Abstract

Abstract

Abstract
A versatile time-domain optical coherence tomography system is presented that can generate cross-sectional images by using either transverse priority or depth priority scanning. This is made possible by using a transmissive scanning delay line compatible with balance detection operating at a speed similar to that of the transverse scanner used to scan the beam across the target. In vivo images from the retina are generated and shown using the same system switched to either transverse or depth priority scanning regime, by using the scanning delay line either in slow or fast scanning modes, respectively. A comparative analysis of different scanning regimes depending on image size to fit different areas to be imaged is presented. Safety thresholds due to the different continuous irradiation time per transverse pixel in different scanning regimes are also considered. We present the maximum exposure level for a variety of scanning procedures, employing either A scanning (depth priority) or T scanning (transverse priority) when generating cross-sectional images, en face images, or collecting 3D volumes. (c) 2007 Optical Society of America.

Abstract
Owing to the limited spectral response of the fiber directional coupler used in a balanced optical coherence tomography configuration, the spectra are different in the two outputs. This affects unfavorably operation of the balanced photodetector unit. Excess photon noise makes a larger contribution than a directional coupler with a flat spectral response. A theoretical model is developed that shows that an optimum set of parameters may be defined to maximize the achievable signal-to-noise ratio. The model leads to a redefinition of the effective noise bandwidth, which takes into account the nonflat response of the directional coupler used. The model also predicts a limitation on the signal-to-noise ratio even when the stray reflectances in the interferometer are brought to zero. (C) 2004 Optical Society of America.

Abstract
Femtosecond Titanium: sapphire lasers can deliver high average power broadband spectra in a high quality beam, being therefore an optical source of choice for high-resolution optical coherence tomography (OCT) at high acquisition rates. We present a brief tutorial on the basic physics behind the operation and design of Kerr-lens modelocked lasers, where the high peak powers associated with femtosecond pulses give rise to nonlinear optical effects that play a major role in the laser operation itself and strongly influence the output spectrum. Additional nonlinear devices, in particular photonic crystal fibers (PCFs), can also be directly pumped with the generated femtosecond pulses to further extend the spectral range of the laser output, both in terms of bandwidth and center wavelength. Two specific laser systems employing different technologies for intracavity dispersion compensation (intracavity prisms in one case, and octave-spanning double-chirped mirrors in the other) will be described, and the corresponding advantages for OCT, namely the maximum achievable resolution and the applicability of spectral tuning and shaping techniques, will be briefly discussed.

Abstract
A new variety of nanoparticles showing unique and characteristic optical properties, appeals for its use as contrast agents in medical imaging. Gold nanospheres, nanorods and nanoshells with a silica core are new forms of promising contrast agents which can be tuned to specific absorption or scattering characteristics within the near-infrared (NIR) spectrum ranging from 650 - 1300 nm. They have the ability to be used for both image enhancement and as photosensitive markers due to their well designable scattering and absorption properties. Furthermore, their strong optical absorption permits treatment of malignant cells by photoablation processes, induced when heating them with a matched light source. Differential absorption optical coherence tomography (DA-OCT) allows for the detection and depth resolved concentration measurement of such markers. So far, reports on DA-OCT systems used A-scan based imaging systems to assess depth resolved information about the absorption properties and the concentration of a chemical compound. En-face OCT (B(T) or C(T) scan based) images allow for better depth localization and a depth resolved concentration measurement of the compound under investigation. For this aim, we evaluate the suitability of a multiscan time-domain OCT set-up, compatible with different light sources providing different wavelengths and bandwidths in the NIR, to perform differential absorption OCT measurements, using gold nanorods as the contrast agent.