Phase-resolved optical coherence tomography and optical doppler tomography for imaging fluid flow in tissue with fast scanning speed and high velocity sensitivity

Abstract

The invention is a fast-scanning ODT system that uses phase information derived from a Hilbert transformation to increase the sensitivity of flow velocity measurements while maintaining high spatial resolution. The significant increases in scanning speed and velocity sensitivity realized by the invention make it possible to image in vivo blood flow in human skin. The method of the invention overcomes the inherent limitations of the prior art ODT by using a phase change between sequential line scans for velocity image reconstruction. The ODT signal phase or phase shifts at each pixel can be determined from the complex function, {tilde over (&Ggr;)} (t), which is determined through analytic continuation of the measured interference fringes function, &Ggr; (t), by use of a Hilbert transformation, by electronic phase demodulation, by optical means, or a fast Fourier transformation. The phase change in each pixel between axial-line scans is then used to calculate the Doppler frequency shift. Sequential measurements of a single line scan, measurements of sequential line scans or measurements of line scans in sequential frames may be used. Because the time between line scans is much longer than the pixel time window, very small Doppler shifts can be detected with this technique. In addition, spatial resolution and velocity sensitivity are decoupled. Furthermore, because two axial-line scans are compared at the same location, speckle modulations in the fringe signal cancel each other and, therefore, will not affect the phase-difference calculation.