A triple-double-core optical fiber wall-embedded PICC guiding and positioning device and method

Abstract

The application provides a kind of three double-core optical fiber wall embedded PICC guiding and positioning device and method, belong to medical instrument and photoelectric sensing technical field, the device includes: PICC catheter, photoelectric control unit, host computer, the PICC catheter has three double-core optical fiber groups in the wall inside, the double-core optical fiber group is evenly distributed with 120 ° angle circumference interval, every double-core optical fiber group includes two single-mode optical fibers, respectively constitutes light incidence channel and scattered light return channel;The photoelectric control unit is connected with the single-mode optical fiber of the PICC catheter, the photoelectric control unit includes modulated light source, photodetector, lock-in amplifier, signal acquisition and digital signal processing unit, the host computer is connected with the photoelectric control unit.The application realizes the real-time guiding and terminal positioning function in the process of PICC catheter intubation, the operation process is intuitive, reduces the complexity of operation, without X ray auxiliary, avoids the risk of medical radiation, significantly improves the intubation success rate and reliability.

Description

Technical Field

[0001] This invention belongs to the field of medical device and optoelectronic sensing technology, specifically relating to a three-core fiber optic tube wall embedded PICC guidance and positioning device and method. Background Technology

[0002] Peripherally inserted central venous catheters (PICCs) are a commonly used medium- to long-term venous access technique in clinical practice. The optimal placement of the PICC catheter tip is in the lower third of the superior vena cava to the cavus junction (CAJ). Ensuring accurate placement of the catheter tip at this location is crucial for maintaining patency and reducing the incidence of complications. Improper catheter tip placement can lead to serious complications such as thrombosis, catheter displacement, vascular injury, and even cardiac tamponade.

[0003] Traditional PICC placement relies primarily on surface measurements to estimate the catheter length, followed by chest X-ray confirmation of the catheter tip's position. This method suffers from significant delays; if the catheter tip fails to reach the target location or becomes displaced, repeated adjustments or even re-insertion under X-ray guidance are necessary, increasing patient discomfort and treatment costs. More importantly, X-ray radiation poses cumulative health hazards to both patients and healthcare workers.

[0004] Currently, various real-time positioning technologies have emerged in clinical practice to compensate for the shortcomings of traditional methods. Electromagnetic navigation positioning systems (such as Sherlock 3CG) use an external magnetic field generator to track electromagnetic sensors at the catheter tip, avoiding exposure to ionizing radiation. However, electromagnetic navigation systems are susceptible to interference from intraoperative metallic implants (such as pacemaker leads, artificial joints, and metal stents) and external electromagnetic devices, and require a stable magnetic field generator outside the patient's body, significantly increasing the complexity of preoperative preparation and operating space setup. While ultrasound-guided techniques can observe vascular structures in real time, it is difficult to continuously track the accurate position of the catheter tip when the catheter enters deep into the thoracic cavity or when sound waves are blocked by bone. Intracardiac electrocardiography (ECG) positioning uses P-wave morphology changes to determine the catheter tip position, but its accuracy is highly dependent on the patient's own electrical rhythm, limiting its application in patients with arrhythmias.

[0005] In recent years, PICC navigation and positioning methods based on fiber optic sensing technology have attracted widespread attention. Stringer et al. published a study in 2017 proposing a method for locating the PICC tip using a single-fiber dual-wavelength reflection spectrum. However, this method requires an additional matching sensing probe that fits against the body surface tissue during insertion, and also suffers from anatomical and tissue interference leading to spectral data distortion.

[0006] In addition, companies such as Bard Access Systems have introduced fiber optic shape sensing technology into the field of medical device navigation, obtaining several related patents (such as USPTO patent 12038338 and US-2023417998-A1). By writing Bragg grating arrays into multi-core optical fibers, wavelength demodulation technology is used to reconstruct the bending shape of guidewires or catheters, enabling the tracking of the trajectory of medical devices in vascular systems. However, this type of solution has high requirements for the optical path system, requiring the writing of multiple grating structures into the optical fiber and the use of tunable lasers or spectral analyzers. The system cost and structural complexity pose certain obstacles to its clinical application, and at the principle level, there is a cumulative positioning error caused by continuous reconstruction during the process. Meanwhile, a force feedback tactile catheter based on circumferential distribution of multimode optical fibers has been patented (publication number CN119655905B). This solution is based on PMMA optical waveguides, has high structural complexity, severe crosstalk in the four optical paths, signal stability affected by many factors, and suffers from severe temperature drift, among other limitations.

[0007] In summary, existing PICC guidance and positioning technologies have not yet achieved comprehensive optimization in terms of radiation safety, anti-interference capability, direction sensing capability, system complexity, and cost. There is an urgent need for a new type of guidance and positioning device that can accurately locate the catheter tip, reliably sense the relative position of the catheter and the blood vessel wall throughout the entire process, and has a simple structure and controllable cost. Summary of the Invention

[0008] The purpose of this invention is to solve the above-mentioned technical problems by providing a three-core fiber optic tube wall-embedded PICC guidance and positioning device and method.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A three-dual-core fiber optic tube-wall embedded PICC guiding and positioning device includes: a PICC conduit, wherein the inner wall of the PICC conduit has three dual-core fiber groups, the dual-core fiber groups are evenly distributed in a circle at 120° intervals, and each dual-core fiber group includes two single-mode fibers, which respectively form a light incident channel and a scattered light return channel.

[0011] The optoelectronic control unit is connected to the single-mode optical fiber of the PICC conduit. The optoelectronic control unit includes a modulation light source, a photodetector, a lock-in amplifier, and a signal acquisition and digital signal processing unit. The modulation light source generates three sinusoidal modulated lights with equal amplitude but different phases, which are injected into the three incident light channels respectively. The photodetector receives scattered light from the light return channel. The lock-in amplifier is connected to the photodetector and demodulates the signal output by the photodetector. The signal acquisition and digital signal processing unit is connected to the lock-in amplifier and converts the demodulated signal into a digital signal for processing.

[0012] The host computer is connected to the photoelectric control unit and is used to receive the processed signal, display the astigmatism intensity curves of the three-channel return in real time, and determine the position of the duct tip based on the curve characteristics.

[0013] Furthermore, the tip of the PICC conduit has a tapered chamfered structure, and the end faces of the three dual-core fiber groups are beveled, which reduces optical crosstalk between the three dual-core fiber groups and expands their respective independent detection areas.

[0014] Furthermore, the angle of the tapered chamfer is 28-32 degrees.

[0015] Furthermore, the tip of the PICC catheter has a rounded chamfered structure.

[0016] Furthermore, the PICC catheter is made of medical-grade thermoplastic polyurethane.

[0017] Furthermore, the modulated light source is a monochromatic sinusoidal light source with a wavelength in the red or near-infrared band, and the minimum light intensity value of its modulated light signal is close to zero.

[0018] The present invention may also include:

[0019] A method for guiding and positioning a PICC embedded in a three-core dual-fiber tube, using the aforementioned device, includes:

[0020] Step 1: The photoelectric control unit generates three sinusoidal modulated lights with equal amplitude but different phases, which are then injected into the incident light channels of three dual-core fiber groups respectively.

[0021] Step 2: The modulated light is output through the end of the optical fiber and is scattered in the blood. Light leakage occurs in the blood vessel wall, which reduces the intensity of the scattered light. Some of the scattered light is transmitted back to the front end of the optical fiber through the return channel.

[0022] Step 3: The return light is picked up by a photodetector, the lock-in amplifier receives the reference signal from the modulated light source, and the lock-in amplifier demodulates the signal to obtain three light intensity signals;

[0023] Step 4: After the demodulated signal is converted from analog to digital and processed by the signal acquisition and digital signal processing unit, it is transmitted to the host computer;

[0024] Step 5: The host computer displays the curves showing the relationship between the intensity of the three-channel return light and the length of the catheter in real time, and judges the status of the catheter tip in the blood vessel and whether it has entered the chamber based on the curve characteristics, thereby determining whether the catheter tip has reached the connection between the central vein and the atrium.

[0025] Furthermore, in the initial stage of catheter placement, when the optical fiber group signal near the blood vessel wall in the light intensity signal displayed by the host computer is lower than that of the other groups, the host computer issues a direction adjustment prompt to guide the adjustment of the pushing direction so that the three signals tend to be balanced.

[0026] Furthermore, when the catheter tip approaches the junction of the vena cava and the atrium, the intensity of at least one light source rapidly increases and reaches its maximum, prompting the host computer to issue a positioning alert.

[0027] Furthermore, the tube length data is collected in real time during the tube placement process.

[0028] The beneficial effects of this invention are as follows:

[0029] The entire placement and positioning process of this invention does not generate any ionizing radiation, thus avoiding the radiation exposure risks associated with traditional X-ray positioning methods. It is especially suitable for special populations that are sensitive to radiation, such as pregnant women and children. At the same time, patients do not need to go to the radiology department for X-ray confirmation after the procedure, which greatly shortens the diagnosis and treatment process and reduces patients' waiting time and medical costs.

[0030] The distributed structure of three dual-core optical fiber groups used in this invention can decouple the position of the catheter tip through the difference of the three return signals. While realizing tip positioning, it can also sense the relative position of the catheter and the blood vessel wall in real time, avoiding catheter apposition to the wall and damage to the blood vessel intima, thus improving safety. Compared with the traditional body surface measurement method, this invention is expected to improve the one-time positioning rate of the catheter tip through real-time signal feedback guidance.

[0031] This invention has natural anti-electromagnetic interference properties and is not affected by internal pacemakers, metal implants or external electromagnetic fields. It solves the pain point of limited application of electromagnetic navigation and positioning technology in complex cases and can provide safe and reliable catheter guidance for patients with various underlying diseases.

[0032] This invention provides real-time signal feedback throughout the catheter placement process. The operator can adjust the catheter's direction and placement speed at any time based on the real-time displayed three-channel signal curves, realizing visual guidance of the placement process and avoiding the discovery of catheter displacement only after placement is completed in traditional methods. It is practical. Attached Figure Description

[0033] Appendix Figure 1 This is a schematic diagram of the structure of the present invention;

[0034] Appendix Figure 2 This is a schematic diagram of the catheter tip of the present invention having a tapered chamfered structure;

[0035] Appendix Figure 3 This is a block diagram of the control system of the present invention;

[0036] Appendix Figure 4 This is a schematic diagram of the return signal curve characteristics at each stage of tube placement according to the present invention. Detailed Implementation

[0037] The present invention will now be further described with reference to the accompanying drawings.

[0038] Example 1:

[0039] This invention provides a three-core fiber optic tube-wall embedded PICC guiding and positioning device, as shown in the attached figure. Figure 1 As shown, it includes: PICC conduit 1, host computer 4, and photoelectric control unit 5. The inside of the PICC conduit 1 has three dual-core fiber groups 2. The dual-core fiber groups 2 are evenly distributed in a circle with a 120° angle interval. Each dual-core fiber group 2 includes two single-mode fibers, which respectively form the incident light channel and the return light channel. The photoelectric control unit 5 is connected to the single-mode fibers of the PICC conduit 1.

[0040] It should be noted that the dual-core fiber optic group described in this invention refers to a structure consisting of two single-mode optical fibers, one of which forms the incident light channel and the other forms the scattered light return channel. Three sets of dual-core fiber optic groups are circumferentially distributed at 120° equal intervals within the conduit wall.

[0041] As attached Figure 3 As shown, the photoelectric control unit includes a modulation light source 6, a photodetector 7, a lock-in amplifier 8, and a signal acquisition and digital signal processing unit 9. The modulation light source 6 is used to generate three sinusoidal modulated lights with equal amplitudes but different phases, which are injected into the three incident light channels respectively. The photodetector 7 is used to receive scattered light from the return light channel. The lock-in amplifier 8 is connected to the photodetector and is used to demodulate the signal output by the photodetector. The signal acquisition and digital signal processing unit is connected to the lock-in amplifier and is used to convert the demodulated signal into a digital signal and process it.

[0042] The host computer 4 is connected to the photoelectric control unit 5 to receive the processed signal, display the intensity curves of the three-way return light in real time, and determine the position of the guide tip based on the curve characteristics.

[0043] As attached Figure 2 As shown, the PICC catheter 1 has a tapered chamfered tip 3, and the end faces of the three dual-core fiber groups 2 are beveled, reducing optical crosstalk between the three dual-core fiber groups and expanding their respective independent detection areas. Simultaneously, by controlling appropriate optical field intensity or lock-in amplifier integration time, it is ensured that when the catheter is in a peripheral vein, all three fiber return signals have a minimum return signal component, while the strongest scattered light return signal is generated when the catheter enters the central vein after passing through the peripheral vein.

[0044] The angle of the tapered chamfer is 28-32 degrees, preferably 30 degrees.

[0045] The tip 3 of the PICC catheter 1 can also be a rounded chamfered structure.

[0046] The modulation light source 6 is a monochromatic sinusoidal light source with a wavelength in the red or near-infrared band, and the minimum light intensity value of its modulation light signal is close to zero.

[0047] Three modulated sinusoidal beams with equal amplitude but different phases are respectively introduced into the incident light channels of three dual-core fiber groups 2. The modulated light is output from the fiber end and scatters to different degrees in the blood vessel or cavity. The scattered light enters the fiber return channel and is transmitted back to the fiber front end, where it is picked up by a photodetector and demodulated by a lock-in amplifier. The demodulated signal is then conditioned and converted from digital to analog before entering the digital signal processing unit and being transmitted to the host computer. The host computer has data receiving, command sending, and process display functions. During the catheter placement process, the host computer receives the return light intensity signals from the three dual-core fiber groups in real time and displays three intensity characterization curves. Based on these three curves, the status of the catheter tip in the blood vessel and whether it has entered the cavity can be determined, thereby realizing the positioning function at the junction of the central vein and the atrium.

[0048] In this embodiment, the dual-core fiber optic group is integrated with the catheter wall for encapsulation. The numerical aperture angle of the fiber optics is close to an appropriate value in the blood to highlight the differences in the returned signals of the three fiber optic groups when the catheter is close to the blood vessel wall. At this time, the returned signal of the fiber optic group closer to the blood vessel wall is the weakest or even disappears. When the catheter tip moves away from the blood vessel wall, the returned signals of the three dual-core fiber optic groups gradually become stronger than the returned signals when they are close to the blood vessel wall, and their magnitudes are similar. When the catheter tip is blocked by the blood vessel wall, the returned signals of the three fiber optic groups decrease simultaneously. When the catheter tip approaches the junction of the central vein and the atrium, due to the rapid disappearance of some or all of the wall light leakage, at least one of the three fiber optic returned signals will increase significantly. When the catheter tip reaches the target position at the junction of the central vein and the atrium, at least one of the three fiber optic returned signals will reach its maximum.

[0049] Furthermore, the host computer can be a personal computer or a dedicated intelligent terminal device, and its software package has functions such as receiving data, displaying curves in real time, providing intelligent prompts, controlling modulation optical signal parameters, and saving data during the tube placement process.

[0050] During the catheter placement process, the host computer receives the return light intensity signals from the three dual-core fiber groups in real time and displays three intensity characterization curves. Based on these three curves, the status of the catheter tip in the blood vessel and the timing of its entry into the chamber can be determined, thereby guiding the PICC operator to perform the placement and achieving the positioning function at the connection between the central vein and the atrium.

[0051] Three modulated sinusoidal beams with equal amplitude and different phases are respectively introduced into the incident light channels of three dual-core fiber groups. The modulated light is output from the end of the fiber and is scattered in the blood vessel or cavity. The scattered light enters the fiber return channel and is transmitted back to the fiber front end, where it is picked up by a photodetector and demodulated by a lock-in amplifier. The demodulated signal is then conditioned and converted from digital to analog before entering the digital signal processing unit and being transmitted to the host computer.

[0052] Appendix Figure 4 The diagram illustrates the characteristic states of three curves displayed on the host computer during catheter placement. These states may occur at various stages of the three curves, including the peripheral venous stage, the central venous stage, and the atrial junction stage. Specifically, "15 - Return Relative Intensity Feature 1" represents the return signal from the group (or two groups) of fibers closest to the vessel wall when the fiber is close to the vessel wall. Due to light leakage and absorption effects from the vessel wall, the reflected light component is greatly reduced, resulting in the lowest signal intensity. "16 - Return Relative Intensity Feature 2" represents the increase in scattered signal component when the fiber end face moves away from the peripheral venous wall. This signal characteristic is an overall increase in intensity relative to "15 - Return Relative Intensity Feature 1". "17 - Return Relative Intensity..." Feature 3” refers to the return signal of at least one of the three dual-core fiber groups that is far from the wall after the optical fiber enters the central vein. Since the light leakage and absorption of the blood vessel wall further decreases and the scattered light further increases, the scattered signal component also rises further. Therefore, the overall intensity of this signal is higher than that of “16-Return Relative Intensity Feature 2”. “18-Return Relative Intensity Feature 4” refers to the return signal of at least one of the three dual-core fiber groups that is far from the wall when the optical fiber enters the atrium from the central vein. Since the leakage and absorption effect of the blood vessel wall almost disappears at this time, the scattered signal component reaches its peak in the open atrium. Therefore, this return signal reaches its highest level. The turning point indicated by the arrow in the figure is the junction of the central vein and the atrium.

[0053] Example 2:

[0054] According to the three-dual-core fiber optic tube wall-embedded PICC guiding and positioning device described in Example 1, the device embeds three dual-core fiber optic groups into the PICC tube wall to achieve guidance and positioning. The specific implementation process is as follows:

[0055] (1) Catheter fabrication: Medical-grade thermoplastic polyurethane (TPU) material is used as the catheter matrix. This material has good biocompatibility and flexibility, meeting the clinical requirements for PICC catheters. During the catheter extrusion molding process, three dual-core fiber groups are uniformly embedded inside the catheter wall using a customized micro-nano extrusion mold. Each dual-core fiber group contains two single-mode fibers with a core diameter of 9μm and a cladding diameter of 125μm, serving as the incident light channel and the light return channel, respectively. The three dual-core fiber groups are distributed at 120° equal intervals on the cross-section of the catheter. The numerical aperture angle of the emitted light in the blood is preferably 14.8°±1° to reduce optical crosstalk.

[0056] The tip of the guide tube is polished with a 30° conical angle, so that the end faces of the three optical fibers are beveled, in order to reduce signal coupling between the three optical fibers and expand their respective independent detection areas.

[0057] (2) System Setup: The fiber optic tail of the prepared PICC catheter is connected to the photoelectric control module, which integrates three independent laser light sources, photodetectors, and lock-in amplifiers. The light source uses an 850nm infrared laser diode, which has the lowest absorption coefficient and moderate penetration capability in biological tissues, effectively acquiring the returned signal. The three light sources output sinusoidal modulated light with an amplitude of 5mW, a modulation frequency of 1kHz, and phases of 0°, 120°, and 240°, respectively. Phase multiplexing is used to distinguish the three signals and avoid mutual interference. After the scattered light is returned, it is converted into an electrical signal by a PIN photodetector and then demodulated by a lock-in amplifier. The integration time of the lock-in amplifier is set to 500ms to ensure the signal-to-noise ratio and response speed. The demodulated signal is then transmitted to a host computer (e.g., a personal computer) after analog-to-digital conversion. The host computer has a dedicated software package that displays the real-time intensity curves of the three returned light sources and provides intelligent prompts for position status.

[0058] (3) Catheter placement and positioning process: Before catheter placement, the patient's catheter depth is assessed to confirm the conditions of the puncture vessel, and then the catheter is inserted into the blood vessel. In the initial stage of catheter placement, the catheter is located in the peripheral venous segment. Due to the small diameter of the peripheral venous vessel, the catheter is prone to contact with the vessel wall. At this time, among the three signals displayed in real time by the host computer, the return signal of the fiber optic group closer to the vessel wall will be significantly lower than that of the other two groups. The operator can adjust the direction of catheter push according to this signal difference, so that the three signals gradually become more balanced, ensuring that the catheter tip always travels in the center of the blood vessel and avoiding catheter apposition to the vessel wall and damage to the vascular intima. Once the catheter passes through the subclavian vein and enters the superior vena cava, the increased distance between the catheter tip and the vessel wall due to the larger diameter of the superior vena cava will cause at least one of the three return signals to rise to a higher intensity level than any of the three signals from the peripheral venous stage. This indicates that the catheter has entered the central venous segment. Continue slow catheter advancement. As the catheter tip approaches the junction of the superior vena cava and the right atrium (CAJ), the right atrium, being a larger chamber, prevents at least one set of optical fibers from the catheter tip from contacting the atrium wall. The emitted light is scattered, resulting in a global maximum return signal intensity and a sharp increase in the intensity of the scattered light. When this signal intensity jumps (see the arrow in "18-Return Relative Intensity Feature 4"), the host computer automatically issues a positioning prompt. At this point, stop catheter advancement to confirm that the catheter tip has reached the target position.

[0059] The PICC catheter involved in this invention can be manufactured using existing mature medical catheter extrusion molding technology. Specifically, three sets of dual-core single-mode optical fibers are embedded into the wall of a medical-grade thermoplastic polyurethane (TPU) tube at 120° equal intervals using a customized micro-nano extrusion mold, achieving integrated encapsulation of the optical fibers and the catheter. This process is compatible with existing PICC catheter production lines, requires no large-scale equipment modification, and enables mass production and standardization. The tapered chamfer at the catheter tip can be processed by precision mechanical grinding or laser cutting, with controllable processing accuracy, suitable for industrial production.

[0060] The modulation light source (such as an 850nm near-infrared laser diode), photodetector (such as a PIN photodetector), lock-in amplifier, and signal acquisition and digital signal processing unit in the photoelectric control unit are all commercially available general industrial components that can be integrated into a miniaturized control box, featuring controllable cost and stable performance.

[0061] The host computer can be a general-purpose personal computer or a dedicated intelligent terminal device, which, together with a dedicated software package, can realize signal display and processing. The software functions can be implemented through conventional programming.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A three-core fiber optic tube wall-embedded PICC guiding and positioning device, characterized in that, include: PICC conduit (1), the inside of the PICC conduit (1) has three dual-core fiber groups (2), the dual-core fiber groups (2) are evenly distributed in a circle with a 120° angle interval, each dual-core fiber group (2) includes two single-mode fibers, which respectively form a light incident channel and a scattered light return channel. The optoelectronic control unit (5) is connected to the single-mode fiber of the PICC conduit (1). The optoelectronic control unit includes a modulation light source (6), a photodetector (7), a lock-in amplifier (8), and a signal acquisition and digital signal processing unit (9). The modulation light source (6) is used to generate three sinusoidal modulated lights with equal amplitude and different phases, which are injected into the three incident light channels respectively. The photodetector (7) is used to receive the returned scattered light; the lock-in amplifier (8) is connected to the photodetector and is used to demodulate the signal output by the photodetector; the signal acquisition and digital signal processing unit is connected to the lock-in amplifier and is used to convert the demodulated signal into a digital signal and process it. The host computer (4) is connected to the photoelectric control unit (5) to receive the processed signal, display the three-way back-transmission light intensity curve in real time, and determine the position of the duct tip based on the curve characteristics.

2. The three-core fiber optic tube wall-embedded PICC guiding and positioning device according to claim 1, characterized in that, The PICC conduit (1) has a tapered chamfered tip (3) and the end faces of the three dual-core fiber groups (2) are beveled, which reduces the crosstalk of scattered light between the three dual-core fiber groups and expands their respective independent detection areas.

3. The three-core fiber optic tube wall-embedded PICC guiding and positioning device according to claim 2, characterized in that, The angle of the tapered chamfer is 28-32 degrees.

4. The three-core fiber optic tube wall-embedded PICC guiding and positioning device according to claim 1, characterized in that, The tip (3) of the PICC catheter (1) has a rounded chamfer structure.

5. The three-core fiber optic tube wall-embedded PICC guiding and positioning device according to claim 1, characterized in that, The PICC catheter (1) is made of medical-grade thermoplastic polyurethane.

6. The three-core fiber optic tube wall-embedded PICC guiding and positioning device according to claim 1, characterized in that, The modulated light source (6) is a monochromatic sinusoidal light source with a wavelength of red light or near-infrared band, and the minimum light intensity value of its modulated light signal is close to zero.

7. A method for guiding and positioning a PICC embedded in a three-core fiber optic tube, characterized in that, Using the apparatus according to any one of claims 1-6, the method comprises: Step 1: The photoelectric control unit (5) generates three sinusoidal modulated lights with equal amplitude and different phases through the modulation light source (6), and injects them into the incident light channels of the three dual-core fiber groups (2). Step 2: The modulated light is output through the end of the optical fiber and is scattered in the blood. Light leakage occurs in the blood vessel wall, which reduces the intensity of the scattered light in the blood. Some of the scattered light is transmitted back to the front end of the optical fiber through the return channel. Step 3: The return light is picked up by the photodetector (7), the lock-in amplifier (8) receives the reference signal from the modulated light source, and the lock-in amplifier (8) demodulates the signal to obtain the intensity signals of the three return light channels. Step 4: The demodulated signal is converted from analog to digital and processed by the signal acquisition and digital signal processing unit (9) and then transmitted to the host computer; Step 5: The host computer displays the curves showing the relationship between the intensity of the three-channel return light and the length of the catheter in real time, and judges the status of the catheter tip in the blood vessel and whether it has entered the chamber based on the curve characteristics, thereby determining whether the catheter tip has reached the connection between the central vein and the atrium.

8. The method according to claim 7, characterized in that, In the initial stage of catheter placement, when the signal of the fiber group closest to the blood vessel wall in the backlight intensity signal displayed by the host computer is lower than that of the other groups, the host computer issues a direction adjustment prompt to guide the adjustment of the pushing direction so that the three signals tend to be balanced.

9. The method according to claim 7, characterized in that, When the catheter tip approaches the junction of the vena cava and the atrium, the intensity of at least one backlight signal reaches its maximum, and the host computer issues a positioning prompt.

10. The method according to claim 7, characterized in that, The tube length data is collected in real time during the tube placement process.

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