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The same disadvantages occur when using the spectrogram method to do in vivo tissue structure and flow velocity imaging, as spectral-domain OCT is limited to fast imaging. Phase-resolved Doppler OCT, based around the invention of Fourier-Domain OCT, was invented to overcome these limitations. [1]
Ocular OCT retinal thickness map, right eye Time-domain OCT of the macular area of a retina at 800 nm, axial resolution 3 μm Spectral-domain OCT macula cross-section scan. Optical coherence tomography (OCT) is a technique for obtaining sub-surface images of translucent or opaque materials at a resolution equivalent to a low-power microscope.
Initial efforts to measure blood flow using OCT utilized the Doppler effect. [41] [42] By comparing the phase of successive A-mode scans, the velocity of blood flow can be determined via the Doppler equation. This was deemed Optical Doppler Tomography; the development of spectral domain OCT (SD-OCT) and swept-source OCT (SS-OCT) greatly ...
For a two dimensional phase retrieval problem, there is a degeneracy of solutions as () and its conjugate () have the same Fourier modulus. This leads to "image twinning" in which the phase retrieval algorithm stagnates producing an image with features of both the object and its conjugate. [3]
The fast Fourier transform process converts time-domain samples into frequency domain spectra. This is sometimes called the bed of nails. Pulse-Doppler signal processing separates reflected signals into a number of frequency filters. There is a separate set of filters for each ambiguous range.
Aroun 2008-2009, the advent of rapid sweep source lasers allowed for the development of intravascular Fourier-Domain OCT (FD-OCT). [ 9 ] [ 10 ] This enabled for the first-time rapid acquisitions of a long coronary segment in a couple of seconds, allowing non occlusive brief contrast injections to clear the arterial lumen from blood.
SV-OCT can be done with spectral domain OCT (SD-OCT) and swept source OCT (SS-OCT). [5] SD-OCT and SS-OCT are both methods of Fourier domain OCT (FD-OCT), which has significantly faster image acquisition speed compared to time domain OCT. In general, OCT measures the echo time delay and intensity of reflected and backscattered light.
Instead, a single-element optical detector can also act like diversity receiver via synthetic array heterodyne detection or Fourier transform heterodyne detection. With a virtual array one can then either adaptively select just one of the LO frequencies, track a slowly moving bright speckle, or add them all in post-processing by the electronics.