All-optical ultrasound imaging system based on phase modulation

Abstract

The present application discloses an all-optical ultrasonic imaging system based on phase modulation, which belongs to the field of imaging technology. The system includes: a laser assembly, an ultrasonic detector, an interference device, and an imaging assembly; the laser assembly is used to provide continuous laser light to the interference device; the interference device includes a reference fiber arm, a sample fiber arm, and an optical path adjustment device, and is located between the ultrasonic detector and the imaging assembly; wherein the interference device is used to separate the laser light into reference light and detection light, and transmit the detection light to the ultrasonic detector for phase modulation; the optical path adjustment device is used to adjust the optical path difference between the two arms, and form interference light between the reference light and the phase-modulated detection light, which is then input into the imaging assembly; the ultrasonic detector is used to generate ultrasonic waves, project the ultrasonic waves to the area to be measured, and phase-modulate the detection light in response to the ultrasonic echo of the area to be measured; and the imaging assembly is used to generate a corresponding image based on the interference light.

Description

Technical Field

[0001] The present application relates to the field of imaging technology, and in particular to an all-optical ultrasound imaging system based on phase modulation. Background Art

[0002] Cardiovascular disease is one of the world's leading causes of death, claiming approximately 20 million lives annually. The most common cause of cardiovascular disease is the rupture of vulnerable atherosclerotic plaques and subsequent thrombosis. Vulnerable plaques are typically characterized by a thin fibrous cap and a large necrotic core. Therefore, accurate assessment of vulnerable plaques requires intravascular imaging with high resolution and a large detection depth to provide information such as fibrous cap thickness and the proportion of the necrotic core. However, current intravascular imaging technologies are unable to provide high-resolution, holistic information on the morphology of the vascular wall. Intravascular ultrasound (IVUS) imaging plays a vital role in the assessment of cardiovascular disease and has been a vital tool in interventional catheterization laboratories for over 30 years. However, IVUS imaging is limited by the bandwidth of conventional piezoelectric transducers, and given the high attenuation of high-frequency ultrasound in tissue, IVUS imaging must strike a balance between resolution and detection depth.

[0003] An all-optical intravascular ultrasound imaging method currently exists. This method uses picosecond laser pulses to excite carbon nanocomposites to generate wide-bandwidth ultrasound, and fiber Bragg gratings for ultrasound detection. This method achieves ultra-wideband (147%) and high-resolution intravascular ultrasound imaging, which are difficult to achieve with traditional technologies. This overcomes the incompatibility between high resolution and large detection depth. This method modulates the ultrasound signal using intensity modulation. Intensity modulation involves tuning the wavelength of a continuous laser to the linear range of the Bragg grating's reflection spectrum, converting wavelength information into intensity information. The main advantages of this intensity modulation technique are its simplicity and relatively low cost, as its implementation requires only a tunable laser and a photodetector.

[0004] However, the main noise source in intensity modulation technology is photodetector noise. Although sensitivity can be easily improved by using higher laser power or resonators with higher Q factors, when the power and Q factor are high enough, laser frequency noise becomes the dominant noise factor, and higher Q factors and laser powers cannot further improve sensitivity. In this case, the optical signal-to-noise ratio can only be improved by reducing the frequency noise of the laser, that is, using a laser with a narrower linewidth. However, narrow linewidth lasers often require more complex optical designs, higher-quality optical components, and more precise manufacturing processes, which are very expensive, resulting in higher costs for the entire imaging system. Therefore, although all-optical ultrasound imaging systems based on intensity modulation have the advantage of simple structure, their sensitivity is often limited by continuous laser frequency noise, making it impossible to achieve high-precision detection of ultrasound signals.

[0005] The existing all-optical ultrasound imaging system based on intensity modulation is affected by laser frequency noise and cannot achieve high-precision detection of ultrasound signals. An effective solution is urgently needed. Summary of the Invention

[0006] The embodiments of the present disclosure provide an all-optical ultrasound imaging system based on phase modulation, which at least solves the technical problem in the prior art that existing all-optical ultrasound imaging systems based on intensity modulation are affected by laser frequency noise and cannot achieve high-precision detection of ultrasound signals.

[0007] According to an embodiment of the present disclosure, an all-optical ultrasonic imaging system based on phase modulation is provided, comprising: a laser assembly, an ultrasonic detector, an interference device and an imaging assembly; the laser assembly is used to provide continuous laser light to the interference device; the interference device comprises a reference optical fiber arm, a sample optical fiber arm and an optical path adjustment device, and is located between the ultrasonic detector and the imaging assembly; wherein the interference device is used to separate the laser light into a reference light input into the reference optical fiber arm and a detection light input into the sample optical fiber arm, and transmit the detection light to the ultrasonic detector for phase modulation; the optical path adjustment device is used to adjust the optical path difference between the reference optical fiber arm and the sample optical fiber arm; and the interference device is further used to form interference light between the reference light and the phase-modulated detection light, and input the interference light into the imaging assembly; the ultrasonic detector is used to generate ultrasonic waves, project the ultrasonic waves to the area to be measured, and phase-modulate the detection light in response to the ultrasonic echo of the area to be measured; and the imaging assembly is used to generate a corresponding image based on the interference light.

[0008] Optionally, the optical path adjustment device includes a fiber stretcher and a first PID controller, and the imaging component includes a balanced detector; and wherein the fiber stretcher is arranged on the reference fiber arm; the balanced detector is used to convert the phase information of the interference light into light intensity information, and transmit the light intensity information to the first PID controller; the first PID controller is used to control the fiber stretcher to stretch the optical fiber of the reference fiber arm according to the light intensity information.

[0009] Optionally, the interference device also includes a wavelength adjustment device, and a 1×2 fiber optic coupler is provided on the sample fiber optic arm; wherein the 1×2 fiber optic coupler is used to split the phase-modulated detection light into two parts, and transmit one part of the phase-modulated detection light to the wavelength adjustment device; the wavelength adjustment device is used to adjust the wavelength of the laser generated by the laser component according to the phase-modulated detection light transmitted by the 1×2 fiber optic coupler.

[0010] Optionally, the wavelength adjustment device includes a photodetector and a second PID controller; wherein the photodetector is used to convert the light intensity information of the phase-modulated detection light transmitted by the 1×2 optical fiber coupler into an analog electrical signal, and transmit the DC data in the analog electrical signal to the second PID controller; the second PID controller is used to adjust the wavelength of the laser generated by the laser component according to the DC data.

[0011] Optionally, the interference device also includes a 20:80 fiber coupler and a 50:50 fiber coupler, and the reference fiber arm and the sample fiber arm are arranged between the 20:80 fiber coupler and the 50:50 fiber coupler; wherein the 20:80 fiber coupler is used to split the laser into a reference light input into the reference fiber arm and a detection light input into the sample fiber arm; the 50:50 fiber coupler is used to form interference light of the reference light and the phase-modulated detection light, and input the interference light into the imaging component.

[0012] Optionally, the sample fiber optic arm includes a fiber optic circulator, which is arranged between the 20:80 fiber optic coupler and the 1×2 fiber optic coupler, and is used to transmit the detection light to the ultrasonic detector, receive the phase-modulated detection light transmitted by the ultrasonic detector, and transmit the phase-modulated detection light to the 1×2 fiber optic coupler.

[0013] Optionally, the sample fiber arm includes an adjustable optical delay line, which is used to introduce a time delay to the reference light.

[0014] Optionally, the imaging component also includes a bandpass filter, a data acquisition card and an image display; wherein the bandpass filter is used to filter the low-frequency signal of the light intensity information transmitted by the balanced detector; the data acquisition card is used to convert the light intensity information after filtering the low-frequency signal into a digital signal; and the image display is used to display an image according to the digital signal.

[0015] Optionally, the ultrasonic detector includes an ultrasonic generating component and an ultrasonic echo detection component; the ultrasonic generating component is used to generate ultrasonic waves and project the ultrasonic waves to the area to be measured; the ultrasonic echo detection component is used to phase modulate the detection light in response to the ultrasonic echo of the area to be measured.

[0016] Optionally, the ultrasonic generating component includes a pulse laser and a laser ultrasonic transducer; wherein the pulse laser is used to generate pulse laser and transmit the pulse laser to the laser ultrasonic transducer; the laser ultrasonic transducer is used to convert the pulse laser into ultrasonic waves and project the ultrasonic waves to the area to be measured.

[0017] The all-optical ultrasonic imaging system based on phase modulation proposed in this application includes a laser component, an ultrasonic detector, an interference device and an imaging component. First, an ultrasonic wave is generated by the ultrasonic detector and projected to the area to be measured. The ultrasonic wave is reflected by the tissue in the area to be measured to generate an ultrasonic echo. Then, a continuous laser is provided to the interference device through the laser component. The interference device divides the laser into reference light and detection light. The reference light is input to the reference optical fiber arm, and the detection light is input to the sample optical fiber arm and then transmitted to the ultrasonic detector. The ultrasonic detector phase-modulates the detection light in response to the ultrasonic echo of the area to be measured, and then transmits the phase-modulated detection light to the interference device. Finally, the optical path difference between the reference optical fiber arm and the sample optical fiber arm is adjusted by the optical path adjustment device. Then, the interference device forms interference light of the reference light and the phase-modulated detection light, and inputs the interference light to the imaging component. The imaging component generates a corresponding image based on the interference light. In this application, the optical path difference between the two arms of the interferometer can be adjusted and locked to orthogonality through an optical path adjustment device. At this time, the output light intensity of the interferometer is most sensitive to phase changes, thus providing the highest conversion efficiency from phase changes to light intensity changes. Any tiny phase changes in the sample fiber arms caused by ultrasound can be efficiently converted into light intensity changes, which can significantly reduce the influence of laser frequency noise, thereby achieving high-precision detection of ultrasonic signals and effectively improving the signal-to-noise ratio of the all-optical ultrasonic imaging system. This solves the technical problem that existing all-optical ultrasonic imaging systems based on intensity modulation are affected by laser frequency noise and cannot achieve high-precision detection of ultrasonic signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide a further understanding of the present disclosure and constitute a part of this application. The illustrative embodiments of the present disclosure and their descriptions are used to explain the present disclosure and do not constitute an improper limitation of the present disclosure. In the drawings:

[0019] Figure 1 This is a block diagram of the overall structure of the all-optical ultrasound imaging system based on phase modulation described in an embodiment of the present application;

[0020] Figure 2 is a more specific structural block diagram of the all-optical ultrasound imaging system based on phase modulation described in an embodiment of the present application;

[0021] Figure 3 This is a specific structural block diagram of the imaging component described in the embodiment of the present application. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the technical solutions of the present disclosure, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present disclosure.

[0023] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may also be a central element. When an element is considered to be "connected" to another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right", "up", "down", "front", "back", "circumferential" and similar expressions used herein are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0024] This application considers that high-resolution visualization of vascular structure and high-precision assessment of tissue function are important for determining the progression of vulnerable plaques. This requires intravascular ultrasound imaging to visualize vascular structure with high resolution. Intensity-demodulated acoustic wave sensors have demonstrated high sensitivity and wide-band response in detecting acoustic waves. However, the solution itself has inherent shortcomings that limit its future application:

[0025] 1) System sensitivity is often limited by continuous laser frequency noise;

[0026] 2) The signal-to-noise ratio of light intensity detection is easily affected by light source fluctuations and the stability of the sensing system, resulting in poor stability of acoustic wave sensing;

[0027] 3) The sensing system itself suffers from significant light intensity loss, relying on optical coupling between optical fibers, optical transmission and reflection from the object under test, and the stability of the sensing structure. This ultimately results in a low signal-to-noise ratio for the acoustic waves sensed by the system.

[0028] 4) This type of solution is only suitable for single-point acoustic wave sensing, making it difficult to reuse sensing units and unable to achieve simultaneous detection of multiple acoustic / ultrasonic waves. To meet the requirements of high-sensitivity and ultra-wideband acoustic wave sensing, we have developed an all-optical ultrasonic imaging method and system based on phase modulation.

[0029] Research has found that phase-modulated fiber optic sensors use changes in the phase of light waves in an optical fiber caused by external interference to detect various physical quantities and their variations. This sensor is highly sensitive, flexible, and versatile, and can be used in a wide range of applications. To increase the sensitivity of fiber optic interferometers to the measured quantity while being insensitive to non-measured quantities, specialized optical fibers are required to meet the requirements for measuring different physical quantities. Interferometric fiber optic sensors use optical fibers as phase modulation elements. The interaction between the measured quantity (parameter) and the optical fiber causes a phase change in the light transmitted through the fiber, thus forming a fiber optic interferometer. Compared to other modulation methods, phase-forced fiber optic sensors have higher sensitivity than conventional demodulation methods due to their use of interferometric demodulation technology. Although phase-modulated sensors have been applied to measure various parameters such as temperature, stress, magnetic field, current, displacement, acceleration, and vibration, they have not yet been applied to ultrasound imaging. Therefore, this application proposes an all-optical ultrasound imaging system based on phase modulation. This imaging system uses phase modulation and modulation to acquire ultrasound signals from the measured area (e.g., within a blood vessel or other locations within a living organism). This allows for high-resolution visualization of vascular structure and high-precision assessment of tissue function, which is of great significance for assessing the progression of vulnerable plaques.

[0030] In order to solve the above problems, this embodiment proposes an all-optical ultrasound imaging system based on phase modulation. Figure 1 As shown, the phase-modulated all-optical ultrasonic imaging system provided in this embodiment includes: a laser assembly, an ultrasonic detector, an interference device and an imaging assembly; the laser assembly is used to provide continuous laser light to the interference device; the interference device includes a reference optical fiber arm, a sample optical fiber arm and an optical path adjustment device, and is located between the ultrasonic detector and the imaging assembly; wherein the interference device is used to divide the laser light into a reference light input into the reference optical fiber arm and a detection light input into the sample optical fiber arm, and transmit the detection light to the ultrasonic detector for phase modulation; the optical path adjustment device is used to adjust the optical path difference between the reference optical fiber arm and the sample optical fiber arm; and the interference device is also used to form interference light between the reference light and the phase-modulated detection light, and input the interference light to the imaging assembly; the ultrasonic detector is used to generate ultrasonic waves, project the ultrasonic waves to the area to be measured, and phase-modulate the detection light in response to the ultrasonic echo of the area to be measured; and the imaging assembly is used to generate a corresponding image based on the interference light.

[0031] Specifically, if Figure 1As shown, first, ultrasonic waves are generated by an ultrasonic detector and projected to the area to be measured. The ultrasonic waves are reflected by the tissue in the area to be measured to generate ultrasonic echoes. Then, a continuous laser is provided to the interference device through the laser assembly. The interference device divides the laser into reference light and detection light. The reference light is input to the reference optical fiber arm, and the detection light is input to the sample optical fiber arm and then transmitted to the ultrasonic detector. The ultrasonic detector phase-modulates the detection light in response to the ultrasonic echo of the area to be measured, and then transmits the phase-modulated detection light to the interference device. The principle of phase modulation of the detection light is that the phase of the detection light is modulated with the frequency and amplitude of the ultrasonic echo. Finally, the optical path difference between the reference optical fiber arm and the sample optical fiber arm is adjusted by the optical path adjustment device. Then, the interference device forms interference light of the reference light and the phase-modulated detection light, and inputs the interference light to the imaging component. The imaging component generates a corresponding image based on the interference light. In this application, the optical path difference between the two arms of the interferometer can be adjusted and locked to orthogonality through an optical path adjustment device. At this time, the output light intensity of the interferometer is most sensitive to phase changes, thus providing the highest conversion efficiency from phase changes to light intensity changes. Any tiny phase changes in the sample fiber arms caused by ultrasound can be efficiently converted into light intensity changes, which can significantly reduce the influence of laser frequency noise, thereby achieving high-precision detection of ultrasonic signals and effectively improving the signal-to-noise ratio of the all-optical ultrasonic imaging system. This solves the technical problem that existing all-optical ultrasonic imaging systems based on intensity modulation are affected by laser frequency noise and cannot achieve high-precision detection of ultrasonic signals.

[0032] It is worth noting that when the optical path difference between the two arms of the interferometer is orthogonal, the system's response to ultrasonic signals is much greater than its response to laser frequency noise. Therefore, in the orthogonal state, the system's sensitivity to phase changes is maximized while minimizing the impact of noise, thereby ensuring that the system can efficiently and accurately extract ultrasonic signals carrying important information from complex environments.

[0033] Optionally, the optical path adjustment device includes a fiber stretcher and a first PID controller, and the imaging component includes a balanced detector; and wherein the fiber stretcher is arranged on the reference fiber arm; the balanced detector is used to convert the phase information of the interference light into light intensity information, and transmit the light intensity information to the first PID controller; the first PID controller is used to control the fiber stretcher to stretch the optical fiber of the reference fiber arm according to the light intensity information.

[0034] Specifically, if Figure 2 As shown, the optical path adjustment device includes a fiber stretcher and a first PID controller. Since the fiber arm is easily affected by low-frequency interference from the environment, the fiber stretcher can be made by winding the optical fiber on the piezoelectric ceramic and then set on the reference fiber arm. Figure 3As shown, the imaging assembly includes a balanced detector, and the interference light output by the interference device is received by the balanced detector in the imaging assembly. The phase information of the interference light is converted into light intensity information by the balanced detector, and the light intensity information is transmitted to the first PID controller. The first PID controller changes the tensile strength of the optical fiber stretcher by changing the working current of the piezoelectric ceramic, thereby changing the length of the stretched optical fiber to adjust the optical path difference between the reference optical fiber arm and the sample optical fiber arm, eliminate the influence of the environment (such as temperature, vibration, etc.) on the optical path difference of the optical fiber arm, improve the stability and reliability of the system, and lock the optical path difference between the reference optical fiber arm and the sample optical fiber arm of the interference device to orthogonality, that is, the phase difference between the two interference light beams is 90°. At this time, the output light intensity of the interference device is most sensitive to phase changes, so it can provide the maximum conversion efficiency of phase change to light intensity change. In addition, the interference device is in an orthogonal state, and any tiny phase change of the sample arm caused by ultrasound can be efficiently converted into light intensity change by the balanced detector, thereby achieving high-precision detection of ultrasonic signals.

[0035] Furthermore, the interference fiber arm is easily affected by low-frequency interference from the environment. Therefore, piezoelectric ceramics that can respond to 50KHz are selected to make the fiber stretcher. The first PID controller controls the radial stretching length of the fiber stretcher, thereby quickly compensating for the optical path difference between the two arms, avoiding the influence of low-frequency vibration on the ultrasonic signal demodulation, and improving the detection sensitivity.

[0036] Optionally, the interference device also includes a wavelength adjustment device, and a 1×2 fiber optic coupler is provided on the sample fiber optic arm; wherein the 1×2 fiber optic coupler is used to split the phase-modulated detection light into two parts, and transmit one part of the phase-modulated detection light to the wavelength adjustment device; the wavelength adjustment device is used to adjust the wavelength of the laser generated by the laser component according to the phase-modulated detection light transmitted by the 1×2 fiber optic coupler.

[0037] Specifically, if Figure 1 and Figure 2As shown, the interferometer device also includes a wavelength adjustment device. A 1×2 fiber coupler is provided on the sample fiber arm. The 1×2 fiber coupler is used to split the phase-modulated probe light into two parts, one of which is transmitted to the wavelength adjustment device. The wavelength adjustment device adjusts the wavelength of the laser light generated by the laser assembly based on the phase-modulated probe light transmitted by the 1×2 fiber coupler. The altered wavelength is output by the laser assembly. A portion of the probe light, after phase modulation by the ultrasonic detector, reenters the wavelength adjustment device. The wavelength adjustment device adjusts the laser assembly based on this probe light, causing the wavelength of the laser output by the laser assembly to change again. This cycle repeats until the wavelength of the laser output by the laser assembly matches the wavelength corresponding to half the light intensity. This wavelength is now the center wavelength of the linear region of the reflectance spectrum of the echo detection assembly in the ultrasonic detector. Phase demodulation at this wavelength maximizes the dynamic range of the echo detection assembly. Maximizing the dynamic range means that the system can more accurately distinguish subtle signal changes and is more sensitive to ultrasonic signals.

[0038] Optionally, the wavelength adjustment device includes a photodetector and a second PID controller; wherein the photodetector is used to convert the light intensity information of the phase-modulated detection light transmitted by the 1×2 optical fiber coupler into an analog electrical signal, and transmit the DC data in the analog electrical signal to the second PID controller; the second PID controller is used to adjust the wavelength of the laser generated by the laser component according to the DC data.

[0039] Specifically, if Figure 2 As shown, the wavelength adjustment device includes a photodetector and a second PID controller. A portion of the probe light output by the 1×2 fiber coupler is transmitted to the photodetector, which converts information such as the power of the probe light into an analog electrical signal. Since the linear region of the echo detection assembly's reflection spectrum refers to the region where wavelength and light intensity have a linear relationship, the photodetector converts the intensity information of the probe light into an analog electrical signal. The DC data (frequency less than 25 kHz) of the analog electrical signal is transmitted to the second PID controller, which then controls the piezoelectric device in the laser assembly based on the DC data, causing the wavelength of the laser output to change. The changed wavelength is then output by the laser assembly, and the photodetector again records the light intensity information. The second PID controller again controls the piezoelectric device in the laser assembly based on the light intensity information, causing the wavelength of the laser output to change again. This cycle repeats until the laser assembly outputs a wavelength that matches the wavelength corresponding to half the light intensity. This wavelength is now the center wavelength of the linear region of the reflection spectrum. Phase demodulation at this wavelength maximizes the dynamic range of the echo detection assembly. Half the wavelength is equal to half the maximum reflectivity of the echo detection assembly's reflection spectrum.

[0040] Furthermore, the echo detection component can be, for example, a Bragg grating, which can be a π-phase-shifted Bragg grating (π-FBG). A π-phase-shifted Bragg grating artificially introduces a π phase shift point at the center of the grating region of a uniform Bragg grating. The discontinuity of the phase shift causes a narrow-bandwidth notch, or a spectral gap, to form in the Bragg grating's reflection spectrum. This results in a steeper spectral efficiency than a conventional grating, enabling better response to ultrasonic echoes over a wider frequency range.

[0041] Optionally, the interference device also includes a 20:80 fiber coupler and a 50:50 fiber coupler, and the reference fiber arm and the sample fiber arm are arranged between the 20:80 fiber coupler and the 50:50 fiber coupler; wherein the 20:80 fiber coupler is used to split the laser into a reference light input into the reference fiber arm and a detection light input into the sample fiber arm; the 50:50 fiber coupler is used to form interference light of the reference light and the phase-modulated detection light, and input the interference light into the imaging component.

[0042] Specifically, if Figure 2 As shown, the interferometer also includes a 20:80 fiber coupler and a 50:50 fiber coupler, with the reference fiber arm and the sample fiber arm positioned between the two fiber couplers. The 20:80 fiber coupler is used to split the laser light into a reference light input to the reference fiber arm and a probe light input to the sample fiber arm. The 50:50 fiber coupler is used to form interference light between the reference light and the phase-modulated probe light, and input the interference light into the imaging assembly. Thus, the interferometer primarily consists of a balanced Mach-Zehnder interferometer structure, a photodetector, and two PID controllers.

[0043] In one embodiment, if Figure 2 As shown, the sample fiber optic arm includes a fiber optic circulator, which is arranged between the 20:80 fiber optic coupler and the 1×2 fiber optic coupler, and is used to transmit the detection light to the ultrasonic detector, receive the phase-modulated detection light transmitted by the ultrasonic detector, and transmit the phase-modulated detection light to the 1×2 fiber optic coupler.

[0044] Specifically, the prototype fiber arm includes a fiber circulator and a 1×2 coupler. A continuous laser is input into one port of the fiber circulator and output through the second port. The continuous laser output from the second port of the fiber circulator is transmitted to the π-FBG in the endoscope of the ultrasound detector through a driving device (such as a helical retraction device and a torsion coil). When the ultrasound echo causes changes in the wavelength, phase, and polarization state of the π-FBG, the single-mode fiber connected to the π-FBG transmits the changes in parameters again through the built-in optical path of the driving device (such as the helical retraction device and the torsion coil) and the fiber circulator to the 1×2 coupler.

[0045] In one embodiment, if Figure 2 As shown, the sample fiber arm includes an adjustable optical delay line, which is used to introduce a time delay for the reference light.

[0046] Specifically, the laser assembly outputs a laser of a fixed wavelength, which passes through a balanced Mach-Zehnder interference structure (MZI) and is received by a balanced detector in the imaging assembly. At this time, the signal output by the balanced detector is a noise signal. The optical delay line can be manually adjusted to change the optical path difference between the MZI arms. The amplitude of the noise signal changes synchronously until the optical path between the MZI arms is the same and the amplitude of the noise signal is minimized. The tensile strength of the fiber stretcher is then adjusted to change the length of the stretched fiber to adjust the optical path difference between the reference fiber arm and the sample fiber arm, eliminating the influence of the environment (such as temperature, vibration, etc.) on the optical path difference of the fiber arms, improving the stability and reliability of the system, and locking the optical path difference between the reference fiber arm and the sample fiber arm of the interferometer to orthogonality.

[0047] In one embodiment, if Figure 3 As shown, the imaging component also includes a bandpass filter, a data acquisition card and an image display; the bandpass filter is used to filter the low-frequency signal of the light intensity information transmitted by the balanced detector; the data acquisition card is used to convert the light intensity information after filtering the low-frequency signal into a digital signal; and the image display is used to display an image according to the digital signal.

[0048] Specifically, if Figure 3 As shown, the imaging assembly includes a balanced detector, a bandpass filter, a data acquisition card, and an image display. Ultrasonic excitation and detection are not performed by the same component, yet crosstalk still exists between the ultrasonic excitation component and the ultrasonic detection component. Interference ultrasound detected by the ultrasonic detection component propagates along the axial direction of the ultrasonic detection component, reducing the ultrasonic detection component's response frequency, resulting in a low-frequency response. The bandpass filter used in the present invention has a range of 5-120 MHz, which can filter out low-frequency ultrasound and effectively reduce interference between the ultrasonic excitation component and the ultrasonic detection component. The upper limit of the ultrasound frequency generated by the photoacoustic transducer used in the present invention exceeds 90 MHz. According to the sampling law, the sampling frequency of the data acquisition card used in the present invention must be no less than 180 MHz. To more accurately capture ultrasonic signals, the data acquisition card used in this system has a sampling frequency of 500 MHz, which fully meets detection requirements. The image display is connected to the data acquisition card and is configured to display images based on digital signals. Photoelectric signal conversion accurately restores image data of the intravascular environment, thereby facilitating high-precision, high-definition imaging of the intravascular environment.

[0049] In one embodiment, if Figure 2As shown, the ultrasonic detector includes an ultrasonic wave generating component and an ultrasonic echo detecting component (corresponding to Figure 2 The ultrasonic wave generating component is used to generate ultrasonic waves and project the ultrasonic waves to the area to be measured; the ultrasonic echo detecting component is used to phase modulate the detection light in response to the ultrasonic echo of the area to be measured.

[0050] In one embodiment, the ultrasonic generating assembly includes a pulsed laser and a laser ultrasonic transducer (corresponding to Figure 2 The pulse laser is used to generate pulse laser and transmit the pulse laser to the laser ultrasonic transducer; the laser ultrasonic transducer is used to convert the pulse laser into ultrasonic waves and project the ultrasonic waves to the area to be measured.

[0051] Specifically, the ultrashort pulse width laser output by a pulsed laser is corrected for its spot by a laser beam expander before being coupled into a multimode optical fiber via a first fiber coupler. This multimode optical fiber transmits the pulsed laser light through a drive device (such as a helical-retraction device and a torsion coil) to an endoscopic probe containing a carbon nanocomposite material. The pulsed laser light strikes the carbon nanocomposite material, generating ultrasonic waves that excite the area under test. Within the test area, the ultrasonic waves generated by the endoscopic probe are reflected by the tissue within the test area, causing a spectral shift in the π-FBG.

[0052] In this embodiment, the drive mechanism includes a spiral-retraction device and a torsion coil. The spiral-retraction device primarily consists of three components: a rotation motor, a retraction motor, and a smooth ring. Two stepper motors control the rotation and retraction of the interventional catheter, respectively. The dual-path smooth ring allows the rotor end (connected to the interventional catheter) to rotate freely without damage. This facilitates real-time two-dimensional and three-dimensional imaging of the intravascular environment.

[0053] Furthermore, the wavelength of the tunable laser is tuned to the resonant center of the π-phase-shifted Bragg grating. Two interfering beams enter the imaging assembly, which then obtains the power of the interference light. The power of the interference light includes the power of phase noise, which is related to the propagation time of the two arms. When the delays of the two arms are the same, the balanced detector in the imaging assembly can eliminate the phase noise, thus obtaining an ultrasound signal with a higher signal-to-noise ratio. When the optical path difference between the two arms of the MZI increases, the noise cancellation obtained by phase modulation decreases.

[0054] In one embodiment, if Figure 2 As shown, the laser assembly includes a tunable laser and a second fiber coupler; the tunable laser is used to generate continuous laser light; and the second fiber coupler is used to couple the laser light generated by the tunable laser to the interference device.

[0055] Specifically, if Figure 2As shown, the continuous laser output by the tunable laser passes through the laser beam expansion system and the objective lens, and is coupled into the interference device by the second optical fiber coupler.

[0056] Furthermore, the modulation frequency of the pulsed laser is 1kHz to 20kHz, the wavelength of the first laser is 500nm to 2000nm, and the pulse width of the pulsed laser is 10ps to 20ns. Ultrasonic excitation is achieved through beam coupling into a 50μm diameter multimode optical fiber with a remote output pulse energy of 6μJ. The output wavelength of the tunable laser is 1520nm to 1570nm, the linewidth is 200kHz, and the tuning rate of the tunable laser is 0.1nm / s to 30nm / s. By controlling the parameters of the pulsed laser and the tunable laser to meet the above relationship, it is beneficial to achieve better ultrasonic detection and imaging within the test area.

[0057] Therefore, the all-optical ultrasound imaging system based on phase modulation proposed in this embodiment has the following advantages:

[0058] 1) Using a continuous wave laser and a balanced MZI to detect phase can significantly reduce the impact of laser phase noise on the detected ultrasonic signal;

[0059] 2) No laser light returns to the laser, which will not cause unstable noise in the laser;

[0060] 3) Existing ultrasonic wave detection schemes use intensity-modulated ultrasonic signals. For a given intensity-modulated system, simply adding a balanced interferometer device can increase the sensitivity of ultrasonic detection, which is simple and compatible.

[0061] 4) By detecting the phase of the optical sensor output rather than the intensity change, the noise of the detected ultrasound signal is significantly reduced, which is conducive to high-resolution visualization of vascular structure and high-precision assessment of tissue function;

[0062] 5) The system has a simple optical path structure, a high degree of integration, and simple multiplexing of sensor units. Compared with traditional ultrasound imaging methods, it has wider bandwidth, higher resolution, higher sensitivity, higher signal-to-noise ratio, greater stability, smaller size, and higher cost-effectiveness. It can achieve simultaneous detection of multiple acoustic / ultrasonic waves, making it suitable for clinical imaging systems.

[0063] 6) The system can be combined with blood flow reserve fraction and other parameters to form a multimodal imaging mode, thereby performing morphological analysis of the blood vessel wall, assessing the risk of myocardial infarction, and guiding clinical coronary intracardiac interventional treatment.

[0064] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An all-optical ultrasound imaging system based on phase modulation, characterized in that: include: Laser components, ultrasonic detectors, interferometers, and imaging components; The laser assembly is used to provide continuous laser light to the interference device; The interferometer comprises a reference fiber arm, a sample fiber arm, and an optical path adjustment device, and is located between the ultrasonic detector and the imaging assembly; wherein the interferometer is used to separate the laser light into a reference light input into the reference fiber arm and a probe light input into the sample fiber arm, and transmit the probe light to the ultrasonic detector for phase modulation; the optical path adjustment device is used to adjust the optical path difference between the reference fiber arm and the sample fiber arm; and the interferometer is further used to form interference light between the reference light and the phase-modulated probe light, and input the interference light into the imaging assembly; The ultrasonic detector is used to generate ultrasonic waves, project the ultrasonic waves to the area to be measured, and phase-modulate the detection light in response to the ultrasonic echo of the area to be measured; and The imaging component is used to generate a corresponding image according to the interference light; The optical path adjustment device includes an optical fiber stretcher and a first PID controller, and the imaging assembly includes a balanced detector; and wherein The optical fiber stretcher is arranged on the reference optical fiber arm; The balanced detector is used to convert the phase information of the interference light into light intensity information, and transmit the light intensity information to the first PID controller; The first PID controller is used to control the tensile strength of the optical fiber of the reference optical fiber arm by the optical fiber stretcher according to the light intensity information; The interferometer device also includes a wavelength adjustment device, wherein a 1×2 fiber coupler is provided on the sample fiber arm; wherein the 1×2 fiber coupler is used to split the phase-modulated probe light into two parts, and transmit one part of the phase-modulated probe light to the wavelength adjustment device; the wavelength adjustment device is used to adjust the wavelength of the laser generated by the laser assembly according to the phase-modulated probe light transmitted by the 1×2 fiber coupler; The wavelength adjustment device includes a photodetector and a second PID controller; wherein the photodetector is used to convert the light intensity information of the phase-modulated detection light transmitted by the 1×2 optical fiber coupler into an analog electrical signal, and transmit the DC data in the analog electrical signal to the second PID controller; the second PID controller is used to adjust the wavelength of the laser generated by the laser assembly according to the DC data.

2. The all-optical ultrasound imaging system according to claim 1, wherein: The interference device also includes a 20:80 fiber coupler and a 50:50 fiber coupler, and the reference fiber arm and the sample fiber arm are arranged between the 20:80 fiber coupler and the 50:50 fiber coupler; wherein the 20:80 fiber coupler is used to split the laser into a reference light input into the reference fiber arm and a detection light input into the sample fiber arm; the 50:50 fiber coupler is used to form interference light between the reference light and the phase-modulated detection light, and input the interference light into the imaging component.

3. The all-optical ultrasound imaging system according to claim 2, wherein: The sample fiber arm includes a fiber circulator, which is arranged between the 20:80 fiber coupler and the 1×2 fiber coupler, and is used to transmit the detection light to the ultrasonic detector, receive the phase-modulated detection light transmitted by the ultrasonic detector, and transmit the phase-modulated detection light to the 1×2 fiber coupler.

4. The all-optical ultrasound imaging system according to claim 1, wherein: The sample fiber arm includes an adjustable optical delay line, which is used to introduce a time delay into the reference light.

5. The all-optical ultrasound imaging system according to claim 1, wherein: The imaging component also includes a bandpass filter, a data acquisition card and an image display; wherein the bandpass filter is used to filter the low-frequency signal of the light intensity information transmitted by the balanced detector; the data acquisition card is used to convert the light intensity information after filtering the low-frequency signal into a digital signal; and the image display is used to display an image according to the digital signal.

6. The all-optical ultrasound imaging system according to claim 1, wherein: The ultrasonic detector includes an ultrasonic wave generating component and an ultrasonic echo detecting component; The ultrasonic wave generating component is used to generate ultrasonic waves and project the ultrasonic waves to the area to be measured; The ultrasonic echo detection component is used to phase-modulate the detection light in response to the ultrasonic echo of the area to be detected.

7. The all-optical ultrasound imaging system according to claim 6, characterized in that: The ultrasonic generating component includes a pulse laser and a laser ultrasonic transducer; wherein the pulse laser is used to generate pulse laser and transmit the pulse laser to the laser ultrasonic transducer; the laser ultrasonic transducer is used to convert the pulse laser into ultrasonic waves and project the ultrasonic waves to the area to be measured.

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