical Coherence Tomography Doppler Modulation for Moving Eye Imaging
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Solution Overview
Problem
Conventional optical image measurement apparatuses using optical coherence tomography face challenges in obtaining clear images of moving objects due to the fringe washout phenomenon, particularly in applications like the living eye where movement from blood flow and accommodative micromovement occurs.
Innovation Solution
An optical image measurement apparatus that modulates the intensity of light based on the movement velocity of the object, using a measurement section to calculate the Doppler frequency shift and adjust the modulation frequency to counteract the effect of fringe washout, ensuring clear image formation even with moving subjects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional OCT apparatus is used to measure moving objects, then the measurement process is simple, but the image clarity deteriorates due to fringe washout
Solution Approach 1:
The system performs preliminary measurement of the movement velocity of the measured object before the main imaging process. Based on this preliminary measurement, the modulation frequency is determined in advance to counteract the Doppler frequency shift that will occur during imaging, thereby preventing fringe washout before it happens.
Solution Approach 2:
The system measures the movement velocity of the measured object and uses this information to adjust the modulation frequency of the light source. This feedback mechanism ensures that the modulation frequency always matches the Doppler frequency shift, maintaining clear images even as the object moves.
2Reliability
If light intensity is modulated at fixed frequency, then the device operation is simple, but the detection sensitivity deteriorates when object movement velocity changes
Solution Approach 1:
The system transitions from fixed-frequency modulation to dynamic frequency modulation. The modulation frequency is adjusted in real-time based on the measured movement velocity of the object, allowing the system to adapt to changing conditions and maintain optimal detection sensitivity throughout the measurement process.
Solution Approach 2:
The system changes the modulation frequency parameter dynamically according to the object's movement velocity. By linking the modulation frequency to the measured velocity, the system maintains the optimal frequency relationship needed for clear interference patterns regardless of how fast or slow the object moves.
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 apparatus effectively tracks the Doppler frequency shift and modulates the light intensity accordingly, enabling the capture of clear images of moving objects by minimizing the impact of fringe washout, thus improving image clarity in dynamic environments such as the living eye.
Implementation Method 1
generates interference light by superimposing signal light passing through the measured object and reference light passing through a reference light path
Implementation Method 2
a phenomenon, namely fringe washout, may occur... Doppler frequency shift occurs with the signal light... the amount of Doppler frequency shift (Doppler frequency shift amount) is expressed as fDoppl=2 nv/λ
Data Source
AI summary
A motion detector 220 calculates the Doppler frequency shift amount based on the movement velocity of an eye E. A drive controller 230 calculates the modulation frequency of the intensity of output light M based on this Doppler frequency shift amount. A light source unit 201 outputs the light M in which the intensity is modulated with this modulation frequency. The light M is divided into a signal light S and a reference light R. Interference light L is generated by superimposing the signal light S passing through the eye E and the reference light R. Two polarized components of the interference light L have a phase difference of 180°, resulting from a quarter-wave plate 207. The polarized components L1, L2 which are divided by a polarization beam splitter 211 are detected by CCD 212, 213. A computer 250 forms a tomographical image based on these detection results.