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R. A. Leitgeb, T. Schmoll, R. Michaely; Novel B-Mode Spectral Optical Coherence Tomography: Mirror-Term Free 3D Imaging of Retinal Structure and 3D Doppler Tomography. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1847.
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© ARVO (1962-2015); The Authors (2016-present)
To apply a novel and cheap B-mode spectral optical coherence tomography system for mirror-term suppression without additional phase-shifting devices and for Doppler imaging of retinal blood flow based on resonant Doppler tomography.
B-mode phase sensitive SOCT uses a carrier phase offset to reconstruct the full complex SOCT signal. The complex signal is produced by analytic continuation of the measured real valued data with its Hilbert transform along the B-scan coordinate. The mirror term free structure is obtained by standard Fourier transform of each complex valued A-scan. The novel approach is to introduce the carrier phase by simply offsetting the beam on the transversally fast scanning galvo-mirror. Hence, no expensive phase shifting devices are needed, and the method is easily integrated into any existing SOCT platform. The dynamic phase offset is effectively a Doppler frequency introduced through the scanning. By tuning the scanning Doppler frequency to that of retinal flow, the latter can be enhanced by virtue of resonant Doppler tomography. On the other hand static signals will be attenuated for large Doppler offsets due to fringe washout, which yields optical vivisectioning of retinal perfusion without elaborate image post-processing.
High-speed mirror-artifact free retinal tomograms have been recorded of healthy subjects with the novel B-mode SOCT system at 20kHz A-scan rate and a center wavelength of 820nm. Studying the performance for mirror term suppression shows an optimal phase shift of π/2 between adjacent A-scans ( >30dB suppression). The method is capable to correct for slight phase errors due to subject motion. For phase shifts >π one observes suppressed static structure signals as well as enhanced flow signals. The lateral scanning direction is directly related to the axial flow direction that will be enhanced. We recorded directionally resolved 3D flow maps of the optic nerve head of a healthy subject in-vivo.
The potential of a novel and cheap method to perform 3D in-vivo retinal tomography and its capability for 3D optical vivisectioning of retinal perfusion is demonstrated. The method is easily integrated into any SOCT platform including swept source OCT. The performance of the method in the presence of large motion artifacts needs further investigation. Nevertheless, B-mode SOCT is less sensitive to motion artifacts than state-of-the art phase sensitive SOCT.
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