Student: Aline Buat
1st Supervisor: Christopher Rowlands, Imperial College London
2nd Supervisor: Mengxing Tang, Imperial College London
Clinical Supervisor: Adrian Lim, Consultant Radiologist, Imperial College London
Aim of the PhD Project:
- Investigate a new method for mapping ultrasound waves using light
- Build a system to perform stand-off high-resolution ultrasound detection
- Demonstrate imaging of a live subject based on this newly-developed technology
Project Description / Background:
Any science fiction fan knows the power of high-resolution whole-body imaging; a patient on a hospital bed is probed by unseen sensors, producing a virtual reconstruction of their body, which hovers over the bed, being manipulated, investigated and examined by the doctor. While existing whole-body imaging methods like CT, MRI, PET and SPECT can get some way towards this ideal, we still lack a truly whole-body imaging technique that is fast, high-resolution, non-invasive and safe for long-term monitoring.
Ultrasound imaging is the best technology for reaching this whole-body imaging ideal; it is non-invasive, can resolve features as small as 100µm, and has extremely high data throughput. Nevertheless, it has traditionally been limited by the lack of high-resolution acoustic transmitters and receivers. Unlike cameras, which can record data with hundreds of megapixels of resolution, ultrasound transducers are limited to a few thousand pixels at most, and usually fewer than one hundred. Furthermore, ultrasound transducers must remain in contact with the patient, since ultrasound doesn’t travel through air efficiently. The dream of creating a whole-body scanner requires a means of bridging this air-gap, and with a megapixel-resolution transducer array.
Fortunately for us, light is transmitted through air efficiently, and can be used to image acoustic waves. Furthermore, light can be patterned with megapixel resolution, sufficient to image a large fraction of an adult human body quickly, provided there is a way to turn the laser signal into an acoustic one and back again. In this project, a new type of approach will be developed, based on imaging the light in an optical fiber. This light changes when a sound wave passes, which is what allows us to detect the optical signal. An image of the proposed instrument in operation can be seen in the Figure.
The student will be part of a large ongoing collaboration to develop high-resolution optical ultrasound systems. They will be responsible for developing a fast ultrasound detector that can be scaled to large numbers of pixels (based on a silicon photomultiplier array and digital capture card) and using it to prototype a system that can image an acoustic field. The project will then progress to creating a small example instrument which can detect ultrasound at a range of several meters, with an initial resolution of 4×4 pixels, but which can be scaled arbitrarily just by adding more detectors.
This project’s ideal student will have a background in physics, engineering or materials, and will be a self-motivated and innovative problem-solver. They will be comfortable with biomedical collaboration, and keen to learn from the breadth of supervisory experience.
Illustration of the principle of evanescent wave acoustic sensing. An LED is coupled into a slab waveguide, creating an evanescent wave very near the surface of the waveguide – confined to within a few hundred nanometers for all practical purposes. The light in the waveguide scatters off nanoparticles near the surface; the scattering increases exponentially with reducing distance to the surface, making the scattering signal highly sensitive to nanoparticle position. As the particles are driven in an acoustic field they move, and this motion can be detected by the camera as a rapid change in the intensity of scattered light.