A rotary retraction unit for multi-modal microcatheter medical imaging

Abstract

This invention discloses a rotational retraction unit for multimodal microcatheter medical imaging, comprising a hollow rotary motor and a photoelectric rotational transmission module. The photoelectric rotational transmission module includes a rotating-end beam-expanding collimating lens, a backlight-eliminating wedge, and a catheter connection part. The three are coaxially arranged in the rotor cavity of the hollow rotary motor and rotate synchronously with the rotor. The backlight-eliminating wedge is configured to deflect the Fresnel reflection light generated by the near-end face of the optical fiber from the effective receiving numerical aperture of the collimating lens, preventing it from coupling back to the fiber core. This unit replaces belt pulley transmission with coaxial direct drive of the hollow motor, eliminating non-uniform rotational distortion at the source and improving scanning accuracy. At the same time, the backlight-eliminating wedge blocks backlight interference from the end face, reduces background noise, and improves the signal-to-noise ratio and contrast of multimodal images.

Description

Technical Field

[0001] This invention relates to the field of medical device technology, specifically to a rotational retraction unit for multimodal microcatheter medical imaging. Background Technology

[0002] Multimodal imaging technologies such as intravascular optical coherence tomography (OCT) and fluorescence lifetime imaging (FLIM) can simultaneously acquire morphological and structural information of the vessel wall and biochemical metabolic information at the molecular level, providing new methods for the precise diagnosis of cardiovascular diseases such as atherosclerosis. In these multimodal microcatheter imaging systems, the rotation and retraction unit is a key component for realizing three-dimensional helical scanning of the lumen. It needs to provide high-speed rotational power and uniform linear retraction power to the microcatheter simultaneously, and act as a cross-interface signal bridge between the stationary host system and the high-speed rotating microcatheter, ensuring bidirectional, low-noise transmission of multi-band optical signals.

[0003] Currently, common rotary retraction units typically use pulleys or synchronous belt eccentric transmission mechanisms to drive the rotary spindle, which mainly presents the following two problems.

[0004] First, regarding the mechanical drive. Because the optical fiber of the fiber optic slip ring must pass through the central axis of rotation to ensure continuous transmission of the optical signal, it occupies the most crucial coaxial space. This prevents conventional motors from being placed on the central rotating shaft for direct coaxial drive. Instead, eccentric transmission is achieved via pulleys or gears on the side of the main shaft. This indirect transmission method inevitably introduces mechanical backlash, belt elastic deformation, and transmission vibration at high speeds. This results in irregular alternation of the actual rotational angular velocity at the distal end of the catheter, manifesting as severe non-uniform rotational distortion in the generated cross-sectional image. The tissue morphology is abnormally stretched or compressed, severely affecting the accurate quantitative measurement of lesion size.

[0005] Secondly, regarding optical coupling, traditional methods use double-clad fiber slip rings between the stationary and rotating ends for cross-interface optical signal coupling. This structure involves multiple fiber endfaces, and the optical path repeatedly experiences abrupt changes in refractive index at multiple docking points, generating strong Fresnel reflections. These reflected lights return along the original path, creating severe background noise that directly masks extremely weak tissue autofluorescence signals, leading to FLIM imaging failure or a very low signal-to-noise ratio. Furthermore, the precise alignment between the core and inner cladding of the double-clad fiber requires extremely high precision; even micrometer-level errors can cause mode crosstalk, producing multipath artifacts and significantly reducing image quality.

[0006] In summary, the non-uniform rotational distortion caused by mechanical eccentric drive and the backlight noise caused by multi-fiber end-face reflections in existing rotary retraction units have become major bottlenecks restricting the development of multimodal microcatheter imaging technology. Therefore, there is an urgent need for a rotary retraction unit that can effectively suppress backlight noise from fiber end-face reflections while ensuring coaxial direct drive to eliminate non-uniform rotational distortion. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a rotational retraction unit for multimodal microcatheter medical imaging, aiming to solve one or more problems existing in the background technology.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a rotational retraction unit for multimodal microcatheter medical imaging, comprising a hollow rotary motor and a photoelectric rotational transmission module; the photoelectric rotational transmission module includes a rotating end beam expander collimating lens, a backlight elimination wedge, and a catheter connection portion; the rotating end beam expander collimating lens, the backlight elimination wedge, and the catheter connection portion are coaxially disposed in the rotor cavity of the hollow rotary motor and rotate synchronously with the rotor; the backlight elimination wedge is configured to cause Fresnel reflection light generated by the proximal end face of the optical fiber connected to the catheter connection portion to deviate from the effective receiving numerical aperture of the rotating end beam expander collimating lens, preventing it from coupling back to the fiber core.

[0009] Furthermore, the near-end face of the optical fiber is an angle-polished end face, and the backlight elimination wedge has a wedge-shaped bevel that matches the angle-polished end face, so that the Fresnel reflected light is deflected at an angle relative to the incident principal optical axis.

[0010] Furthermore, the propagation path of the Fresnel reflected light has an equivalent optical path, which deflects the angle at the plane where the near end face of the optical fiber is located as a lateral displacement, and the lateral displacement exceeds the mode field radius of the fiber core; the equivalent optical path is jointly constituted by the air gap between the near end face of the optical fiber and the far end slope of the backlight elimination wedge, the air optical path calculated by the thickness of the backlight elimination wedge, and the spatial distance between the near end face of the backlight elimination wedge and the rotating end beam expanding collimating lens.

[0011] Furthermore, the distance between the distal bevel of the backlight-eliminating wedge and the proximal end face of the optical fiber is less than 0.5 mm, so that the refractive indices of the two interfaces are nearly matched to reduce the Fresnel reflection intensity.

[0012] Furthermore, the backlight elimination wedge is made of ultraviolet-grade fused silica material, and both surfaces are provided with broadband antireflection films, which cover the short-wave fluorescence excitation band, the visible fluorescence emission band, and the near-infrared OCT band.

[0013] Furthermore, the photoelectric rotation transmission module also includes a hollow electric slip ring, which includes an electric slip ring stator, a brush, and an electric slip ring rotor. The electric slip ring rotor is located radially outside the rotating end beam expanding collimating lens and the backlight elimination wedge. At least one annular conductive ring is provided on the outer circumferential surface of the electric slip ring rotor. The brush is fixed on the electric slip ring stator and slides in contact with the annular conductive ring. The rotating end beam expanding collimating lens, the backlight elimination wedge, and the conduit connection are all disposed inside the electric slip ring rotor. The electric slip ring rotor is coaxially disposed in the rotor cavity of the hollow rotary motor and rotates synchronously with the rotor.

[0014] Furthermore, the distal end of the electric slip ring rotor is provided with a conduit connection electrode, which is connected to the annular conductive ring via a wire and extends into the conduit connection portion for electrical connection with the ultrasonic transducer of the microcatheter.

[0015] Furthermore, the inner wall of the electric slip ring rotor has a light-absorbing surface to absorb the Fresnel reflected light deflected by the backlight elimination wedge.

[0016] Furthermore, the light-absorbing surface is any one of a black anodized layer, a black light-absorbing coating, or a black light-absorbing material layer.

[0017] Furthermore, it also includes a multi-wavelength fusion optical path, a straight-line retraction platform, and a signal control transceiver circuit. The multi-wavelength fusion optical path includes at least two independent stationary collimators and a dichroic mirror beam combiner assembly. Each stationary collimator has independent axial position, lateral position, and tilt angle adjustment degrees of freedom to compensate for focal shift and incident angle difference at the common rotating end beam expander collimating lens and backlight elimination wedge interface for different working wavelengths. The output optical axis of the multi-wavelength fusion optical path is collinear with the mechanical rotation axis of the hollow rotating motor and the optical central axis of the photoelectric rotating transmission module. The hollow rotating motor, photoelectric rotating transmission module, multi-wavelength fusion optical path, and signal control transceiver circuit are all integrated and mounted on the straight-line retraction platform to provide uniform linear retraction power along the rotation axis direction.

[0018] This invention describes a rotary retraction unit for multimodal microcatheter medical imaging. Its advantages lie in the following: By coaxially integrating the rotating end beam-expanding collimating lens, the backlight-eliminating wedge, and the catheter connection part within the rotor cavity of a hollow rotary motor, the rotation is directly driven by the rotor. This eliminates the traditional belt-driven eccentric transmission method, fundamentally eliminating mechanical backlash and jitter, and thoroughly suppressing non-uniform rotational distortion, ensuring high precision and uniformity in catheter scanning and retraction. Simultaneously, the backlight-eliminating wedge causes Fresnel reflections generated near the fiber end face to deviate from the effective receiving numerical aperture of the collimating lens, preventing coupling back to the fiber core. This effectively blocks interference from end-face backlight on OCT and fluorescence signals, significantly reducing background noise and improving the signal-to-noise ratio and contrast of multimodal images. The overall structure is compact, with a synergistic mechanical and optical design that ensures optical axis stability under high-speed rotation while achieving high-fidelity cross-interface transmission of multi-band signals. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of the rotation retraction unit according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the internal structure of the multi-wavelength fusion optical path according to an embodiment of the present invention; Figure 3 This is a schematic cross-sectional view of the photoelectric rotation transmission module according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the optical signal transmission path according to an embodiment of the present invention.

[0020] Explanation of reference numerals in the attached drawings: 1. Linear retraction platform; 2. Hollow rotary motor; 21. Rotor; 3. Photoelectric rotary transmission module; 31. Hollow electric slip ring; 311. Electric slip ring stator; 312. Brush; 313. Electric slip ring rotor; 314. Light-absorbing surface; 32. Rotating end beam expander collimating lens; 33. Wedge; 34. Conduit connecting electrode; 4. Multi-wavelength fusion optical path; 41. First reflecting mirror; 42. First dichroic mirror; 43. Second dichroic mirror; 44a. Short-wavelength excitation light independent stationary collimator; 44b. OCT light independent stationary collimator; 46. Multimode fiber interface; 47a. Short-wavelength excitation light single-mode fiber interface; 47b. OCT light single-mode fiber interface; 48. Second reflecting mirror; 5. Signal control transceiver circuit; 6. Light passage. Detailed Implementation

[0021] Typical embodiments embodying the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various variations in different embodiments without departing from the scope of the present invention, and the descriptions and illustrations herein are for illustrative purposes only and not intended to limit the present invention.

[0022] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0023] To further illustrate the principles and structure of this invention, the appendix is ​​now provided. Figure 1-4 The preferred embodiments of the present invention will be described in detail below.

[0024] This invention relates to a rotation and retraction unit for multimodal microcatheter medical imaging. It provides the power for high-speed rotation and uniform linear retraction of disposable interventional microcatheters, while simultaneously acting as a cross-interface signal bridge between the stationary host signal processing system and the high-speed rotating microcatheter, ensuring bidirectional, low-noise transmission of high-frequency ultrasound electrical signals and multi-band optical signals. In typical multimodal imaging scenarios, this unit can simultaneously support optical coherence tomography (OCT), fluorescence lifetime imaging (FLIM), and intravascular ultrasound (IVUS), providing multidimensional information for identifying high-risk vulnerable plaques.

[0025] The entire rotary retraction unit adopts a bottom-base support and opto-mechatronics integrated layout. At its bottom is a linear retraction platform 1, which can be any of the following: a voice coil motor, a stepper motor with a ball screw, or a piezoelectric ceramic motor. This platform provides millimeter-level precision and uniform linear motion to simulate the retraction of a catheter within a blood vessel. The linear retraction platform 1 integrates and fixes a hollow rotary motor 2, a multi-wavelength fusion optical path 4, a signal control transceiver circuit 5, and all components of the optoelectronic rotary transmission module 3 that need to rotate with the rotor. All functional modules move synchronously and uniformly linearly with the platform, ensuring a constant interfacial air gap, and that the output optical axis of the multi-wavelength fusion optical path 4, the mechanical rotation axis of the hollow rotary motor 2, and the optical central axis of the optoelectronic rotary transmission module 3 are always collinear.

[0026] The signal control transceiver circuit 5 is integrated on the linear retraction platform 1. Based on a field-programmable gate array (FPGA), it implements low-level timing control of high-frequency ultrasound signals, generating high-voltage ultrasound pulses that meet clinical requirements. It also performs low-noise amplification, analog-to-digital conversion, and preprocessing on the weak ultrasound echo signal returned from the catheter. The processed digital signal is transmitted to the back-end host for vascular wall ultrasound image reconstruction. This circuit is electrically connected to the stationary side of the slip ring, enabling bidirectional lossless transmission of ultrasound electrical signals during rotation.

[0027] The stator of the hollow rotary motor 2 is fixed to the surface of the slide table, while its rotor 21 is supported by high-speed bearings and rotates about a horizontal axis. The rotor 21 of the hollow rotary motor 2 has a cylindrical through-cavity machined inside, the diameter and length of which are designed to fit the size and number of integrated optical and electrical components. An electric slip ring rotor 313 is coaxially mounted in the rotor cavity. The electric slip ring rotor 313 is a hollow cylinder and is rigidly connected to the inner wall of the rotor 21 by interference fit, key connection, or pressure ring fastening, rotating synchronously with the rotor 21 at high speed. Multiple annular conductive rings arranged circumferentially are provided on the outer circumferential surface of the electric slip ring rotor 313 for sliding contact with the brush 312 on the stationary side.

[0028] The internal space of the slip ring rotor 313 is used to install optical components—from back to front, a rotating end beam expander collimating lens 32 and a backlight elimination wedge 33, with a guide tube connection (not shown) fixed at the front end. The rotating end beam expander collimating lens 32 is fixed to the rear section of the inner cavity of the slip ring rotor 313 by a metal spacer and a pressure ring, while the backlight elimination wedge 33 is fixed to the front of the lens by a set thread or a pressure ring. The guide tube connection is threaded to the front end of the slip ring rotor 313 or engages with the front port of the rotor's inner cavity for locking. The aforementioned optical components and the slip ring rotor 313 constitute an integral rotating assembly that rotates together with the motor rotor 21.

[0029] The slip ring stator 311 is mounted on the stator housing of the hollow rotary motor 2, located on the outer end of the rotor 21, without interfering with the rotor cavity. The brush 312 is fixed to the slip ring stator 311 and maintains sliding contact with the annular conductive ring on the slip ring rotor 313 by means of elastic force, thereby leading the rotating ultrasonic electrical signal to the stationary side. The distal end of the slip ring rotor 313 is also provided with a conduit connection electrode 34. This conduit connection electrode 34 is connected to the annular conductive ring through an internal wire and extends into the conduit connection part for electrical docking with the ultrasonic transducer inside the conduit after the microcatheter is inserted. The conduit connection part includes a precision flange and a self-locking conduit socket (not shown). After the microcatheter is inserted, the proximal connector of the double-clad optical fiber inside is automatically centered and locked, so that the angle-polished end face of the optical fiber is at a preset distance of less than 0.5 mm from the distal inclined surface of the wedge 33. The conduit connection part is provided with conductive contacts (not shown) that cooperate with the conduit connection electrode 34. When locked, they elastically abut to achieve signal transmission.

[0030] The rotating-end beam expander and collimator lens 32 is a short focal length lens group, preferably with an effective focal length of 8 mm. Its function is to focus the parallel light beam from the stationary end into a very small spot and ensure that it falls precisely on the core end face of the preceding optical fiber. The backlight elimination wedge 33 is a wedge-shaped thin sheet made of ultraviolet-grade fused silica, with a wedge angle between 6° and 10°, more preferably 8°. The distal bevel of the wedge 33 is polished and is positioned opposite to the near-end face of the optical fiber locked in the guide tube connection.

[0031] To achieve efficient transmission over a wide spectral range, both sides of the wedge 33 are coated with broadband antireflection films. The film system is designed to cover the short-wavelength fluorescence excitation band of 355nm to 488nm, the visible fluorescence emission band of 400nm to 700nm, and the near-infrared OCT band of approximately 1310nm, thereby minimizing interface reflection loss and suppressing the fluorescence background of the film itself.

[0032] The backlight elimination wedge 33 plays a crucial role in suppressing optical noise. In traditional microcatheter optical interfaces, the fiber end face inevitably reflects some of the illumination light back, forming strong Fresnel echoes. These echoes not only generate background noise in OCT images but also directly drown out weak tissue autofluorescence signals. This invention completely solves this problem through a physical mechanism involving the synergistic action of three elements.

[0033] The primary element is angular deflection, which is also the dominant mechanism: the near-end face of the fiber in the guide tube is processed into an 8° angle polished surface, and the angle of the far-end bevel of the backlight-eliminating wedge 33 is precisely matched to it. When forward-propagating light is incident from the backlight-eliminating wedge 33 onto the fiber core end face, since the refractive indices of the wedge 33 and the fiber core are very close (both approximately 1.46), the illumination light enters the fiber core with almost no deflection; however, the Fresnel reflection light inevitably generated at the fiber end face produces an intrinsic angular deflection of approximately 23.5° because the reflection interface is not perpendicular to the optical axis. Instead of returning along the original path, it propagates at an inclined angle toward the direction of the rotating end beam-expanding collimating lens 32.

[0034] The second key element is the lever amplification effect of the equivalent optical path: as the reflected light travels backward, it needs to pass sequentially through the tiny air gap between the fiber end face and the distal inclined surface of the wedge 33, the internal thickness of the wedge 33, and the air gap between the proximal end face of the wedge 33 and the rotating beam-expanding collimating lens 32. These three distances together constitute the equivalent optical path, the length of which is equal to the physical thickness of the wedge 33 divided by the refractive index, plus the actual distance between the two air gaps. In this embodiment, the equivalent optical path is designed to be approximately 10 mm, where the thickness of the wedge 33 is selected within the range of 0.5 mm to 5 mm, and the corresponding air gaps are adjusted to make up for it. It is this approximately 10 mm equivalent optical path that amplifies the cumulative angular deflection of the reflected light into a significant lateral displacement at the focal plane where the fiber end face is located. Taking SMF-28, a commonly used single-mode fiber, as an example, its core mode field radius is only about 5μm, while the lateral offset of the reflected light from the end face in this plane can reach 30μm to 80μm, which is much larger than the mode field radius. Therefore, these reflected lights cannot be refocused and coupled back to the core by the rotating end beam expander collimating lens 32. It should be noted that the so-called "defocus" here does not refer to axial defocusing of the forward optical path—on the forward coupling path, the equivalent optical path is designed to ensure that the illumination light is precisely focused to the center of the core; its accurate physical meaning is that the reflected light deviates laterally from the receiving numerical aperture of the core, thus failing to couple back. For shorter wavelength excitation light, the lateral offset is even more considerable: for example, 355nm light has a offset of 40.87μm, 405nm light has a offset of 31.80μm, and 488nm light has a offset of 22.63μm. The third factor is the intensity suppression effect of the proximity spacing: the spacing of less than 0.5 mm between the far end bevel of wedge 33 and the near end face of the optical fiber reduces the Fresnel reflectivity of the air-quartz interface by about an order of magnitude due to the near matching of refractive indices, while avoiding the formation of a parasitic Fabry-Perot cavity between the two.

[0035] The synergy of these three elements ensures that end-face reflections of any wavelength band lose their physical path to re-enter the single-mode fiber core, eliminating backlight interference at its source. To ensure that the deflected reflected light does not re-enter the receiving optical path after multiple reflections within the rotor cavity, the inner wall of the slip ring rotor 313 is provided with a light-absorbing surface 314. The light-absorbing surface 314 undergoes a blackening light-absorbing treatment, which can be achieved through various processes such as black anodizing, coating with black epoxy resin or carbon nanotube coatings, and attaching black flocked paper. It also serves as an absorption darkroom, completely absorbing these stray lights.

[0036] On the stationary side at the motor's tail end, a multi-wavelength fusion optical path 4 is installed, serving as the optical registration and beam combining hub for the entire system. The module's outer shell is made of aluminum alloy, and an L-shaped folded spatial optical path is constructed internally. On the left input panel of the module, from top to bottom, are arranged a short-wavelength fluorescence excitation single-mode fiber interface 47a and a near-infrared OCT single-mode fiber interface 47b, with a tissue autofluorescence recovery large-core multimode fiber interface 46 located at the lower left. Behind the short-wavelength excitation single-mode fiber interface 47a and the near-infrared OCT single-mode fiber interface 47b, respectively, are installed independent stationary collimators 44a and 44b for short-wavelength excitation and near-infrared OCT, respectively. Each collimator has three-dimensional adjustment capabilities, allowing independent adjustment of axial position, lateral position, and tilt angle. During operation, the OCT light is first connected, and its corresponding stationary collimator shapes the divergent laser beam into a parallel beam, which then propagates horizontally forward along the system's main optical axis. Simultaneously, the short-wavelength excitation light from above, after being collimated by its corresponding stationary collimator, is first refracted downwards by a first reflecting mirror 41 placed at a 45° angle. It then illuminates a first dichroic mirror 42, which transmits long wavelengths and reflects short wavelengths. This first dichroic mirror refracts the short-wavelength light again by 90°, precisely merging it spatially with the OCT parallel light to form a coaxial composite parallel beam. This composite beam continues forward, passing through a second dichroic mirror 43, exiting from the light-transmitting hole 6 at the front of the module, crossing an air gap, and stationarily entering the rear end of the rapidly rotating photoelectric rotation transmission module 3.

[0037] Multi-wavelength light is refocused at the rotating end by the rotating end beam expander collimating lens 32, passes through the backlight elimination wedge 33, and is efficiently coupled into the fiber core of the catheter fiber, then transmitted along the microcatheter to the target area in the body. The autofluorescence emitted by the stimulated tissue and the reflected and scattered OCT light, carrying the structural and biochemical information of the lesion, return in reverse along the same fiber. The mixed backlight leaves the fiber end face, passes through the backlight elimination wedge 33 and the rotating end beam expander collimating lens 32, and becomes parallel light again, crossing the air gap and re-entering the multi-wavelength fusion optical path module 4. Here, the fluorescence component in the backlight has a longer wavelength than the excitation light, so it is reflected downwards by the second dichroic mirror 43, while the OCT light passes through in a straight line. The downwardly separated fluorescence light path is deflected by the second reflecting mirror 48, focused by the built-in fluorescence recovery beam expander collimating lens of the module, and coupled to the large-core multimode fiber interface 46 at the lower left, and finally guided to the high-sensitivity detector at the back end, such as a photomultiplier tube or a single-photon counter. With this optical path layout, the weak fluorescence signal is completely separated from the strong excitation light background in space, and the signal-to-noise ratio is greatly improved.

[0038] To achieve precise confocal transmission of the aforementioned wideband light in a single optical fiber, it is necessary to compensate for the focal shift and incident angle difference caused by the material dispersion of the rotating-end beam expander collimating lens 32 and the backlight elimination wedge 33. This invention employs a one-time factory calibration method. First, the near-infrared OCT light source is turned on. An optical power meter is placed at the output end of the guide tube connection. The three-dimensional orientation of the stationary collimator corresponding to the OCT is adjusted until the optical power meter reading reaches its peak value. At this point, the OCT light is precisely focused at the center of the fiber core, and the collimator is locked. Subsequently, keeping the rotating end state unchanged, each short-wavelength excitation source is turned on sequentially, and its corresponding stationary collimator is adjusted accordingly, again with the maximum output optical power as the standard. Taking the rotating-end beam expander collimating lens 32 with a focal length of 8mm as an example, simulations show that the 355nm excitation light requires a lateral compensation of approximately 32.69μm, the 405nm light approximately 25.44μm, and the 488nm light approximately 18.11μm. These minute adjustments are entirely within the capabilities of conventional mechanical adjustment frames. Once all collimators are calibrated, they are permanently fixed, eliminating the need for users to perform any repetitive light adjustments during clinical use. The system automatically ensures that the multimodal light sources are confocal at the fiber end face of the catheter.

[0039] When the entire system is in operation, the linear retraction platform 1 drags all integrated modules backward at a uniform speed, while the rotor of the hollow rotary motor 2 rotates stably at a high speed of tens to hundreds of revolutions per second. The composite beam achieves static-to-rotation coupling in a contactless air gap, without any backlash or jitter introduced by belts or gears. The rotational angular velocity at the distal end of the duct is extremely uniform, fundamentally eliminating non-uniform rotational distortion, resulting in a true reproduction of tissue morphology in the cross-sectional image and more reliable quantitative measurement of circumferential dimensions. The blackened inner wall continuously absorbs residual reflected light, ensuring that the dark background noise of the fluorescence detection channel remains at an extremely low level.

[0040] In alternative implementations, the above solution still has several flexible variations. When the application scenario requires the imaging system to cover a wide wavelength range from near-ultraviolet to near-infrared, such as the coexistence of 355nm excitation light and 1310nm OCT light, and there are more stringent restrictions on the angular dispersion of the beam after passing through the wedge 33, the backlight elimination wedge 33 can be replaced by an ultraviolet-compatible dual-material composite wedge assembly. This assembly consists of two wedges with opposite wedge angles or combined at a preset angle. The first wedge is made of ultraviolet-grade fused silica, and the second wedge is made of low-dispersion, low-autofluorescence optical materials such as calcium fluoride or magnesium fluoride. The two wedges can be integrated through optical contact, molecular bonding, or plasma-assisted bonding, without the need for organic adhesives, thereby avoiding fluorescence caused by adhesive layer aging under ultraviolet irradiation. This composite wedge can significantly reduce the angular difference between transmitted light of different wavelengths and lateral beam drift while maintaining the core function of deflecting the reflected light from the end face out of the effective receiving range, and reducing the complexity of pre-compensation at the stationary end. The type of hollow rotary motor 2 can be selected according to actual needs. For example, a brushless DC hollow motor is preferred for high speed, a hollow cup motor can be used to obtain lower rotational inertia, or a stepper hollow motor can be used to meet the needs of low speed but high torque. The optical and electrical composite structure can also be flexibly adjusted: the electric slip ring rotor 313 can not only be set on the outer periphery of the optical element to achieve radial layering, but also be arranged in series with the optical element axially when space permits, or be uniformly packaged as an independent rotating module in the rotor cavity, and the electric slip ring stator 311 can be adjusted accordingly. The folding topology inside the multi-wavelength fusion optical path 4 is not limited to the L-shaped arrangement described in the text. Z-shaped, U-shaped or X-shaped folding can be adopted according to the actual housing and fiber interface direction. The number and position of the dichroic mirrors can be adjusted accordingly with the number of imaging modes being fused. The rotation and retraction unit of this invention is not limited to IVUS-OCT-FLIM trimodal imaging in coronary arteries, but can also be directly applied to various luminal diagnostic scenarios such as peripheral vascular imaging, gastrointestinal endoscopy, tracheal and bronchial endoscopy, and urinary tract endoscopy. After removing the intravascular ultrasound channel, it can also form a dual-modal rotation and retraction unit combining OCT and near-infrared fluorescence or OCT and photoacoustic imaging. Furthermore, its precise and stable rotation and retraction control is also suitable for helical scanning detection in industrial endoscopes and rotational scanning operations of precision samples under a microscope.

[0041] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A rotary retraction unit for multimodal microcatheter medical imaging, comprising a hollow rotary motor and a photoelectric rotary transmission module; characterized in that, The photoelectric rotating transmission module includes a rotating end beam expander collimating lens, a backlight elimination wedge, and a conduit connection. The rotating end beam expander collimating lens, the backlight elimination wedge, and the conduit connection are coaxially disposed in the rotor cavity of the hollow rotating motor and rotate synchronously with the rotor. The backlight elimination wedge is configured to cause Fresnel reflection light generated by the near end face of the optical fiber connected to the conduit connection to deviate from the effective receiving numerical aperture of the rotating end beam expander collimating lens, so that it cannot be coupled back to the fiber core.

2. The rotational retraction unit according to claim 1, characterized in that, The near-end face of the optical fiber is an angle-polished end face, and the backlight elimination wedge has a wedge-shaped bevel that matches the angle-polished end face, so that the Fresnel reflected light is deflected at an angle relative to the incident principal optical axis.

3. The rotational retraction unit according to claim 2, characterized in that, The propagation path of the Fresnel reflected light has an equivalent optical path, which deflects the angle at the plane where the near end face of the optical fiber is located as a lateral displacement, and the lateral displacement exceeds the mode field radius of the fiber core; the equivalent optical path is composed of the air gap between the near end face of the optical fiber and the far end slope of the backlight elimination wedge, the air optical path calculated by the thickness of the backlight elimination wedge, and the spatial distance between the near end face of the backlight elimination wedge and the rotating end beam expanding collimating lens.

4. The rotational retraction unit according to claim 1, characterized in that, The distance between the distal bevel of the backlight-eliminating wedge and the proximal end face of the optical fiber is less than 0.5 mm, so that the refractive indices of the two interfaces are nearly matched to reduce the Fresnel reflection intensity.

5. The rotational retraction unit according to claim 4, characterized in that, The backlight elimination wedge is made of ultraviolet-grade fused silica material, and both surfaces are provided with broadband antireflection films. The broadband antireflection films cover the short-wave fluorescence excitation band, the visible fluorescence emission band, and the near-infrared OCT band.

6. The rotational retraction unit according to claim 1, characterized in that, The photoelectric rotation transmission module further includes a hollow electric slip ring, which includes a slip ring stator, a brush, and a slip ring rotor. The slip ring rotor is located radially outside the rotating end beam expanding collimating lens and the backlight elimination wedge. At least one annular conductive ring is provided on the outer circumferential surface of the slip ring rotor. The brush is fixed on the slip ring stator and slides in contact with the annular conductive ring. The rotating end beam expanding collimating lens, the backlight elimination wedge, and the conduit connection are all located inside the slip ring rotor. The slip ring rotor is coaxially located in the rotor cavity of the hollow rotary motor and rotates synchronously with the rotor.

7. The rotational retraction unit according to claim 6, characterized in that, The distal end of the electric slip ring rotor is provided with a conduit connection electrode. The conduit connection electrode is connected to the annular conductive ring through a wire and extends into the conduit connection part for electrical connection with the ultrasonic transducer of the microcatheter.

8. The rotational retraction unit according to claim 6, characterized in that, The inner wall of the electric slip ring rotor has a light-absorbing surface to absorb the Fresnel reflected light deflected by the backlight elimination wedge.

9. The rotational retraction unit according to claim 8, characterized in that, The light-absorbing surface is any one of a black anodized layer, a black light-absorbing coating, or a black light-absorbing material layer.

10. The rotational retraction unit according to claim 1, characterized in that, It also includes a multi-wavelength fusion optical path, a straight-line retraction platform, and a signal control transceiver circuit. The multi-wavelength fusion optical path includes at least two independent stationary collimators and a dichroic mirror beam combiner assembly. Each stationary collimator has independent axial position, lateral position, and tilt angle adjustment degrees of freedom to compensate for focal shift and incident angle difference at the common rotating end beam expander collimating lens and backlight elimination wedge interface for different working wavelengths. The output optical axis of the multi-wavelength fusion optical path is collinear with the mechanical rotation axis of the hollow rotating motor and the optical central axis of the photoelectric rotating transmission module. The hollow rotating motor, photoelectric rotating transmission module, multi-wavelength fusion optical path, and signal control transceiver circuit are all integrated and mounted on the straight-line retraction platform to provide uniform linear retraction power along the rotation axis direction.

Images