Search

In optical coherence tomography (OCT), differential contrast can be generated by resonant nanoparticles using spectral multiplexing. Differential contrast can be of interest for medical applications for improving detection specificity of structures with low endogenous contrast. Differential contrast has been shown using OCT systems with one bandwidth; how- ever, this requires post-processing that is time consum- ing and reduces image resolution. In this study, we used a dual-band OCT prototype system with two far separated bandwidths in the clinically relevant optical window, and in search for the optimal differential contrast-generating particles for this prototype system, three different gold nanorods (AuNR) samples were investigated. The samples with different particle volume, aspect ratio, and absorption-maximum were imaged in a highly scattering phantom and on chicken muscle. In vitro, differential contrast was observed for the nanorods large (NRL) sample having the absorption- maximum within one bandwidth of the OCT and an average length of 75 nm. For the smaller AuNR (48 nm length) with comparable absorption-maximum, the obtained signal intensities were too low for being visible, although differences in signal intensities be- tween both bandwidths could be measured. NRL optimal concentration for differential contrast using this prototype system is between 100 and 500 lg Au/mL (0.51-2.54 mM). These results demonstrate the potential of real-time imaging of differential contrast in dual-band OCT and motivate in vivo application of plasmon resonant AuNR in order to improve the detection sensitivity for structures that are difficult to identify by OCT such as small blood vessels.

In this study, the optical properties of two nano-sized polymer colloids in optical coherence tomography (OCT) were compared in vitro with respect to their potential use as contrast agents. We used two types of particles: compact hydrophobic spherical polystyrene (PS) particles and soft water-swollen nanogel (NG) particles both with grafted hydrophilic shell, both prepared at two different sizes (PS at 300 and 150 nm, NG at 300 and 200 nm). The OCT backscattering signals of the particles in a vessel-mimicking highly scattering agar/TiO2 phantom were compared on either number of particles or weight percent. Larger particles and higher concentrations produced higher OCT contrast. At each concentration tested, a markedly higher contrast was achieved by PS particles than NG particles. PS particles generated a markedly higher OCT contrast than the phantom at concentrations of at least 1 × 1010 or 0.1 % for PS 300 nm and at least 3 × 1011 particles/mL or 0.4 % for PS 150 nm. The contrast generated by NG 300 nm was above the phantom contrast at concentrations of at least 3 × 1011 particles/mL or 1 %, whereas NG 200 nm only at 4 %. At any given weight percent, the differences in OCT contrast between differently sized particles were much less evident than in the comparison based on particle number. PS 300 nm generated also a good contrast ex vivo on chicken muscle tissue. These results strongly suggest that PS spheres have strong potential as intravascular OCT contrast agent, while NG particles need further contrast enhancer for being used as OCT contrast agent.

Enhanced visualization of tissue contrast and morphological boundaries is demonstrated by analyzing OCT volume data in two distinct wavelength regions. The extension of this so-called simultaneous dual-band method to three dimensions is realized by a custom-built 3D spectral domain OCT system imaging in the 800 und 1200 nm wavelength domain. Color representations of the spectral differences of high resolution OCT volume data significantly simplify the discrimination of different tissue structures beyond the capabilities of cross-sectional spectroscopic OCT approaches.

In optical sampling, a transient waveform under study is sampled with time delayed laser pulses, achieving a high time resolution. The limitations in measurement time due to the mechanical adjustment of the time delay can be overcome by asynchronous optical sampling (ASOPS) [1], where two pulsed lasers with slightly detuned repetition rates are employed. This technique is commonly used for studying transient characteristics [1], for infrared spectrometry [2] as well as remote sensing applications [3] and optical coherence tomography [4]. However, a static difference in repetition rates leads to static scanning ranges, resulting in unnecessary large measurement times and large amounts of measured data especially for the latter applications.

Electronically controlled coherent linear optical sampling for low coherence interferometry (LCI) and optical coherence tomography (OCT) is demonstrated, using two turn-key commercial mode-locked fiber lasers with synchronized repetition rates. This novel technique prevents repetition rate limitations present in previous implementations based on asynchronous optical sampling. Adjustable scanning ranges and scanning rates are realized within an interferometric setup by full electronic control of the mutual time delay of the two laser pulse trains. We implement this novel linear optical sampling scheme with broad spectral bandwidths for LCI, optical filter characterization and OCT imaging in two and three dimensions.

A fiber-based spectral domain optical coherence tomography (OCT) system is described, imaging simultaneously at 740 and 1300 nm central wavelengths. Real-time imaging is demonstrated with axial resolutions

We present a high-speed, high-resolution, non-mechanical time-domain method for low coherence interferometry, utilizing multiheterodyne detection via two mode-locked femtosecond lasers. Tomographic depth sensing over 150 mm with 5.9 kHz scanning rates and 8 µm depth resolution is demonstrated.

A time domain optical coherence tomography (OCT) system without moving parts is described, which is based on multiheterodyning utilizing two mode-locked femtosecond lasers. By synchronizing the two lasers to slightly different repetition rates and coupling to an interferometric OCT setup, we obtain amplitude-modulated beat signals representing the structure of the specimen under investigation. Our system is suitable for biological imaging as well as technical applications. We demonstrate high axial imaging depths of 150 mm with up to 5000 axial scans per second, achieving equivalent path scanning velocities of 750 m/s.

A Fourier domain optical coherence tomography system is demonstrated, employing a commercial supercontinuum light source for the 1300nm wavelength region. Ultrahigh axial resolution of 1mm and 100dB sensitivity are achieved.

An off-the-shelf turn-key supercontinuum light source based on a passively mode-locked fiber laser, a fiber amplifier and a highly nonlinear fiber is evaluated for its application in ultrahigh resolution optical coherence tomography (OCT). Two spectral bands — one red shifted and one blue shifted in reference to the wavelength of the fiber laser — are employed as low coherence sources in OCT. Usable spectral bandwidths exceed 300 nm centered either at 790 or 1340 nm, with corresponding coherence lengths of 1.2 and 2.6 —, respectively. Optimization of the spectrum for simultaneous imaging at both spectral bands results in spectral bandwidths exceeding 200 nm for each band after filtering. A free-space OCT setup supporting the full spectral bandwidth is introduced which allows for ultrahigh resolution OCT imaging using both spectral bands simultaneously. Axial free space resolutions were measured to be less than 2 and 4 μm at 840 and 1230 nm, respectively. This approach combines ultrahigh resolution obtained at 840 nm with large penetration depths at 1230 nm. Frequency compounding of the OCT images can be used for speckle reduction while extracting spatially resolved spectroscopic features facilitates enhanced image contrast.

For chemical burns a considerable lack of methods exists for defining penetration kinetics and effects of decontamination within biological structures. We demonstrate that time-resolved high-resolution optical coherence tomography can close this gap by monitoring changes in scattering properties and thicknesses of rabbit cornea ex vivo after topical application of different corrosives. Modifications in the corneal microstructure due to direct chemical interaction or changes in the hydration state as a result of osmotic imbalance compromise the corneal transparency. The associated increase in light scattering intensity within the cornea is observed with high spatial and temporal resolution. Parameters affecting the severity of pathophysiological damage like diffusion velocity, depth of penetration, resistance of barriers, and effectiveness of emergency treatment procedures are obtained. This study demonstrates the potential of high-resolution OCT for the visualization and direct non-invasive measurement of specific interaction of chemicals with the eye, exemplified on hydrofluoric acid burn.

The use of high-resolution optical coherence tomography OCT to visualize penetration kinetics during the initial phase of chemical eye burns is evaluated. The changes in scattering properties and thickness of rabbit cornea ex vivo were monitored after topical application of different corrosives by time-resolved OCT imaging. Eye burn causes changes in the corneal microstructure due to chemical interaction or change in the hydration state as a result of osmotic imbalance. These changes compromise the corneal transparency. The associated increase in light scattering within the cornea is observed with high spatial and temporal resolution. Parameters affecting the severity of pathophysiological damage associated with chemical eye burns like diffusion velocity and depth of penetration are obtained. We demonstrate the potential of high-resolution OCT for the visual- ization and direct noninvasive measurement of specific interaction of chemicals with the eye. This work opens new horizons in clinical evaluation of chemical eye burns, eye irritation testing, and product testing for chemical and pharmacological products. © 2007 Society of

Ultra-high resolution optical coherence tomography (OCT) imaging is demonstrated simultaneously at 840 nm and 1230 nm central wavelength using an off-the-shelf turn-key supercontinuum light source. Spectral filtering of the light source emission results in a double peak spectrum with average powers exceeding 100 mW and bandwidths exceeding 200 nm for each wavelength band. A free-space OCT setup optimized to support both wavelengths in parallel is introduced. OCT imaging of biological tissue ex vivo and in vivo is demonstrated with axial resolutions measured to be