The feasibility of a new full bridge high intensity focused ultrasound(HIFU) amplifier system with harmonic cancellation is evaluated in this study. Harmonic cancellation technique is applied to these power amplifiers, which can eliminate the 3rd harmonic and all even harmonics. Since this technique requires two channels of phase signal to control one channel of power amplifier, the signal generator is required to double its output. The transducer array proposed in this study has 100 elements. So we choose an FPGA chip to generate 200 driving signals, and each channel has a phase resolution of 2ns, less than 1°. The phase signal from the FPGA meets the requirement of driving the power amplifiers. The output waveform of one channel of power amplifier(voltage across the transducer) is evaluated, and shows fewer harmonic components.
Exploring the distribution of focused ultrasound field attracts more and more investigators' attention.Making use of the heat property of focused ultrasound, we can measure the distribution of temperature to calculate the distribution of focused ultrasound field. During the exploration, we found that the temperature rise rate had a liner relation to sound intensity. So we conducted experiments and got the infrared images with noise. In order to obtain an accurate distribution of focused ultrasound field, it's necessary to find out a solution to get rid of the noise in infrared images. In traditional, we use hydrophone to explore the distribution of focused ultrasound field even in nonlinear area. So the result got by hydrophone was considered as standard. So the investigation was focused on the experimental validation of a filter which was the most suitable way for image process of infrared chart. So the ability of the filter should be that removing most noise and the distribution of temperature rise rate is unchanged. Six kinds of filters were used to deal with the raw data to obtain related information, from the results, we drew a conclusion that gauss filter was superior to the others filter, and a non- distortion distribution of focused ultrasound field would be get by the use of Gaussian filter.
Ultrasound hyperthermia is one of the most important methods in tumor treatment and characterized by non-invasiveness. Magnetic resonance imaging(MRI)-based temperature mapping techniques are safe compared with invasive methods and have been applied to detect temperature changes for a variety of applications. Among these techniques, the proton resonance frequency(PRF) method is relatively advanced. With a temperature measuring experiment, the effectiveness of PRF method has been proved, because the outcome temperature curve and the real temperature curve fit well. After that, an experiment has been conducted on tumors inside rabbit legs and the result indicates that this system is able to performance hyperthermia at targets based on PRF method in temperature mapping.
High-intensity focused ultrasound (HIFU) has attracted increasing interests as a promising noninvasive modality for the treatment of deep tumors in the thoracic and abdominal cavity.A 90-element HIFU spherical phased array applicator operated at 1 MHz has been developed for deep tissue ablation.The spherical array with a 5 cm wide central hole has a 21 cm diameter and an 18 cm radius of curvature.Annular element distribution with unequal element spacing is used to reduce the number of elements.The array is constructed with piezoelectric lead zirconate titanate (PZT-8) circular elements that are 1.4 cm in diameter and have a wall with thickness of 0.2 cm.The array offers an effective ablating depth of at least 8 cm in the tissue for both simulations and ex vivo experiments.The simulations demonstrate that the developed array can steer the focus with good quality of intensity distributions up to 6 mm off center over ranges from 17 to 21 cm when the water depth is set at 11 cm.We also present the beam focusing capability in deep tissue through a series of ex vivo experiments by measuring discoloration areas after sonications.These results indicate that the developed array is ideal for the ablation of deep-seated tissue.
Under some circumstances surgical resection is feasible in a low percentage for the treatment of deep tumors. Nevertheless, high-intensity focused ultrasound （HIFU） is beginning to offer a potential noninvasive alternative to conventional therapies for the treatment of deep tumors. In our previous study, a large scale spherical HIFU-phased array was developed to ablate deep tumors. In the current study, taking into account the required focal depth and maximum acoustic power output, 90 identical circular PZT-8 elements （diameter=1.4 cm and frequency=l MHz） were mounted on a spherical shell with a radius of curvature of 18 cm and a diameter of 21 cm. With the developed array, computer simulations and ex vivo experiments were carried out. The simulation results theoretically demonstrate the ability of the array to focus and steer in the specified volume （a 2 cm×2 cm×3 cm volume） at the focal depth of 15 to 18 cm. Ex vivo experiment results also verify the capability of the developed array to ablate deep target tissue by either moving single focal point or generating multiple foci simultaneously.
