CN114451988A - Microwave ablation real-time carbonization regulation and control method based on bioimpedance - Google Patents
Microwave ablation real-time carbonization regulation and control method based on bioimpedance Download PDFInfo
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Abstract
The invention discloses a microwave ablation real-time carbonization regulation and control method based on bioimpedance, which comprises the following steps: s1, constructing a biological impedance acquisition device applied to microwave ablation real-time carbonization regulation and control; s2, acquiring real-time change data of the biological impedance in the ablation process; and S3, adjusting the output power of the microwave source according to the change of the biological impedance. The invention has the beneficial effects that: (1) the invention indirectly reflects the coagulation and carbonization conditions of tissues at the ablation part by measuring the biological impedance, and compared with single-point temperature measurement, the biological impedance can reflect the ablation effect of one region between two copper foil electrodes; (2) the invention adopts the high-precision impedance measurement analog front-end chip AD5940 to realize impedance measurement, and the impedance measurement function is easy to be integrated into the existing microwave ablation instrument, so the cost is low; (3) the method has great significance for judging the real-time curative effect of the tumor microwave ablation, and has important value for carrying out carbonization regulation and control on the tumor microwave ablation.
Description
Technical Field
The invention relates to the technical field of precise microwave ablation treatment, in particular to a real-time microwave ablation carbonization regulation and control method based on bioimpedance.
Background
The microwave thermal ablation therapy is considered to be a novel and effective method for treating malignant tumors after operations, chemotherapy, radiotherapy, immunotherapy and the like due to the advantages of obvious curative effect, minimal invasion, small toxic and side effects, few complications and the like, plays a great role in clinical tumor treatment, and is widely applied to common tumors such as liver cancer, lung cancer, kidney cancer, thyroid cancer, intestinal cancer, uterine fibroids and the like. However, there are still many scientific and technical problems to be solved in the microwave tumor thermal ablation, and the most important problem is the real-time efficacy evaluation in the microwave ablation treatment. At present, the temperature is mainly used as a determination factor for tumor cell inactivation clinically, a thermistor or a thermocouple or other thermosensitive elements are inserted into a patient body to measure the temperature of an ablation part, and when the temperature reaches 60 ℃, tissue cells are determined to be necrotic. However, the method can only measure the local temperature of the probe, and cannot reflect the overall temperature of the ablation region, so that the overall inactivation condition of the tissue in the ablation region cannot be reflected, and the carbonization condition of the whole tissue at high temperature cannot be reflected. Searching for more accurate evaluation factors to realize real-time evaluation of the curative effect becomes the key of accurate ablation.
The bioelectrical impedance technology is a detection technology for extracting physiological information related to human physiology and pathological conditions by utilizing the electrical characteristics and change rules of biological tissues and organs. Because the electrical impedance of different biological tissues is different, and the impedance characteristic depends on the composition and the structure of the biological tissues and the magnitude of the applied signal frequency, the physiological information of the biological tissues can be better understood according to the characteristic. Microscopically, a cell consists of a cell membrane and intracellular fluid, while the cell is filled with extracellular fluid and extracellular matrix. The intracellular fluid and the extracellular fluid are composed of electrolytes with good conductivity, and can be equivalent to resistance components; the cell membrane is composed of a phospholipid bilayer and proteins, and can be equivalently a capacitance component. Thus, intracellular fluid, cell membranes and extracellular fluid constitute a three-element bioimpedance model. Macroscopically, the biological tissue is composed of a large number of cells, and the measurement of the biological impedance of the human tissue can reflect the physiological condition of a large number of biological tissues between the electrodes.
It has been shown that lesions in human tissue and inactivation of cells can result in changes in bioimpedance on a macroscopic scale. During thermal ablation, as the cell membrane ruptures with increasing temperature, intracellular fluid escapes from the cell, resulting in a decrease in impedance; as the temperature continues to rise, the tissue dehydrates and evaporates, and then carbonizes, resulting in a significant rise in impedance. There is a significant correlation between changes in the bioimpedance of the thermal ablation process and the coagulation and carbonization of biological tissue.
The impedance measuring instrument on the market at present has high measuring accuracy and wide measuring range, but is expensive, large in size, lack of an upper computer interface, cannot be integrated into the existing microwave ablation instrument, and cannot perform subsequent processing on impedance data.
Disclosure of Invention
The invention aims to solve the technical problem of providing a real-time carbonization regulation and control method for microwave ablation based on bioimpedance, which can reflect the ablation effect of an area between two copper foil electrodes, has great significance in judging the real-time curative effect of tumor microwave ablation, and has important value in carbonization regulation and control of tumor microwave ablation.
In order to solve the technical problem, the invention provides a microwave ablation real-time carbonization regulation and control method based on bioimpedance, which comprises the following steps:
s1, constructing a biological impedance acquisition device applied to microwave ablation real-time carbonization regulation and control;
s2, acquiring real-time change data of the biological impedance in the ablation process;
and S3, adjusting the output power of the microwave source according to the change of the biological impedance.
Preferably, in the step (1), the biological impedance acquisition device comprises a copper foil electrode, a high-precision impedance measurement analog front-end chip and an ARM microcontroller; the copper foil electrode is connected with the high-precision impedance measurement simulation front-end chip through a wire, the ARM microcontroller controls the high-precision impedance measurement simulation front-end chip to carry out impedance measurement, returned data are received and an impedance value is obtained through calculation, and the ARM microcontroller sends the impedance to an upper computer through the communication module to display.
Preferably, the copper foil electrode is attached to the surface of the microwave ablation needle; one copper foil electrode is attached to the position 5mm away from the rear end of the microwave ablation needle medium sleeve, the other copper foil electrode is attached to the position 15mm away from the rear end of the medium sleeve, and the distance between the two copper foil electrodes is 10 mm; the two copper foil electrodes are respectively connected to the biological impedance measuring circuit board through leads.
Preferably, the high-precision impedance measurement analog front-end chip is AD 5940; an AD5940 built-in digital waveform generator and a 12-bit digital-to-analog converter DAC generate a sinusoidal excitation signal; the on-chip 16-bit 800kSPS analog-to-digital converter ADC measures sinusoidal input voltage up to 200kHz, and digital filtering can be carried out on the measurement result; the on-chip high-speed trans-impedance amplifier HSTIA processes a high-bandwidth sine input signal of 200kHz, and converts a weak current signal into a voltage signal which can be measured by the ADC; and the on-chip Discrete Fourier Transform (DFT) engine performs DFT calculation on the measurement result and stores the real part measurement result and the imaginary part measurement result in corresponding registers.
Preferably, the ARM microcontroller selects STM32F411RET6, and the main frequency is 100 MHz; the ARM microcontroller is communicated with the AD5940 by adopting a serial peripheral interface SPI; the ARM microcontroller sends a control instruction to the AD5940, configures a digital waveform generator, an HSTIA and ADC peripherals of the AD5940, and reads real part and imaginary part measurement results of response voltage and response current from the data FIFO; and after reading the measurement result, the measurement result is converted into impedance by the ARM microcontroller.
Preferably, the communication module adopts a CH340C USB to serial port chip, and the baud rate is set to be 115200 bps.
Preferably, in the step (2), the copper foil electrode is attached to the surface of the microwave ablation needle and is sent into the in-vitro pig liver along with the microwave ablation needle; the two copper foil electrodes are respectively connected to the biological impedance measuring circuit board through leads; when microwave ablation starts, a microwave source is turned on, and AD5940 is started to measure impedance; the AD5940 sends out excitation voltage to the electrode, measures response voltage and response current and sends to the ARM microcontroller, and the ARM microcontroller calculates the impedance and sends to the host computer for impedance information reading and storage.
Preferably, in the step (3), as the microwave ablation is performed, intracellular fluid escapes from the cell due to the rupture of the cell membrane by the gradual increase of temperature, and the ion mobility is increased by the increase of temperature, the impedance of the ablation site is gradually reduced to about 400 Ω; by a certain time, the further temperature rise causes the tissue at the ablation part to be dehydrated and evaporated, and the impedance is obviously increased; after the impedance rises to a certain threshold value, cutting off the output of the microwave source before carbonization occurs at the ablation part; then the impedance is reduced to about 300 omega due to the diffusion of tissue fluid around the ablation part back to the measurement area, at the moment, the microwave source is turned on again, and the impedance rises again; the process is cycled until the actual on time of the microwave source reaches the predetermined ablation time.
The invention has the beneficial effects that: (1) the invention indirectly reflects the coagulation and carbonization conditions of tissues at the ablation part by measuring the biological impedance, and compared with single-point temperature measurement, the biological impedance can reflect the ablation effect of one region between two copper foil electrodes; (2) the invention adopts the high-precision impedance measurement analog front-end chip AD5940 to realize impedance measurement, and the impedance measurement function is easy to be integrated into the existing microwave ablation instrument, so the cost is low; (3) the method has great significance for judging the real-time curative effect of the tumor microwave ablation, and has important value for carbonization regulation and control of the tumor microwave ablation.
Drawings
FIG. 1 is a schematic flow chart of the method of the present invention.
Fig. 2 is a schematic structural diagram of the collecting device of the present invention.
Fig. 3 is a schematic structural view of the microwave ablation needle with the copper foil electrode of the invention.
Fig. 4 is a schematic diagram of an AD5940 circuit structure of the present invention.
Fig. 5 is a circuit topology diagram of the impedance measurement of the present invention.
Fig. 6 is a schematic diagram of real-time change of data of bio-impedance Ω and time T in a microwave ablation experiment without a carbonization control measure according to a certain group of embodiments of the present invention.
Fig. 7 is a schematic diagram of real-time variation of bio-impedance Ω and time T data in a certain set of microwave ablation experiments with carbonization control measures according to the present invention.
Detailed Description
As shown in fig. 1, a real-time carbonization control method based on bio-impedance microwave ablation includes the following steps:
s1, constructing a biological impedance acquisition device applied to microwave ablation real-time carbonization regulation and control;
s2, acquiring real-time change data of the biological impedance in the ablation process;
and S3, adjusting the output power of the microwave source according to the change of the biological impedance.
As shown in fig. 2, it is a schematic structural diagram of the bio-impedance collecting device. Wherein 1 is a microwave ablation needle, 2 is a biological impedance acquisition board, 3 is an upper computer, 4 is a 2450MHz solid microwave source, and 5 is an in vitro pork liver; the microwave ablation needle is provided with a copper foil electrode, and the copper foil electrode is connected to the biological impedance acquisition board through a lead. A high-precision impedance measurement analog front-end chip of the biological impedance acquisition board adopts AD5940, and an ARM microcontroller adopts STM32F411RET 6.
Fig. 3 is a schematic diagram of a microwave ablation needle with a copper foil electrode. The copper foil electrode 6 is attached to the surface of the microwave ablation needle and is respectively positioned at the rear end of the dielectric sleeve 7 by 5mm and 15mm, and the dielectric sleeve are connected to the biological impedance measurement circuit board through a lead 8; the copper foil electrode enters the body along with the insertion of the microwave ablation needle into the human body, and the impedance of the ablation part is measured.
As shown in fig. 4, it is a schematic diagram of an AD5940 circuit of the present invention. An AD5940 built-in digital waveform generator and a 12-bit digital-to-analog converter DAC generate a sinusoidal excitation signal; the on-chip 16-bit 800kSPS analog-to-digital converter ADC measures sinusoidal input voltage up to 200kHz, and digital filtering can be carried out on the measurement result; the on-chip high-speed trans-impedance amplifier HSTIA processes a high-bandwidth sine input signal of 200kHz, and converts a weak current signal into a voltage signal which can be measured by the ADC; and the on-chip Discrete Fourier Transform (DFT) engine performs DFT calculation on the measurement result and stores the real part measurement result and the imaginary part measurement result in corresponding registers.
As shown in fig. 5, is a circuit topology diagram of impedance measurement. The waveform generator and DAC generate a sinusoidal excitation signal that drives the external load impedance through the excitation buffer. The waveform generator stores a phase amplitude table of sine waves inside, frequency control words are set to adjust counting step length, and a phase accumulator carries out phase accumulation according to the counting step length every time an external clock generates a pulse. The waveform generator searches a phase amplitude table according to the phase accumulation result, and the DAC outputs voltage according to the corresponding amplitude. The output voltage of the excitation buffer passes through a resistor RlimAnd current limiting, namely limiting the output current within the safe current which can be borne by a human body. The positive and negative input ends of the differential amplifier or the instrument amplifier are connected with two ends of the load impedance, and the response voltage U of the load impedance is measuredX. Current through load impedance IXFlows into the negative input terminal of the transimpedance amplifier which converts it into a voltage UOThe conversion formula is:
UO＝-IXRTIA
wherein R isTIAIs the gain resistance of the transimpedance amplifier.
The ADC measures the voltages Ux and Uo respectively, and the impedance to be measured can be calculated by adopting the following formula:
after the measurement result of the ADC is subjected to DFT operation by the DFT engine, a real part r and an imaginary part i are obtained, and using response voltage as an example, the amplitude and the phase of the response voltage are respectively:
the amplitude and phase of the response current can be obtained in the same way. The amplitude and phase of the impedance can thus be derived:
θX＝θU-θI
wherein the phase of the current needs to be shifted 180 ° from the result found by the DFT engine, since the output voltage U is output during the current-to-voltage conversionOThere is a phase shift of 180 deg..
The initialization and workflow of the AD5940 is described below:
s1, configuring AD5940 peripherals, including system clock frequency, gain resistance RTIAResistance value, excitation sine signal frequency, sequencer length, DFT points, system interrupts, and the like. The invention selects the gain resistor RTIAThe resistance value is 1K omega, the excitation sine signal is 25kHz, and the number of DFT points is 8192.
S2, calibrating gain resistor RTIA. Configuring programmable switch matrix to respectively measure gain resistance R of AD5940TIAAnd an external calibration resistor RCALCalculating a gain resistance RTIAAnd a calibration resistor RCALIs multiplied by the calibration resistance RCALThe resistance value of (2) can obtain the actual gain resistor RTIAThe resistance value of (c). The invention selects the gain resistor RTIAThe resistance is 10K omega.
S3, configuring and enabling the sequencer. The present invention uses two sequences, an initialization sequence and a measurement sequence. The initialization sequence comprises initializing peripheral parameters of the AD5940, and the measurement sequence comprises switching the programmable switch matrix and switching the ADC input channel. After the initialization sequence and the measurement sequence are written into the SRAM of the AD5940, the sequencer is enabled, the sequencer starts to run the operation stored in advance, therefore, the initialization of the AD5940 is completed, and the AD5940 starts to circularly measure the external impedance.
S4, the ARM microcontroller receives the interrupt signal sent by the AD 5940. When the ARM microcontroller receives the interrupt signal sent by the AD5940, the data FIFO of the AD5940 is indicated to be full of the calculation results of the DFT engine. At the moment, the ARM microcontroller reads the data FIFO, acquires the real part and the imaginary part of the voltage and the current, and converts the real part and the imaginary part into impedance values. After the reading is finished, the AD5940 continues to execute the measurement operation and loads the data to the data FIFO again.
The microwave ablation carbonization control test is described as follows:
before the experiment, a microwave ablation needle attached with a copper foil electrode is inserted into the liver by 8cm so as to ensure that the whole ablation area is in the liver parenchyma; in multiple sets of data acquisition experiments, ablation power was selected from 30W, 40W and 50W, and the bioimpedance acquisition system was activated at the same time as ablation was initiated.
As shown in fig. 6, it is a set of real-time variation of the biological impedance and time T data of the ablation experiment in the real-time carbonization control method for microwave ablation based on biological impedance according to the embodiment of the present invention. The experimental ablation power of the group was selected to be 40W, no carbonization control was performed, and microwave ablation was started from 45 s. Observing the images, it was found that as the ablation time increased, the impedance of the ablation site first gradually decreased from about 800 Ω to about 400 Ω, then began to rise at 120s, reached 20k Ω at 300s and remained around 20k Ω. The microwave ablation ends at 350s and the impedance begins to drop rapidly to around 400 Ω. And after the ablation is finished, taking down the microwave ablation needle, cutting the liver tissue along the insertion direction of the microwave ablation needle, measuring the length of the ablation part to be about 5cm, measuring the length of the ablation part to be about 3cm, and measuring the front end of the ablation needle to be provided with an obvious carbonization trace which is about 2 cm.
Fig. 7 shows that the biological impedance and the time T data of a certain group of ablation experiments in the method for real-time carbonization control based on biological impedance for microwave ablation according to the embodiment of the present invention are changed in real time. The ablation power of the experimental group is selected to be 50W, carbonization regulation and control are carried out, microwave ablation starts from 12s, and when impedance rises to be about 7k omega, a microwave source is turned off. Observing the images, it was found that as the ablation time increased, the impedance of the ablation site first gradually decreased from about 850 Ω to about 500 Ω, then began to rise at 65s, reached the threshold for the first time at 115s, after which the impedance began to rapidly decrease to about 400 Ω or so. The process was repeated a total of 6 times, with microwave ablation ending at 555 s. And after the ablation is finished, the microwave ablation needle is taken down, the liver tissue is cut along the insertion direction of the microwave ablation needle, the long diameter of the ablation part is measured to be about 4cm, the short diameter of the ablation part is measured to be about 2cm, the carbonization mark at the front end of the ablation needle is obviously reduced, and the carbonization mark only appears at the tip of the ablation needle.
Claims (8)
1. A microwave ablation real-time carbonization regulation and control method based on bioimpedance is characterized by comprising the following steps:
s1, constructing a biological impedance acquisition device applied to microwave ablation real-time carbonization regulation and control;
s2, acquiring real-time change data of the biological impedance in the ablation process;
and S3, adjusting the output power of the microwave source according to the change of the biological impedance.
2. The real-time carbonization control method based on the bio-impedance microwave ablation as claimed in claim 1, wherein in the step (1), the bio-impedance acquisition device comprises a copper foil electrode, a high-precision impedance measurement analog front-end chip and an ARM microcontroller; the copper foil electrode is connected with the high-precision impedance measurement simulation front-end chip through a wire, the ARM microcontroller controls the high-precision impedance measurement simulation front-end chip to carry out impedance measurement, returned data are received and an impedance value is obtained through calculation, and the ARM microcontroller sends the impedance to an upper computer through the communication module to display.
3. The real-time carbonization control method based on bioimpedance for microwave ablation according to claim 2, wherein the copper foil electrode is attached to the surface of the microwave ablation needle; one copper foil electrode is attached to the position 5mm away from the rear end of the microwave ablation needle medium sleeve, the other copper foil electrode is attached to the position 15mm away from the rear end of the medium sleeve, and the distance between the two copper foil electrodes is 10 mm; the two copper foil electrodes are respectively connected to the biological impedance measuring circuit board through leads.
4. The real-time carbonization control method based on bioimpedance of claim 2, wherein the high-precision impedance measurement analog front-end chip is AD 5940; an AD5940 built-in digital waveform generator and a 12-bit digital-to-analog converter DAC generate a sinusoidal excitation signal; the on-chip 16-bit 800kSPS analog-to-digital converter ADC measures sinusoidal input voltage up to 200kHz, and digital filtering can be carried out on the measurement result; the on-chip high-speed trans-impedance amplifier HSTIA processes a high-bandwidth sine input signal of 200kHz, and converts a weak current signal into a voltage signal which can be measured by the ADC; and the on-chip Discrete Fourier Transform (DFT) engine performs DFT calculation on the measurement result and stores the real part measurement result and the imaginary part measurement result in corresponding registers.
5. The real-time carbonization control method based on the bio-impedance microwave ablation as claimed in claim 2, wherein the ARM microcontroller selects STM32F411RET6 with a main frequency of 100 MHz; the ARM microcontroller is communicated with the AD5940 by adopting a serial peripheral interface SPI; the ARM microcontroller sends a control instruction to the AD5940, configures a digital waveform generator, an HSTIA (high speed TIA) and an ADC (analog-to-digital converter) peripheral of the AD5940, and reads real part and imaginary part measurement results of response voltage and response current from a data FIFO (first in first out); and after reading the measurement result, the measurement result is converted into impedance by the ARM microcontroller.
6. The real-time carbonization control method for microwave ablation based on bioimpedance of claim 2, wherein the communication module is a CH340C USB serial port chip, and the baud rate is set to 115200 bps.
7. The real-time carbonization control method based on bioimpedance during microwave ablation according to claim 1, wherein in step (2), the copper foil electrode is attached to the surface of the microwave ablation needle and is sent into the in-vitro pork liver along with the microwave ablation needle; the two copper foil electrodes are respectively connected to the biological impedance measuring circuit board through leads; when microwave ablation starts, a microwave source is turned on, and meanwhile, AD5940 is started to carry out impedance measurement; the AD5940 sends out excitation voltage to the electrode, measures response voltage and response current and sends to the ARM microcontroller, and the ARM microcontroller calculates the impedance and sends to the host computer for impedance information reading and storage.
8. The real-time carbonization regulating method based on bioimpedance microwave ablation according to claim 1, wherein in the step (3), the impedance of the ablation part is gradually reduced to about 400 Ω as the microwave ablation is performed; by a certain time, the further temperature rise causes the tissue at the ablation part to be dehydrated and evaporated, and the impedance is obviously increased; after the impedance rises to a certain threshold value, cutting off the output of the microwave source before carbonization occurs at the ablation part; then the impedance is reduced to about 300 omega due to the diffusion of tissue fluid around the ablation part back to the measurement area, and at the moment, the microwave source is turned on again, and the impedance rises again; the process is cycled until the actual on time of the microwave source reaches the predetermined ablation time.
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| CN104739506A (en) * | 2015-03-24 | 2015-07-01 | 南京康友医疗科技有限公司 | Microwave ablation therapeutic apparatus with microwave ablation needle protected based on microwave power detection |
| CN112566576A (en) * | 2018-08-23 | 2021-03-26 | 波士顿科学国际有限公司 | Microwave ablation probe with radio frequency impedance sensing |
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| CN104739506A (en) * | 2015-03-24 | 2015-07-01 | 南京康友医疗科技有限公司 | Microwave ablation therapeutic apparatus with microwave ablation needle protected based on microwave power detection |
| CN112566576A (en) * | 2018-08-23 | 2021-03-26 | 波士顿科学国际有限公司 | Microwave ablation probe with radio frequency impedance sensing |
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| CN115844524A (en) * | 2022-12-21 | 2023-03-28 | 南京瑞波医学科技有限公司 | Ablation instrument microwave output power control method and device and electronic equipment |
| CN115844524B (en) * | 2022-12-21 | 2023-09-15 | 南京瑞波医学科技有限公司 | Ablation instrument microwave output power control method and device and electronic equipment |
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