Identification of denatured and normal biological tissues based on compressed sensing and refined composite multi-scale fuzzy entropy during high intensity focused ultrasound treatment

In high intensity focused ultrasound(HIFU)treatment,it is crucial to accurately identify denatured and normal biological tissues.In this paper,a novel method based on compressed sensing(CS)and refined composite multi-scale fuzzy entropy(RCMFE)is proposed.First,CS is used to denoise the HIFU echo signals.Then the multi-scale fuzzy entropy(MFE)and RCMFE of the denoised HIFU echo signals are calculated.This study analyzed 90 cases of HIFU echo signals,including 45 cases in normal status and 45 cases in denatured status,and the results show that although both MFE and RCMFE can be used to identify denatured tissues,the intra-class distance of RCMFE on each scale factor is smaller than MFE,and the inter-class distance is larger than MFE.Compared with MFE,RCMFE can calculate the complexity of the signal more accurately and improve the stability,compactness,and separability.When RCMFE is selected as the characteristic parameter,the RCMFE difference between denatured and normal biological tissues is more evident than that of MFE,which helps doctors evaluate the treatment effect more accurately.When the scale factor is selected as 16,the best distinguishing effect can be obtained.

Influence of dynamic tissue properties on temperature elevation and lesions during HIFU scanning therapy:Numerical simulation

When large tumors are treated,ablation of the entire volume of tumors requires multiple treatment spots formed by high intensity-focused ultrasound(HIFU)scanning therapy.The heating effect of HIFU on biological tissue is mainly reflected in temperature elevation and tissue lesions.Tissue property parameters vary with temperature and,in turn,the distribution of temperature as well as the heating effects change accordingly.In this study,an HIFU scanning therapy model considering dynamic tissue properties is provided.The acoustic fields and temperature fields are solved combining the Helmholtz wave equation with Pennes bio-heat transfer equation based on the finite element method(FEM)to investigate the effects of various tissue properties(i.e.,the attenuation coefficient,acoustic velocity,thermal conductivity,specific heat capacity,density,and blood perfusion rate)on heating performance.Comparisons of the temperature distribution and thermal lesions under static and dynamic properties are made based on the data of tissue property parameters varying with temperature.The results show that the dynamic changes of thermal conductivity,specific heat capacity,and acoustic velocity may account for the decrease of temperature elevation in HIFU treatment,while the dynamic changes of attenuation coefficient,density,and blood perfusion rate aggravate the increase of temperature on treatment spots.Compared with other properties,the dynamic change of attenuation coefficient has a greater impact on tissue temperature elevation.During HIFU scanning therapy,the temperature elevation and tissue lesions of the first treatment spot are smaller than those of the subsequent treatment spots,but the temperature on the last treatment spot drops faster during the cooling period.The ellipsoidal tissue lesion is not symmetrical;specifically,the part facing toward the previous treatment spot tends to be larger.Under the condition of the same doses,the temperature elevation and the size of tissue lesions under dynamic properties present significant growth in comparison to static properties.Besides,the tissue lesion begins to form earlier with a more unsymmetrical shape and is connected to the tissue lesion around the previous treatment spot.As a result,lesions around all the treatment spots are connected with each other to form a closed lesion region.The findings in this study reveal the influence of dynamic tissue properties on temperature elevation and lesions during HIFU scanning therapy,providing useful support for the optimization of treatment programs to guarantee higher efficacy and safety.

Dynamics of an ultrasound contrast agent microbubble near spherical boundary in ultrasound field

The goal of this article is to establish the conditions of excitation where one has to deal with ultrasound contrast agent(UCA) microbubbles pulsating near biological tissues with spherical boundary in ultrasound field for targeted drug delivery and cavitation-enhanced thrombolysis, etc., and contributes to understanding of mechanisms at play in such an interaction. A modified model is presented for describing microbubble dynamics near a spherical boundary(including convex boundary and concave boundary) with an arbitrary-sized aperture angle. The novelty of the model is such that an oscillating microbubble is influenced by an additional pressure produced by the sound reflection from the boundary wall. It is found that the amplitude of microbubble oscillation is positively correlated to the curve radius of the wall and negatively correlated to the aperture angle of the wall and the sound reflection coefficient. Moreover, the natural frequency of the microbubble oscillation for such a compliable wall increases with the wall compliance, but decreases with the reduction of the wall size, indicating distinct increase of the natural frequency compared to a common rigid wall. The proposed model may allow obtaining accurate information on the radiation force and signals that may be used to advantage in related as drug delivery and contrast agent imaging.