An ultrasound transducer usually has an acoustic lens on top of its transmitting elements. This acoustic lens helps focus the acoustic energy in the imaging plane.
For the acoustic lens to be able to focus the acoustic waves it needs to have a propagation speed different from the propagation speed in the tissue. The propagation speed in the acoustic lens is usually around as oposed to in soft tissue. Although the effect of the lens helps prevent power loss and noise from outside the imaging plane, it also introduces a change in travel time inside the imaging plane. This change in travel time will result in reduced image quality if not accounted for.
The image below shows how the shortest path from a transducer element to some target pixel changes with different propagations speeds in the lens.
- If the speed in the lens is very low, the smallest travel time will be achieved by exiting the lens as soon as possible and the traveling through the medium.
- If the speed in the lens is very high, the smallest travel time will be achieved by traveling the largest distance within the lens.
- If the speed in the lens is equal to , the smallest travel time will be achieved by traveling in a straight line towards the pixel.
The code used to generate these plots is available via this link:
