National Physical Laboratory

Ultrasonic fields and dosimetry

Determining the acoustic output of medical devices is essential for manufacturers to demonstrate standards compliance, but is also important in prototype evaluation and type testing. NPL provides measurement services and facilities to meet this need, using a unique range of reference hydrophones.

With ultrasound scanners becoming more complex, there is a growing need for simpler methods that may be used to quantify acoustic output. One such approach, which is now established in the International Electrotechnical Commission (IEC) Standards framework, is to use tissue-like Thermal Test Objects. These can assess the bulk and surface heating produced by medical ultrasound devices, and are produced by NPL. Two key indicators of potential hazards posed by medical devices are Mechanical and Thermal Indices (MI and TI), and simple, economical QA test methods to determine these quantities will be developed and trialled in collaboration with UK hospitals.

The emerging application area of HIFU is the subject of ongoing study at NPL, in particular through developing a computational model to predict the temperature distribution in tissue, and measuring in vitro thermal effects (using thermocouple arrays) which arise from application of a HIFU field. The destructive nature of HIFU is such that hydrophones are not appropriate for use at clinical output levels, and so for the first time at NPL, optical measurement methods (fibre optic hydrophones and a scanning laser vibrometer) will be investigated.

The use of ultrasonic contrast agents to enhance image quality is established worldwide, and existing technology is being extended to encompass localised drug delivery through deployment of nanoparticles. The potential role of ultrasound in characterising these will be the subject of a feasibility study.

Through BSI, IEC and emerging groups such as ISTU, NPL contributes to the maintenance of existing standards and development of new measurement approaches, and such representations will continue in the research programme.

Last Updated: 24 Aug 2016
Created: 29 May 2007

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