A miniature HIFU excitation scheme to eliminate switching-induced grating lobes and nullify hard tissue attenuation

Abstract

Abstract-Phased array transducers are increasingly prevalent in a therapeutic contex as they facilitate precise control of the beam intensity and focus. To produce enough acoustic energy for ablation, large and costly amplifiers are required. Miniaturised switched circuits provide an alternative that is both more cost effective and more efficient. However, the high Q factor and curved geometry of a therapeutic transducer lends itself to grating lobes that deposit energy in undesirable areas when driven with switched circuitry. In this work, harmonic reduction pulse with modulation (HRPWM) is applied to a simulation of a therapeutic array. An array was simulated along with a skull that varied in attenuation. A number of switching schemes were tested and where possible, their amplitude was adjusted to reduce pressure variation in the acoustic field after propagation through the skull. Of the switched schemes tested, HRPWM performed best; reducing harmonically induced grating lobes by 12 dB and limiting pressure field variance to 0.1 dB which increases intensity at the focal point and makes therapy more efficient.

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].…”

HIFU Power Monitoring Using Combined Instantaneous Current and Voltage Measurement

“…Switched circuits, which are highly desirable alternatives to linear amplifiers, due to their improved efficiency and reduced size [19], [42], conduce harmonic distortion. Even minor harmonics generated by these circuits, greatly influence the voltage signal due to the frequency-varying reactance of the source and load impedances.…”

“…The technique is highly localised, and it can be used to non-invasivley treat an area while sparing surrounding tissue. The main application area of HIFU is the treatment of soft tissue tumours [8], [9] in liver [10], kidney [11], prostate [12], [13], breast [14] and in the brain [15]- [19].…”