KEYWORDS: Optical coherence tomography, Signal detection, Mirrors, Retinal scanning, In vivo imaging, Reconstruction algorithms, Microscopes, Spectroscopy, Imaging systems, Signal processing
The dispersion mismatch between sample and reference arm in frequency-domain OCT can be used to iteratively
suppress complex conjugate artifacts and thereby increase the imaging range. We propose a fast dispersion
encoded full range (DEFR) algorithm that detects multiple signal components per iteration. The influence of
different dispersion levels on the reconstruction quality is analyzed for in vivo retinal tomograms at 800 nm. Best
results have been achieved with about 30 mm SF11, with neglectable resolution decrease due to finite resolution
of the spectrometer. Our fast DEFR algorithm achieves an average suppression ratio of 55 dB and converges
within 5 to 10 iterations. The processing time on non-dedicated hardware was 5 to 10 seconds for tomograms
with 512 depth scans and 4096 sampling points per depth scan. Application of DEFR to the more challenging
1060 nm wavelength region is demonstrated by introducing an additional optical fibre in the sample arm.
Conventionally, cell chemotaxis is studied on two-dimensional (2D) transparent surfaces due to limitations in optical and
image data-collection techniques. However, substrates which more closely mimic the natural environment of cells are often opaque
or three-dimensional (3D). The non-invasive label-free imaging technique of frequency domain optical coherence tomography (OCT)
has high axial and transverse resolution of >4μm, comparatively high penetration depth and the ability to acquire volumes in a few
seconds, therefore offering the potential to visualize moving cells in 3D (2D+time) and 4D (3D+time). Cell migration is
demonstrated in 3D on opaque surfaces, and in 4D within an agarose gel. The speed and directionality of wild type (Ax2) cell
movement is seen to be comparable on agar and nitrocellulose filter substrates. Differences can be clearly seen in the character of cell
movement between Ax2, myosin knockout (mhcA-) and PLC null ~10μm Dictyostelium discoideum cells in 4D using ultrahigh
resolution OCT. OCT is therefore shown to be a useful technique for the study of cell migration.
Using high speed ultrahigh resolution optical coherence tomography (OCT) at 800nm, non-invasive 3D cellular imaging
has been accomplished. Cellular resolution imaging on and within these types of substrates is not possible with
conventional microscopy techniques such as interference contrast microscopy, and requires the use of fluorescent
staining. It is possible to achieve data acquisition rates of 20,000 samples per second with OCT which, in combination
with its high axial and transverse resolution (>2-3μm), allows it to be used as a non-invasive technique to analyze cell
migration in 3D with time. Comparatively high penetration depth also makes OCT a uniquely suited imaging technique
for visualization of cells within a 3D construct.
In this paper it is demonstrated that it is possible to resolve ~10μm Dictyostelium discoideum cells, a well established
and useful model for investigation of cell motility and chemotaxis, in 3D and follow them in time lapse using an 800nm
ultrahigh resolution high speed frequency domain based OCT microscope. Ultimately, these visualization techniques
could enable monitoring of cell behavior in regenerative medicine, for example tracking of individual cells within a cell
scaffold.
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