Cerebral capillary flow imaging by wavelength-division-multiplexing swept-source optical Doppler tomography.

Swept-source-based optical coherence tomography (SS-OCT) has demonstrated the unique advantages for fast imaging rate and long imaging distance; however, limited axial resolution and complex phase noises restrict swept-source optical Doppler tomography (SS-ODT) for quantitative capillary blood flow imaging in the deep cortices. Here, the wavelength-dividing-multiplexing optical Doppler tomography (WDM-ODT) method that divides a single interferogram into multiple phase-correlated interferograms is proposed to effectively enhance the sensitivity for cerebral capillary flow imaging. Both flow phantom and in vivo mouse brain imaging studies show that WDM-ODT is able to significantly suppress background phase noise and image cerebral capillary flow down to the vessel size of 5.6 μm. Comparison between the wavelength-division-multiplexing SS-ODT and the spectral-domain ultrahigh-resolution ODT (uODT) reveals that SS-ODT outpaces uODT by extending the capillary flow imaging depth to 1.6 mm in mouse cortex. Thus, for the first time, quantitative capillary flow imaging is demonstrated using SS-ODT in the deep cortex.