Analysis and measurement of spectral characteristics and spatial resolution of high frequency ultrasound imaging systems

High frequency ultrasound (HFUS) in the range above 20 MHz is utilized for high resolution skin and eye imaging. With increasing frequencies, the attenuation of water, which is used as propagation medium between mechanically scanned single element transducers and tissue, becomes increasingly significant. The low pass characteristics of water result in a reduction of the system´s center frequency and bandwidth, and thus in a loss of spatial resolution. In this paper, spectral characteristics and spatial resolution of HFUS imaging systems are analyzed. taking the frequency dependent attenuation of water into account. Analytical predictions are compared with measurement results. Spectral analyses, performed on phantoms as well as B-mode images of phantom and in vivo measurements, are presented.