Using a fiber-based swept-source (SS) polarization-sensitive optical coherence tomography (PS-OCT) system, we investigate the degree of polarization (DOP) of light backscattered from the retinal nerve fiber layer (RNFL) in normal human subjects. Algorithms for processing data were developed to analyze the deviation in phase retardation and intensity of backscattered light in directions parallel and perpendicular to the nerve fiber axis (fast and slow axes of RNFL). Considering superior, inferior, and nasal quadrants, we observe the strongest degradation in the DOP with increasing RNFL depth in the temporal quadrant. Retinal ganglion cell axons in normal human subjects are known to have the smallest diameter in the temporal quadrant, and the greater degradation observed in the DOP suggests that higher polarimetric noise may be associated with neural structure in the temporal RNFL. The association between depth degradation in the DOP and RNFL structural properties may broaden the utility of PS-OCT as a functional imaging technique.
Many studies have found that hypoxia, particularly cycling hypoxia (CH), can lead to enhanced tumor metastasis and resistance to radiation and chemotherapy. It was also reported that tumor total hemoglobin content (THb), which is directly related to tumor angiogenesis, can have significant impact on tumor’s response to radiation and neoadjuvant chemotherapy. There is a growing demand for technologies to measure tumor hypoxia and angiogenesis temporally in vivo. In this paper, a side-firing fiber optic sensor based on a multi-wavelength frequency-domain near infrared spectroscopy (FD-NIRS) instrument was used to quantify tumor oxygenation and hemoglobin concentrations in nude rats bearing human FaDu head and neck (H and N) tumors during normoxia and forced hyperoxia and cyclic hypoxia. Significant increase (with carbogen gas inhalation) or decrease (with reduced O2 supply) in tumor oxygenation was observed. The studies demonstrated the feasibility of the technology for longitudinal monitoring of H and N tumor’s response to therapy.
Holmium:YAG laser lithotripsy is effective for all stone compositions. However, stone retropulsion is
a big concern during laser ablation. The use of metal based anti-retropulsion devices reduces stone
retropulsion during laser treatment. However, Ho:YAG laser can also ablate metal based antiretropulsion
devices such as metal basket or metal wires and cause the failure of anti-retropulsion
device. BackStop is a novel reverse thermosensitive polymer-based anti-retropulsion device.
Response of Backstop polymer to pulsed Ho:YAG radiation is unknown, but predicted to withstand
energy better than metal based anti-retropulsion devices since BackStop retains a solid form at
increased temperature. Further, a solid shape, form, and function should not be compromised even
if an ablation crater may be created. This study tests the ability of BackStop polymer to withstand
shape and function in response to Ho:YAG laser energy at various pulse energies. Laser polymer
interaction is characterized using fast flash imaging technique and pressure transient measurement.
We report design and construction of an FPGA-based high-speed swept-source polarization-sensitive optical coherence
tomography (SS-PS-OCT) system for clinical retinal imaging. Clinical application of the SS-PS-OCT system is accurate
measurement and display of thickness, phase retardation and birefringence maps of the retinal nerve fiber layer (RNFL)
in human subjects for early detection of glaucoma. The FPGA-based SS-PS-OCT system provides three incident
polarization states on the eye and uses a bulk-optic polarization sensitive balanced detection module to record two
orthogonal interference fringe signals. Interference fringe signals and relative phase retardation between two orthogonal
polarization states are used to obtain Stokes vectors of light returning from each RNFL depth. We implement a
Levenberg-Marquardt algorithm on a Field Programmable Gate Array (FPGA) to compute accurate phase retardation
and birefringence maps. For each retinal scan, a three-state Levenberg-Marquardt nonlinear algorithm is applied to 360
clusters each consisting of 100 A-scans to determine accurate maps of phase retardation and birefringence in less than 1
second after patient measurement allowing real-time clinical imaging-a speedup of more than 300 times over previous
implementations. We report application of the FPGA-based SS-PS-OCT system for real-time clinical imaging of patients
enrolled in a clinical study at the Eye Institute of Austin and Duke Eye Center.
Segmentation of the retinal nerve fiber layer (RNFL) from swept source polarization-sensitive optical coherence
tomography (SS-PSOCT) images is required to determine RNFL thickness and calculate birefringence. Traditional
RNFL segmentation methods based on image processing and boundary detection algorithms utilize only optical
reflectivity contrast information, which is strongly affected by speckle noise. We present a novel approach to segment
the retinal nerve fiber layer (RNFL) using SS-PSOCT images including both optical reflectivity and phase retardation
information. The RNFL anterior boundary is detected based on optical reflectivity change due to refractive index
difference between the vitreous and inner limiting membrane. The posterior boundary of the RNFL is a transition zone
composed of birefringent axons extending from retinal ganglion cells and may be detected by a change in birefringence.
A posterior boundary detection method is presented that segments the RNFL by minimizing the uncertainty of RNFL
birefringence determined by a Levenberg-Marquardt nonlinear fitting algorithm. Clinical results from a healthy
volunteer show that the proposed segmentation method estimates RNFL birefringence and phase retardation with lower
uncertainty and higher continuity than traditional intensity-based approaches.
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