In ultrasound imaging, the time delay used to focus the channel data into a pixel is conventionally calculated as the transit delay (time for the pulse to reach the imaged pixel) plus the receive delay (time for reflection to reach the probe elements). This assumes that the pulse insonifies the medium once, and works well because the waves usually dissipate before multiple reflections become an issue.
If, however, a reflecting surface (e.g., a smooth steel plate) is placed somewhere in the medium, the transmit pulse will be reflected back in such a way that the transmitting probe is mirrored in the plate, and the mirror image is called an image source. This concept is used extensively in both acoustics and electromagnetism to match the boundary conditions on the reflector:
In this project, we aim to explore to which extent the use of known reflecting surfaces can be used to improve the image quality by extracting multiple transmit delays for different image sources. The use of multiple transmit delays have previously been reported in the literature in a different setting to have improved the image [1].
In the project, you will do the following:
- Design and perform experiments to record data with and without image sources.
- Implement beamforming algorithms to extract images from the image source.
- Assess what opportunities and limitations lie in using this technique (e.g., how many reflecting surfaces can be used, SNR considerations, "contamination" from guided modes).
- Read the literature; what resolution gains can be expected (k-space), geometrical acoustics, and other uses of image sources in acoustics.
- See if one can determine/calibrate the position of reflecting surfaces where they are not exactly known.
Qualifications:
- Excellent MATLAB programming skills (Object oriented MATLAB)
- Signal Processing (e.g., IN3015/4015, IN3190/4190, IN5450, IN5340)
- An interest for physics/acoustics
Literature:
[1] "Ultrasound Pixel-Based Beamforming With Phase Alignments of Focused Beams", N.Q. Nguyen, R.W. Prager (2017)