Optical fiber sensor package structure and method for navigation of minimally invasive surgical instruments

Abstract

The application provides a navigation optical fiber sensor packaging structure and method for a minimally invasive surgical instrument. An elongated guide rod of the minimally invasive surgical instrument is provided with a circular elongated hole, and the optical fiber sensor is freely placed in the elongated hole, and a gap exists between the optical fiber sensor and the inner wall of the elongated hole. The application packages the navigation optical fiber sensor in a non-fixed manner into the hole designed in advance in the interior of the minimally invasive surgical instrument, so that the neutral axis of the optical fiber sensor coincides with the intermediate core, greatly reduces the bending strain of the core under high curvature, and significantly widens the curvature measurement range. The defects of strain over-limit, narrow curvature measurement range, low strain transmission efficiency and easy damage caused by the existing surface attachment or improper embedding mode are overcome. The application is widely applicable to minimally invasive surgical instruments in various medical scenes, and provides key technical support for the accurate navigation and reliable operation of intelligent minimally invasive surgical instruments.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing technology, specifically relating to a fiber optic sensor packaging structure and method for navigation of minimally invasive surgical instruments. Background Technology

[0002] Currently, minimally invasive surgical instruments such as guidewires, catheters, flexible endoscopes, and continuum robots play a crucial supporting role in minimally invasive diagnosis and treatment. Especially in complex physiological structures such as the intestines, hepatic arteries, and bronchi, achieving real-time, high-precision sensing and navigation of the three-dimensional morphology of these flexible minimally invasive surgical instruments within the body has become one of the core technologies for improving surgical safety, accuracy, and efficiency. Fiber optic shape sensing technology, especially distributed fiber optic sensing technology based on optical frequency domain reflectance (OFDR), is widely used in the morphological navigation of minimally invasive surgical instruments due to its significant advantages such as millimeter-level spatial resolution, high precision, resistance to electromagnetic interference, and ease of integration. The navigation fiber optic sensor integrates multiple sensing fibers or multiple fiber cores. By calculating the strain distribution of each fiber core under bending conditions, the three-dimensional spatial morphology of the sensor can be accurately reconstructed.

[0003] However, effectively encapsulating sensors into minimally invasive surgical instruments and achieving precise shape sensing still faces a series of severe technical challenges. The core issue is that the encapsulation method of the sensor directly affects the strain measurement accuracy and curvature measurement range of the sensor. Taking surface-mount encapsulation as an example, this method directly attaches the sensor to the outer surface of the minimally invasive surgical instrument. While simple to operate, it causes the sensing fiber core to be far from the instrument's bending neutral axis. This results in the fiber core generating huge tensile or compressive strains even with small curvature bends, easily exceeding the measurement limits of commercial OFDR systems (typically ±15000 με), and even causing fiber breakage and failure. Furthermore, the sensor is directly exposed to the complex human body environment, making it prone to detachment or damage during frequent bending and twisting operations in clinical practice, leading to poor long-term reliability. Another common fixed-embedding encapsulation method involves embedding the sensor into the internal channels of the instrument and fixing it with adhesives or other materials. While this method provides physical protection for the sensor, the strain of the instrument substrate material must be transferred layer by layer through the adhesive layer and fiber coating to the fiber core, resulting in significant strain transfer efficiency problems. If parameters such as adhesive layer thickness and elastic modulus are not finely optimized or strain values ​​are not calibrated and compensated, large errors will occur in the strain measurement results, which will significantly reduce the accuracy of shape reconstruction.

[0004] Existing technologies indicate that while the two aforementioned encapsulation structures may be barely suitable for minimally invasive surgical instruments with smaller diameters, their curvature measurement range and navigation accuracy are severely limited for other surgical instruments such as endoscopes with slightly larger diameters (e.g., 5-10 mm), making it difficult to meet the precise control requirements of clinicians in complex, large-deformation scenarios. Therefore, there is an urgent need to develop a novel encapsulation solution that can simultaneously achieve a large curvature measurement range, high strain transfer fidelity, and excellent clinical reliability to overcome the current technological bottlenecks. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a fiber optic sensor packaging structure and method for navigation of minimally invasive surgical instruments, which effectively expands the curvature measurement range of minimally invasive surgical instruments and significantly improves navigation accuracy and the reliability of clinical operation.

[0006] To solve the above-mentioned technical problems, the present invention first provides a fiber optic sensor packaging structure for navigation of a minimally invasive surgical instrument. The slender guide rod of the minimally invasive surgical instrument has a circular slender channel, and the fiber optic sensor is freely placed in the slender channel. There is a gap between the fiber optic sensor and the inner wall of the slender channel.

[0007] Preferably, the diameter ratio of the elongated channel to the fiber optic sensor is greater than 0.26.

[0008] More preferably, the inner wall of the elongated channel has a coating with a friction coefficient of 0.05 to 0.1.

[0009] The packaging method of the navigation fiber optic sensor packaging structure of the minimally invasive surgical instrument provided by the present invention is as follows: a circular elongated channel with a length greater than the length of the navigation fiber optic sensor and a diameter greater than the diameter of the fiber optic sensor is opened in the elongated guide rod of the minimally invasive surgical instrument so that the navigation fiber optic sensor can be completely accommodated; the navigation fiber optic sensor is completely inserted into the elongated channel.

[0010] Furthermore, after the circular, slender channel is excavated, a hydrophilic polymer coating or a thermosetting hydrophilic coating is applied to its inner wall, with a friction coefficient of 0.05 to 0.1.

[0011] The optimized ratio of the elongated channel to the diameter of the fiber optic sensor is greater than 0.26.

[0012] Compared with traditional fiber optic sensor packaging solutions for navigation, such as surface mount or fixed embedding, the non-fixed embedding packaging solution proposed in this invention exhibits significant advantages in terms of structural design, measurement reliability, and system maintainability, specifically in the following aspects:

[0013] (1) Effectively avoids the risk of fiber breakage and broadens the applicable range of bending curvature. In traditional adhesive fixing methods, especially when minimally invasive surgical instruments undergo complex bending or large curvature deformation, the optical fiber may break due to strain exceeding the material limit. In this solution, the sensor is freely placed in the channel, and the bending strain of the fiber core is determined only by its own geometric position, even at a height of up to 50m. -1 Under varying curvatures, the maximum bending strain of the fiber core is far below the ultimate strain that the material can withstand. This enables the sensor to navigate over a wider range of bending curvatures and in complex shapes.

[0014] (2) Flexible channel layout significantly improves sensor lifespan. Since the sensor does not require adhesive bonding, the position of the sensor channel inside the minimally invasive surgical instrument is unrestricted and can be flexibly selected according to structural design requirements, significantly enhancing its adaptability to minimally invasive surgical instruments of different structures and diameters. At the same time, the sensor is completely placed inside the instrument, avoiding direct contact and friction with human tissue during surgery, effectively reducing the risk of surface wear and chemical corrosion, and greatly extending the sensor's lifespan and long-term reliability.

[0015] (3) Detachable design enhances system practicality and economy. The sensor adopts a detachable design, with no adhesive connection between it and the channel, which facilitates quick replacement or maintenance when the sensor is damaged. It is especially suitable for medical scenarios that require multiple reuses or sterilization, greatly improving the practicality and cost-effectiveness of the system.

[0016] (4) Mechanical coupling model guides parameter optimization, balancing flexibility and accuracy. By establishing a mechanical coupling model between minimally invasive surgical instruments and sensors, and by optimizing the orifice diameter and coating the inner wall of the orifice with a low-friction coefficient coating, the additional strain is controlled to a low level. This allows the system to maintain high-precision navigation capabilities while maintaining high degrees of freedom and flexible operation, providing reliable technical support for the navigation of minimally invasive surgical instruments.

[0017] In summary, this packaging solution outperforms traditional methods in terms of safety, adaptability, maintainability, and measurement accuracy, opening up new avenues for the practical application of fiber optic shape sensing technology in minimally invasive surgical instruments. Attached Figure Description

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] Figure 1 This is a schematic diagram of the encapsulation structure in cross-section after the endoscope and the navigation fiber optic sensor are coupled.

[0020] Figure 2 Simulation results of fiber core strain under different bending curvatures.

[0021] Figure 3 The correspondence between the position of the fiber core inside the sensor and the bending strain.

[0022] Figure 4 A mechanical coupling model of the endoscope and sensors.

[0023] Figure 5 The relationship curve between the pore diameter and the additional strain of the sensor. Detailed Implementation

[0024] Existing minimally invasive surgical instruments, depending on their specific functions and uses, have several elongated channels within their slender guide rods, such as channels for inserting forceps or graspers, or channels for water or air passage. This invention specifically incorporates a circular, elongated channel within the slender guide rod of the minimally invasive surgical instrument, capable of completely accommodating a navigation fiber optic sensor. The length of the circular, elongated channel is greater than the length of the navigation fiber optic sensor, and its diameter is greater than the diameter of the fiber optic sensor. The diameter ratio of the elongated channel to the fiber optic sensor is greater than 0.26. The inner wall of the elongated channel is coated with a coating with a friction coefficient of 0.05–0.1, such as a hydrophilic polymer coating or a thermosetting hydrophilic coating. The fiber optic sensor is freely placed within the elongated channel, with a gap between the sensor and the inner wall of the channel. Thus, the fiber optic sensor is not bonded or fixed to the inner wall of the channel in any way, but rather embedded in it in a non-fixed manner, thereby retaining a certain amount of free movement within the channel. This design effectively avoids the problem of reduced strain transmission efficiency that may be caused by the use of adhesives, and also eliminates the limitations on sensor position imposed by traditional fixing methods.

[0025] exist Figure 1 In order to facilitate theoretical analysis and clear illustrations, we appropriately enlarged the size of the sensor and established a coordinate system. The origin of the coordinate system The location is set at the geometric center of the sensor. The diagram shows the curved neutral axis, which passes through the origin and is perpendicular to the neutral axis. The axes coincide, and The axial direction is the same as the bending direction. Maintain consistency. This coordinate system provides the geometric basis for subsequent strain analysis. The figure also shows in detail an outer core inside the sensor, its position determined by the coordinate system (…). , The sensor can be made of multi-core optical fiber or multi-core fiber bundle, and the layout of its internal fiber cores is determined by the inter-core spacing. The spacing between the fibers is determined by the number of cores. Taking a common commercial seven-core optical fiber as an example, its core spacing... =42 μm, this parameter directly affects the coordinate values. The value range of is also marked in the figure, which is the angle between the fiber core position and the bending direction of the sensor. Based on geometric relationships, the bending strain of the fiber core inside the sensor can be expressed as... ,in Let be the bending curvature of the sensor. It is worth noting that, due to the coordinates... Therefore, the strain expression can also be simplified to This relationship shows that the strain experienced by the fiber core during bending is proportional to its projected distance in the direction perpendicular to the bending neutral axis, further illustrating the direct influence of the fiber core position on strain sensitivity.

[0026] Based on the model established above, Figure 2 Simulation results of fiber core strain under different bending curvatures are presented. The simulations consider parameters of the fiber core at different locations. The strain response under the following conditions covers from (correspond (i.e., the fiber core is located on the bending neutral axis) to (correspond The full range of values ​​for (i.e., the area where the fiber core is furthest from the neutral axis) is noteworthy. Even at relatively high curvatures... Under these conditions, the bending strain in this configuration is also far lower than the maximum strain that the optical fiber material itself can withstand. As shown by the star-shaped mark in the figure, when That is, the angle between the fiber core and the bending direction. At that time, the bending strain reached its maximum value in the simulation. While this value is the most significant across the entire parameter space, it still retains approximately seven times the safety margin compared to the strain limit of optical fiber. Even if the endoscope faces more extreme bending conditions in practical applications, such as further increases in curvature, this non-fixed embedded sensor layout can still operate reliably without causing excessive bending strain on the fiber core. This excellent strain tolerance is mainly attributed to the sensor's free-moving space design within the channel, which effectively avoids reduced strain transmission efficiency and mechanical constraints, facilitating reliable navigation capabilities for flexible manipulation of the endoscope in complex cavities.

[0027] Figure 3 This indicates that when the curvature of the endoscope is fixed at a certain value... The figure shows the quantitative relationship between the position of the fiber core inside the sensor and the bending strain it experiences. The white dashed box in the figure shows the range of fiber core positions that may occur during actual operation of the endoscope. Since the sensor can move freely within the channel, the position of the fiber core relative to the bending neutral axis varies when the endoscope is bent in different directions. It will vary within a symmetrical range. (Based on the core spacing) The range is defined as .from Figure 3 As can be seen from this, within this range, the bending strain corresponding to all possible core positions is strictly limited to... Within. when At that time, the strain reaches its extreme value. (As shown by the two endpoints of the curve in the figure); while when the fiber core approaches the neutral axis ( Approaching 0), the strain rapidly decreases to near zero. The curve is symmetrical about the origin, reflecting the consistency of the strain response of the sensor structure in different bending directions. This result fully demonstrates that this non-fixed embedding packaging method can readily support the higher curvatures that endoscopes may encounter in practical applications. Even in At this relatively high curvature, the maximum strain is still far below the strain limit of the optical fiber material. This design preserves ample safety margins. The bending strain experienced by the fiber core inside the sensor is determined solely by its geometric position, without the additional local strain concentration that might be introduced by forced bonding and encapsulation.

[0028] Figure 4 A detailed mechanical coupling model between the endoscope and the navigation fiber optic sensor is presented, revealing the physical contact mechanism between the two in a non-fixed connection mode and its impact on measurement accuracy. Figure 4 As shown, a diameter of [missing information] is reserved inside the endoscope. The endoscope features a circular channel into which the sensor is freely inserted, with a gap between them. This arrangement allows one side of the sensor to contact the inner wall of the channel, while the other side is exposed to air, naturally creating an air gap between the sensor and the endoscope body. The purpose of this design is to allow the sensor to undergo relative displacement within the channel, avoiding the additional constraints imposed by rigid fixation. It also ensures that the fiber core strain remains within a suitable range under large bending curvatures. However, this non-fixed embedding method also introduces new mechanical problems. When the endoscope bends, the sensor comes into contact with the inner wall of the channel, generating contact forces at the interface. and friction As shown in the figure, these two forces act together on the sensor, causing additional strain that is superimposed on the fiber core bending strain caused by shape change, thus affecting the measurement accuracy of the fiber core strain. Therefore, accurate quantification... and The influence of this becomes crucial in the design of the aforementioned coupling model. To reduce the additional strain on the sensor caused by the inner wall of the channel when the endoscope bends, simulation analysis is used to determine the optimal channel diameter for a specific sensor diameter.

[0029] According to Hertz's contact theory and The sum can be expressed as

[0030]

[0031] in, This represents the equivalent elastic modulus of the two materials used in the fiber optic sensor and the endoscope body. , These are Young's modulus and Poisson's ratio of the sensor material, respectively. , These are Young's modulus and Poisson's ratio of the material inside the endoscope channel, respectively. The effective contact radius between the fiber optic sensor and the aperture reflects the influence of the diameter matching degree on the geometric characteristics of the contact area; δ is the contact deformation; and μ is the coefficient of friction. Considering that the inner wall of the endoscope aperture is coated with a hydrophilic polymer coating, a thermosetting hydrophilic coating, or other material coatings, the static friction coefficient between the fiber optic and the polymer material is in the range of 0.05~0.1. Therefore, without loss of generality, the friction coefficient is taken as 0.1 in the simulation. To further analyze the... To address the additional strain caused by the contact force, the Euler-Bernoulli beam theory was employed, simplifying the fiber optic sensor into a beam model. This revealed that the maximum curvature of the sensor-channel contact area is proportional to the applied force. Based on this theory, the bending differential equation of the beam was numerically solved using the finite difference method, yielding the displacement field of the sensor under the contact force. ,in For along Figure 4 Position coordinates along the Y-axis. Second derivative of the displacement field. This directly corresponds to the bending curvature of the sensor. As shown in the figure, the contact force acts on... Near point A, the curvature reaches its maximum. Therefore, the resulting additional strain can be expressed as:

[0032]

[0033] in, The constant is determined by the beam length, bending stiffness, and the location of the force. Substituting equation (1) into equation (2), we can obtain the final expression for the additional strain:

[0034]

[0035] in, For a constant term, when As the value approaches 1, the additional strain approaches infinity, which is consistent with the sharp increase in contact force when the channel is close to the diameter of the sensor in actual practice.

[0036] Figure 5 This demonstrates the relationship between the sensor's additional strain and the orifice diameter. The quantitative relationship between them provides an important basis for optimizing the mechanical coupling design between the endoscope and the sensor. Since the magnitude of the additional strain depends on the sensor diameter... With the diameter of the channel The degree of matching, therefore, a reasonable selection. Crucial. Based on the aforementioned mechanical coupling model, Figure 5 With sensor diameter For example, the additional strain as a function of the pore diameter was plotted. The relationship curve shows the change. The horizontal axis represents the diameter of the channel. Its value range is set to This range takes into account both the sensor's size and the space constraints of the endoscope's internal structure. The vertical axis represents the additional strain caused by contact and friction forces. From Figure 5 The overall trend of the curves shows that the additional strain decreases monotonically with increasing pore diameter. When Lower limit of proximity sensor diameter ( When the sensor is in the vicinity of the pore (near the pore wall), the gap between the sensor and the pore wall is extremely small, making contact almost inevitable. At this point, the additional strain is at its highest level throughout the entire range. With... As the strain gradually increases, the sensor's free space within the duct increases, reducing both the probability of contact with the duct wall and the contact force, thus causing the additional strain to decrease rapidly. In practical engineering applications, the turning point where the decreasing trend significantly slows down can be quantitatively determined by analyzing the relative rate of change of the additional strain in formula (3). The threshold for the relative rate of change of the additional strain is set as follows: In mechanical design, control engineering, and other fields, 10% is often used as an empirical dividing line between "significant change" and "negligible change," meaning that for every 1mm increase in the orifice diameter, the additional strain decreases by 10%. The corresponding theoretical value can then be obtained. diameter ratio Therefore, in order to effectively reduce the impact of additional strain on the accuracy of shape measurement, it is necessary to ensure... .from Figure 5 As can also be seen from the curve, when the aperture is larger than... Afterward, the decreasing trend of the additional strain slowed significantly, entering a relatively stable low-value region. When the duct diameter reached... When, the corresponding additional strain is approximately This has little impact on the strain measurement results of the sensor.

[0037] A larger aperture size can effectively reduce the mechanical contact between the sensor and the aperture wall, thus reducing the interference of contact force and friction on fiber optic strain measurement. However, as can be seen from the figure, pursuing a large aperture cannot completely eliminate contact-introduced errors. When the diameter is too large, the fiber optic sensor lacks sufficient constraint within the channel, potentially exhibiting a helical distribution under certain bending postures. This helical shape causes a deviation between the actual geometric path of the sensor and the idealized planar bending model, introducing additional measurement errors and potentially reducing the accuracy of shape reconstruction. Therefore, the selection of the channel diameter requires striking a balance between reducing additional strain and avoiding helical deformation. (The curve in the figure...) ( The region provides a reasonable reference range for this purpose, within which additional strain can be kept at a low level (e.g., (Left and right), and can also prevent the sensor from spiraling through appropriate constraint of the hole wall.

[0038] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A fiber optic sensor packaging structure for navigation in a minimally invasive surgical instrument, characterized in that, The minimally invasive surgical instrument has a slender, circular channel inside its slender guide rod. An optical fiber sensor is freely placed inside the slender channel, and there is a gap between the optical fiber sensor and the inner wall of the slender channel.

2. The fiber optic sensor packaging structure for navigation of minimally invasive surgical instruments according to claim 1, characterized in that, The diameter ratio of the elongated channel to the fiber optic sensor is greater than 0.

26.

3. The fiber optic sensor packaging structure for navigation of minimally invasive surgical instruments according to claim 2, characterized in that, The inner wall of the elongated channel has a coating with a friction coefficient of 0.05 to 0.

1.

4. A packaging method for a fiber optic sensor packaging structure for navigation in minimally invasive surgical instruments, characterized in that, Includes the following steps: A long, narrow circular channel with a length and diameter greater than that of the navigation fiber optic sensor is opened inside the slender guide rod of the minimally invasive surgical instrument, so that it can completely accommodate the navigation fiber optic sensor; the navigation fiber optic sensor is then completely inserted into the narrow channel.

5. The packaging method for the fiber optic sensor packaging structure for navigation of minimally invasive surgical instruments according to claim 4, characterized in that, The diameter ratio of the elongated channel to the fiber optic sensor is greater than 0.

26.

6. The packaging method for the fiber optic sensor packaging structure for navigation of minimally invasive surgical instruments according to claim 4 or 5, characterized in that, After the circular elongated channel is drilled, a hydrophilic polymer coating or a thermosetting hydrophilic coating is applied to its inner wall, and the coefficient of friction of the coating is 0.05 to 0.1.

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