Tissue blood oxygen saturation measuring system and method for multispectral Cherenkov imaging

Abstract

The invention provides a tissue blood oxygen saturation measuring system and method for multispectral Cherenkov imaging, and relates to the technical field of Cherenkov imaging. The system comprises a single-pixel modulation imaging device, and the single-pixel modulation imaging device comprises a digital micromirror device which modulates Cherenkov light according to a plurality of different sampling templates; the circular-to-rectangular optical fiber is used for converting a light spot of the modulated composite light beam of each sampling template into a rectangle; the spectrograph comprises a slit for receiving the composite light beam of the rectangular light spot of each sampling template to form a linear light source of each sampling template; the blazed grating is used for carrying out spectrum separation on the line light source of each sampling template; the linear array photomultiplier is used for carrying out light intensity detection on the light beams subjected to spectrum separation to obtain multi-channel light intensity signals; and the processing unit is used for obtaining the oxyhemoglobin saturation of the to-be-detected tissue based on the light intensity data of each sampling template under the plurality of channels.

Description

Technical Field

[0001] At least one embodiment of the present disclosure relates to the technical field of Cerenkov imaging, and more particularly to a system and method for measuring tissue oxygen saturation using multispectral Cerenkov imaging. Background Art

[0002] In radiotherapy, real-time monitoring of radiation dose is crucial for both efficacy and treatment safety. Cerenkov imaging has attracted attention for its ability to directly measure in vivo dose over a large area, in real time. However, the Cerenkov signal is extremely weak and further attenuated by scattering and absorption during its propagation within tissue. Furthermore, the Cerenkov signal generated by medical linear accelerators lasts only a few microseconds, making detection challenging. Therefore, clinical Cerenkov imaging systems often employ image-intensified cameras to improve imaging sensitivity and temporal resolution. In recent years, multispectral Cerenkov imaging has become a research hotspot. It not only provides information on dose distribution but also reveals tissue functional status and physiological responses to radiation, providing immediate feedback for treatment. However, existing imaging systems typically employ beam splitting with a spectroscope, requiring different wavelengths of light to enter separate channels, each of which is imaged by a separate camera. This approach suffers from limitations such as low light transmission efficiency, low signal-to-noise ratio, and a limited number of separable wavelengths. This makes it difficult to meet the requirements for multi-band detection in extremely low light conditions, limiting its potential for clinical application. Summary of the Invention

[0003] In view of the above problems, the present disclosure provides a tissue oxygen saturation measurement system and method based on multispectral Cerenkov imaging, which integrates single-pixel imaging and high-throughput spectrometer, and can be used for quantitative evaluation of tissue functional parameters in clinical radiotherapy environment.

[0004] According to a first aspect of the present disclosure, a tissue blood oxygen saturation measurement system using multispectral Cherenkov imaging is provided. The system includes: a single-pixel modulation imaging device, the single-pixel modulation imaging device including: a digital micromirror device for modulating Cherenkov light according to a plurality of different sampling templates to output a modulated composite light beam for each sampling template; a circular-to-rectangular optical fiber for converting the spot of the modulated composite light beam for each sampling template into a rectangular spot at the rectangular end of the circular-to-rectangular optical fiber; a spectrometer including: a slit for receiving the composite light beam of the rectangular spot for each sampling template to form a line light source for each sampling template; a blazed grating for spectrally separating the line light source for each sampling template; and a linear array photomultiplier tube for detecting the light intensity of the spectrally separated light beam to obtain multi-channel light intensity data; and a processing unit for obtaining the blood oxygen saturation of the tissue to be measured based on the light intensity data for each sampling template in multiple channels.

[0005] According to an embodiment of the present disclosure, the system further comprises a controller configured to control the DMD to switch between different sampling patterns for a preset time length, and configured to perform denoising on the light intensity data of the plurality of channels for each sampling pattern.

[0006] According to an embodiment of the present disclosure, the processing unit is configured to obtain a plurality of Cherenkov images for the plurality of channels respectively based on each sampling pattern and the light intensity data of the plurality of channels respectively, and obtain the blood oxygen saturation of the tissue under test based on the plurality of Cherenkov images for the plurality of channels respectively.

[0007] According to an embodiment of the present disclosure, the single-pixel modulation imaging device further comprises a lens configured to receive the Cherenkov light, a relay lens group configured to focus the Cherenkov light to the DMD, a reflector configured to reflect the first reflected light beam of each sampling pattern from the DMD to obtain a second reflected light beam of each sampling pattern, and an imaging lens group configured to receive the second reflected light beam of each sampling pattern from the reflector and converge the second reflected light beam of each sampling pattern to obtain a modulated composite light beam of each sampling pattern.

[0008] According to an embodiment of the present disclosure, the spectrometer further comprises a first spherical mirror configured to collimate the line light source from the slit and reflect to the blazed grating, and a second spherical mirror configured to receive the diffracted light from the blazed grating and focus the diffracted light to the linear array photomultiplier tube.

[0009] Another aspect of the present disclosure provides a measurement method of a tissue blood oxygen saturation measurement system based on the multi-spectral Cherenkov imaging, the method comprising: receiving Cherenkov light from a tissue under test; modulating the Cherenkov light according to a plurality of different sampling patterns by a DMD to output a modulated composite light beam of each sampling pattern; converting a light spot of the modulated composite light beam of each sampling pattern into a rectangle at a rectangular end of a circular-to-rectangular fiber; receiving a composite light beam of the rectangular light spot of each sampling pattern by a slit to form a line light source of each sampling pattern; spectrally separating the line light source of each sampling pattern by a blazed grating; detecting light intensity of the spectrally separated light beam by a linear array photomultiplier tube to obtain multi-channel light intensity data; and obtaining a blood oxygen saturation of the tissue under test based on the light intensity data of the plurality of channels for each sampling pattern.

[0010] According to an embodiment of the present disclosure, before receiving the Cerenkov light from the tissue to be measured, the above-mentioned method also includes performing system calibration on the tissue oxygen saturation measurement system of the multispectral Cerenkov imaging; the above-mentioned system calibration of the tissue oxygen saturation measurement system of the multispectral Cerenkov imaging includes: flat-field calibration of the tissue oxygen saturation measurement system of the multispectral Cerenkov imaging; spectral calibration of the tissue oxygen saturation measurement system of the multispectral Cerenkov imaging; and wavelength response consistency calibration of the tissue oxygen saturation measurement system of the multispectral Cerenkov imaging.

[0011] According to an embodiment of the present disclosure, obtaining the blood oxygen saturation of the tissue to be tested based on the light intensity data of each sampling template under multiple channels includes: obtaining Cerenkov images of each of the multiple channels based on each sampling template and the light intensity data of the respective multiple channels; and obtaining the blood oxygen saturation of the tissue to be tested based on the Cerenkov images of the respective multiple channels.

[0012] According to an embodiment of the present disclosure, the above method further includes: performing the operations in the above method multiple times to obtain multiple groups of Cerenkov images for multiple channels; accumulating the multiple groups of Cerenkov images for each channel, and normalizing the accumulated results.

[0013] According to the embodiments of the present disclosure, a digital micromirror device modulates Cherenkov light based on multiple different sampling templates. Using a reflective optical path with a circular-to-rectangular fiber and a millimeter-wide slit design, optical loss can be significantly reduced and the spectrometer's light throughput increased. The high gain characteristics of linear array photomultiplier tubes are utilized to enhance detection sensitivity and expand wavelength channel capacity. Based on the sampling templates and demodulation of multi-channel light intensity data, high-precision single-pixel multispectral measurements can be achieved, providing reliable support for the quantitative assessment of tissue functional parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above contents and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0015] Figure 1 The principle diagram of the tissue oxygen saturation measurement system using multispectral Cerenkov imaging according to an embodiment of the present disclosure is schematically shown;

[0016] Figure 2 The following schematically shows a principle diagram of a tissue oxygen saturation measurement system using multispectral Cerenkov imaging according to another embodiment of the present disclosure;

[0017] Figure 3 The application scenario of the tissue oxygen saturation measurement system using multispectral Cerenkov imaging according to an embodiment of the present disclosure is schematically shown;

[0018] Figure 4 A flowchart schematically illustrates an operation flow of a method for measuring tissue oxygen saturation using multispectral Cerenkov imaging according to an embodiment of the present disclosure; and

[0019] Figure 5 The following schematically illustrates an operational flow chart of a method for measuring tissue oxygen saturation using multispectral Cerenkov imaging according to another embodiment of the present disclosure. DETAILED DESCRIPTION

[0020] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present disclosure. In the detailed description below, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0021] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise," "include," etc. used herein indicate the presence of the features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0022] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0023] When expressions such as "at least one of A, B, and C, etc." are used, they should generally be interpreted in accordance with the meaning commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0024] During radiotherapy, real-time monitoring of radiation dose is crucial for ensuring treatment safety and efficacy. Cherenkov imaging, currently the only technology capable of directly measuring in-vivo doses over a large area in real time during radiotherapy, has garnered widespread attention. However, the Cherenkov radiation signal generated by medical linear accelerators is inherently extremely weak, typically with an intensity of only approximately 0.1 mW / cm². During its propagation within tissue, the signal encounters significant scattering and absorption, further reducing its detectable intensity. Furthermore, medical linear accelerators typically operate in pulsed mode, generating high-energy radiation that results in each Cherenkov signal having an effective duration of only a few microseconds. To address the need to detect these short-duration, low-intensity signals, clinical Cherenkov imaging systems commonly utilize image-intensified cameras to enhance imaging sensitivity and enable acquisition with high temporal resolution.

[0025] In recent years, multispectral Cherenkov imaging has become a research hotspot. It can be used to obtain information about tissue function and reflect the physiological response of tissues to radiation, thereby providing immediate feedback during treatment. Current multispectral imaging systems often use a spectroscope combined with multi-channel detection: incident light is split by multiple spectroscopes, with light of different wavelengths entering multiple independent channels. Each channel is equipped with an image-intensified camera, such as an ICCD (Intensified Charge-Coupled Device) or an ICMOS (Intensified Complementary Metal-Oxide-Semiconductor), for imaging. However, this approach still has certain limitations.

[0026] As the number of wavelength decomposition channels increases, the number of spectroscopes required increases. Multiple reflections and absorptions of the signal reduce the transmittance efficiency and signal-to-noise ratio of the multispectral Cerenkov imaging system. Furthermore, to achieve spatial redirection of the beam, the multispectral Cerenkov imaging system requires the introduction of additional reflective elements, further weakening the effective signal. Furthermore, the transmittance efficiency of this multispectral Cerenkov imaging system limits the number of separable wavelengths, typically supporting a maximum of three imaging channels.

[0027] The multispectral Cerenkov imaging system uses an intensified camera for detection in each imaging channel. The typical gain of the traditional intensified camera ICMOS / ICCD is limited, usually around 10 4 ~10 5 It is difficult to meet the multi-band detection requirements under extremely low light conditions.

[0028] To address these limitations, the present invention proposes a multispectral Cherenkov imaging method based on single-pixel detection. This single-pixel imaging technique combines spatial light modulation with single-channel detection, employing a digital micromirror device to perform multi-mode encoding of the target light field. High-sensitivity detectors collect the overall light intensity signal, and algorithms such as compressed sensing are used to reconstruct the image. Compared to traditional array detection methods, this method exhibits higher sensitivity and lower system cost in infrared, low-light, and special-band imaging.

[0029] Based on single-pixel imaging technology and combined with a high-throughput spectrometer, while significantly improving detection sensitivity, the number of resolvable spectral channels is increased to more than 5 times that of traditional methods, providing an effective solution for multispectral Cherenkov imaging under clinical weak signal conditions.

[0030] Traditional single-pixel systems typically rely on TIR prisms for telecentric optical path design, using two glued triangular prisms to fully reflect the incident light from the digital micromirror array and deflect the outgoing light, respectively, to achieve effective spatial light modulation; or by increasing the image-side or object-side intercept of the digital micromirror array's incident / output sub-components, spatial light modulation can be effectively achieved within the digital micromirror array's deflection angle range. However, these solutions often result in a decrease in system light throughput due to factors such as insufficient prism transmittance and a small F-number of a long-intercept lens group, which increases the single exposure time and reduces the measurement signal-to-noise ratio. In terms of the optical path design of this system, the single-pixel imaging optical path is based on a reflective transmission structure, effectively avoiding the inefficiency problems brought about by refractive solutions using TIR prisms.

[0031] Furthermore, conventional spectrometers are limited by their micron-scale slit design, which also limits their light throughput. This embodiment significantly increases the overall light throughput of the system by increasing the size of the grating and collimator, and combining it with a millimeter-wide slit architecture to fully utilize reflective light transmission.

[0032] On the detection side, this system uses linear array photomultiplier tubes as its core detector device. Compared to traditional image intensifiers, linear array photomultiplier tubes offer approximately four orders of magnitude improvement in measurement gain and one order of magnitude improvement in dynamic range, respectively, and possess picosecond-level time resolution. This provides a key opportunity for the subsequent acquisition of time-resolved Cherenkov signals.

[0033] In summary, this invention integrates single-pixel imaging technology with a high-throughput spectrometer to construct a single-pixel multispectral Cerenkov imaging system with high sensitivity and a large dynamic range. This system is suitable for the efficient acquisition of Cerenkov light signals in clinical radiotherapy settings, ultimately enabling the quantitative assessment of functional parameters such as tissue oxygen saturation, providing reliable support for personalized precision radiotherapy.

[0034] Figure 1A schematic diagram of a multi-spectral Cherenkov imaging tissue oxygen saturation measurement system is shown according to an embodiment of the present disclosure.

[0035] As shown in Figure 1 The multi-spectral Cherenkov imaging tissue oxygen saturation measurement system includes a single-pixel modulated imaging device 1, a circular-to-rectangular fiber 3, a spectrometer 2, and a processing unit 4. The spectrometer 2 includes a slit 23, a blazed grating 21, and a linear array photomultiplier tube 22.

[0036] The single-pixel modulated imaging device 1 is adapted to receive Cherenkov light from a tissue to be measured, and modulate the incident Cherenkov light based on a plurality of different sampling templates using a digital micromirror device 11, outputting a modulated composite light beam for each sampling template. For example, the pixel values of the sampling templates include 0 or 1. When the pixel value is 0, the micromirror of the digital micromirror device 11 is tilted to the 'off' state, causing the Cherenkov light to be reflected to a non-imaging direction; when the pixel value is 1, the micromirror is tilted to the 'on' state, causing the Cherenkov light to be reflected into the detection light path.

[0037] The circular-to-rectangular fiber 3 is adapted to convert the light spot of the modulated composite light beam for each sampling template into a rectangle at the rectangular end of the circular-to-rectangular fiber. The slit 23 is adapted to receive the composite light beam of the rectangular light spot of each sampling template, forming a line light source for each sampling template. The blazed grating 21 is adapted to spectrally separate the line light source for each sampling template. By increasing the size of the blazed grating 21 and the millimeter-level wide slit 23, combined with the reflective light path of the single-pixel modulated imaging device 1, the light flux can be increased.

[0038] The linear array photomultiplier tube 22 is adapted to detect the light beam after spectral separation, convert the optical signal into an electrical signal output, and obtain multi-channel light intensity data. The linear array photomultiplier tube 22 can improve the measurement gain by about 4 orders of magnitude to improve the measurement sensitivity. The dynamic range of the linear array photomultiplier tube 22 can be improved by 1 order of magnitude, which can be used to measure weak optical signals. The linear array photomultiplier tube 22 can achieve a time resolution of picoseconds.

[0039] The processing unit 4 is adapted to obtain the oxygen saturation of the tissue to be measured according to the light intensity data of each sampling template and the respective plurality of channels, and can also obtain other physiological parameters such as the total hemoglobin concentration of the tissue to be measured.

[0040] According to the embodiments of the present disclosure, a digital micromirror device 11 is used to encode and modulate Cherenkov light based on multiple different sampling templates. The combination of a circular-to-rectangular optical fiber 3 and a slit 23 increases the luminous flux of Cherenkov light entering the spectrometer 2, reduces Cherenkov light loss in the optical path, and improves the signal-to-noise ratio. A linear array photomultiplier tube 22 is used to detect the intensity of the spectrally separated light beam. Due to its multi-channel structure, the linear array photomultiplier tube 22 can simultaneously acquire spectral information from more channels; at the same time, its higher measurement gain can enhance detection sensitivity, thereby improving overall measurement accuracy. Therefore, by processing the multi-channel light intensity data for each sampling template, a single-pixel multispectral measurement result with higher sensitivity and accuracy can be obtained, thereby enabling quantitative assessment of the functional parameters of the tissue being measured.

[0041] According to an embodiment of the present disclosure, a tissue oxygen saturation measurement system using multispectral Cerenkov imaging also includes a controller. The controller is configured to control the digital micromirror device to switch between different sampling templates at preset durations. The controller is also configured to perform denoising on the light intensity data of multiple channels in each sampling template.

[0042] The controller may be a field programmable array.

[0043] According to an embodiment of the present disclosure, the processing unit 4 is adapted to obtain Cerenkov images of the respective channels based on each sampling template and the respective light intensity data of the respective channels; and obtain the blood oxygen saturation of the tissue to be measured based on the Cerenkov images of the respective channels.

[0044] Figure 2 The principle diagram of a tissue oxygen saturation measurement system using multispectral Cerenkov imaging according to another embodiment of the present disclosure is schematically shown.

[0045] like Figure 1 and Figure 2 As shown, the single-pixel modulation imaging device 1 may further include a lens 12 , a relay lens group 210 , a reflector 15 and an imaging lens group 220 .

[0046] Lens 12 is suitable for receiving Cherenkov light. Lens 12 can be a C-mount lens. A C-mount lens can be connected to a relay lens assembly via a standard threaded interface and can also adjust the focal length, making it suitable for the optical path of a single-pixel modulation imaging device with a large aperture design.

[0047] The relay lens assembly 210 is adapted to focus the Cerenkov light onto the digital micromirror device.

[0048] The relay lens assembly 210 may include a first lens 13 and a second lens 14. The first lens 13 may be connected to the lens 12, and the second lens 14 may be connected to the digital micromirror device. By adjusting the coaxial distance between the first lens 13 and the second lens 14, the effective back focal length of the single-pixel modulation imaging device 1 can be appropriately extended, allowing the Cherenkov light to be effectively focused onto the reflective surface of the digital micromirror device 11, thereby optimizing the luminous flux of the single-pixel modulation imaging device 1 and improving the energy utilization of the Cherenkov light.

[0049] The reflector 15 is adapted to reflect the first reflected light beam from each sampling template of the digital micromirror device 11 to obtain a second reflected light beam from each sampling template.

[0050] The imaging lens group 220 is adapted to receive the second reflected light beam of each sampling template from the reflector 15 and converge the second reflected light beam of each sampling template to obtain a composite light beam of each sampling template.

[0051] The imaging lens assembly 220 may include a third lens 16 and a fourth lens 18. The third lens 16 may receive the second reflected light beam from each sampling template from the reflector 15. By adjusting the coaxial distance between the third lens 16 and the fourth lens 18, the second reflected light beam from each sampling template may be converged to obtain a modulated composite light beam for each sampling template. The modulated composite light beam from each sampling template is directed to the circular end 31 of the circular-to-rectangular optical fiber 3 and output at the rectangular end 32 of the circular-to-rectangular optical fiber 3.

[0052] The imaging lens group 220 may further include a filter 17 to filter the Cherenkov light to further remove environmental noise.

[0053] In one example, Cherenkov light can enter the single-pixel imaging device 1 through a C-mount lens. The C-mount lens can have a focal length range of 12.5 mm to 75 mm and a nominal size of 1 / 1.8". The first lens 13 can be a biconcave lens, and the focal length of the biconcave lens can be 50 mm. The second lens 14 can be a plano-convex lens, and the focal length of the plano-convex lens can be 60 mm. The focal length of the third lens 16 can be 100 mm. The focal length of the fourth lens 18 can be 30 mm.

[0054] like Figure 1 and Figure 2 As shown, the spectrometer 2 may further include a first spherical mirror 24 and a second spherical mirror 25 .

[0055] The first spherical mirror 24 is adapted to collimate the linear light source from the slit 23 and reflect to the blaze grating 21. The distance between the first spherical mirror 24 and the slit 23 can be a preset first focal length of the first spherical mirror 24; the distance between the first spherical mirror 24 and the blaze grating 21 can be the preset first focal length; the slit 23 and the blaze grating 21 are located at different positions.

[0056] The second spherical mirror 25 is adapted to receive the diffracted light from the blaze grating 21 and focus the diffracted light to the linear array photomultiplier tube 22. The distance between the second spherical mirror 25 and the blaze grating 21 can be a preset second focal length of the second spherical mirror 25; the distance between the second spherical mirror 25 and the linear array photomultiplier tube 22 can be the preset second focal length; the slit 23, the linear array photomultiplier tube 22 and the blaze grating 21 are located at different positions.

[0057] The preset first focal length of the first spherical mirror 24 and the preset second focal length of the second spherical mirror 25 can be equal. For example, the preset first focal length of the first spherical mirror 24 can be 75 mm, and the preset second focal length of the second spherical mirror 25 can be 75 mm. The distance between the first spherical mirror 24 and the slit 23 and the distance between the first spherical mirror 24 and the blaze grating 21 can be similar, the distance between the second spherical mirror 25 and the blaze grating 21 and the distance between the second spherical mirror 25 and the linear array photomultiplier tube 22 can be similar, and the slit 23, the first spherical mirror 24, the blaze grating 21, the second spherical mirror 25 and the linear array photomultiplier tube 22 can form an M-shaped structure of the spectrometer.

[0058] In one example, the slit 23 is in close contact with the rectangular end 32 of the circular-to-rectangular fiber, and two shielding pieces can be used to fix the slit with a width of 0.8 mm and a height of 7.9 mm. The ruling of the blaze grating 21 can be 600 line / mm. The second spherical mirror 25 can focus the diffracted light to the photocathode of the linear array photomultiplier tube 22.

[0059] Figure 3 The application scenario of the multi-spectral Cherenkov imaging tissue oxygen saturation measurement system according to the embodiments of the present disclosure is schematically shown.

[0060] As Figure 3As shown, the to-be-measured tissue 330 can be placed on a treatment machine bed 340, and a linear accelerator 320 can be used as a radiation source of a high-energy ray beam. The linear accelerator 320 generates a ray beam to irradiate the to-be-measured tissue 330, and the to-be-measured tissue 330 generates Cerenkov light under the irradiation of the ray beam. The Cerenkov light generated by the to-be-measured tissue 330 is collected by using the single-pixel multispectral imaging system 310. A lead plate 350 can be arranged between the single-pixel multispectral imaging system 310 and the to-be-measured tissue 330, so as to prevent sensitive detection elements in the single-pixel multispectral imaging system 310 from being directly affected by ionizing radiation. The lead equivalent of the lead plate 350 can be 10 mm Pb, and a central observation window with a diameter of 10 cm is formed in the lead plate 350, and the observation window is embedded in lead glass with a lead equivalent of 5 mm Pb, so as to allow the Cerenkov light to pass through while achieving radiation shielding.

[0061] Another aspect of the present disclosure provides a method for measuring tissue oxygen saturation by multispectral Cerenkov imaging.

[0062] Figure 4 An operation flowchart of the method for measuring tissue oxygen saturation by multispectral Cerenkov imaging according to the embodiments of the present disclosure is schematically shown.

[0063] As Figure 4 shown, the method for measuring tissue oxygen saturation by multispectral Cerenkov imaging includes operations S410-S470.

[0064] In operation S410, Cerenkov light from a to-be-measured tissue is received.

[0065] In operation S420, the Cerenkov light is modulated according to a plurality of different sampling templates by using a digital micromirror device, and a modulated composite light beam of each sampling template is output.

[0066] In operation S430, a light spot of the modulated composite light beam of each sampling template is converted into a rectangle at a rectangular end of a circular-to-rectangular optical fiber.

[0067] In operation S440, a slit is used to receive a composite light beam of the rectangular light spot of each sampling template, and a line light source of each sampling template is formed.

[0068] In operation S450, a blazed grating is used to perform spectral separation on the line light source of each sampling template.

[0069] In operation S460, a linear array photomultiplier tube is used to perform light intensity detection on the light beam after spectral separation, and multi-channel light intensity data is obtained.

[0070] In operation S470, oxygen saturation of the to-be-measured tissue is obtained based on the light intensity data of each sampling template at a plurality of channels.

[0071] According to an embodiment of the present disclosure, the multispectral Cherenkov imaging tissue oxygen saturation measurement system can be systemically calibrated before receiving Cherenkov light from the tissue to be measured.

[0072] The system calibration of the multispectral Cherenkov imaging tissue oxygen saturation measurement system can include flat field calibration of the multispectral Cherenkov imaging tissue oxygen saturation measurement system, spectral calibration of the multispectral Cherenkov imaging tissue oxygen saturation measurement system, and wavelength response consistency calibration of the multispectral Cherenkov imaging tissue oxygen saturation measurement system.

[0073] According to an embodiment of the present disclosure, the flat field calibration of the multispectral Cherenkov imaging tissue oxygen saturation measurement system can weaken the non-uniformity of Cherenkov image intensity caused by the non-uniform response of linear array photomultiplier tubes, the inconsistency of optical path, or the lens dark corner, etc. in the multispectral Cherenkov imaging tissue oxygen saturation measurement system, and improve the accuracy and comparability of the Cherenkov image. The spectral calibration of the multispectral Cherenkov imaging tissue oxygen saturation measurement system can obtain the spectral range of each channel of the linear array photomultiplier tube. The wavelength response consistency calibration of the multispectral Cherenkov imaging tissue oxygen saturation measurement system can effectively correct the response deviation of the multispectral Cherenkov imaging tissue oxygen saturation measurement system at different wavelengths.

[0074] According to an embodiment of the present disclosure, the Cherenkov image of each channel is obtained according to each sampling template and the light intensity data of the respective multiple channels. The oxygen saturation of the tissue to be measured is obtained according to the Cherenkov image of each channel.

[0075] According to an embodiment of the present disclosure, the operation in the multispectral Cherenkov imaging tissue oxygen saturation measurement method is performed multiple times to obtain multiple groups of Cherenkov images of each channel. The multiple groups of Cherenkov images of each channel are accumulated, and the accumulated results are normalized.

[0076] Figure 5 An operation flowchart of a multispectral Cherenkov imaging tissue oxygen saturation measurement method according to another embodiment of the present disclosure is schematically shown.

[0077] As shown in Figure 5 The multispectral Cherenkov imaging tissue oxygen saturation measurement method can include operations S510-S560.

[0078] In operation S510, the multispectral Cherenkov imaging tissue oxygen saturation measurement system is systemically calibrated.

[0079] Flat-field calibration of a tissue oxygen saturation measurement system for multispectral Cerenkov imaging. A uniform light source is used to illuminate the tissue oxygen saturation measurement system for multispectral Cerenkov imaging. Multiple flat-field images are acquired using the tissue oxygen saturation measurement system for multispectral Cerenkov imaging and median filtered to obtain a stable flat-field image. By blocking the lens, the background noise image of the tissue oxygen saturation measurement system using multispectral Cerenkov imaging under the same exposure conditions is obtained. . Stable flat-field image It can be used to characterize the response inhomogeneity of tissue oxygen saturation measurement systems using multispectral Cerenkov imaging. Image after flat-field calibration It can be expressed as:

[0080] (1);

[0081] in, is the initial measurement image.

[0082] Spectral calibration of a tissue oxygen saturation measurement system using multispectral Cerenkov imaging. A mercury lamp can be used as a standard light source. A linear array CCD (for example, placed in the position of a linear array photomultiplier tube, temporarily replacing the linear array photomultiplier tube) is used as a reference detector, and a continuous spectrum is detected by the linear array CCD. The continuous spectrum is compared with the standard light source spectrum of the mercury lamp, and multiple characteristic emission peaks are identified and matched. A mapping relationship between the pixel position of the linear array CCD and the continuous spectrum is established. Based on the spatial relationship between the linear array CCD and the linear array photomultiplier tube on the focal plane, the wavelength range covered by each channel of the linear array photomultiplier tube is mapped to obtain the spectral range of each channel of the linear array photomultiplier tube.

[0083] The wavelength response consistency calibration of the tissue oxygen saturation measurement system based on multispectral Cerenkov imaging. The original sample value of each channel Perform calibration, the calibration value is:

[0084] (2);

[0085] (3);

[0086] in, and They are the first The lower and upper limits of the wavelength range corresponding to each channel; is the quantum efficiency curve of linear array CCD; is the measured result of the spectral distribution of mercury lamp; is the spectrum measurement result based on linear array CCD, For And Wavelength. Based on the ratio between the actual emission spectrum of the reference light source (mercury lamp) and the system measurement value, combined with the quantum efficiency compensation of the CCD, the response deviation of the multi-spectral Cherenkov imaging tissue oxygen saturation measurement system at different wavelengths can be effectively corrected, thereby improving the consistency of spectral sampling and the accuracy of subsequent blood oxygen saturation inversion.

[0087] In operation S520, the application scenario is built, and initial parameters are set in the host computer.

[0088] The phantom is made. Edible yeast, glucose and heparin are added to the pig blood sample, wherein the edible yeast can consume dissolved oxygen in the blood during the process of decomposing glucose under aerobic conditions, thereby reducing the content of oxygenated hemoglobin; heparin can be used to prevent blood clotting. The mixed pig blood sample is placed in a water bath to culture, promote the rapid growth of edible yeast and accelerate oxygen consumption, thereby preparing a low-oxygen blood sample (hypoxic pig blood sample). By adjusting the amount of added edible yeast, water bath time and water volume fraction, the level of blood oxygen saturation (SaO2) in the sample can be flexibly controlled, and a phantom of the measured tissue with different oxygenation states can be constructed. The phantom is placed in the treatment center position of the linear accelerator of the treatment machine bed within the imaging field of view of the multi-spectral Cherenkov imaging tissue oxygen saturation measurement system. Initial parameters are set in the host computer, including setting the number of measurement groups and the number of sampling templates.

[0089] The sampling template of the digital micromirror device can be a Hadamard matrix arranged in ascending order of total variation. The resolution of the sampling template can be set to 128x128, and the number of sampling templates can be set to 1310x2.

[0090] The Hadamard matrix can be represented as:

[0091]

[0092] (4);

[0093] (5);

[0094] (6);

[0095] wherein, is a Kronecker product operator; represents the i-th Hadamard matrix. The sampling templates are arranged in ascending order of total variation, and the total variation of the i-th sampling template can be represented as: ​​​​​

[0096] (7);

[0097] wherein, and are discrete gradient operators, respectively, for characterizing the sign changes of the sampling mask in and directions; represents the i-th row of the Hadamard matrix.

[0098] The elements of the Hadamard matrix are composed of ±1, and the digital micro-mirror device cannot directly modulate the light field representing negative values. The differential measurement technology can be used to indirectly realize the negative value modulation. A Hadamard matrix containing ±1 elements can be split into two sampling masks containing only 0 and 1, which correspond to the modulation regions of positive and negative values, respectively. By performing a differential operation on the two measurement results, not only the modulation effect of the original ±1 mask can be equivalently restored, but also the environmental interference and system noise can be effectively suppressed, thereby improving the robustness and signal-to-noise ratio of the multi-spectral Cherenkov imaging tissue oxygen saturation measurement system.

[0099] At operation S530, the linear accelerator generates rays, and the multi-spectral Cherenkov imaging tissue oxygen saturation measurement system starts measurement in response to the trigger signal.

[0100] Turn off all lighting lights in the treatment room to avoid environmental light interference. Set the linear accelerator output ray energy to 6 MV, and the dose rate to 600 MU / min.

[0101] The controller can control the collection of Cherenkov light and control the digital micro-mirror device to switch different sampling masks for a preset time length.

[0102] The linear accelerator outputs high-energy rays in a pulse mode, and simultaneously sends a synchronization signal with a repetition frequency of and a pulse width of about . After the synchronization signal is shaped and processed by the conditioning module, it can be converted into a logic signal that can be recognized by the controller. The controller can delay for a preset time length after detecting the rising edge of the synchronization signal, and output a trigger signal to the digital micro-mirror device. The digital micro-mirror device responds to the trigger signal to trigger the frame conversion mode of the digital micro-mirror device, and the multi-spectral Cherenkov imaging tissue oxygen saturation measurement system starts measurement. The preset time length can be 2 ms, which can make the digital micro-mirror device complete the switching of the sampling mask before the next pulse arrives, reducing the sampling error.

[0103] The 16 channels of the linear array photomultiplier tube can have an effective detection area of 0.8 mm x 16 mm per channel, covering a spectral range of 400 nm to 700 nm. The exposure time of the linear array photomultiplier tube can be consistent with the pulse width of the high-energy rays.​

[0104] In operation S540 , the controller pre-processes the light intensity data of the multiple channels of each sampling template.

[0105] The absolute median difference method is used to remove outliers in the light intensity data of multiple channels of each sampling template.

[0106] The linear array photomultiplier tube can collect the light beam of each sampling template multiple times during the switching cycle of the sampling template, and obtain multiple sets of 16 channels of light intensity data. Can include multiple sets of 16 channels of light intensity values ​​for each sampling template, data sets include 、 、…、 、…、 , For each sampling template The light intensity data set of the channels is a univariate data sequence. The median of absolute deviations (MAD):

[0107] (8);

[0108] in, Represents the median of a data series.

[0109] Make consistent estimates of the standard deviation of a univariate data series:

[0110] (9);

[0111] in, is a constant, take 1.4826.

[0112] Setting a threshold for a univariate data series :

[0113] (10);

[0114] in, The rejection criterion chosen empirically is 3.

[0115] For each sampling template The light intensity data of the channels is greater than the threshold The light intensity values ​​of each sampling template are eliminated and the average value of the remaining light intensity data is calculated to obtain the The denoised light intensity value of each channel can eliminate the noise interference caused by leakage and scattering.

[0116] In operation S550 , the host computer reconstructs 16 Cerenkov images.

[0117] According to the light intensity data of the 16 channels corresponding to each sampling template after removing outliers and the sampling template, the Cherenkov image of each channel can be reconstructed independently based on the regularized reconstruction model of compressed sensing:

[0118] (11);

[0119] in, is the sampling template, is the target scene to be reconstructed, represents the 1 norm, Indicates the target scene to be reconstructed In position The discrete gradient vector at .

[0120] By performing the above operation multiple times, multiple groups of 16 Cherenkov images can be obtained, the multiple groups of Cherenkov images of each channel are accumulated, and the accumulated results are normalized.

[0121] In operation S560 , a forward model is established based on diffusion theory, and the blood oxygen saturation of the tissue to be measured is inverted according to the forward model and the simplex optimization algorithm.

[0122] Photon yield of Cherenkov light in the forward model. Incident direction , for the wavelength range , per unit length The photon yield of Cherenkov light in It can be expressed as:

[0123] (12);

[0124] (13);

[0125] in, represents the refractive index of the medium, is the incident electron energy at the tissue surface (unit: MeV), is the actual range of the electron (unit: mm).

[0126] Theoretical light intensity in the forward model. The Cherenkov light generated in the tissue is discretized into M point light sources. Combined with the diffusion theory, for a given detection position, the detected light intensity for:

[0127] (14);

[0128] in, It can be obtained from formula (12); constant a dose rate and a conversion constant from the light fluence rate to the detector signal strength; and are the reduced scattering coefficient and the absorption coefficient, respectively; is the distance from the th point source to the given detection point, i.e., the source-detection distance.

[0129] The scattering coefficient and the absorption coefficient in the forward model. In practical applications, it is assumed that the scattering coefficient has the following relationship with the wavelength

[0130] (15);

[0131] wherein and are the scattering amplitude and the scattering energy, respectively, , .

[0132] The absorption coefficient has the following relationship with the wavelength

[0133] (16);

[0134] wherein is the tissue oxygen saturation; is the total hemoglobin concentration; represents the concentration of water; is the extinction coefficient of oxyhemoglobin at the wavelength , is the extinction coefficient of deoxyhemoglobin (Hb) at the wavelength , is the absorption coefficient of pure water at the wavelength .

[0135] According to the forward model, the single-pixel measurement results of the to-be-measured tissue are inversed. According to the 16 Chernikov images, each pixel position corresponds to a light intensity, and according to formula (14), formula (15) and formula (16), the absorption coefficients at different wavelengths can be obtained, a total of 16 wavelengths. Further, by using the absorption coefficients at the 16 wavelengths, combining formula (16) and the polynomial fitting method, the tissue oxygen saturation and the total hemoglobin concentration corresponding to the to-be-measured tissue can be inversed.

[0136] ​​The single-pixel multispectral imaging method of the disclosed embodiment combines spatial light modulation with multi-channel detection, uses a digital micromirror device to perform multi-mode encoding on the target light field of Cherenkov light, collects light intensity through a high-sensitivity linear array photomultiplier tube, and combines compressed sensing imaging for image reconstruction to obtain tissue blood oxygen saturation and total hemoglobin concentration. This method can achieve higher sensitivity and lower cost in infrared, low-light and special band imaging.

[0137] Those skilled in the art will appreciate that the features described in the various embodiments of the present disclosure may be combined and / or coupled in various ways, even if such combinations or couplings are not explicitly described in the present disclosure. In particular, the features described in the various embodiments of the present disclosure may be combined and / or coupled in various ways without departing from the spirit and teachings of the present disclosure. All such combinations and / or couplings fall within the scope of the present disclosure.

[0138] The above describes the embodiments of the present disclosure. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Although each embodiment has been described separately above, this does not mean that the measures in each embodiment cannot be advantageously used in combination. Without departing from the scope of the present disclosure, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. A tissue oxygen saturation measurement system based on multispectral Cerenkov imaging, characterized in that: The system comprises: A single-pixel modulation imaging device, comprising: a digital micromirror device, which modulates Cherenkov light according to a plurality of different sampling templates and outputs a modulated composite light beam for each sampling template; A circular-to-rectangular optical fiber adapted to convert the spot of the modulated composite light beam of each sampling template into a rectangular shape at the rectangular end of the circular-to-rectangular optical fiber; A spectrometer, comprising: The slit is adapted to receive the composite light beam of the rectangular light spot of each sampling template to form a line light source for each sampling template; a blazed grating adapted to perform spectral separation on the line light source of each sampling template; and Linear array photomultiplier tubes, suitable for detecting the light intensity of the spectrally separated light beam and obtaining multi-channel light intensity data; and The processing unit is adapted to obtain the blood oxygen saturation of the tissue to be tested based on the light intensity data of each sampling template under multiple channels.

2. The system according to claim 1, wherein: The system further comprises: The controller is adapted to control the digital micromirror device to switch between different sampling templates at preset time lengths; and is also adapted to perform denoising processing on the light intensity data of multiple channels of each sampling template.

3. The system according to claim 1, wherein: The processing unit is suitable for: Obtaining Cerenkov images of the multiple channels according to each sampling template and the light intensity data of the multiple channels; The blood oxygen saturation of the tissue to be measured is obtained according to the Cerenkov images of each of the multiple channels.

4. The system according to claim 1, wherein: The single-pixel modulation imaging device further includes: a lens adapted to receive the Cherenkov light; a relay lens assembly, adapted to focus the Cherenkov light onto the digital micromirror device; a reflector adapted to reflect a first reflected light beam from each sampling template of the digital micromirror device to obtain a second reflected light beam from each sampling template; and The imaging lens group is adapted to receive the second reflected light beam of each sampling template from the reflector and converge the second reflected light beam of each sampling template to obtain a modulated composite light beam of each sampling template.

5. The system according to claim 1, wherein: The spectrometer further comprises: a first spherical mirror, adapted to collimate the line light source from the slit and reflect it toward the blazed grating; The second spherical mirror is adapted to receive the diffracted light from the blazed grating and focus the diffracted light onto the linear array photomultiplier tube.

6. A measurement method of a tissue oxygen saturation measurement system based on the multispectral Cerenkov imaging according to any one of claims 1 to 5, characterized in that: The method comprises: receiving Cherenkov light from the tissue to be tested; Using a digital micromirror device to modulate the Cherenkov light according to a plurality of different sampling templates, and outputting a modulated composite light beam for each sampling template; The spot of the modulated composite beam of each sampling template is converted into a rectangle at the rectangular end of the circular-to-rectangular optical fiber; Using the slit, the composite light beam of the rectangular light spot of each sampling template is received to form a line light source for each sampling template; Using a blazed grating, spectrally separating the line light source of each sampling template; Use linear array photomultiplier tubes to detect the light intensity of the spectrally separated light beam and obtain multi-channel light intensity data; Based on the light intensity data of each sampling template under multiple channels, the blood oxygen saturation of the tissue to be tested is obtained.

7. The method according to claim 6, characterized in that Before receiving the Cerenkov light from the tissue to be measured, the method further includes calibrating the tissue oxygen saturation measurement system of the multispectral Cerenkov imaging; The system calibration of the tissue oxygen saturation measurement system of the multispectral Cerenkov imaging includes: Flat-field calibration of tissue oximetry systems for multispectral Cerenkov imaging; Spectral calibration of tissue oxygen saturation measurement systems for multispectral Cerenkov imaging; Wavelength response consistency calibration of a tissue oximetry system for multispectral Cerenkov imaging.

8. The method according to claim 6, characterized in that Obtaining the blood oxygen saturation of the tissue to be measured based on the light intensity data of each sampling template in multiple channels includes: Obtaining Cerenkov images of the multiple channels according to each sampling template and the light intensity data of the multiple channels; The blood oxygen saturation of the tissue to be measured is obtained according to the Cerenkov images of each of the multiple channels.

9. The method according to claim 8, characterized in that The method further comprises: Perform the operation of the method according to claim 6 multiple times to obtain multiple groups of Cerenkov images of multiple channels; Multiple groups of Cherenkov images of each channel are accumulated and the accumulated results are normalized.

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