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The quantification of (blood) flow velocity within the vasculature has potent diagnostic and prognostic potential.
Assessment of flow irregularities in the form of increased permeability (micro haemorrhaging), the presence of avascular
areas, or conversely the presence of vessels with enlarged or increased tortuosity in the acral regions of the body may
provide a means of non-invasive in vivo assessment. If assessment of dermal flow dynamics were performed in a routine
manner, the existence and prevalence of ailments such as diabetes mellitus, psoriatic arthritis and Raynaud's condition
may be confirmed prior to clinical suspicion. This may prove advantageous in cases wherein the efficacy of a prescribed
treatment is dictated by a prompt diagnosis and to alleviate patient discomfort through early detection.
Optical Coherence Tomography (OCT) is an imaging modality which utilises the principle of optical interferometry to
distinguish between spatial changes in refractive index within the vasculature and thus formulate a multi-dimensional
representation of the structure of the epi- and dermal skin layers. The use of the Doppler functionality has been the
predominant force for the quantification of moving particles within media, elucidated via estimation of the phase shift in
OCT A-scans. However, the theoretical formulation for the assessment of these phase shifts dictates that the angle
between the incident light source and the vessel under question be known a priori; this may be achieved via excisional
biopsy of the tissue segment in question, but is counter to the non-invasive premise of the OCT technique.
To address the issue of angular dependence, an alternate means of estimating absolute flow velocity is presented. The
design and development of a dual-beam (db) system incorporating an optical switch mechanism for signal discrimination
of two spatially disparate points enabling quasi-simultaneous multiple specimen scanning is described. A crosscorrelation
(c-c) of interference fluctuations between these positions is performed computationally, yielding a transit
time for particle flow.
This paper summarises the findings of the c-c db-Sd-OCT technique for absolute velocity estimation within capillary
phantoms of various sizes using IntralipidTM solution to emulate red blood corpuscles (RBCs) and related blood
constituents, driven by a calibrated syringe flow pump. The findings of the preliminary experimentation reveal the
technique to be capable of estimating absolute velocity values with a maximum error difference of 0.077 mm s-1 using
Bland Altman plots. Application of this technique and rigorous testing of the c-c db-Sd-OCT method with biological
samples will be the focus of future work.
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