Dual-edge k-clock sampling for aliasing-free OCT depth imaging
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Solution Overview
Problem
Current Optical Coherence Tomography (OCT) systems face performance tradeoffs when imaging both the anterior segment and full eye length, particularly in swept-source OCT, where the choice of k-clock period affects imaging depth and requires compromises in system design or performance.
Innovation Solution
The OCT data acquisition and processing circuit includes a k-clock circuit that outputs k-clock signals across a range of frequencies, an anti-aliasing filter with a cut-off frequency greater than one-half the minimum k-clock frequency but less than the minimum k-clock frequency, and an A/D converter that samples the filtered interference signal at twice the k-clock frequency, preventing aliasing and enabling optimized imaging performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the k-clock frequency is reduced to extend imaging depth for full eye length measurement, then imaging depth is improved, but aliasing occurs in the sampled OCT signal
Solution Approach 1:
The patent applies preliminary action by performing anti-aliasing filtering on the OCT interference signal before it reaches the A/D converter. The filter is configured with a cut-off frequency that is greater than one-half the minimum k-clock frequency but less than the minimum k-clock frequency, which pre-prevents aliasing artifacts before sampling occurs. This allows the system to use lower k-clock frequencies for extended imaging depth without compromising signal accuracy.
2Reliability
If the k-clock frequency is increased to prevent aliasing, then signal accuracy is improved, but imaging depth is reduced
Solution Approach 1:
The patent extracts the aliasing problem from the sampling process by introducing a separate anti-aliasing filter stage before the A/D converter. Instead of relying solely on high k-clock frequencies to prevent aliasing, the system removes the aliasing components through filtering, thereby allowing the use of lower k-clock frequencies that enable extended imaging depth while maintaining signal accuracy.
3Measurement precision
If the anti-aliasing filter cut-off frequency is set high to preserve signal bandwidth, then frequency resolution is improved, but aliasing prevention is compromised
Solution Approach 1:
The patent applies parameter changes by carefully selecting the anti-aliasing filter cut-off frequency to be greater than one-half the minimum k-clock frequency but less than the minimum k-clock frequency. This optimized parameter setting allows the filter to effectively prevent aliasing while preserving sufficient signal bandwidth for accurate frequency resolution in the OCT imaging process.
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 allows for optimized OCT performance across various application modes by preventing aliasing and ensuring accurate depth information without compromising system performance, facilitating both anterior segment and full-eye length measurements.
Implementation Method 1
an anti-aliasing filter configured to filter the swept-source OCT interference signal to produce a filtered OCT interference signal
Implementation Method 2
an analog-to-digital (A/D) converter circuit coupled to the anti-aliasing filter and configured to sample the filtered OCT interference signal at twice the k-clock frequency to produce a sampled OCT interference signal
Implementation Method 3
a swept optical source and an interferometer coupled to an output of the swept optical source, the interferometer in turn comprising a detector circuit configured to generate the swept-source OCT interference signal from an optical interference signal produced by the interferometer
Data Source
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AI summary
Techniques and apparatus for producing sampled Optical Coherence Tomography (OCT) interference signals without aliasing, based on a swept-source OCT interference signal. An example apparatus comprises a k-clock circuit configured to selectively output a k-clock signal at any of a plurality of k-clock frequencies ranging from a minimum k-clock frequency to a maximum k-clock frequency, and an anti-aliasing filter configured to filter a swept- source OCT interference signal, to produce a filtered OCT interference signal, where the anti- aliasing filter has a cut-off frequency greater than one-half the minimum k-clock frequency but less than the minimum k-clock frequency. The apparatus further comprises an analog-to- digital (A/D) converter circuit configured to sample the filtered OCT interference signal at twice the k-clock frequency, to produce a sampled OCT interference signal. In some embodiments, the A/D converter circuit samples the filtered OCT interference signal at both rising and falling edges of the k-clock signal.