Clutter rejection filters for optical Doppler tomography.

The phase-resolved (PR) method is widely used in optical Doppler tomography (ODT) to estimate flow velocity from sequential axial line (A-line) signals. However, the A-line signal contains clutter components induced by stationary or relative slow moving clutter scatterers such as the blood vessel wall or the overall sample with motion artifacts. The clutter component affects the accuracy in quantifying Doppler flow. In this paper, we present a delay line filter (DLF) to reject the clutter effect and enables moving-scatterer-sensitive ODT (MSS-ODT) imaging of flow. The frequency response of DLFs of different orders is theoretically analyzed and we find that a first-order phase-shifted DLF is effective for clutter rejection and for improving the sensitivity to moving scatterers such as moving blood cells. The proposed MSS-ODT method has been experimentally applied to Doppler flow imaging in a capillary flow phantom and a mouse ear in vivo. The ODT data were acquired using a real-time spectral-domain optical coherence tomography (SD-OCT) system with an A-line acquisition rate of 12.3k/s. Doppler flow images obtained with MSS-ODT and the conventional PR-ODT techniques are compared and MSS-ODT is found to be more sensitive to Doppler flow and more accurate in determining vessel size. Small blood vessels that might be masked by clutter signals in PR-OCT are successfully recovered by MSS-ODT.