All-optical ultrasonic imaging system based on phase modulation

Abstract

The invention discloses an all-optical ultrasonic imaging system based on phase modulation, and belongs to the technical field of imaging. The system comprises a laser assembly, an ultrasonic detector, an interference device and an imaging assembly, the laser assembly is used for providing continuous laser for the interference device; the interference device comprises a reference optical fiber arm, a sample optical fiber arm and an optical path adjusting device and is located between the ultrasonic detector and the imaging assembly. Wherein the interference device is used for dividing laser into reference light and detection light, and transmitting the detection light to the ultrasonic detector for phase modulation; the optical path adjusting device is used for adjusting the optical path difference of the two arms, forming interference light of the reference light and the phase-modulated detection light and inputting the interference light into the imaging assembly; the ultrasonic detector is used for generating ultrasonic waves, projecting the ultrasonic waves to a to-be-detected area, and performing phase modulation on the detection light in response to ultrasonic echoes of the to-be-detected area; and the imaging assembly is used for generating a corresponding image according to the interference light.

Description

Technical Field

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

[0002] Cardiovascular disease is one of the diseases with the highest mortality rate in the world, with approximately 20 million people dying from the disease each year. The most common cause of cardiovascular disease is the rupture of vulnerable atherosclerotic plaques and the subsequent formation of thrombi, and vulnerable plaques are typically characterized by a thin fibrous cap and a large necrotic core. Therefore, accurate assessment of vulnerable plaques requires intravascular imaging technology with high resolution and large detection depth to provide information such as the thickness of the fibrous cap and the proportion of the necrotic core. However, current intravascular imaging technology cannot provide high-resolution, holistic morphological information of the vascular wall. Intravascular ultrasound imaging equipment plays an active role in the assessment of cardiovascular disease and has been an important tool in the interventional catheterization laboratory for more than 30 years. However, intravascular ultrasound imaging equipment is limited by the bandwidth of traditional piezoelectric transducers, and considering the high attenuation of high-frequency ultrasound in tissues, intravascular ultrasound imaging must strike a balance between resolution and detection depth.

[0003] At present, there is an all-optical intravascular ultrasound imaging method, which uses picosecond laser pulses to excite carbon nanocomposites to generate wide-bandwidth ultrasound, and uses fiber Bragg gratings for ultrasound detection, achieving ultra-wideband (147%) and high-resolution intravascular ultrasound imaging that is difficult to achieve with traditional technologies, and solving the problem of incompatibility between high resolution and large detection depth. This method uses intensity modulation technology to modulate ultrasound signals. Intensity modulation is to adjust the wavelength of a continuous laser to the linear range of the Bragg grating reflection spectrum, so that wavelength information is converted into intensity information. The main advantages of this intensity modulation technology are simplicity and relatively low cost, because its implementation only requires a tunable laser and a photodetector.

[0004] However, the main noise source in intensity modulation technology is the photodetector noise. Although the sensitivity can be easily improved by using higher laser power or higher Q-factor resonators, when the power and Q-factor are high enough, the laser frequency noise becomes the dominant noise factor, and higher Q-factor and laser power cannot further improve the 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 a higher cost for the entire imaging system. Therefore, although the all-optical ultrasound imaging system based on intensity modulation has the advantage of a simple structure, its sensitivity is often limited by the continuous laser frequency noise, and it is impossible to achieve high-precision detection of ultrasound signals.

[0005] An effective solution is urgently needed to address the problem that 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. Summary of the invention

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

[0007] According to an embodiment of the present disclosure, there is provided an all-optical ultrasonic imaging system based on phase modulation, 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 divide the laser light into a reference light input to the reference optical fiber arm and a detection light input to 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 a region to be measured, and phase modulate the detection light in response to the ultrasonic echo of the region 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 a 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 coupler is arranged on the sample fiber arm; wherein the 1×2 fiber coupler is used to divide 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 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 between 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 circulator, which is disposed 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 optic arm comprises an adjustable optical delay line for introducing 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 detecting 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 detecting 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 the present 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 a reference light and a detection light. The reference light is input into the reference optical fiber arm. The detection light is input into 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, and then the interference device forms interference light of the reference light and the phase-modulated detection light, and inputs the interference light into the imaging component, and the imaging component generates a corresponding image according to the interference light. In the present application, the optical path difference of the two arms of the interference device can be adjusted by the optical path adjustment device to be locked to orthogonality. 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. Any tiny phase change of the sample fiber arm caused by ultrasound can be efficiently converted into light intensity change, 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 the existing all-optical ultrasonic imaging system based on intensity modulation is 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 the present 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 on the present disclosure. In the drawings:

[0019] Figure 1 is an overall structural block diagram 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 It 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 embodiments of a part of the present disclosure, not all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of the present disclosure.

[0023] It should be noted that when an element is referred to as "fixed to" another element, it can be directly on another element or there can also be a centered element. When an element is considered to be "connected" to another element, it can be directly connected to another element or there may be a centered 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 position relationship shown in the accompanying drawings, 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 a limitation of the present invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by technicians in the technical field of the present invention. The terms used in the specification of the present invention herein 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 of great significance for judging the progression of vulnerable plaques, which requires intravascular ultrasound imaging to visualize vascular structure with high resolution. Intensity demodulated acoustic wave sensors have shown high sensitivity and wide-band response in detecting acoustic waves, but the shortcomings of the solution itself also limit its application in the later stage:

[0025] 1) System sensitivity is often limited by the 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 light intensity loss of the sensing system itself is large, and it depends on the optical coupling between optical fibers, the optical transmission and reflection of the object to be measured, the stability of the sensing structure, etc., which ultimately leads to a small signal-to-noise ratio of the system sensing acoustic waves;

[0028] 4) This type of solution is only suitable for single-point acoustic wave sensing, and it is difficult to reuse the sensing unit, and it is impossible to achieve simultaneous detection of acoustic waves / ultrasonic waves at multiple points. In order to meet the requirements of high-sensitivity and ultra-wide frequency band acoustic wave sensing, we have developed an all-optical ultrasonic imaging method and system based on phase modulation.

[0029] It has been found through research that phase modulation fiber optic sensors use the change in the phase of light waves in optical fibers caused by external interference to detect various physical quantities and their changes. This sensor has high sensitivity, is flexible and diverse, and has a wide range of objects. In order to increase the sensitivity of the fiber optic interferometer to the measured physical quantity and make it insensitive to non-measured physical quantities, special optical fibers need to be used to meet the requirements of measuring different physical quantities. Interference fiber optic sensors use optical fibers as phase modulation elements, and through the interaction between the measured (parameter) and the optical fiber, the phase of the transmitted light in the optical fiber changes, thereby forming a fiber optic interferometer. Compared with other modulation methods, due to the use of interference demodulation technology, phase-enforced fiber optic sensors have higher sensitivity than ordinary demodulation methods. Although phase modulation sensors have been applied to the measurement of various parameters such as temperature, stress, magnetic field, current, displacement, acceleration, vibration, etc., they have not been applied to the field of ultrasonic imaging. Therefore, this application proposes an all-optical ultrasonic imaging system based on phase modulation. The imaging system obtains ultrasonic signals of the area to be measured (such as in a blood vessel or other locations in a living body) through phase modulation and mediation, and can visualize vascular structures with high resolution and evaluate tissue functions with high precision, which is of great significance for judging 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 to the reference optical fiber arm and a detection light input to 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, 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 a laser assembly. The interference device divides the laser into reference light and detection light. The reference light is input into the reference optical fiber arm, and the detection light is input into 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. Among them, 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, and 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, and the imaging component generates a corresponding image based on the interference light. In the present application, the optical path difference of the two arms of the interference device can be adjusted by the optical path adjustment device to be locked to orthogonality. 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. Any tiny phase change of the sample fiber arm caused by ultrasound can be efficiently converted into light intensity change, 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 the existing all-optical ultrasonic imaging system based on intensity modulation is affected by laser frequency noise and cannot achieve high-precision detection of ultrasonic signals.

[0032] It is particularly noted that when the optical path difference between the two arms of the interference device is in an orthogonal state, 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 a 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, Figure 2 As shown, the optical path adjustment device includes an optical fiber stretcher and a first PID controller. Since the optical fiber arm is easily affected by low-frequency interference from the environment, the optical fiber stretcher can be made by winding the optical fiber on the piezoelectric ceramic and the optical fiber stretcher is set on the reference optical 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 optical fiber stretching, so as 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 changes to light intensity changes. In addition, the interference device is in an orthogonal state, and any slight phase change of the sample arm caused by ultrasound can be efficiently converted into light intensity changes by the balanced detector, thereby achieving high-precision detection of ultrasonic signals.

[0035] Furthermore, the interference fiber arm is easily affected by environmental low-frequency interference. 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 ultrasonic signal demodulation, and improving the detection sensitivity.

[0036] Optionally, the interference device also includes a wavelength adjustment device, and a 1×2 fiber coupler is arranged on the sample fiber arm; wherein the 1×2 fiber coupler is used to divide 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 coupler.

[0037] Specifically, Figure 1 and Figure 2As shown, the interference device also includes a wavelength adjustment device, and a 1×2 fiber coupling is provided on the sample fiber arm. The 1×2 fiber coupler is used to divide 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 coupler. The changed wavelength is output by the laser component, and a part of the detection light after phase modulation by the ultrasonic detector enters the wavelength adjustment device again. The wavelength adjustment device adjusts the laser component again according to the detection light, causing the laser wavelength output by the laser component to change again, and the cycle repeats, and finally the laser wavelength output by the laser component is the same as the wavelength corresponding to half the light intensity. At this time, the wavelength is the central wavelength of the linear region of the reflection spectrum of the echo detection component in the ultrasonic detector. Phase demodulation at this wavelength can maximize the dynamic range of the echo detection component. Maximizing the dynamic range means that the system can more accurately distinguish small signal changes, and the system responds more sensitively 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, Figure 2 As shown, the wavelength adjustment device includes a photodetector and a second PID controller. A portion of the detection light output by the 1×2 optical fiber coupler is transmitted to the photodetector, and the photodetector converts information such as the power of the detection light into an analog electrical signal; since the linear region in the reflection spectrum of the echo detection component refers to the region in which the wavelength and the light intensity are linearly related in the reflection spectrum, the light intensity information of the detection light is converted into an analog electrical signal through the photodetector, and the DC (frequency is less than 25KHz) data of the analog electrical signal is transmitted to the second PID controller, and the second PID controller regulates the piezoelectric device in the laser component according to the DC data, causing the laser wavelength output by the laser component to change. The changed wavelength is output by the laser component, and the photodetector records the light intensity information again. The second PID controller regulates the piezoelectric device in the laser component according to the light intensity information again, causing the laser wavelength output by the laser component to change again, and the cycle repeats, and finally the output wavelength of the laser component is the same as the wavelength corresponding to half the light intensity. At this time, the wavelength is the central wavelength of the linear region of the reflection spectrum. Phase demodulation at this wavelength can maximize the dynamic range of the echo detection component. Among them, half the wavelength is equal to half of the maximum reflectivity of the reflection spectrum of the echo detection component.

[0040] Furthermore, the echo detection component is, for example, a Bragg grating, and the Bragg grating may be a π-phase-shifted Bragg grating (π-FBG). The π-phase-shifted Bragg grating is a π-phase-shifted point artificially introduced at the center of the grating region of the uniform Bragg grating. The discontinuity of the phase shift causes a narrow-bandwidth notch to be formed in the Bragg grating reflection spectrum, or a spectral gap is formed, resulting in a steeper spectral efficiency than an ordinary grating, and can better respond to ultrasonic echoes in a larger 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 between the reference light and the phase-modulated detection light, and input the interference light into the imaging component.

[0042] Specifically, Figure 2 As shown, 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 two fiber couplers. The 20:80 fiber coupler is used to split the laser into a reference light input to the reference fiber arm and a detection light input to the sample fiber arm. The 50:50 fiber coupler is used to form interference light of the reference light and the detection light after phase modulation, and input the interference light to the imaging component. Thus, the interference device is mainly composed of a balanced Mach-Zehnder interference structure, a photodetector and two PID controllers.

[0043] In one embodiment, if Figure 2 As shown, the sample fiber optic arm includes a fiber 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 sample 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 probe of the ultrasound detector through a driving device (devices such as a spiral-withdrawal device and a torsion coil); when the ultrasonic echo causes changes in information such as the wavelength, phase, and polarization state of the π-FBG, the single-mode optical fiber connected to the π-FBG transmits the parameter changes again through the driving device (devices such as a spiral-withdrawal device and a torsion coil) and the fiber circulator and other built-in optical paths 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, and the laser 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, and 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 the minimum. Then, the stretching strength of the fiber stretcher is adjusted to change the length of the fiber stretching to adjust the optical path difference between the reference fiber arm and the sample fiber arm, eliminate the influence of the environment (such as temperature, vibration, etc.) on the optical path difference of the fiber arm, improve the stability and reliability of the system, and lock the optical path difference between the reference fiber arm and the sample fiber arm of the interference device to be orthogonal.

[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; 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.

[0048] Specifically, Figure 3 As shown, the imaging component includes: a balanced detector, a bandpass filter, a data acquisition card and an image display. The excitation and detection of ultrasound are not completed by the same component. However, there is still mutual crosstalk between the ultrasound excitation component and the ultrasound detection component. The interference ultrasound detected by the ultrasound detection component is propagated along the axial direction of the ultrasound detection component, which reduces the response frequency of the ultrasound detection component to it, showing a low-frequency response. The bandpass filter used in the present invention has a range of 5-120MHz, which can filter low-frequency ultrasound, thereby effectively reducing the interference between the ultrasound excitation component and the ultrasound detection component. The upper limit of the ultrasound frequency generated by the photo-induced ultrasonic transducer used in the present invention exceeds 90MHz. According to the sampling law, the sampling frequency of the data acquisition card used in the present invention needs to be no less than 180MHz. In order to more accurately collect ultrasound signals, the sampling frequency of the data acquisition card used in this system is 500MHz, which fully meets the detection requirements. The image display is connected to the data acquisition card and is configured to display images according to digital signals. The image data of the intravascular environment can be accurately restored through photoelectric signal conversion, which is conducive to achieving high-precision and high-definition intravascular environment imaging.

[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 tested; the ultrasonic echo detecting component is used to phase modulate the detection light in response to the ultrasonic echo of the area to be tested.

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

[0051] Specifically, the ultrashort pulse width laser output by the pulse laser is coupled to the multimode optical fiber through the first optical fiber coupler after the spot is corrected by the laser beam expansion system. The multimode optical fiber transmits the pulse laser to the endoscope probe through the driving device (devices such as the spiral-retreat device and the torsion coil). The endoscope probe contains carbon nanocomposites. The pulse laser hits the carbon nanocomposites to generate ultrasonic waves, thereby exciting and generating ultrasonic waves in the area to be tested. In the area to be tested, the ultrasonic waves generated by the endoscope probe are reflected by the tissue in the area to be tested, causing the spectral shift of π-FBG.

[0052] In this embodiment, the driving device includes a spiral-withdrawal device and a torsion coil. The spiral-withdrawal device is mainly composed of three devices: a rotating motor, a withdrawing motor and a smooth ring. Two stepping motors control the rotation and withdrawal of the interventional catheter respectively. The double-path smooth ring allows the rotor end (connected to the interventional catheter) to rotate freely without damage. This is conducive to real-time two-dimensional and three-dimensional imaging of the intravascular environment.

[0053] Furthermore, the laser wavelength of the tunable laser is tuned to the resonance center of the π phase-shifted Bragg grating, and two beams of interference light enter the imaging component. The imaging component obtains the interference light power respectively. The power of the interference light includes the power of the phase noise. The phase noise 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 component can eliminate the phase noise, and an ultrasonic signal with a higher signal-to-noise ratio can be obtained. 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, 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 pulse laser is 1KHz to 20KHz, the wavelength of the first laser is 500nm to 2000nm, the pulse width of the pulse laser is 10ps to 20ns, and the beam is coupled to the multimode optical fiber with a remote output pulse energy of 6μJ and a diameter of 50μm for ultrasonic excitation; the output wavelength of the tunable laser is 1520nm to 1570nm, the line width is 200kHz, and the tuning rate of the tunable laser is 0.1nm / s to 30nm / s. By controlling the pulse laser and the tunable laser parameters to meet the above relationship, it is conducive to better ultrasonic detection imaging in the area to be tested.

[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 the 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 of the laser;

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

[0061] 4) The noise of the detected ultrasound signal can be significantly reduced by detecting the phase of the optical sensor output instead of the intensity change, 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 a larger bandwidth, higher resolution, higher sensitivity, higher signal-to-noise ratio, more stability, smaller size, and higher cost-effectiveness. It can realize simultaneous detection of multiple points of sound waves / ultrasound waves, which is conducive to adapting to the imaging system for clinical detection;

[0063] 6) The system can be combined with blood flow reserve fraction to form a multimodal imaging mode, thereby performing morphological analysis of the vascular wall, assessing the risk of myocardial infarction, and guiding clinical coronary 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 principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An all-optical ultrasonic imaging system based on phase modulation, characterized in that: include: Laser assemblies, ultrasound detectors, interferometers, and imaging assemblies; 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 component; wherein the interference device is used to separate the laser into a reference light input to the reference fiber arm and a detection light input to the sample 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 fiber arm and the sample fiber arm; and the interference device is also used to form interference light between the reference light and the detection light after phase modulation, and input the interference light to the imaging component; 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.

2. The all-optical ultrasound imaging system according to claim 1, characterized in that: 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.

3. The all-optical ultrasound imaging system according to claim 1, characterized in that: The interference device also includes a wavelength adjustment device, and a 1×2 fiber coupler is arranged on the sample fiber arm; wherein the 1×2 fiber coupler is used to divide 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 coupler.

4. The all-optical ultrasound imaging system according to claim 3, characterized in that: 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.

5. The all-optical ultrasound imaging system according to claim 3, characterized in that: 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 to the reference fiber arm and a detection light input to 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.

6. The all-optical ultrasound imaging system according to claim 5, characterized in that: 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.

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

8. The all-optical ultrasound imaging system according to claim 2, characterized in that: 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.

9. The all-optical ultrasound imaging system according to claim 1, characterized in that: 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 tested; 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.

10. The all-optical ultrasound imaging system according to claim 9, characterized in that: The ultrasonic wave generating component comprises a pulse laser and a laser ultrasonic transducer; wherein the pulse laser is used to generate a 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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