| The experiment proved that ultrasound could accelerate the process of pathological tissue processing by cavitation,and the cavitation state induced by ultrasound was directly related to the result of pathological tissue processing.Subharmonic signal detection is one of the many methods used to detect cavitation.Conventional subharmonic signal method was used to detect when the cavitation is mostly in the steady-state cavitation or transient-state cavitation,on the one hand,the steady-state cavitation or transient cavitation ultrasound power density value is much higher than required by the tissue samples can afford,and thus causes damage to tissue samples to be processed,and this kind of situation in clinic is unacceptable;On the other hand,the traditional subharmonic signal detection method becomes unstable in the region where the ultrasonic power density is much lower than the steady state cavitation or transient cavitation(we define it as the critical cavitation region),so it is necessary to study the detection method of cavitation in the critical cavitation region.In this paper,we developed an ultrasonic pathological tissue processing system which can accelerate the pathological tissue processing and has the function of cavitation detection.The working frequency of the system is 200 kHz and the power value is adjustable.The ultrasonic sensor mounted on the side wall can detect the subharmonic signal generated by cavitation bubble oscillation.In this paper,we use the subharmonic signal detection method to detect the cavitation activity during ultrasonic accelerated pathological tissue processing,and after the target signal detected by the cavitation detection system is subjected to signal processing such as amplification,low-pass filtering and discretization processing,Finally,the target signal is subjected to FFT processing to extract the target signal amplitude as an indicator for evaluating cavitation activity.In the research work of this paper,we detect the 1/2 subharmonic signal in the liquid environment under different ultrasonic power densities according to the traditional subharmonicsignal detection method.In order to simulate the actual process of ultrasonic acceleration of pathological tissue processing,we added objects of different volumes or materials,such as tissue embedding box,rubber block or magnetic ring,into the processing container,and continued to observe whether the characteristics of the detected subharmonic signal changed.Finally,we investigated the effect of temperature on cavitation activity.It is found that each subharmonic signal detected in the liquid environment can be clearly divided into non-cavitation region,critical cavitation region and cavitation region,but the characteristic factors such as signal amplitude and cavitation threshold are slightly different.When we simulated the actual process of ultrasonic-accelerated pathological tissue processing,and tried to add different objects into the processing container,we found that the detected new subharmonic signal became extremely unstable,so the state of cavitation could not be determined.Therefore,this paper proposes a method of taking multiple subharmonic signals as eigenvectors.In this paper,multiple subharmonic signals are taken as feature vectors,and multiple feature vectors of different frequencies can be combined with different parameters to obtain a new combined feature vectors,which can be used as the judgment basis to evaluate cavitation activities and realize the stable detection of cavitation under the condition of presence of foreign bodies in ultrasonic processing container.In addition,in order to quickly determine the cavitation,this paper takes the ultrasonic power density and subharmonic signal strength as the signal characteristics,use linear classification method to classify the feature vectors,and obtains the determination curve that can determine whether cavitation occurs.Finally,in the experiment to explore the influence of temperature on cavitation,we draw a conclusion: appropriate increase of temperature is conducive to the occurrence of cavitation within limits.This study is the first to examine the cavitation activity during ultrasound accelerated pathological tissue processing.In addition,after a large number of experiments,it was found that the conventional subharmonic signal detection method was not suitable for the detection of cavitation during ultrasound accelerated pathological tissue processing.This paper innovatively proposes a method to detect cavitation activity by taking the subharmonic signal as the eigenvector and the combined eigenvectors of multiple eigenvectors with different frequencies and different parameters as the basis.The research content of this paper can provide reference forenvironmental parameters of ultrasound accelerated pathological tissue processing,can greatly promote the application of pathological diagnosis in clinical treatment,and also lays a foundation for the application of ultrasound cavitation in clinical rapid pathological tissue processing. |
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