A Prototype MR Compatible Positioning Device for Guiding a Focused Ultrasound System for the Treatment of Abdominal and Thyroid Cancer

A Prototype MR Compatible Positioning Device for Guiding a Focused Ultrasound System for the Treatment of Abdominal and Thyroid Cancer

Nicos Mylonas (Frederick University Cyprus, Limassol, Cyprus & City University, London, UK) and Christakis Damianou (Cyprus University of Technology, Limassol, Cyprus)
DOI: 10.4018/ijmstr.2013100105
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A prototype magnetic resonance imaging (MRI)-compatible positioning device that navigates a high intensity focused ultrasound (HIFU) transducer is presented. The intended application is to treat eventually tumours in the abdominal and thyroid. The positioning device has 3 user-controlled stages that allow access to various targets using a top to bottom coupling approach. Materials and Methods. The positioning device incorporates only MRI compatible materials such as piezoelectric motors, ABS plastic, brass screws, and brass rack and pinion. Results The MRI compatibility and the accuracy of the system were successfully demonstrated in an open MRI scanner. The robot has the ability to accurately move the transducer thus creating discrete and overlapping lesions in rabbit liver in vivo. This simple, cost effective positioning device can be placed mostly on the structure of an open MRI gantry. Due to the size of this positioning device, the proposed prototype in its current form cannot be used in any closed MRI system. The novelty of this positioning device is the MRI compatible design and its intended application which is the treatment of tumors in the abdominal area using focused ultrasound. This system can be utilized in the future to treat patients with cancer in the liver, kidney, pancreas and thyroid provided that the accuracy of the positioning device is greatly improved.
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1. Introduction

High intensity focused ultrasound (HIFU) has the potential to induce thermal changes in tissue and therefore it is used extensively for medical applications (Stewart et al 2006). Nowadays HIFU is utilized to selectively heat biological tissues for oncological applications with minimal invasiveness by using magnetic resonance imaging (MRI) to provide, to the operator performing the procedure, images of a region within the subject being heated.

HIFU was explored in almost every tissue that is accessible by ultrasound. The following literature represents some examples of some applications explored: eye ablation for the treatment of Glaukoma (Lizzi, 1978), prostate ablation using ultrasound guidance (Chapelon, 1992), liver ablation for the intention to treat cancer (Haar, 1989), brain ablation for the intention to treat cancer (Lele, 1962; Vykhodtseva, 1994) and kidney ablation for oncological applications (Linke, 1973; Hynynen, 1995; Bihrle, 1994).

In commercial systems (for example, (Chapelon, 1992; Bihrle, 1994; Hynynen, 2001) HIFU is either guided by ultrasound or MRI. Ultrasonic imaging is the simplest and most inexpensive method to guide HIFU, however MRI offers superior contrast than ultrasound, having the only disadvantage that is more expensive.

In order to treat large areas by creating tissue necrosis the HIFU transducer which has focal beam of few mms should be moved to create overlapping lesions. The positioning device is responsible for this motion and should operate inside the MRI scanner. The use of the positioning device inside MRI scanner may interfere with the RF field and as a result the quality of the images captured could be harmed. Therefore all the components must be non-magnetic materials. Generally the positioning device has to be small to fit the gantry MRI scanners. An MRI compatible robotic system refers to a system that is not hazardous in any way and neither generates any interference to the MRI scanner nor affected by the strong electromagnetic field of the MRI scanner (Gassert, 2008).

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