hu dong

During the treatment of soft tissue tumors with high-intensity focused ultrasound (HIFU), the focus may shift away from the desired point due to tissue heterogeneity. By studying the effect of biological tissue on focus shift, it can provide a theoretical basis for the safety and reliability of HIFU therapy.
The finite difference time domain (FDTD) method was used to construct the simulation model of HIFU irradiated multi-layer biological tissue. Based on the Westervelt nonlinear acoustic propagation equation, the focus position change caused by the thickness of biological tissue and ultrasonic transducer during HIFU irradiation were simulated and calculated. The effects of ultrasonic transducer's electric power, irradiation frequency and tissue thickness on the focus position shift were analyzed and discussed.
With the increase of electric power of HIFU transducer, the sound pressure at the focal point rose and the focal point approached the transducer side. With the increase of irradiation frequency of transducer, the sound pressure at the focus increased and the focus shifted away from transducer. With the increase of the thickness of biological tissue, the amplitude of sound pressure at the focal point decreased gradually. If the sound velocity of biological tissue was greater than that of water, the focus was close to the transducer side. If the sound velocity of biological tissue was less than the sound velocity of water, the focus moved to the side away from the transducer. For biological tissue with sound velocity greater than (or less than) water, the greater the sound velocity, the greater the relative shift distance difference of focal position.
As the electric power and frequency of ultrasonic transducer increased, the focus of HIFU moved toward and away from the transducer, respectively. For multi-layer biological tissue, the focus shift direction depended on the sound velocity relationship between biological tissue and water

Accurate temperature and thermal lesion prediction is very important for high-intensity focused ultrasound (HIFU) in the treatment of tumors. The traditional focal temperature and thermal lesion prediction methods usually use constant acoustic and thermal parameters. However, HIFU irradiation of biological tissue will cause its temperature rise and change the tissue characteristic parameters, which will affect the sound field and temperature field. The constant acoustic and thermal parameters, dynamic acoustic and thermal parameters, constant acoustic and dynamic thermal parameters, dynamic acoustic and constant thermal parameters were used for simulation by Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation and Pennes biological heat transfer equation (PBHTE), and their effects and differences on the focal temperature and thermal lesion of biological tissue were compared and analyzed. The focal temperature predicted by constant acoustic parameters was less than that predicted by dynamic acoustic parameters, and the thermal lesion area predicted by constant acoustic parameters was also smaller than that predicted by dynamic acoustic parameters. On the premise of using dynamic acoustic parameters, the focal temperature predicted by dynamic thermal parameters was higher than that predicted by constant thermal parameters. When the acoustic parameters remained constant, the focal temperature predicted by dynamic thermal parameters was lower than that predicted by constant thermal parameters, but their predicted thermal lesion areas were almost the same. The temperature-dependent acoustic and thermal parameters should be considered when predicting focal temperature and thermal lesion of biological tissue, so that doctors can use the appropriate thermal dose in the surgical treatment of HIFU.

The large aperture concave spherical focused ultrasonic transducer has stronger acoustic focusing effect and can obtain good temperature rise effect. The purpose of this study was to explore the effect of different frequency, duty cycle and inner radius parameters on temperature rise of multi-layer biological tissue.
The simulation model of high-intensity focused ultrasound (HIFU) irradiated multi-layer biological tissue was constructed. By changing the irradiation frequency, duty cycle and inner radius of large aperture concave spherical focused ultrasonic transducer, the sound field and temperature field of multi-layer biological tissue were simulated and calculated by using Westervelt nonlinear acoustic wave equation and Pennes biological heat conduction equation, respectively.
The intensity of sound field increased with the increase of frequency, while it decreased with the increase of inner radius, but the duty cycle almost had no effect on the intensity of sound field. The focal temperature increased with the increase of frequency and duty cycle, but decreased with the increase of inner radius.
By selecting appropriate parameters of transducer, the optimum temperature rise in the target area of biological tissue can be obtained by using a large aperture concave spherical focused ultrasonic transducer.

High-intensity Focused Ultrasound (HIFU) treatment is a non-invasive technology. The purpose of this study was to explore the effects of different treatment depths, tissue types and treatment interval on biological tissue thermal lesions under continuous and intermittent treatment modes. A simulation model of biological tissue irradiated by HIFU was established by finite difference time domain (FDTD). The thermal lesion of biological tissue irradiated by HIFU was calculated using the spherical beam equation (SBE) and Pennes biological heat transfer equation (PBHTE). Parameters such as treatment depth, tissue type, and treatment interval were varied to explore their effects on the thermal lesion to biological tissues in both continuous and intermittent treatment modes. For the same biological tissue or treatment depth, with the increase of HIFU irradiation time, the focal temperature under continuous treatment was higher than that under intermittent treatment, and the thermal lesion area under continuous treatment was greater than that under intermittent treatment. Whether continuous or intermittent treatment, with the increase of treatment depth, the temperature rise rate of deep tissue was slower than that of superficial tissue, and the thermal lesion area decreased gradually. Moreover, in the intermittent treatment mode with a long single treatment time and short treatment interval, the focal temperature rase quickly and the thermal lesion area was large. For the same tissue type, treatment depth, or any treatment interval, the focal temperature and thermal lesion area corresponding to continuous treatment were greater than those corresponding to intermittent treatment.

As a non-invasive method of tumor hyperthermia, high intensity focused ultrasound (HIFU) has been widely used in the treatment of various solid tumors in recent years. The purpose of this study was to investigate the effect of HIFU combined with ethanol on biological tissue lesions.
Firstly, 0.5ml 95% ethanol was injected into the porcine liver tissue in vitro, then HIFU was used to irradiate the porcine liver. The B-mode ultrasound and needle hydrophone were used to monitor the cavitation. A thermocouple was also used to measure the real-time focal temperature. The ultrasonic signal scattered at the focal point of HIFU irradiation was collected by the fiber hydrophone, and the attenuation coefficient was calculated. Finally, the attenuation coefficient was input into the Khokhlov-Zabolotskaya-Kuznetov (KZK) equation and combined with the Pennes equation. The thermal lesion of the porcine liver was simulated by MATLAB software.
The length of the long axis of the lesion area simulated by the attenuation coefficient of cavitation was closer to the length of the long axis of the actual measured lesion area with ethanol injection, but the length of the short axis of the simulated lesion area was smaller than that of the measured lesion area. However, the length of the long axis of the lesion area simulated by the attenuation coefficient of cavitation was larger than the length of the long axis of the lesion area simulated by the attenuation coefficient of liver at room temperature. The same results were obtained for the length of short axis.
HIFU combined with ethanol can produce larger lesions to biological tissues and improve the therapeutic effect.