The material behaviour of sutured tendons is important in healing models as mechanical trauma to the tendon during
surgery can compromise the healing process. This work demonstrates the use of spectral domain optical coherence
tomography (SD-OCT) for the monitoring of normal and injured, and subsequently repaired flexor tendons and their
behaviour under load. Vertical crimp patterns in normal tendons were observed to be replaced by uniform scattering as
the load increases, but the crimp periods in sutured tendons were constrained at the suture site, with gap separation at the
suture joint tapering off at high loads. This information could be useful for surgeons who need to balance gap separation
in healing tendons and sustainable load.
The control of image contrast is essential toward optimizing a contrast enhancement procedure in optical coherence tomography (OCT). In this study, the in vivo control of optical contrast in a mouse tumor model with gold nanoshells as a contrast agent is examined. Gold nanoshells are administered into mice, with the injected dosage and particle surface parameters varied and its concentration in the tumor under each condition is determined using a noninvasive theoretical OCT modeling technique. The results show that too high a concentration of gold nanoshells in the tumor only enhances the OCT signal near the tissue surface, while significantly attenuating the signal deeper into the tissue. With an appropriate dosage, IV delivery of gold nanoshells allows a moderate concentration of 6.2×109 particles/ml in tumor to achieve a good OCT signal enhancement with minimal signal attenuation with depth. An increase in the IV dosage of gold nanoshells reveals a corresponding nonlinear increase in their tumor concentration, as well as a nonlinear reduction in the fractional concentration of injected gold nanoshells. Furthermore, this fractional concentration is improved with the use of antiepodermal growth factor receptor (EGFR) surface functionalization, which also reduces the time required for tumor delivery from 6 to 2 h.
This work investigates the use of optical coherence tomography (OCT) to identify virus infection in orchid plants. Besides revealing the cross-sectional structure of orchid leaves, highly scattering upper leaf epidermides are detected with OCT for virus-infected plants. This distinct feature is not observable under histological examination of the leaf samples. Furthermore, the leaf epidermides of stressed but healthy plants, which exhibit similar visual symptoms as virus-infected plants, are not highly scattering and are similar to those of healthy plants. The results suggest that virus-infected orchid plants can be accurately identified by imaging the epidermal layers of their leaves with OCT. The OCT modality is suitable for fast, nondestructive diagnosis of orchid virus infection, which may potentially lead to significant cost savings and better control of the spread of viruses in the orchid industry.
We present the implementation of a fluorescence lifetime imaging microscopy (FLIM) system for cellular
characterisation. FLIM system can be used as an investigative tool to identify minor biochemical changes in cellular
abnormalities. These subtle changes could possibly alter cellular fluorescence properties such as emission wavelength
and lifetime. In this study, the fluorescence lifetime of haematoxylin and eosin (H&E)-stained tissues were investigated
using a wide-field time-domain FLIM system. The transient response of epithelial fluorescence was investigated and the
lifetime extracted using a bi-exponential model. It was found that the fluorescence lifetimes of eosin can be correlated to
the tissue histology. The preliminary result suggests that tumor-associated molecules are retained in the tissues even after
tissue fixation and staining. The developed FLIM system was successfully applied to detect the histological changes in
the tissue samples. Optimization of system parameters is also discussed.
In this paper, we address the problem of spectral data sampling in Fourier domain optical coherence
tomography (FD-OCT). The interferometric information in a Fourier Domain OCT system is retrieved from spectral
measurements made using a linear array spectrometer. In such spectrometers, spectral data are available as an array
of points equally spaced in the wavelength domain. To obtain the spatial profile, the spectral data have to be
converted to the frequency domain before applying the Fourier transform. The inverse relationship between these
domains causes an unequal spacing of data points after the spectral data is converted to the frequency domain,
resulting in the degradation of the FD-OCT images. The current practice typically utilizes zero-padding and spline
interpolation to circumvent this problem. While these algorithms do improve the FD-OCT images, our
investigations showed that more can be done to enhance the images. Toward this end, we propose a signal
processing algorithm based on non-uniform discrete Fourier transform (NUDFT). The results of our algorithm are
compared against the current algorithms on both simulated and experimental results.
The application of gold nanoparticles as a contrast agent in optical bioimaging is well appreciated, but limited to a
narrow excitation range due to its rather invariable optical resonance typically at 520 nm. Compared to gold
nanoparticles, the optical response of gold nanoshells can be tuned to match the higher excitation wavelength of many
promising clinical reflectance-based imaging modalities such as the optical coherence tomography (OCT). In this study,
we demonstrate the tunability of gold nanoshells to improve the optical contrast of backscattering signal under confocal
reflectance microscopy and OCT. The gold nanoshells were synthesized and conjugated to antibodies for in vitro
demonstration of their selective optical contrast in cancer cells over normal cells under the confocal reflectance
microscopy. The OCT signals from these gold nanoshells were compared to that from bare silica cores and intrinsic
tissue scattering using 1% Intralipid. We have shown that gold nanoshells are able to elicit an optical contrast to
discriminate between cancerous and normal cells under the confocal reflectance microscopy based on differences in
molecular markers expression. Compared to bare silica core, the presence of the gold shell is able to effect a higher
backscattered OCT signal with an apparent contrast over 1% Intralipid. This contrast can be made to be dependent on
the molecular marker expression with antibody specificity.
Estimation of the tissue optical characteristics using optical coherence tomography (OCT) requires good modeling.
Present modeling of the system includes effects such as scattering of light in tissues. However, absorption effects were
often neglected in the model. They may be significant depending on the tissue type and the wavelength of the light
source. We present a study where the effects of absorption in light propagation in biological tissue were examined in the
theoretical modeling of OCT based on the single-scattering model. OCT M-scans were performed on liquid tissue
phantoms at 1% concentration. In order to mimic the effects of absorption, India ink was added to the solution. Different
concentrations of Indian ink were used to vary the absorption coefficient in the tissue phantoms. Estimation of the
absorption, scattering coefficients from the OCT signal were obtained. Substantial reduction in the slope of the
logarithmic OCT signal was observed when India ink was introduced to the liquid tissue phantoms. The results suggest
that the effects of the absorption clearly affected the estimation of the overall extinction coefficient. In order to improve
the accuracy of estimation of these characteristics, absorption effects should be taken into account.
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