A synthetic aperture ultrasonic imaging method: Simulation

The synthetic aperture imaging method under study uses holographic approach to produce a two-dimensional image comparable to a B-scan. Instead of focused ultrasound a relatively wide beam with sector shaped beamprofile is applied in object insonification. Image is focused numerically in a microcomputer. Since reconstruction is performed in the spatial frequency domain the FFT-algorithms can be employed efficiently both in the wavefront backpropagation and in the near-field curvature compensation. Therefore the proposed method is fast enough to be applied in a real-time imaging system. In simulation a well-known tissue model with a continuous distribution of point scatterers combined with a simulated phantom is used in order to study the dynamical range and resolution of the imaging method. In medical diagnosis the poor dynamical range and resolution have been a serious limitation of the synthetic aperture imaging methods resulting, for example, in poor detection of cysts. This study indicates that with the present imaging system good spatial and contrast resolution can be achieved througout the image. The errors in phase angle detection, however, have a strong effect on the image quality. Therefore, a compromise has to be made between the spatial resolution (beam width) and the sensitivity to phase angle errors.