An ultrasonic thermal strain thermometry method and system based on equivalent thermal dose correction

Abstract

This application discloses an ultrasonic thermal strain measurement method and system based on equivalent thermal dose correction, relating to the field of thermotherapy monitoring: acquiring the initial temperature of biological tissue; during the heating process of biological tissue, acquiring ultrasonic echo signal sequences of the target area at preset time intervals; calculating the cumulative thermal strain of the target area at each measurement moment based on the ultrasonic echo signal sequence; coupling and predicting the temperature and equivalent thermal dose at the current moment based on the equivalent thermal dose and temperature at the previous measurement moment, obtaining the predicted values ​​of the temperature and equivalent thermal dose at the current moment; establishing a temperature inversion equation including cumulative thermal strain and equivalent thermal dose, iteratively solving the equation using the predicted value as the initial value, and outputting the corrected temperature value and updated equivalent thermal dose value at the current moment. This application achieves dynamic compensation for the nonlinear changes in acoustic parameters caused by tissue thermal denaturation, thereby improving the temperature measurement accuracy during the ablation stage, expanding the temperature measurement range, and realizing real-time synchronous monitoring of temperature and equivalent thermal dose.

Description

Technical Field

[0001] This application relates to the field of hyperthermia monitoring, and more specifically, to an ultrasonic thermal strain measurement method and system based on equivalent thermal dose correction. Background Technology

[0002] In recent years, in-situ thermal therapy techniques, represented by focused ultrasound, radiofrequency ablation, and microwave ablation, have been widely used in the treatment of diseases such as tumors due to their advantages of being minimally invasive / non-invasive and repeatable. The key to successful treatment lies in applying a sufficient and uniform thermal dose to the target area to achieve thorough treatment while maximizing the protection of surrounding normal tissue. Therefore, real-time and precise monitoring of tissue temperature and the degree of cumulative thermal damage during treatment is crucial.

[0003] Ultrasound imaging technology, with its radiation-free operation, real-time performance, relatively low cost, and excellent soft tissue imaging capabilities, has become one of the most promising guidance and monitoring methods in thermotherapy. Among these methods, ultrasound thermal strain measurement, a representative non-invasive temperature measurement technique, utilizes the time delay (i.e., thermal displacement, the spatial difference of which is thermal strain) of the ultrasound echo signal caused by changes in sound velocity and thermal expansion after tissue denaturation due to heat. By establishing a mapping relationship between thermal strain and temperature, the temperature distribution can be inverted. However, this technology faces two significant technical bottlenecks in its path towards clinical application: First, the linear assumption of the model fails in the high-temperature region, leading to a decrease in accuracy. Most existing ultrasonic thermal strain measurement methods (e.g., the scheme disclosed in US Patent 20160015417) are generally based on a key assumption: there is a simple linear relationship between tissue thermal strain and temperature change. However, when the tissue temperature rises above a certain threshold (typically above 50-60°C), its characteristic parameters (such as sound velocity and coefficient of thermal expansion) undergo drastic nonlinear changes. This shift in tissue parameters caused by high temperature renders the original linear mapping model inapplicable, resulting in a significant deterioration or even complete inaccuracy in temperature measurement accuracy in the core treatment area, severely limiting the reliable temperature measurement range of this technology.

[0004] Second, the temperature monitoring and thermal dose monitoring processes are disconnected and lack feedback. In clinical practice, the core indicator for evaluating the effectiveness of thermotherapy is not only instantaneous temperature, but also the "equivalent thermal dose" (such as the commonly used CEM43 model) that reflects the cumulative effect of thermal damage. Existing technical solutions (for example, the solution disclosed in Chinese invention patent CN 200810099779.1) typically adopt an open-loop process of "measure temperature first, then calculate": that is, the temperature field is first estimated by some method, and then it is substituted into the thermal dose model for post-processing calculation. This process results in temperature monitoring and thermal dose monitoring being two independent, unidirectional links. Errors in temperature estimation are directly transmitted and accumulated in the thermal dose calculation results, and the thermal dose calculation results cannot provide any feedback correction for the temperature estimation process, making it impossible to achieve adaptive optimization based on the real-time state of the tissue.

[0005] In summary, overcoming the nonlinear effects of tissue property changes (thermal denaturation) at high temperatures to expand the temperature measurement range and achieve synchronous, closed-loop, and high-precision monitoring of temperature and equivalent thermal dose is a technical challenge that urgently needs to be overcome to improve the clinical practical value of ultrasonic thermal strain measurement technology. Summary of the Invention

[0006] To address the problems in existing ultrasonic thermal strain measurement technologies, such as the accumulation and amplification of temperature measurement errors caused by nonlinear changes in acoustic parameters due to tissue thermal denaturation during the high-temperature ablation stage, and the inability to synchronize temperature monitoring and equivalent heat dose assessment in real time, this application provides an ultrasonic thermal strain measurement method and system based on equivalent heat dose correction. By introducing an equivalent heat dose correction term into the temperature inversion equation and establishing a coupled prediction-iterative solution closed-loop mechanism for temperature and equivalent heat dose, dynamic compensation for nonlinear changes in acoustic parameters caused by tissue thermal denaturation is achieved. This improves the temperature measurement accuracy during the ablation stage, broadens the temperature measurement range, and enables real-time synchronous monitoring of temperature and equivalent heat dose.

[0007] One aspect of this application provides an ultrasonic thermal strain measurement method based on equivalent heat dose correction, comprising: S1: acquiring the initial temperature T0 of biological tissue; S2: acquiring an ultrasonic echo signal sequence during tissue heating; S3: calculating the cumulative thermal strain of the target area at the measurement time based on the ultrasonic echo signal sequence; S4: performing coupled prediction of the temperature and equivalent heat dose at the current time based on the equivalent heat dose and temperature at the previous measurement time; S5: establishing a temperature inversion equation including cumulative thermal strain and equivalent heat dose correction terms, using the result of coupled prediction as the initial value for iteration to solve the problem, so as to dynamically compensate for the nonlinear changes in acoustic parameters caused by tissue thermal denaturation, and synchronously outputting the temperature correction value and the updated equivalent heat dose value at the current time; S6: performing coupled prediction and iterative solution for the next measurement time based on the output result at the current time, realizing synchronous closed-loop monitoring of temperature and equivalent heat dose.

[0008] Furthermore, the equivalent heat dose is characterized and calculated using a cumulative equivalent minute model, specifically the CEM43 model, whose expression for calculating the equivalent heat dose TD is as follows: ;in, Let be the tissue temperature at time i, Δt be the time interval, and R be the temperature compensation coefficient related to the tissue's sensitivity to thermal damage.

[0009] Furthermore, the coupling prediction at the current moment satisfies: ,in, and They are the current time t. i The initial temperature prediction and the initial equivalent heat dose prediction, and Each is the previous moment Temperature correction values ​​and equivalent heat dose update values.

[0010] Furthermore, the temperature inversion equation has the following form: , in, The temperature value is obtained from the nth iteration. The cumulative thermal strain at the current moment, The equivalent heat dose value is substituted into the nth iteration; This is the temperature-thermal strain mapping coefficient. This is the heat dose correction factor. This is the initial temperature.

[0011] Furthermore, during the iterative solution process, the equivalent heat dose value is updated with each iteration according to the following formula: ,in, The temperature value is input for the nth iteration.

[0012] Furthermore, the convergence condition for iterative solution is: the absolute value of the difference between the temperature values ​​obtained from two adjacent iterations is less than a preset threshold, or the number of iterations reaches a preset upper limit.

[0013] Furthermore, the specific steps for calculating the cumulative thermal strain include: estimating the cumulative time delay of the ultrasonic echo signal sequence by block matching or zero-pole tracking, and obtaining the spatial gradient of the cumulative time delay along the ultrasonic beam direction.

[0014] Furthermore, the method also includes: traversing multiple temperature measurement points within the target area, and reconstructing the spatial temperature distribution field and spatial equivalent heat dose distribution field of the biological tissue at the measurement time based on the corrected temperature and updated equivalent heat dose of each point; wherein the calculation process of traversing multiple temperature measurement points is implemented through matrix parallel operation.

[0015] Another aspect of this application provides an ultrasonic thermal strain measurement system based on equivalent heat dose correction, comprising: an ultrasonic probe for acquiring ultrasonic echo signal sequences of a target area at preset time intervals during the heating process of biological tissue; a processor connected to the ultrasonic probe for executing the method of this application; a memory connected to the processor for storing an initial temperature T0, ultrasonic echo signal sequences, cumulative thermal strain, temperature correction values, and updated equivalent heat dose values; and a display connected to the processor for displaying temperature correction values, updated equivalent heat dose values, spatial temperature distribution field, and spatial equivalent heat dose distribution field.

[0016] Compared to existing technologies, the advantages of this application are: This application introduces the biological indicator of equivalent thermal dose and constructs a temperature inversion equation and a two-way iterative solution process that includes cumulative thermal strain and equivalent thermal dose correction terms. This overcomes the inherent defect of traditional ultrasonic thermal strain measurement technology, which suffers from a significant increase in error at high temperatures due to the nonlinear shift of acoustic parameters caused by tissue denaturation. This significantly expands the temperature measurement range and improves overall accuracy. Simultaneously, this application establishes a two-way feedback mechanism for temperature and dose, using thermal dose calculation results to correct temperature estimation. This achieves synchronous, closed-loop monitoring of both in time and space. The feedback mechanism can adaptively compensate for individual tissue differences and real-time denaturation states, not only avoiding error propagation and accumulation but also providing precise decision-making basis for clinical hyperthermia by integrating instantaneous temperature and cumulative biological effects, greatly enhancing the controllability and safety of treatment. Attached Figure Description

[0017] Figure 1 The flowchart shows the ultrasonic thermal strain measurement method based on equivalent heat dose correction. Figure 2 This is a schematic diagram of the device in Example 2; Figure 3 a represents the two-dimensional distribution of thermal strain within the subcutaneous fat of a heated pig, as determined in Example 2; Figure 3 b represents the two-dimensional temperature distribution obtained in Example 2 using the evaluation method of this application; Figure 3 c represents the two-dimensional distribution of equivalent heat dose obtained by evaluation using this application in Example 2; Figure 4 a represents the result of the temperature change assessment of pig subcutaneous fat in Example 2 of this application; Figure 4b represents the result of the equivalent heat dose change assessment of pig subcutaneous fat in Example 2 of this application.

[0018] Figure labels: 01, ultrasonic heating probe; 02, ultrasonic imaging probe; 03, thermocouple probe; 04, subcutaneous fat mass in pigs. Detailed Implementation

[0019] The present application will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0020] Example 1 Combination Figure 1 The ultrasonic thermal strain measurement method and system based on equivalent heat dose correction of this application includes the following steps: (1) Obtain the initial temperature T0 of the biological tissue; Specifically, the heating methods for biological tissues include, but are not limited to, focused ultrasound, radio frequency or microwave, and the methods for obtaining the initial temperature include, but are not limited to, thermocouples, infrared thermometers or alcohol thermometers.

[0021] (2) Acquire ultrasonic echo signal sequences during tissue heating; Specifically, the process of acquiring ultrasonic echo signal sequences is as follows: The relative position of the ultrasonic probe and the area to be measured is kept fixed, and ultrasonic echo signals are acquired at constant time intervals from before heating to the heating process. The ultrasonic echo signals include the raw radio frequency signal or the envelope signal after demodulation.

[0022] (3) Calculate the cumulative thermal strain of the target area at the measurement time based on the ultrasonic echo signal sequence; Specifically, the steps for calculating cumulative thermal strain include: estimating the cumulative time delay of the ultrasonic echo signal sequence using block matching or zero-pole tracking methods, and obtaining the spatial gradient of the cumulative time delay along the ultrasonic beam direction. Further, a relevant example is Chinese invention patent CN 201910112033.8, which discloses a method for calculating cumulative signal time delay and thermal strain.

[0023] (4) Based on the equivalent heat dose and temperature at the previous measurement time, the temperature and equivalent heat dose at the current time are coupled and predicted. Specifically, the equivalent heat dose is characterized and calculated using the cumulative equivalent minute model, which is the CEM43 model. The expression for calculating the equivalent heat dose TD is as follows: , in, Let be the tissue temperature at time i, Δt be the time interval, and R be the temperature compensation coefficient related to the tissue's sensitivity to thermal damage. It is worth noting that the equivalent thermal dose also encompasses thermal dose calculation models based on other reference temperatures or the Arrhenius equation for tissue damage.

[0024] Furthermore, the coupling prediction at the current moment satisfies: , in, and Each represents the current time. The initial temperature prediction and the initial equivalent heat dose prediction, and Each is the previous moment Temperature correction values ​​and equivalent heat dose update values.

[0025] (5) Establish a temperature inversion equation that includes cumulative thermal strain and equivalent thermal dose correction terms, use the results of coupled prediction as the initial value for iteration to solve the problem, so as to dynamically compensate for the nonlinear changes in acoustic parameters caused by tissue thermal denaturation, and synchronously output the corrected temperature and updated equivalent thermal dose at the current moment. Specifically, the temperature inversion equation has the following form: , in, The temperature value is obtained from the nth iteration. The cumulative thermal strain at the current moment, The equivalent heat dose value is substituted into the nth iteration; This is the temperature-thermal strain mapping coefficient. This is the heat dose correction factor. The initial temperature. Parameter and The thermal strain at the corresponding point can be determined in a priori experiments involving heated biological tissue by the thermocouple probe.

[0026] Furthermore, during the iterative solution process, the equivalent heat dose value is updated with each iteration according to the following formula: , in, The temperature value is input for the nth iteration.

[0027] Furthermore, the convergence condition for the iterative solution is: the absolute value of the difference between the temperature values ​​obtained from two consecutive iterations is less than a preset threshold, or the number of iterations reaches a preset upper limit. After the convergence condition is met, the corrected temperature and the updated equivalent heat dose are output synchronously.

[0028] It is worth noting that this application only illustrates fixed-point iteration as a general method for iterative computation; iterative computation can also be replaced by other methods, including but not limited to well-known methods such as bisection method, secant method, and Newton's iteration method.

[0029] (6) Based on the output results at the current moment, perform coupled prediction and iterative solution for the next measurement moment to achieve synchronous closed-loop monitoring of temperature and equivalent heat dose.

[0030] Specifically, at the current time t i The output is returned in step (4) as prior information for the next measurement; furthermore, multiple temperature measurement points within the target area are traversed, and the spatial temperature distribution field and spatial equivalent heat dose distribution field of the biological tissue at the measurement time are reconstructed based on the corrected temperature and updated equivalent heat dose of each point. The calculation of traversing multiple temperature measurement points is achieved through matrix parallel operation.

[0031] Example 2 This embodiment uses the method described in Example 1 above to perform focused ultrasound heating and temperature measurement experiments on isolated porcine subcutaneous fat. The specific operation steps of the method are as follows: Implementing device such as Figure 2 As shown, the heating experiment was conducted in a constant-temperature water bath environment. The focusing area of ​​the ultrasonic heating probe 01 passes through the imaging plane of the ultrasonic imaging probe 02; the needle guides the thermocouple probe 03 to pierce the subcutaneous fat block 04 of the pig, ensuring that the measurement point of the thermocouple probe is located within the ultrasonic imaging plane and approximately 2-3 mm away from the focusing heating center. The thermocouple probe is controlled by the temperature data acquisition module, with a sampling frame rate of 100 Hz. The output signal of the signal generator is fed to the ultrasonic heating probe 01 through the gain of the power amplifier, emitting high-intensity focused ultrasound with a center frequency of 1.34 MHz and a duty cycle of approximately 45%; in addition, the signal generator controls the data acquisition timing of the ultrasonic imaging probe 02 via a synchronous trigger signal through the ultrasonic data acquisition module, ensuring that the working periods of the heating probe and the imaging probe are staggered, avoiding interference of high-intensity focused ultrasound on the ultrasonic echo signal. The sampling rate for ultrasound imaging data was 50 MHz; imaging probe 02 was a 128-element linear array probe with a center frequency of 10.5 MHz; the imaging depth was set to 4 cm; and ultrasound echo signal sequences of 2600 (axial) × 126 (lateral) pixels per frame were acquired at a frame rate of 50 Hz. The ultrasound data acquisition module and temperature data acquisition module were controlled by a computer terminal to simultaneously acquire and store ultrasound imaging data and thermocouple probe data throughout the heating process, with the acquisition time set to 40 s.

[0032] Choosing a time interval Δt = 0.5 s, calculate the two-dimensional distribution of thermal strain as a function of time, as follows: Figure 3As shown in Figure a. Based on step (1) of Example 1, the initial temperature T0 of the pig subcutaneous fat was measured to be 33.6℃ using a thermocouple in a constant temperature water environment. Based on step (5) of Example 1, the temperature-thermal strain mapping coefficient k = 195.4℃ and the heat dose correction factor of the pig subcutaneous fat were calibrated. The convergence threshold for the iterative solution was set to 0.1 ℃, and the upper limit for the number of iterations was set to 100. Furthermore, the evaluation method of this application was applied to obtain the two-dimensional temperature distribution (e.g., Figure 3 (as shown in b) and the two-dimensional distribution of the equivalent heat dose (as shown in b) Figure 3 (as shown in c).

[0033] The highest temperature reached by the tissue at the thermocouple probe location was 57.2 ℃, with an equivalent heat dose of 2.6 × 10⁻⁶. 3 min; extract the temperature change at this location based on ultrasonic assessment, compare it with the thermocouple measurement value, and the result is as follows. Figure 4 As shown in figure a; the equivalent heat dose change assessed by ultrasound at this location was extracted and compared with the thermocouple measurement value, and the result is as follows. Figure 4 As shown in b. The evaluation method of this application has a high degree of consistency with the thermocouple temperature measurement values, with an average absolute error of 0.43 ℃ and a maximum error of 1.23 ℃. In summary, this application can significantly broaden the temperature measurement range and achieve synchronous, closed-loop, high-precision monitoring of temperature and equivalent heat dose.

[0034] The foregoing illustrative description of the present application and its embodiments is not restrictive and can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. The accompanying drawings are only one embodiment of the present application, and the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present application, such designs should fall within the scope of protection of this application. Furthermore, the word "comprising" does not exclude other elements or steps, and the word "a" preceding an element does not exclude the inclusion of "a plurality" of that element. Terms such as "first," "second," etc., are used to indicate names and do not indicate any specific order.

[0035] The foregoing illustrative description of the present application and its embodiments is not restrictive and can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. The accompanying drawings are only one embodiment of the present application, and the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present application, such designs should fall within the scope of protection of this application. Furthermore, the word "comprising" does not exclude other elements or steps, and the word "a" preceding an element does not exclude the inclusion of "a plurality" of that element. Terms such as "first," "second," etc., are used to indicate names and do not indicate any specific order.

Claims

1. An ultrasonic thermal strain measurement method based on equivalent heat dose correction, characterized in that, include: S1, obtain the initial temperature T0 of the biological tissue; S2, during the heating process of biological tissue, the ultrasonic echo signal sequence of the target area is collected at preset time intervals; S3, calculate the cumulative thermal strain of the target area at each measurement time based on the ultrasonic echo signal sequence; S4. Based on the equivalent heat dose and temperature at the previous measurement moment, the temperature and equivalent heat dose at the current moment are coupled and predicted to obtain the predicted values ​​of the temperature and equivalent heat dose at the current moment. S5. Establish a temperature inversion equation that includes cumulative thermal strain and equivalent heat dose. Use the predicted value as the starting value for iteration and solve iteratively. Output the temperature correction value and the updated value of equivalent heat dose at the current moment.

2. The ultrasonic thermal strain measurement method based on equivalent heat dose correction according to claim 1, characterized in that: Also includes: S6, the temperature correction value and the equivalent heat dose update value at the current moment are used as the temperature and equivalent heat dose of the previous measurement moment in the next measurement moment step S4.

3. The ultrasonic thermal strain measurement method based on equivalent heat dose correction according to claim 2, characterized in that: The equivalent heat dose data were calculated using a cumulative equivalent minute numerical model.

4. The ultrasonic thermal strain measurement method based on equivalent heat dose correction according to claim 3, characterized in that: The cumulative equivalent minutes numerical model is the CEM43 model.

5. The ultrasonic thermal strain measurement method based on equivalent heat dose correction according to claim 4, characterized in that: The equivalent heat dose is calculated using the following formula: ， Where TD is the equivalent heat dose; Ti is the tissue temperature at time i; Δt is the time interval; and R is the temperature compensation coefficient related to the tissue's thermal damage sensitivity.

6. The ultrasonic thermal strain measurement method based on equivalent heat dose correction according to claim 4, characterized in that: The current temperature and equivalent heat dose are coupled and predicted using the following formula: ， in, and Each represents the current time. The initial temperature prediction and the initial equivalent heat dose prediction, and These are the temperature correction value and the updated equivalent heat dose value for the previous time step ti-1, respectively.

7. The ultrasonic thermal strain measurement method based on equivalent heat dose correction according to any one of claims 3 to 6, characterized in that: The temperature inversion equation is expressed as follows: ， in, The temperature value is obtained from the nth iteration. The cumulative thermal strain at the current moment, The equivalent heat dose value is substituted into the nth iteration; This is the temperature-thermal strain mapping coefficient. This is the heat dose correction factor. This is the initial temperature.

8. The ultrasonic thermal strain measurement method based on equivalent heat dose correction according to claim 7, characterized in that: Calculate the cumulative thermal strain of the target region at each measurement time, including: The cumulative time delay of the ultrasonic echo signal sequence can be estimated by block matching or zero-pole tracking. The spatial gradient is obtained by calculating the cumulative time delay along the direction of the ultrasonic beam, and the cumulative thermal strain is then obtained.

9. The ultrasonic thermal strain measurement method based on equivalent heat dose correction according to claim 8, characterized in that: Also includes: S7. Traverse multiple temperature measurement points within the target area, execute steps S3 to S5 for each temperature measurement point, obtain the temperature correction value and equivalent heat dose update value for each temperature measurement point, and generate the spatial temperature distribution field and spatial equivalent heat dose distribution field at the measurement time based on the temperature correction value and equivalent heat dose update value for each temperature measurement point.

10. An ultrasonic thermal strain measurement system based on equivalent heat dose correction, characterized in that, include: An ultrasonic probe collects ultrasonic echo signal sequences of a target area at preset time intervals during the heating process of biological tissue. A processor, connected to an ultrasound probe, performs the method according to any one of claims 1 to 9; The memory, connected to the processor, stores the initial temperature. Ultrasonic echo signal sequence, cumulative thermal strain, temperature correction value, and updated equivalent heat dose value; The display, connected to the processor, shows the temperature correction value, the updated equivalent heat dose value, the spatial temperature distribution field, and the spatial equivalent heat dose distribution field.

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