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Acoustic resolution photoacoustic flowmetry

Bücking, Thore Mainart; (2019) Acoustic resolution photoacoustic flowmetry. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Acoustic Resolution PhotoAcoustic Flowmetry (AR-PAF) is a young and promising flow speed imaging modality based on the photoacoustic effect. The photoacoustic effect is the generation of ultrasound upon absorption of light. Utilising this effect for imaging of vasculature allows for optical contrast while maintaining the deep tissue imaging capabilities inherent to medical ultrasound. Owing to the excellent optical contrast of blood, it is thought that AR-PAF can achieve non-invasive imaging of spatially resolved flow maps. In order to characterise the capabilities of AR-PAF with regards to physiological blood flow phenomena (RBC aggregation, RBC heterogeneity and flow unsteadiness), a dual-mode imaging setup was developed, capable of acquiring photoacoustic signals concurrently with optical microscopy images. This involved development of novel microfluidic channels with unique imaging characteristics to allow both acoustic interrogation for photoacoustic imaging as well as optical microscopy imaging using Particle Image Velocimetry (PIV). This allowed both blood microstructure and flow velocity to be resolved simultaneously. AR-PAF and PIV were simultaneously performed under the challenging conditions of fast data acquisition (10 frames per measurement), highlighting the possibility of real- time measurements. Novel processing methods were developed to extract spatially resolved velocity information from the measured photoacoustic signals. The effects of increasing displacement and increasing velocity were analysed independently in order to identify optimal imaging conditions. Compelling agreement between optical and photoacoustic flow measurements was achieved indicating that AR-PAF can accurately measure microscale blood flow velocities. AR-PAF was found to be robust, performing accurately even beyond physiological RBC concentrations. Furthermore, it was found that physiological RBC aggregation did not significantly affect the performance of AR-PAF. Lastly, the developed methods were used to demonstrate successful AR-PAF measurements using a clinical ultrasound scanner and whole blood. This study highlighted that clinical translation of AR-PAF should be the next step in development of this promising modality.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Acoustic resolution photoacoustic flowmetry
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2019. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
URI: https://discovery.ucl.ac.uk/id/eprint/10079090
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