Spectroscopic Doppler analysis for visible-light optical coherence tomography

Abstract

Abstract. Retinal oxygen metabolic rate can be effectively measured by visible-light optical coherence tomography (vis-OCT), which simultaneously quantifies oxygen saturation and blood flow rate in retinal vessels through spectroscopic analysis and Doppler measurement, respectively. Doppler OCT relates phase variation between sequential A-lines to the axial flow velocity of the scattering medium. The detectable phase shift is between −π and π due to its periodicity, which limits the maximum measurable unambiguous velocity without phase unwrapping. Using shorter wavelengths, vis-OCT is more vulnerable to phase ambiguity since flow induced phase variation is linearly related to the center wavenumber of the probing light. We eliminated the need for phase unwrapping using spectroscopic Doppler analysis. We split the whole vis-OCT spectrum into a series of narrow subbands and reconstructed vis-OCT images to extract corresponding Doppler phase shifts in all the subbands. Then, we quantified flow velocity by analyzing subband-dependent phase shift using linear regression. In the phantom experiment, we showed that spectroscopic Doppler analysis extended the measurable absolute phase shift range without conducting phase unwrapping. We also tested this method to quantify retinal blood flow in rodents in vivo.

Visible-light optical coherence tomography: a review

“…The first report of vis-OCT dates back to 2002, 31 after which both the system implementation and processing algorithms have evolved significantly 22 , 24 , 32 , 33 . Investigations of vis-OCT have moved from phantom demonstration 34 – 36 to in vivo verification, 25 , 37 from animal experiments 38 , 39 to clinical studies, 22 , 40 , 41 and from technical development 21 , 42 , 43 to pathological investigations of several diseases 44 …”

Dual-Modal Photoacoustic Imaging and Optical Coherence Tomography [Review]

“…It is currently the preferred technology in ophthalmology for corneal imaging, as well as retinal structural and vascular imaging [61][62][63]. Various functional extensions of OCT have been developed including: Doppler OCT [64], OCT angiography (OCTA) [65], polarization sensitive OCT (PS-OCT) [66], OCT elastography [67], and spectroscopic OCT [68]. Besides ophthalmic applications, OCT has been applied in other clinical applications such as brain imaging [69,70], tissue engineering [71], cardiology and cardiovascular imaging [72], skin imaging [73], neuroimaging [74], gynecology [75], oncology [76], and dental imaging [77].…”

Optical Coherence Tomography for Three-Dimensional Imaging in the Biomedical Field: A Review

“…The angiography results obtained from OCTA have a higher pixel density and fewer motion artifacts and can also measure blood oxygen or provide information about neurological diseases [50,51]. Besides, OCT can provide more comprehensive imaging and then get the oxygen metabolism of biological tissues combined with multi-spectral polarizing film dispersion while obtaining molecular level biochemical information with Raman spectroscopy [52,53].…”