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Title: Acoustic resolution photoacoustic flowmetry
Author: Bücking, Thore Mainart
ISNI:       0000 0004 8499 905X
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2019
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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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available