Abstract

A phased array ultrasonic imaging system performs a scan in which beamforming time delay errors due to nonuniformity in ultrasound speed within the transmission medium are corrected by estimating and correcting phase aberrations in accordance with the maximum likelihood theory. The system employs a multiple-channel transmitter and receiver, and estimates phase values, not phase difference values, thereby eliminating any need to perform an integration to produce the phase aberration profile. The method can be implemented in real-time, allowing correct data to flow out of the circuit which at the same time can be receiving new input data. Delays can be added to allow for phase aberration correction of past measurements. The method allows tracking, to some extent, of variations that may occur in the phase aberrations. Depending on the number of channels that are simultaneously considered, different closed loop circuits can be employed. A one-dimensional closed loop circuit, for example, estimates the phase aberration affecting one single channel, while a two dimensional closed loop circuit jointly estimates the phase aberrations affecting two of the channels.

Other References

• Flax et al., "Phase-Aberration Correction Using Signals from Point Reflectors and Diffuse Scatters: Basis Principles", IEEE Trans. on Ultrasonics, Ferroelectrics and Frequency Control, vol. 35, No. 6, Nov. 1988, pp.758-76