Series: Acoustics Research and Technology
BISAC: MED098000

High intensity focused ultrasound (HIFU) is an increasingly popular physical tool with a wide range of applications in medicine. One of the drivers of this advancement is the development of ultrasound phased arrays, which, although more complex and costly than the traditional single focused bowl transducers used in earlier studies, are capable of electronically controlled dynamic focusing. Such systems not only steer a single focus without movement of the array itself, but can also generate several foci simultaneously and create focal regions with complex configurations. This book addresses the design, research and development, and medical applications of both relatively small HIFU arrays that can be inserted into body cavities (so called linear arrays) and larger two dimensional arrays for extracorporeal use. A key safety issue in the design of these arrays is to ensure that only targeted tissue is exposed to high levels of acoustic intensity and in this regard, this book highlights the advantages of designs involving spatial randomization of array elements to reduce the level of potentially dangerous grating lobes. In particular, phased arrays with a random distribution of elements are discussed and compared to regular arrays, and methods for calculating ultrasound fields generated by different phased arrays including the generation of multiple simultaneous foci and focal regions with complex geometrical shapes are presented.

A detailed discussion of the influence of the dimensions, number, and shape of individual elements, errors in phase setting at the elements, and the frequency modulation of the signal on the quality of the intensity distributions produced by random arrays is included. As well as addressing technical issues of ultrasound phased arrays, current and potential medical applications are discussed. Much clinical experience of HIFU has been gained in the treatment of prostate diseases, including prostate cancer, and uterine fibroids. The ability of phased arrays to sonicate through the skull and create a focal volume within the brain without excessive heating of the skull opens up the possibilities of non-invasive treatments of not only brain tumours but also neurological disorders, intracerebral haemorrhrage, and drug delivery across the blood-brain barrier whilst focusing acoustic energy at targets distal to the ribs provides an opportunity for HIFU ablation of cardiac tissue. Exciting new developments such as stimulation of neural structures leading to the development of tactile displays or a prosthesis of a degenerating retina are also included.