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The optimisation of acoustic fields for ablative therapies of tumours in the upper abdomen.

Gélat, P N; ter Haar, G*; Saffari, N* (2012) The optimisation of acoustic fields for ablative therapies of tumours in the upper abdomen. Phys. Med. Biol., 57 (24). p. 8471.

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Abstract

High intensity focused ultrasound (HIFU) enables highly localised, non-invasive tissue ablation and its efficacy has been demonstrated in the treatment of a range of cancers, including those of the kidney, prostate and breast. HIFU offers the ability to treat deep-seated tumours locally, and potentially bears fewer side effects than more invasive treatment modalities such as resection, chemotherapy and ionising radiation. There remains however a number of significant challenges which currently hinder its widespread clinical application. One of these challenges is the need to transmit sufficient energy through the ribcage to ablate tissue at the required foci whilst minimising the formation of side lobes and sparing healthy tissue. Ribs both absorb and reflect ultrasound strongly. This sometimes results in overheating of bone and overlying tissue during treatment, leading to skin burns. Successful treatment of a patient with tumours in the upper abdomen therefore requires a thorough understanding of the way acoustic and thermal energy is deposited. Previously, a boundary element approach based on a Generalised Minimal Residual (GMRES) implementation of the Burton-Miller formulation was developed to predict the field of a multi-element HIFU array scattered by human ribs, the topology of which was obtained from CT scan data (Gélat et al, 2011). The present paper describes the reformulation of the boundary element equations as a least-squares minimisation problem with non-linear constraints. The methodology has subsequently been tested at an excitation frequency of 1 MHz on a spherical multi-element array in the presence of ribs. A single array-rib geometry was investigated on which a 50% reduction in the maximum acoustic pressure magnitude on the surface of the ribs was achieved with only a 4% reduction in the peak focal pressure compared to the spherical focusing case. This method was then compared with a binarised apodisation approach based on ray tracing and against the decomposition of the time-reversal operator (DORT). In both cases, the constrained optimisation provided a superior ratio of focal peak pressure to maximum pressure magnitude on the surface of the ribs. Gélat P, ter Haar G and Saffari N 2011 Modelling of the acoustic field of a multi-element HIFU array scattered by human ribs Phys. Med. Biol. 56 5553.

Item Type: Article
Keywords: HIFU, ribs, trans-costal, boundary element methods, multi-element array
Subjects: Acoustics
Acoustics > Ultrasound
Identification number/DOI: 10.1088/0031-9155/57/24/8471
Last Modified: 02 Feb 2018 13:14
URI: http://eprintspublications.npl.co.uk/id/eprint/5671

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