We demonstrate a full-field swept-source OCT using an off-axis geometry of the reference illumination. By using holographic refocusing techniques, a uniform lateral resolution is achieved over the measurement depth of approximately 80 Rayleigh lengths. Compared to a standard on-axis setup, artifacts and autocorrelation signals are suppressed and the measurement depth is doubled by resolving the complex conjugate ambiguity. Holographic refocusing was done efficiently by Fourier-domain resampling as demonstrated before in inverse scattering and holoscopy. It allowed to reconstruct a complete volume with about 10<i>μ</i>m resolution over the complete measurement depth of more than 10mm. Off-axis full-field swept-source OCT enables high measurement depths, spanning many Rayleigh lengths with reduced artifacts.
We demonstrate Holoscopy -- a combination of full-field swept-source optical coherence tomography and digital holography. By using a simple Michelson interferometer setup, a rapidly tunable laser and combining scalar diffraction theory with standard Fourier-domain OCT signal processing we obtain depth invariant imaging quality.
Proc. SPIE. 8091, Optical Coherence Tomography and Coherence Techniques V
KEYWORDS: Point spread functions, Biomedical optics, Coherence (optics), Cameras, Optical coherence tomography, Image quality, In vivo imaging, Electroluminescent displays, Lawrencium, Current controlled current source
Recently, in-vivo full eld (FF) optical coherence tomography (OCT) with an ultra-high speed camera has been
presented for fast in vivo retinal imaging. By parallel A-scans acquisition, imaging with 1,5 million A-scans/s
was shown with an extended illumination of the retina. In this paper, the image quality of FF-OCT images will
be compared to conventional scanning OCT systems. The eect of the absence of a confocal aperture leading to
crosstalk between adjacent image points will be shown and an experimental analysis of the systems lateral point
spread function (PSF) in dependence of depth will be given and discussed.
Considerable improvement in the reproducibility of retinal photocoagulation is expected if degree and extend of the heat-induced tissue damage can be visualized on-line during the treatment. Experimental laser treatments of the retina with enucleated pig eyes were investigated by high speed phase-sensitive OCT. OCT could visualize the increase of tissue scattering during the photocoagulation in a time-resolved way. Immediate and late tissue changes were visualized with more than 15 µm resolution. Changes of the reflectance in the OCT images had a similar sensitivity in detecting tissue changes than macroscopic imaging. By using Doppler OCT slight movements of the tissue in the irradiated spot were detected. At low irradiance the thermal expansion of the tissue is observed. At higher irradiance irreversible tissue changes dominate the tissue expansion. OCT may play an important role in understanding the mechanisms of photocoagulation. This may lead to new treatment strategies. First experiments with rabbits demonstrate the feasibility of in-vivo measurements.
In-vivo full field (FF) optical coherence tomography (OCT) images of human retina with up to 6.8 million A-lines/s are presented by using a rapidly tunable laser source in combination with an ultra-high speed CMOS camera. It is shown that Fourier domain (FD) full field OCT could provide a way to overcome limitations in imaging speed which are posed by the maximal possible exposure (MPE) of the retina. With a 100~Hz sweep rate FF-OCT was fast enough to acquire OCT images without motion artifacts, but with rather low sensitivity of 77 dB limited by an undesired incoherent background. Nevertheless, FF-OCT may become an attractive alternative for ultrafast retinal imaging boosting image speed by a lack of moving parts and the use of considerably higher irradiation power, if it is possible to to increase the sensitivity by reducing incoherent straylight.
A well established navigation method is one of the key conditions for successful brain surgery: It should be accurate,
safe and online operable. Recent research shows that Optical Coherence Tomography is a potential solution for this
application by providing a high resolution and small probe dimension. In this study a fiber Spectral-Domain OCT system
with a super luminescent diode with the center wavelength of 840 nm providing 13.6 μm axial resolution was used. A
single mode fiber (Ø 125 μm) was employed as the detecting probe. The information acquired by OCT was reconstructed
into grayscale images by vertically aligning several A-scans from the same trajectory with different depth, i.e. forward
scanning. For scans of typical white matter, the images showed a higher reflection of light intensity with lower
penetration depth as well as a steeper attenuation rate compared to the scans typical for grey matter. Since the axial
resolution of this OCT system is very high, some microstructures lying on the striatum, hippocampus and thalamic
nucleus were visible in these images. The research explored the potential of OCT to be integrated into a stereotactic
surgical robot as a multi-modal navigation method.