Amplitude decorrelation measurement is sensitive to transverse flow and immune to phase noise in comparison to Doppler and other phase-based approaches. However, the high axial resolution of OCT makes it very sensitive to the pulsatile bulk motion noise in the axial direction. To overcome this limitation, we developed split-spectrum amplitude-decorrelation angiography (SSADA) to improve the signal-to-noise ratio (SNR) of flow detection. The full OCT spectrum was split into several narrower bands. Inter-B-scan decorrelation was computed using the spectral bands separately and then averaged. The SSADA algorithm was tested on in vivo images of the human macula and optic nerve head. It significantly improved both SNR for flow detection and connectivity of microvascular network when compared to other amplitude-decorrelation algorithms.

A novel label-free depth resolved technique, nano-sensitive optical coherence tomography (nsOCT), to detect structural changes at the nanoscale is presented.

Publication InformationS. Alexandrov, H. Subhash, M. Leahy (2014) 'Nanosensitive optical coherence tomography for the study of changes in static and dynamic structures'. Quantum Electronics, 44 (7):657-663. Publisher IOP ScienceLink to publisher's version http://dx.doi.org/10.1070/QE2014v044n07ABEH015487Item record http://hdl.handle.net/10379/4532Quantum Electronics 44 (7) 657 - 663 (2014) © 2014 Kvantovaya Elektronika and Turpion Ltd Abstract. We briefly discuss the principle of image formation in Fourier domain optical coherence tomography (OCT). The theory of a new approach to improve dramatically the sensitivity of conventional OCT is described. The approach is based on spectral encoding of spatial frequency. Information about the spatial structure is directly translated from the Fourier domain to the image domain as different wavelengths, without compromising the accuracy. Axial spatial period profiles of the structure are reconstructed for any volume of interest within the 3D OCT image with nanoscale sensitivity. An example of application of the nanoscale OCT to probe the internal structure of medico-biological objects, the anterior chamber of an ex vivo rat eye, is demonstrated.

Publication InformationSubhash HM, Leahy MJ; Microcirculation imaging based on full-range high-speed spectral domain correlation mapping optical coherence tomography. J. Biomed. Opt. 0001;19(2):021103-021103. Abstract. Microcirculation imaging is a key parameter for studying the pathophysiological processes of various disease conditions, in both clinical and fundamental research. A full-range spectral-domain correlation mapping optical coherence tomography (cm-OCT) method to obtain a complex-conjugate-free, full-range depth-resolved microcirculation map is presented. The proposed system is based on a high-speed spectrometer at 91 kHz with a modified scanning protocol to achieve higher acquisition speed to render cm-OCT images with highspeed and wide scan range. The mirror image elimination is based on linear phase modulation of B-frames by introducing a slight off-set of the probe beam with respect to the lateral scanning fast mirror's pivot axis. An algorithm that exploits the Hilbert transform to obtain a complex-conjugate-free image in conjunction with the cm-OCT algorithm is used to obtain full-range imaging of microcirculation within tissue beds in vivo. The estimated sensitivity of the system was around 105 dB near the zero-delay line with ∼20 dB roll-off from AE0.5 to AE3 mm imagingdepth position. The estimated axial and lateral resolutions are ∼12 and ∼30 μm, respectively. A direct consequence of this complex conjugate artifact elimination is the enhanced flow imaging sensitivity for deep tissue imaging application by imaging through the most sensitive zero-delay line and doubling the imaging range. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.