Method for non-invasive temperature control of biomaterial during its processing with laser probe and device for its implementation

Abstract

FIELD: laser therapeutic; surgical technologies.SUBSTANCE: invention relates to technologies for cleaning, sanitizing and processing technical surfaces using thermal cavitation, and allows for a contactless method to obtain information about the temperature of a small volume of biomaterial directly during exposure to a laser probe due to a preliminary experimental determination of the relationship between the number of acoustic pressure pulses, isolated programmatically from the recorded cavitation noise, and the maximum permissible heating temperature of the biomaterial analogue. The method is carried out using a device equipped with a laser with a fibre optic probe, a computing unit, and a small wave volume chamber equipped with a temperature sensor and a microphone.EFFECT: contactless acquisition of information about the temperature of a small volume of biomaterial directly during exposure to a laser probe.4 cl, 1 dwg

Description

[0001] The invention relates to the field of technologies for cleaning, sanitizing and processing technical surfaces, as well as laser therapeutic and surgical technologies using thermal cavitation, and can be used to study both the cavitation processes themselves and their impact on various environments and materials.

[0002] Thermocavitation, as a phenomenon of the emergence, pulsation and collapse of gas microbubbles in a liquid volume under the influence of a laser heating tool (chemically treated end of a fiber optic probe), is actively studied using optical, acoustic, thermal imaging and other methods, as well as high-speed video recording (Skvortsov S.P. Methods for monitoring ultrasonic cavitation parameters https: / / cyberleninka.ru / article / n / metody-kontrolya-parametrov-ultrazvukovoy-kavitatsii; V.I. Yusupov. Features of laser-induced thermal cavitation of water. ACOUSTIC JOURNAL, 2024, Vol. 70, No. 6, pp. 828-837, 2024; Laser engineering of cartilage / Ed. by V.N. Bagratashvili, E.N. Sobolya, A.B. Shekhter. - M. FIZMATLIT. 2006. - 488 p). However, due to the complexity of the mechanical, hydrodynamic and thermodynamic interrelated processes in the cavitation region, its modeling and description remain incomplete.One of the reasons for this situation is the lack of sensors capable of operating under cavitation and high temperature conditions without the risk of mechanical destruction, while maintaining the linearity of amplitude characteristics during direct measurements.

[0003] The use of thermal cavitation in laser surgical technologies, particularly low-trauma ones using fiber-optic probes, is hampered by the lack of means to control the energy impact of the laser heating element (the chemically treated end of the fiber-optic probe) on the treated volume of biomaterial and to ensure that it reaches the maximum heating temperature beyond which hyperthermia or thermal ablation begins. Direct temperature measurement using temperature sensors inserted into the tissue to the desired depth (an invasive method) is rarely used due to the painful and traumatic nature of the procedure, as well as the potential for a body response that distorts the desired temperature distribution. Therefore, the development of non-invasive methods for measuring temperature distribution in biological tissues and within biological objects is a pressing issue.

[0004] Non-invasive methods are known – magnetic resonance (NMR) thermometry, microwave radiothermometry, acousto-thermometry, and the equipment implementing them. However, their use requires special operating conditions and is characterized by the high cost of the devices, which limits their widespread use (L.V. Zhorina. Methods of non-invasive measurement of core body temperature. Tomsk State University Bulletin, Vol. 22, Issue 2, 2017. ISSN 1810-0198). The work also notes that "contactless acquisition of information in real time with computer processing of the results in a form convenient for the physician, without harmful effects on the patient's body, is becoming increasingly important." In practice, for example, for minimally invasive surgeries using laser exposure via fiber-optic probes, it is necessary to measure the temperature in a volume of only a few cubic centimeters using a small number of sensors.

[0005] It is known that during laser heating of biomaterial near the end of an optical fiber, cavitation phenomena occur within the fiber or the surrounding liquid phase, accompanied by the noise of collapsing gas microbubbles. Cavitation and the accompanying acoustic phenomena have been studied by many researchers. However, the problem of monitoring biomaterial heating during intervals up to the first tens of seconds of laser operation, when hyperthermia begins, remains unresolved. In a temporal representation, individual bubbles arising on the laser heating element collapse, creating pressure pulses in the medium. These pulses are clearly visible against the background noise level, allowing their quantification. Each bubble generates a cumulative jet and shock waves, which make the largest energy contribution to the cavitation process (as confirmed by quantitative studies using high-speed cameras).

[0006] As noted in the paper "Study of the Dependence of Acoustic Cavitation Activity on Liquid Temperature" (https: / / cyberleninka.ru / article / n / issledovanie-zavisimosti-aktivnosti-akusticheskoy-kavitatsii-ot-temperatury-zhidkosti), cavitation activity, or in other words, the degree of its impact on a given process, is determined by the concentration of cavitation cavities in the liquid and the efficiency with which they convert ultrasound energy into other forms of energy. Cavitation activity can be assessed using various cavitation effects. The most widely used method is erosion testing, which measures the mass loss of metal test samples placed for a period of time in the cavitation zone. The intensity of the glow generated in the cavitation zone—sonic luminescence—can also serve as an indicator of cavitation activity. To measure cavitation activity in the cited work, a 1CA-3M cavitation meter was used.The device consists of a hydrophone and an electronic unit. The cavitation meter operates on the spectral analysis of the acoustic signal generated by the cavitation region.

[0007] The total energy impact on the working or model environment is also determined by the number of bubbles formed, which can be used as indirect information about the degree of heating of the material being processed.

[0008] In this and many other studies, cavitation processes in liquid media are observed using sound pressure receivers (hydrophones) designed to operate underwater (for example, Yusupov V.I. Features of laser-induced thermal cavitation of water. Acoustic Journal, 2024, Vol. 70, No. 6, pp. 828-837. 2024). In the article "Acoustics of boiling with subcooling on a laser heating element" (Lebedev M.S., Tagiltsev A.A., Kulik A.V., Chudnovsky V.M. Underwater research and robotics. 2024. No. 2 (48). Pp. 16-28) it was shown that as a result of amplitude and spectral processing of acoustic signals excited by thermal cavitation in a water-filled cuvette by a laser heating element at an optical power of 6 W, and recorded using an 8103 B&K hydrophone and an external sound card connected to a PC, resonant vibrations of the cuvette walls are present in the acoustic noise, which are interference in assessing the energy characteristics of cavitation.Rough estimates of the acoustic power emitted by the laser into the environment were also made there.

[0009] At the same time, it is known that cavitation is accompanied by cavitation noise, which is audible in the air and can be recorded by a microphone, for example, to determine its onset by the occurrence of subharmonics of the fundamental ultrasound frequency in the cavitation noise. For example, in the work "Monitoring of Cavitation Parameters in Ultrasonic Surgery" (authors S.P. Skvortsov, N.S. Maslennikov, V.I. Nechaev, A.P. Kravchenko. Medical Equipment. 2019. No. 5. (317) pp. 38-42) the material is presented on the conducted experimental study with the verification of the mathematical model of the occurrence of subharmonics in cavitation noise, which was recorded by a microphone located near the cuvette with liquid, and its output signal was recorded and processed on a computer. A drawback of the experiment is the lack of an assessment of the relationship between noise level and temperature.

[0010] Unlike the effect of an ultrasonic transducer, when a laser probe (laser heating element) is applied to a liquid or biomaterial, the rapid heating and boiling of the liquid volume is accompanied by broadband cavitation noise with numerous short pulses reflecting the collapse of cavitation microbubbles.

[0011] The review article "Acoustic characterization of cavitation intensity: A review" (Pengfei Wu, Xiuming Wang, Weijun Lin, Lixin Bai. Ultrason Sonochem. 2022 Jan:82:105878. doi: 10.1016 / j.ultsonch.2021.105878.) concludes that the acoustic method, especially using cavitation noise to characterize cavitation intensity, has advantages in real-time measurements and is easy to implement. It also recommends estimating the overall cavitation noise intensity by integrating the real cavitation noise spectrum.

[0012] The microphones have sufficient sensitivity and a uniform amplitude-frequency response over a wide frequency range, which predetermines their use in such studies.

[0013] The invention is aimed at solving the problem of contactless monitoring of the temperature of biomaterial in a volume of several cubic centimeters directly during laser-induced exposure.

[0014] A solution to a similar problem is described in the paper "Analysis of Laser-Induced Modification of a Collagen Scaffold Using Nonlinear Optical Microscopy" (authors O.L. Zakharkina, E.A. Sergeeva, M.Yu. Kirillin, N.Yu. Ignatyeva, Quantum Electronics, 50, No. 1 (2020), pp. 76-79), where the task was to determine the irradiation duration to achieve a target temperature of 60 °C at a selected laser power. The problem was solved by determining the dynamics of changes in the surface temperature of biological tissue depending on the exposure time in a separate experiment. For this purpose, the dynamics of temperature fields on the surface of the biomaterial were recorded using a FLIRA655*sc thermal imager (FLIR Systems Inc., USA) with a frame rate of up to 200 Hz and a FOL25 objective. Thermograms were processed using FLIR Research IR Max software.

[0015] The disadvantage of the method of temperature control using a thermal imager is its significant weight and size characteristics (216×73×75 mm, 0.9 kg), which limit the view of the surgical field, as well as the view of the temperature of only the outer surface of the biological tissue.

[0016] Thus, the problem of contactless obtaining of temperature information of a small volume of biomaterial directly during exposure to a laser probe remains.

[0017] The method proposed by this application for non-invasive monitoring of the temperature of biomaterial during its processing with a laser probe consists of conducting an additional experiment before laser processing of a real volume of biotissue, in which, using a measuring device, a correspondence is found between the energy of cavitation noise (by continuously counting the number of pulses in the noise, the amplitude of which exceeds the established threshold), excited by a laser heating element in a biomaterial-like medium filling the CMO, and the maximum permissible heating temperature under the influence of cavitation of the biomaterial in the chamber, wherein, using a microphone outside the chamber, quantitative characteristics of the cavitation noise are obtained, and using a temperature sensor located in the CMO, the heating of the biotissue to the established temperature limit is synchronously monitored, upon reaching which a sound alarm is turned on, the number of pulses is recorded, and laser processing in the chamber is stopped.The subsequent laser-induced treatment of real biomaterial is carried out under identical conditions - on the same volume, and with the same operating modes of the laser heating element, while the pulses in the cavitation noise are also counted up to the value obtained earlier in an additional experiment, and the heating is switched off, and, if necessary, a signal from the sounder is given.

[0018] Identical equipment modes and conditions, similar properties of real and control biomaterial in an additional experiment help to reduce the error of the method.

[0019] The method for non-invasively monitoring the temperature of biomaterial during its processing with a laser probe can be implemented using a device comprising a medical laser with a fiber optic probe and a measuring device shown in Fig., where 1 is a single-board computer, for example, Raspberry Pi ZeroW; 2 is an audio module, for example, Py-Audio-HAT based on the WM8960 codec; 3 is a microphone, for example, PCB 377B02 with a 426E01 pre-amplifier connected to the audio module; 4 is a sound alarm, 5 is a small wave chamber (SWC), filled with liquid or a biomaterial simulator; 6 is a fiber optic probe, the end of which is a laser heating element; 7 is a medical laser (for example, with a wavelength of 1.47 μm and 0.97 μm, with a power in the range of 1-10 W); 8 - digital temperature sensor, for example, DS18B20 in a sealed design, connected to single-board computer 1.Possible electrical connection of the KMO to the audio module in case it is made of piezoactive material is not shown.

[0020] The Raspberry Pi single-board computer and audio module are common and inexpensive devices that have all the necessary ports for connecting sensors and a sounder. This allows for software-based solutions for synchronously recording and counting cavitation noise pulses and the temperature of heated biomaterial in the CMO, as well as reporting the maximum heating temperature with a sounder and turning off the laser's optical radiation.

[0021] The beneficial effects of using a CMO include eliminating reverberation noise inherent in cuvettes and minimizing the number of resonating elements in the oscillatory system, which ultimately facilitates the reliable detection of individual microbubble collapse pulses in the recorded cavitation noise. As chamber sizes become smaller, using hydrophones within them becomes difficult. However, hydrophones can be replaced with a microphone installed outside the chamber. The energy of the cavitation noise generated by the laser heating element in the chamber is sufficient to transfer it into the air and be recorded by the microphone.

[0022] The proposed CMO measuring device is designed as a piezoelectric ring transducer, which will replace hydrophones typically used to record and analyze cavitation noise. Its active surface area is significantly larger than that of hydrophones, significantly increasing its sensitivity to sound pressure, while the lower specific pressure on the piezoelectric material under cavitation loads helps maintain its functionality. Unlike closed CMO designs, the chamber used is open at one end for immersion of biomaterial and a laser probe, and can be sealed with an elastic membrane at the other end. This design ensures the transfer of cavitation noise into the air and represents a monopole sound source, which is recorded by a microphone for counting cavitation pulses.

[0023] It's important to note that when using a CMO simulating a real workspace, the microphone's recording of cavitation noise is not accompanied by reflected sounds, allowing for the counting of individual, sequentially emerging cavitation bubbles. At the same time, the cavitation pulses recorded by the piezoelectric ring and the microphone are similar, demonstrating the comparability of the amplitude-frequency characteristics of the two types of acoustic sensors and the possibility of different CMO designs depending on the laser-induced impact task.

[0024] The use of a microphone for quantitative assessment of the energy impact (dosage) on the volumes and surfaces being treated is applicable to various equipment, such as a laser scalpel used in surgical technology, as well as in devices for cavitation cleaning, hardening, quenching or sanitization of technical surfaces.

[0025] The device operates as follows. Before laser treatment of a volume of real biomaterial, the operating modes of laser 7 are set. The volume of the CMO is selected based on the volume of the real biomaterial and filled with a biomaterial simulator with similar properties. Single-board computer 1 is turned on and the mode for synchronous signal recording from microphone 3 and temperature sensor 8 is activated. Threshold values ​​for recording cavitation pulses and the maximum permissible temperature of the biomaterial are programmatically set. Fiber-optic probe 6 (laser heating element) is immersed in the biomaterial volume and its position is fixed. By turning on laser 7, cavitation is excited at the end of the optical fiber in the material filling the CMO. The heating of the material in the chamber accompanying cavitation is recorded by temperature sensor 8 installed in the chamber, and the cavitation noise generated in the chamber is recorded by microphone 3 located near the chamber. Sensor signals are processed in real time.Microphone data processing consists of isolating cavitation noise and counting the number of cavitation pulses whose amplitude exceeds a preset threshold using the envelope. Temperature sensor data is processed up to a preset threshold. When the temperature exceeds the threshold, a signal is generated to activate the sounder and stop counting the pulses. The temperature value and the total number of cavitation pulses recorded to that point are recorded.

[0026] The obtained temperature values ​​and the corresponding number of acoustic pressure pulses are then used during laser heating of the actual biomaterial. During surgical interventions using laser-induced stimulation of the biomaterial, the activation of the sound alarm signals the end of laser operation due to the biomaterial temperature exceeding the set limit.

[0027] To detect and count acoustic pressure pulses in cavitation noise, the CMO proposes using the envelope of sound pulses. Digital processing methods in standard software packages (Matlab, the Python scipy library, etc.) allow for the calculation of the modulus of the analytical signal (a complex signal consisting of the actual, recorded signal and its Hilbert conjugate, quadrature signal). This makes it possible to extract the envelope of the acoustic signal of an individual bubble collapse based on the sequentially alternating phases (positive, negative, and then positive again) of the oscillatory process, and to perform peak tracking of the noise detected by the microphone, identifying the maximum values ​​relative to the set threshold.

[0028] Furthermore, the process structure can be traced using time-frequency analysis of non-stationary signals based on a continuous wavelet transform with multi-scale frequency and time decomposition. This allows for obtaining different time and frequency resolutions over a wide frequency range, which is particularly useful for processing complex signals.

Claims

1. A method for non-invasively monitoring the temperature of biomaterial during its processing with a laser probe, including determining the relationship between the established maximum permissible heating temperature of an analogue of a real biomaterial and the number of acoustic pressure pulses isolated from the cavitation noise formed during heating, recorded by a microphone, wherein the analogue of a real biomaterial is placed in a small wave volume chamber, inside which a temperature sensor is installed, and outside of it - a microphone, connected to an electronic computer unit equipped with a program for calculating the number of acoustic pressure pulses by continuously synchronously counting the number of pulses in the cavitation noise, the amplitude of which exceeds the established threshold, and the permissible heating temperature of the biomaterial;then, without changing the operating modes of the laser probe, the volume of real biomaterial is processed with the computer simultaneously calculating the number of acoustic pressure pulses, and at the moment the programmatically calculated number of acoustic pressure pulses coincides with the value of the maximum permissible temperature, the heating is automatically stopped.

2. A device for monitoring the temperature of biomaterial during laser heating, including equipment for laser exposure, a laser probe connected to it, characterized in that the device is equipped with equipment for recording and processing in the form of a computer and is equipped with a small wave volume chamber with a temperature sensor located inside the chamber, and a microphone installed outside the chamber volume, which are connected to a computer equipped with a program for calculating the number of acoustic pressure pulses in cavitation noise corresponding to the heating temperature, while the microphone is connected to the computer through an audio module.

3. The device according to paragraph 2, characterized in that the small wave volume chamber is made in the form of a cylinder, open at the top, and sealed with an elastic membrane at the bottom.

4. The device according to paragraph 2, characterized in that a single-board computer is used as a computer.

Images