Ophthalmic Apparatus Blood Flow Velocity Calculation
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Solution Overview
Problem
Existing scanning laser ophthalmoscopes face challenges in accurately calculating blood flow velocity due to variations in image capturing timing across the retina, leading to inaccuracies in determining the period between scanning positions of blood cells in successive images.
Innovation Solution
The apparatus utilizes the scanning period and interval of the scanning unit, along with the time required for acquiring one planar image, to accurately calculate blood flow velocity by accounting for the displacement and time difference between blood cell positions in successive images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the beam diameter of the measurement beam is increased to improve horizontal resolution, then the resolution is improved, but the signal-to-noise ratio decreases and aberration increases
Solution Approach 1:
The patent changes the parameter of beam diameter to improve horizontal resolution. By increasing the beam diameter, the apparatus achieves better resolution while managing the trade-off with signal-to-noise ratio through the confocal detection principle and adaptive optics correction.
Solution Approach 2:
The patent introduces a pinhole aperture as an intermediary element in the confocal detection path. This pinhole acts as a spatial filter that blocks out-of-focus light and aberrations, thereby improving the signal-to-noise ratio while maintaining the benefits of the increased beam diameter for resolution.
2Manufacturing precision
If the beam diameter is increased to achieve high resolution, then resolution is improved, but aberration of the measurement beam increases
Solution Approach 1:
The patent employs adaptive optics as an intermediary system that includes a wavefront sensor and deformable mirror. The wavefront sensor measures the aberration introduced by the increased beam diameter, and the deformable mirror compensates for this aberration in real-time, thereby maintaining high resolution without the detrimental effects of uncorrected aberration.
Solution Approach 2:
The patent implements a feedback loop through the adaptive optics system. The wavefront sensor continuously monitors the aberration caused by the measurement beam, and this information is fed back to the deformable mirror which adjusts its shape to compensate for the measured aberration, thereby maintaining beam quality despite the increased diameter.
3Productivity
If raster scan is used to capture planar images, then high speed acquisition is achieved, but image capturing timing varies from position to position
Solution Approach 1:
The patent performs preliminary action by pre-calculating and storing the scanning timing information for each position in the raster scan pattern. This timing information is prepared in advance and used during blood flow velocity calculation to correctly associate each detected blood cell position with its actual capture time, thereby compensating for the position-dependent timing variations inherent in raster scanning.
4Ease of operation
If conventional blood flow velocity calculation is performed using planar image acquisition period, then calculation is simplified, but accuracy decreases due to scanning timing variations
Solution Approach 1:
The patent incorporates feedback by using the known scanning timing information to correct the blood flow velocity calculation. Instead of using a simple uniform time interval, the system feeds back the position-specific scanning timing data to adjust the time difference calculation, thereby maintaining accuracy while building upon the conventional calculation framework.
Solution Approach 2:
The patent changes the time parameter from a uniform acquisition period to a position-dependent time interval. By incorporating the actual scanning timing information for each raster position, the calculation uses variable time differences that reflect the true capture timing, thereby improving accuracy without completely abandoning the conventional calculation approach.
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 enables precise calculation of blood flow velocity by considering the scanning dynamics, improving accuracy over conventional methods, especially when blood cells move minimally in the Y direction.
Implementation Method 1
A scanning laser ophthalmoscope (SLO) which is an ophthalmic apparatus using the principle of a confocal laser microscope is a device that performs raster scan on an eye fundus with a laser as a measurement beam
Implementation Method 2
an adaptive optics system which measures the aberration of the subject's eye in real time using a wavefront sensor
Implementation Method 3
corrects the aberration of the measurement beam or the return beam thereof occurring in the subject's eye using a wavefront correction device
Data Source
Figure 1
Figure 2A~2D
Figure 3A~3B
AI summary
OPHTHALMIC APPARATUS, OPHTHALMIC SYSTEM, PROCESSING APPARATUS, AND BLOOD FLOW VELOCITY CALCULATION METHOD An ophthalmic apparatus includes irradiation means configured to irradiate a subject's eye with a measurement beam scanned by scanning means (119), acquisition means (125) configured to acquire an image of the subject's eye based on a return beam returned from the subject's eye, of the measurement beam irradiated by the irradiation means, and calculation means (125) configured to calculate a blood flow velocity of the subject's eye based on a displacement between a position of a blood cell in a first image obtained by the acquisition means (125) and a position of the blood cell in a second image obtained by the acquisition means (125) at a different time from the first image and on a difference between time when an image of the blood cell in the first image is obtained and time when an image of the blood cell in the second image is obtained.