Improvement of high-voltage staircase drive circuit waveform for high-intensity therapeutic ultrasound

Abstract

Recently, in the treatment of diseases such as cancer, noninvasive or low-invasive modality, such as high-intensity focused ultrasound (HIFU), has been put into practice as an alternative to open surgery. HIFU induces thermal ablation of the target tissue to be treated. To improve the efficiency of HIFU, we have proposed a “triggered-HIFU” technique, which uses the combination of a short-duration, high-voltage transmission and a long-duration, medium-voltage transmission. In this method, the transmission device must endure high peak voltage for the former and the high time-average power for the latter. The triggered-HIFU sequence requires electronic scanning of the HIFU focus to maximize its thermal efficiency. Therefore, the transmission device must drive an array transducer with the number of elements on the order of a hundred or more, which requires that each part of the device that drives each element must be compact. The purpose of this work is to propose and construct such a transmission device by improving the staircase drive circuit, which we previously proposed. The main point of improvement is that both N and P MOSFETs are provided for each staircase voltage level instead of only one of them. Compared with the previous ultrasonic transmission circuit, high-voltage spikes were significantly reduced, the power consumption was decreased by 26.7%, and the transmission circuit temperature rise was decreased by 14.5 °C in the triggered-HIFU heating mode.

HIFU Drive System Miniaturization Using Harmonic Reduced Pulsewidth Modulation

“…These harmonics can be within the bandwidth of HIFU transducers which are highly resonant devices that produce acoustic energy at their harmonics [44], [45]. These harmonics could cause unwanted effects [46], such as disruption of the focal region [41], heating of the transducer [47], and the generation of grating lobes [48].…”

“…Alternatively, additional levels can be introduced to the circuit to implement staircase converters. This naturally disrupts the generation of harmonics [52] and several authors have demonstrated harmonic reduction this way at ever increasing frequencies and powers [47], [53]. However, the constraints placed on the waveform with these techniques mean that each array element would require its own adjustable supply to achieve apodisation which is costly and cumbersome.…”

Development of temperature controller-integrated portable HIFU driver for thermal coagulation

“…The function generator utilized a CMOS synthesizer (AD9851, Analog Device, Norwood, MA) to produce pulse-width modulated (PWM) signals with duty cycles ranging from 20 to 80% at 2 MHz frequency. The high-voltage ultrasonic signal transmission, with a PWM voltage amplitude up to 50 V, was achieved using four high-speed dual MOSFET drivers (MD1213, Microchip Technology, Chandler, AZ) and N- and P-channel MOSFETs (TC6320, Microchip Technology, Chandler, AZ) [23–25]. A maximum amplitude of 50 V was selected in the present study to achieve the target temperature (around 60 °C) with minimum driver size.…”

Multifunctional pulse generator for high-intensity focused ultrasound system

“…Especially, in a high-intensity focused ultrasound (HIFU) system with multi-channel focusing, to realize a compact and highly reliable ultrasonic transmission circuit is a major challenge. We have already proposed a four-stage high-voltage staircase HIFU transmission circuit 1) , which has a pair of P-channel and N-channel MOSFETs for each power supply stage, and reported its effectiveness. The proposed method could reduce the excessive spike noise caused by the switching operation of the MOSFET, without depending on the load characteristics.…”