A study of localized waves and their application to medical ultrasound imaging

• Main Author: Bie, Linda
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/5121

A study of localized waves and their potential for application to medical ultrasound imaging is conducted using analytical and numerical simulation techniques. Simulated focused ultrasound fields representing approximations to the focus wave modes and modified power spectrum pulses are generated from synthesized, two-dimensional arrays. The results in terms of attenuation and diffraction are compared with previously published data for continuous waves and X waves, which are another localized wave solution. Through the course of simulations different array sizes and source element densities are examined to determine the consequent effects on the generated localized waves. Array size determines the distance to which the wave will propagate while source element density affects the smoothness or amount of error in the reconstruction. In addition, the effect of ‘folding’ is examined and found to reduce attenuation but to have little effect on beam waist width within the depth of interest for medical ultrasound imaging (up to O.4m). Introducing folding terms increases substantially the complexity and magnitude of the required source waveforms. Pure focus wave mode beams are found to differ insignificantly from the modified power spectrum pulse when generated by a finite array. Simulations show that for a square source array as small as nine by nine elements with element spacing 5.5mm, the lateral beam half-width (at the 1/e point) at 30cm depth penetration in water is only 10mm, and the depth of field, defined as the distance where the wave falls to half its orig- inal magnitude, is 405mm. This is a substantial improvement over continuous waves—on the order of 23% for the beam half-width—and is comparable to results reported for X waves launched from a circular array with the same area.