Gélat, P N; ter Haar, G*; Saffari, N* (2014) A comparison of methods for focusing the field of a HIFU array transducer through human ribs. Phys. Med. Biol., 59 (12). pp. 3139-3171.

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Abstract

An approach which predicts the scattering of the acoustic field of a multi-element high-intensity focused ultrasound (HIFU) transducer by human ribs, the topology of which was obtained from CT scan data, has been developed, implemented and validated. It is based on the boundary element method and features a complex surface impedance condition at the surface of the ribs. A reformulation of the boundary element equations as a constrained optimization problem was carried out to solve the inverse problem of determining the complex surface normal velocities of a multi-element HIFU array that best fitted a required acoustic pressure distribution in a least-squares sense. This was done whilst ensuring that an acoustic dose rate parameter at the surface of the ribs was kept below a specified threshold. The methodology was tested at an excitation frequency of 1 MHz on a spherical section multi-element array in the presence of human and idealised ribs. It was compared for six transducer array-rib topologies against other methods of focusing through the ribs, including spherical focusing, binarized apodization based on geometric ray tracing, phase conjugation and the DORT (decomposition of the time reversal operator) method. The constrained optimization approach offers greater potential than the other focusing methods in terms of maximising the ratio of acoustic pressure magnitudes at the focus to those on the surface of the ribs whilst taking full advantage of the dynamic range of the phased array.

Item Type:	Article
Keywords:	HIFU, ribs, trans-costal, boundary element methods, optimization, acoustic dose rate
Subjects:	Acoustics Acoustics > Ultrasound
Identification number/DOI:	10.1088/0031-9155/59/12/3139
Last Modified:	02 Feb 2018 13:13
URI:	http://eprintspublications.npl.co.uk/id/eprint/6213

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