| dc.description.abstract | The detection of micro-embolic signals (MES) is a mature application of transcranial
Doppler (TCD) ultrasound. It involves the identification of abnormally highpitched
signals within the arterial waveform as a method of diagnosis and prediction
of embolic complications in stroke patients. More recently, algorithms have
been developed to help characterise and classify MES using advanced signal processing
techniques. These advances aim to improve our understanding of the causes
of cereberovascular disease, helping to target the most appropriate interventions
and quantifying the risk to patients of further stroke events. However, there are a
number of limitations with current TCD systems which reduce their effectiveness.
In particular, improvements in our understanding of the scattering effects in TCD
ultrasound propagation channels will benefit our ability to develop algorithms that
more robustly and reliably identify the consistency and material make-up of MES.
This thesis explores TCD propagation channels in three related research areas.
Firstly, a method of characterising TCD ultrasound propagation channels is proposed.
Isotropic and non-isotropic three dimensional space (3-D) spherical scattering
channel models are described in terms of theoretical reference models, simulation
models, and sum of sinusoids (SoS) simulators, allowing the statistical properties to
be analysed and reported. Secondly, a TCD ultrasound medical blood
flow phantom
is described. The phantom, designed to replicate blood
flow in the middle cerebral
arteries (MCA) for TCD ultrasound studies, is discussed in terms of material selection,
physical construction and acoustic characteristics, including acoustic velocity,
attenuation and backscatter coefficients. Finally, verification analysis is performed
on the non-isotropic models against firstly, the blood
flow phantom, and secondly,
a patient recordings database. This analysis expands on areas of agreement and
disagreement before assessing the usefulness of the models and describing their potential
to improve signal processing approaches for detection of MES.
The proposed non-isotropic channel reference model, simulation model, SoS simulator,
and blood
flow phantom are expected to contribute to improvements in the
design, testing, and performance evaluation of future TCD ultrasound systems. | en_US |
