A Study Of The Acoustic Profile Of A Segmented Clinical Focused Ultrasound Transducer

The use of focused ultrasound as a minimally invasive treatment for tumours is expanding in the UK. The main target organs are the liver and kidneys. Single element and phased array transducers may be used clinically. In this paper some of the possibilities available with a linear array transducer in which all elements are driven in phase are investigated. An acoustic field program based on the optical Fresnel-Kirchhoff diffraction theory has been used to model a segmented transducer. This device is a 15 cm focal length spherical bowl with an aperture diameter of 11 cm and a 5 cm diameter central hole in which may be placed an ultrasound imaging probe. It operates at 1.7 MHz and consists of ten equal area parallel strips. The aim of this study was to investigate how, by removing the contribution of individual segments to the field, a useful beam profile can be achieved using a combination of different active segments. An example of its possible use is to spare the ribs from potentially harmful intensities when treating liver tumours. Simulations of the acoustic field at the focus and in the area of the beam where ribs might be present were performed. The profile of the beam is compared for a number of combinations of active segments. It is shown that it is possible, by appropriate switching of the segments, to significantly reduce the intensity at the rib surface.