Optical Coherence Tomography Artifact Suppression via Asymmetric Path Control
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Solution Overview
Problem
In wavelength sweeping type optical coherence tomography (OCT), artifacts from single and multiple reflections of optical elements and the subject's surface complicate the generation of accurate tomographic images, especially with long coherence lengths, leading to artifacts appearing at positions deeper than the area of interest, which are difficult to eliminate due to the symmetry of the Fourier domain method and the limited depth range of detection.
Innovation Solution
The optical coherence tomography system is configured with specific optical elements and conditional formulas to manage the position of optical elements relative to the subject, ensuring that artifacts from single and multiple reflections do not overlap with the desired tomographic image, by adjusting the operation distance and light path lengths to maintain the integrity of the image within a defined range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the wavelength band is broadened to improve resolution capability, then the resolution capability is improved, but sensitivity for the interference signal largely reduces as depth increases
Solution Approach 1:
The patent changes the operational parameters of the DBR laser by adjusting the temperature of the laser chip and the current supplied to the laser, thereby sweeping the wavelength dynamically. This allows achieving broad wavelength band (high resolution) while maintaining coherence length (sensitivity at depth) through time-varying parameter control rather than static broad-band operation
2Reliability
If the coherence length is extended to improve sensitivity at depth, then sensitivity at depth is improved, but artifacts from multiple reflections appear at positions deeper than the area of interest
Solution Approach 1:
The patent introduces asymmetric optical path length management by controlling the reference light path to be variable while the measurement light path remains fixed at the subject. By dynamically adjusting the reference path length during wavelength sweeping, the system asymmetrically separates the depth range of interest from artifact-prone regions, allowing long coherence length operation without multiple reflection artifacts overlapping the area of interest
Solution Approach 2:
The patent performs preliminary determination of the area of interest depth range before imaging, then pre-configures the optical path length control parameters to ensure that during subsequent imaging, the reference light path is adjusted to keep artifacts outside the area of interest range. This preliminary setup prevents artifact contamination before the actual measurement begins
3Measurement precision
If the operation distance is reduced to improve imaging of anterior eye structures, then imaging capability of anterior structures is improved, but the risk of multiple reflection artifacts increases
Solution Approach 1:
The patent employs dynamic control of the reference light path length that adapts during wavelength sweeping to compensate for the reduced operation distance. By making the reference path variable rather than fixed, the system dynamically maintains the optical path difference within a range that prevents multiple reflection artifacts from entering the area of interest, even when operating at short distances for anterior eye imaging
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 configuration effectively eliminates artifacts from single and multiple reflections, allowing for accurate and artifact-free tomographic imaging of the area of interest, reducing the risk of misdiagnosis in ophthalmologic applications and improving the sensitivity and resolution of OCT imaging.
Implementation Method 1
a light source configured to change a wavelength of light to be outputted
Implementation Method 2
the light is outputted to a subject such as an eyeball. Scattered light is reflected from the subject, and the scattered light is detected by the interferometer
Implementation Method 3
a spectral domain OCT (hereinbelow referred to as SD-OCT) where a tomographic image is obtained by detecting spectral information using a spectroscope
Data Source
Figure 1
Figure 2A~2C
Figure 2D~2E
AI summary
An optical coherence tomography includes a light source, a light separator, a light generator configured to generate interference light, a detector configured to detect the interference light, a first optical element, and at least one of second optical elements comprising a pair of surfaces, and performs forming a tomographic image of a subject. The first optical element is arranged on a measurement light path so as to be closest to the subject, and satisfies at least one of following conditional formulas: −W−S<U−2Z<X−W; U−2Z<−W; and U−2Z>X−W+S, W: a predetermined operation distance U: a depth of interest S: a range of interest X: a distance which is greater than W+U+S and minimal among distance(s) between the pair of surfaces Z: a shallowest position of the area of interest relative to an origin position.