Optical Needle Bevel Angle for Calibration Reliability
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Solution Overview
Problem
Medical photonic needles with small bevel angles suffer from unreliable optical calibration due to internal reflection issues when transitioning from air to tissue, leading to increased calibration time and variability, and are prone to tissue sticking and manufacturing inconsistencies.
Innovation Solution
Optical needles with a bevel angle range of 30°-35° for the optical fibers and elongate tube, ensuring a sharp tip for easy insertion and reduced tissue sticking, while minimizing sensitivity to material changes and manufacturing variations, using undoped fused silica fibers and reflective coatings to enhance light coupling and reduce side lobes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the bevel angle of the optical fiber is decreased to create a sharp tip, then insertion ease is improved, but calibration reliability deteriorates due to increased internal reflection and side-lobe light emission
Solution Approach 1:
The patent applies parameter changes by optimizing the bevel angle to a specific range (30°-35°) that balances two competing requirements: sharpness for easy insertion and optical performance for reliable calibration. This specific angle range minimizes internal reflection issues while maintaining needle sharpness, resolving the contradiction between insertion ease and calibration reliability.
2Ease of operation
If the bevel angle is small to facilitate insertion, then needle sharpness is improved, but manufacturing precision deteriorates due to sensitivity to angle variations
Solution Approach 1:
The patent specifies a bevel angle range of 30°-35° that provides an optimal compromise between needle sharpness and manufacturing tolerance. This angle range is sharp enough for easy insertion but tolerant enough to accommodate normal manufacturing variations, thereby maintaining both needle sharpness and manufacturing precision.
3Loss of time
If calibration is performed in air with small bevel angles, then calibration time is reduced, but measurement precision deteriorates due to refractive index mismatch
Solution Approach 1:
By optimizing the bevel angle to 30°-35°, the patent reduces the magnitude of internal reflection effects, thereby reducing the sensitivity to refractive index differences between air and tissue. This allows calibration in air to yield results that remain accurate when used in tissue, eliminating the need for time-consuming recalibration in liquid media.
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 30°-35° bevel angle range enhances calibration reliability, reduces tissue sticking, and maintains optical performance stability over time, allowing for cost-effective disposable medical kits with improved positioning accuracy and efficient light coupling.
Implementation Method 1
The optical performance is determined on the basis of the proportion of supplied light that is subsequently received, and on the basis of the optical properties of the reference optical surface. A problem resulting from the usual in-air calibration is that the amount of internal reflection of light within the optical fiber at the fiber tip is dependent upon the refractive index of the optical medium that is in contact with the fiber tip.
Implementation Method 2
As the bevel angle of such an optical fiber is decreased and the fiber tip becomes sharper, the proportion of light emitted sideways in a side-lobe, termed an indirect beam, in relation to that emitted in a direct, or forward-looking beam, is increased.
Data Source
Figure 1a~1b
Figure 2
Figure 3~5
AI summary
The present invention relates to a medical needle which comprises an elongate tube and at least one optical fiber, e.g. two fibers, arranged within the elongate tube, for making optical measurements at the distal end of the needle. The optical fibers(s) has a beveled distal end surface, wherein a plane touching the beveled distal end surface and a longitudinal extension axis of the optical fiber forms a bevel angle which is 30º-35º. Such needle is advantageous for providing a medical needle which is reliable and long term stable, can be manufactured in low cost using known optical fiber materials, thus allowing it to form part of disposable medical kits. Still, the bevel angle of 30º-35º provides a needle which is easy to insert and which provides a low tendency to cause tissue sticking. Especially, the elongate tube and the optical fiber end(s) have the same beveled angle within the range 30º- 35º, thus allowing a smooth front surface of the needle.