Kaupinmäki, Jaakko Aku Santeri; (2023) Ultrasound tomography using pyroelectric and piezoelectric sensors. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Acoustic absorption is one of several quantities which can differentiate healthy breast tissue from cancerous tissue. In order to accurately quantify the acoustic absorption, the sensor system must be able to accurately distinguish acoustic power loss due to absorption from other modes of attenuation. Traditional piezoelectric sensors are susceptible to phase-cancellation artifacts due to their directional signal response, and thus pyroelectric ultrasound sensors, which have a much flatter directional response, have been suggested as an alternate measurement device for improved absorption reconstructions in ultrasound tomography (UST). In this thesis we investigate the use of pyroelectric phase-insensitive sensors in UST — the thesis is divided into two parts. In the first part we present a model for a pyroelectric ultrasound sensor and investigate its directional response and sensitivity properties. The model’s time-series response and directional response are compared to real-world measurements to confirm accuracy. The second part focuses on the inverse problem aspect of ultrasound tomography, where we consider various reconstruction methods and sensor geometries to determine which situations can benefit from phase-insensitive data for acoustic absorption reconstruction. Reconstructions for both phase-insensitive as well as phase-sensitive sensors are analysed, with future work considerations for combined sensor systems.

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