Phase aberration correction applied to annular array transducers when focusing through a stratified medium

It has previously been presented that under some assumptions phase aberrations in medical ultrasound can be corrected with linear array transducers. In this presentation it is shown that a similar technique can be applied to annular array transducers with spherical dome. MR-images of two patients, producing ultrasound images with high and low quality, are used to make models. The tissue of the two patients, including probe fluid and cap, are modelled as layers with smooth boundaries. Calculations using ray tracing show small/large phase aberrations for the patient producing ultrasound images with high/low quality. It is noticed that variation in geometry give larger phase aberrations than variations in layer thickness. The main effect is focus displacement in depth. Simulations show that the algorithm for electronic focusing does not work well if focus is displaced in depth. Different solutions to the problem are suggested: 1) Tuning of parameters used in the algorithm for electronic focusing. 2) Adjustment of the geometry of the probe cap