Optimisation of the acousto optic signal detection for biomedical applications.
Doctoral thesis, UCL (University College London).
Near infrared light has been widely used to probe human tissue oxygenation non-invasively. However the highly scattering nature of tissue limits light penetration depths and optical measurement is more sensitive to optical changes in the superficial region (SFR) of tissue. It is proposed that the penetration depth and the localisation of the optical measurement can be improved by the Acousto-Optic (AO) method. The AO method tags diffuse photons in an optically tissue mimicking medium by using focused ultrasound waves. Generally it is believed that the region probed by the AO method is decided by the position of the focused ultrasound region (FUR). Therefore the AO method can potentially improve the penetration depth and reduce the susceptibility in the SFR of the optical measurement by relocating the FUR to deeper region in tissue. The spatial sensitivity of the AO measurement is mapped and compared to the spatial sensitivity of the optical measurement experimentally. The AO method can monitor absorption and scattering changes in deeper regions than the optical measurement. The AO method is less affected by the optical changes in the SFR. The most sensitive region probed by the AO method can be relocated by re-positioning the FUR. But it does not always coincide with the FUR. The AO spatial sensitivity depends on the overlap of the FUR and the photon path distribution. This overlap region affects the AO signal differently for absorption and scattering changes. Thus, concurrent monitoring of absorption and scattering changes require careful positioning of the FUR. Finally, it is also demonstrated that the pulsed-wave ultrasound can be used with the AO method in a cylindrical geometry. An optimal optodes’ positions for the AO signal detection can be predicted experimentally for a given location of the FUR within a cylindrical geometry.
|Title:||Optimisation of the acousto optic signal detection for biomedical applications|
|Open access status:||An open access version is available from UCL Discovery|
|Additional information:||Third party copyright material has been removed from the e-thesis.|
|UCL classification:||UCL > School of BEAMS > Faculty of Engineering Science > Medical Physics and Bioengineering|
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