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1.
Biomed Opt Express ; 15(5): 3094-3111, 2024 May 01.
Article in English | MEDLINE | ID: mdl-38855698

ABSTRACT

Two-photon excited fluorescence (TPEF) is a powerful technique that enables the examination of intrinsic retinal fluorophores involved in cellular metabolism and the visual cycle. Although previous intensity-based TPEF studies in non-human primates have successfully imaged several classes of retinal cells and elucidated aspects of both rod and cone photoreceptor function, fluorescence lifetime imaging (FLIM) of the retinal cells under light-dark visual cycle has yet to be fully exploited. Here we demonstrate a FLIM assay of photoreceptors and retinal pigment epithelium (RPE) that reveals key insights into retinal physiology and adaptation. We found that photoreceptor fluorescence lifetimes increase and decrease in sync with light and dark exposure, respectively. This is likely due to changes in all-trans-retinol and all-trans-retinal levels in the outer segments, mediated by phototransduction and visual cycle activity. During light exposure, RPE fluorescence lifetime was observed to increase steadily over time, as a result of all-trans-retinol accumulation during the visual cycle and decreasing metabolism caused by the lack of normal perfusion of the sample. Our system can measure the fluorescence lifetime of intrinsic retinal fluorophores on a cellular scale, revealing differences in lifetime between retinal cell classes under different conditions of light and dark exposure.

2.
Opt Express ; 32(3): 3290-3307, 2024 Jan 29.
Article in English | MEDLINE | ID: mdl-38297554

ABSTRACT

Multiplexed fluorescence detection has become increasingly important in the fields of biosensing and bioimaging. Although a variety of excitation/detection optical designs and fluorescence unmixing schemes have been proposed to allow for multiplexed imaging, rapid and reliable differentiation and quantification of multiple fluorescent species at each imaging pixel is still challenging. Here we present a pulsed interleaved excitation spectral fluorescence lifetime microscopic (PIE-sFLIM) system that can simultaneously image six fluorescent tags in live cells in a single hyperspectral snapshot. Using an alternating pulsed laser excitation scheme at two different wavelengths and a synchronized 16-channel time-resolved spectral detector, our PIE-sFLIM system can effectively excite multiple fluorophores and collect their emission over a broad spectrum for analysis. Combining our system with the advanced live-cell labeling techniques and the lifetime/spectral phasor analysis, our PIE-sFLIM approach can well unmix the fluorescence of six fluorophores acquired in a single measurement, thus improving the imaging speed in live-specimen investigation.


Subject(s)
Diagnostic Imaging , Fluorescence Resonance Energy Transfer , Fluorescence Resonance Energy Transfer/methods , Fluorescent Dyes
3.
Clin Transl Radiat Oncol ; 43: 100670, 2023 Nov.
Article in English | MEDLINE | ID: mdl-37736140

ABSTRACT

Aims: The number of Proton Therapy (PT) facilities is still limited worldwide, and the access to treatment could be characterized by patients' logistic and economic challenges. Aim of the present survey is to assess the support provided to patients undergoing PT across Europe. Methods: Through a personnel contact, an online questionnaire (62 multiple-choice and open-ended questions) via Microsoft Forms was administered to 10 European PT centers. The questionnaire consisted of 62 questions divided into 6 sections: i) personal data; ii) general information on clinical activity; iii) fractionation, concurrent systemic treatments and technical aspects of PT facility; iv) indication to PT and reimbursement policies; v) economic and/ or logistic support to patients vi) participants agreement on statements related to the possible limitation of access to PT. A qualitative analysis was performed and reported. Results: From March to May 2022 all ten involved centers filled the survey. Nine centers treat from 100 to 500 patients per year. Paediatric patients accounted for 10-30%, 30-50% and 50-70% of the entire cohort for 7, 2 and 1 center, respectively. The most frequent tumours treated in adult population were brain tumours, sarcomas and head and neck carcinomas; in all centers, the mean duration of PT is longer than 3 weeks. In 80% of cases, the treatment reimbursement for PT is supplied by the respective country's Health National System (HNS). HNS also provides economic support to patients in 70% of centers, while logistic and meal support is provided in 20% and 40% of centers, respectively. PT facilities offer economic and/or logistic support in 90% of the cases. Logistic support for parents of pediatric patients is provided by HNS only in one-third of centers. Overall, 70% of respondents agree that geographic challenges could limit a patient's access to proton facilities and 60% believe that additional support should be given to patients referred for PT care. Conclusions: Relevant differences exist among European countries in supporting patients referred to PT in their logistic and economic challenges. Further efforts should be made by HNSs and PT facilities to reduce the risk of inequities in access to cancer care with protons.

4.
Biomed Eng Educ ; 2(2): 197-202, 2022.
Article in English | MEDLINE | ID: mdl-35789898

ABSTRACT

We describe our experiences with the first offering of a new program, BMEntored, for supporting first-year doctoral students in Biomedical Engineering (BME) during their first semester. The goal of BMEntored was to enhance the first-semester experience of first-year doctoral students in BME with an emphasis on guiding students in selecting a research supervisor and promoting cross-cohort, cross-lab social connections.

5.
Commun Biol ; 5(1): 18, 2022 01 11.
Article in English | MEDLINE | ID: mdl-35017629

ABSTRACT

Fluorescence lifetime imaging microscopy (FLIM) is a powerful tool to quantify molecular compositions and study molecular states in complex cellular environment as the lifetime readings are not biased by fluorophore concentration or excitation power. However, the current methods to generate FLIM images are either computationally intensive or unreliable when the number of photons acquired at each pixel is low. Here we introduce a new deep learning-based method termed flimGANE (fluorescence lifetime imaging based on Generative Adversarial Network Estimation) that can rapidly generate accurate and high-quality FLIM images even in the photon-starved conditions. We demonstrated our model is up to 2,800 times faster than the gold standard time-domain maximum likelihood estimation (TD_MLE) and that flimGANE provides a more accurate analysis of low-photon-count histograms in barcode identification, cellular structure visualization, Förster resonance energy transfer characterization, and metabolic state analysis in live cells. With its advantages in speed and reliability, flimGANE is particularly useful in fundamental biological research and clinical applications, where high-speed analysis is critical.


Subject(s)
Cytological Techniques/methods , Deep Learning , Image Processing, Computer-Assisted/methods , Microscopy, Fluorescence/methods , Molecular Imaging/methods , Algorithms , Fluorescent Dyes/analysis , Fluorescent Dyes/chemistry , HeLa Cells , Humans
6.
Opt Lett ; 38(21): 4374-7, 2013 Nov 01.
Article in English | MEDLINE | ID: mdl-24177097

ABSTRACT

A low-resolution path-length-multiplexed scattering angle diverse optical coherence tomography (PM-SAD-OCT) is constructed to investigate the scattering properties of the retinal nerve fiber layer (RNFL). Low-resolution PM-SAD-OCT retinal images acquired from a healthy human subject show the variation of RNFL scattering properties at retinal locations around the optic nerve head. The results are consistent with known retinal ganglion cell neural anatomy and principles of light scattering. Application of PM-SAD-OCT may provide potentially valuable diagnostic information for clinical retinal imaging.


Subject(s)
Retina/cytology , Scattering, Radiation , Tomography, Optical Coherence/methods , Animals , Humans , Phantoms, Imaging
7.
Invest Ophthalmol Vis Sci ; 53(8): 4380-95, 2012 Jul 01.
Article in English | MEDLINE | ID: mdl-22570345

ABSTRACT

PURPOSE: We identified candidate optical coherence tomography (OCT) markers for early glaucoma diagnosis. Time variation of retinal nerve fiber layer (RNFL) thickness, phase retardation, birefringence, and reflectance using polarization sensitive optical coherence tomography (PS-OCT) were measured in three non-human primates with induced glaucoma in one eye. We characterized time variation of RNFL thickness, phase retardation, birefringence, and reflectance with elevated intraocular pressure (IOP). METHODS: One eye of each of three non-human primates was laser treated to increase IOP. Each primate was followed for a 30-week period. PS-OCT measurements were recorded at weekly intervals. Reflectance index (RI) is introduced to characterize RNFL reflectance. Associations between elevated IOP and RNFL thickness, phase retardation, birefringence, and reflectance were characterized in seven regions (entire retina, inner and outer rings, and nasal, temporal, superior and inferior quadrants) by linear and non-linear mixed-effects models. RESULTS: Elevated IOP was achieved in three non-human primate eyes with an average increase of 13 mm Hg over the study period. Elevated IOP was associated with decreased RNFL thickness in the nasal region (P = 0.0002), decreased RNFL phase retardation in the superior (P = 0.046) and inferior (P = 0.021) regions, decreased RNFL birefringence in the nasal (P = 0.002) and inferior (P = 0.029) regions, and loss of RNFL reflectance in the outer rings (P = 0.018). When averaged over the entire retinal area, only RNFL reflectance showed a significant decrease (P = 0.028). CONCLUSIONS: Of the measured parameters, decreased RNFL reflectance was the most robust correlate with glaucomatous damage. Candidate cellular mechanisms are considered for decreased RNFL reflectance, including mitochondrial dysfunction and retinal ganglion cell apoptosis.


Subject(s)
Disease Models, Animal , Glaucoma/diagnosis , Nerve Fibers/pathology , Optic Nerve Diseases/diagnosis , Retinal Ganglion Cells/pathology , Animals , Birefringence , Disease Progression , Intraocular Pressure , Macaca fascicularis , Macaca mulatta , Pilot Projects , Tomography, Optical Coherence
8.
Dis Esophagus ; 25(5): 410-5, 2012 Jul.
Article in English | MEDLINE | ID: mdl-21899654

ABSTRACT

Previous randomized studies comparing the two commonly used palliative treatments for incurable esophageal cancer, i.e. stent insertion and intraluminal brachytherapy, have revealed the pros and cons of each therapy. While stent treatment offers a more prompt effect, brachytherapy results in more long-lasting relief of dysphagia and a better health-related quality of life (HRQL) in those living longer. This prospective pilot study aimed to explore the feasibility and safety of combining these two regimes and incorporating a single high dose of internal radiation. Patients with newly diagnosed, incurable cancer of the esophagus and dysphagia were eligible for inclusion, and stent insertion followed by a single dose (12 Gy) of brachytherapy was performed as a two-stage procedure. Clinical parameters including HRQL and adverse events were registered at inclusion, and 1, 2, 3, 6, and 12 months later. Twelve patients (nine males) with a median age of 73 years (range 54-85) were included. Stent insertion followed by a single dose of brachytherapy was successfully performed in all but one patient who was treated with stent only. Relief of dysphagia was achieved in the majority of cases (10/11, P < 0.05), but HRQL did not improve except for dysphagia-related items. Only minor adverse events, including chest pain, reflux, and restenosis, were reported. The median survival time after inclusion was 6.6 months. Our conclusion is that the combination of stent insertion and single high-dose brachytherapy seems to be a feasible and safe palliative regime in patients with advanced esophageal cancer. Randomized trials comparing the efficacy of this strategy to stent insertion or brachytherapy alone are warranted.


Subject(s)
Adenocarcinoma/therapy , Brachytherapy/methods , Carcinoma, Squamous Cell/therapy , Esophageal Neoplasms/therapy , Palliative Care/methods , Prosthesis Implantation/methods , Stents , Adenocarcinoma/complications , Aged , Aged, 80 and over , Carcinoma, Squamous Cell/complications , Combined Modality Therapy , Deglutition Disorders/etiology , Deglutition Disorders/therapy , Esophageal Neoplasms/complications , Feasibility Studies , Female , Humans , Karnofsky Performance Status , Male , Middle Aged , Pilot Projects , Prospective Studies , Quality of Life , Treatment Outcome
9.
Lung Cancer ; 71(2): 166-72, 2011 Feb.
Article in English | MEDLINE | ID: mdl-20541833

ABSTRACT

BACKGROUND: Several attempts to increase the locoregional control in locally advanced lung cancer including concurrent chemotherapy, accelerated fractionation and dose escalation have been made during the last years. As the EGFR directed antibody cetuximab has shown activity concurrent with radiotherapy in squamous cell carcinoma of the head and neck, as well as in stage IV NSCLC combined with chemotherapy, we wanted to investigate radiotherapy with concurrent cetuximab in locally advanced NSCLC, a tumour type often over expressing the EGF-receptor. METHODS: Between February 2006 and August 2007 75 patients in stage III NSCLC with good performance status (PS 0 or 1) and adequate lung function (FEV1>1.0) were enrolled in this phase II study at eight institutions. Treatment consisted of 2 cycles of induction chemotherapy, docetaxel 75 mg/m² and cisplatin 75 mg/m² with 3 weeks interval. An initial dose of cetuximab 400 mg/m² was given before start of 3D-CRT to 68 Gy with 2 Gy per fraction in 7 weeks concurrent with weekly cetuximab 250 mg/m². TOXICITY was scored weekly during radiotherapy (CTC 3.0), and after treatment the patients were followed every third month with CT-scans, toxicity scoring and QLQ. RESULTS: Seventy-one patients were eligible for analysis as four were incorrectly enrolled. HISTOLOGY: adenocarcinoma 49%, squamous cell carcinoma 39% and other NSCLC 12%. The majority had PS 0 (62.5%), median age 62.2 (42-81), 50% were women and 37% had a pre-treatment weight loss>5%. TOXICITY: esophagitis grade 1-2: 72%; grade 3: 1.4%. Hypersensitivity reactions grade 3-4: 5.6%. Febrile neutropenia grade 3-4: 15.4%. Skin reactions grade 1-2: 74%; grade 3: 4.2%. Diarrhoea grade 1-2: 38%; grade 3: 11.3%. Pneumonitis grade 1-2: 26.8%; grade 3: 4.2%; grade 5: 1.4%. The median follow-up was 39 months for patients alive and the median survival was 17 months with a 1-, 2- and 3-year OS of 66%, 37% and 29% respectively. Until now local or regional failure has occurred in 20 patients and 22 patients have developed distant metastases. Weight loss, PS and stage were predictive for survival in univariate as well as in multivariate analysis. CONCLUSION: Induction chemotherapy followed by concurrent cetuximab and RT to 68 Gy is clearly feasible with promising survival. TOXICITY, e.g. pneumonitis and esophagitis is low compared to most schedules with concurrent chemotherapy. This treatment strategy should be evaluated in a randomised manner vs. concurrent chemoradiotherapy to find out if it is a valid treatment option.


Subject(s)
Antineoplastic Agents/administration & dosage , Antineoplastic Agents/therapeutic use , Antineoplastic Combined Chemotherapy Protocols/therapeutic use , Carcinoma, Non-Small-Cell Lung/therapy , Lung Neoplasms/therapy , Adult , Aged , Aged, 80 and over , Antibodies, Monoclonal/administration & dosage , Antibodies, Monoclonal/therapeutic use , Antibodies, Monoclonal, Humanized , Antineoplastic Agents/toxicity , Antineoplastic Combined Chemotherapy Protocols/toxicity , Carcinoma, Non-Small-Cell Lung/drug therapy , Carcinoma, Non-Small-Cell Lung/pathology , Carcinoma, Non-Small-Cell Lung/radiotherapy , Cetuximab , Cisplatin/administration & dosage , Cisplatin/therapeutic use , Combined Modality Therapy , Docetaxel , Female , Humans , Lung Neoplasms/drug therapy , Lung Neoplasms/pathology , Lung Neoplasms/radiotherapy , Male , Middle Aged , Neoplasm Staging , Patient Compliance , Quality of Life , Recurrence , Survival Analysis , Sweden , Taxoids/administration & dosage , Taxoids/therapeutic use , Treatment Outcome
11.
Opt Express ; 17(16): 13402-17, 2009 Aug 03.
Article in English | MEDLINE | ID: mdl-19654746

ABSTRACT

Complex polarization ratio (CPR) in materials with birefringence and biattenuance is shown as a logarithmic spiral in the complex plane. A multi-state Levenberg-Marquardt nonlinear fitting algorithm using the CPR trajectory collected by polarization sensitive optical coherence tomography (PS-OCT) was developed to determine polarization properties of an anisotropic scattering medium. The Levenberg-Marquardt nonlinear fitting algorithm using the CPR trajectory is verified using simulated PS-OCT data with speckle noise. Birefringence and biattenuance of a birefringent film, ex-vivo rodent tail tendon and in-vivo primate retinal nerve fiber layer were determined using measured CPR trajectories and the Levenberg-Marquardt nonlinear fitting algorithm.


Subject(s)
Algorithms , Image Enhancement/methods , Image Interpretation, Computer-Assisted/methods , Microscopy, Polarization/methods , Tomography, Optical Coherence/methods , Animals , Humans , Rats
12.
Invest Ophthalmol Vis Sci ; 50(11): 5238-46, 2009 Nov.
Article in English | MEDLINE | ID: mdl-19494208

ABSTRACT

PURPOSE: To determine the degree of correlation between spatial characteristics of the retinal nerve fiber layer (RNFL) birefringence (Delta n(RNFL)) surrounding the optic nerve head (ONH) with the corresponding anatomy of retinal ganglion cell (RGC) axons and their respective organelles. METHODS: RNFL phase retardation per unit depth (PR/UD, proportional to Delta n(RNFL)) was measured in two cynomolgus monkeys by enhanced polarization-sensitive optical coherence tomography (EPS-OCT). The monkeys were perfused with glutaraldehyde and the eyes were enucleated and prepared for transmission electron microscopy (TEM) histologic analysis. Morphologic measurements from TEM images were used to estimate neurotubule density (rho(RNFL)), axoplasmic area (A(x)) mode, axon area (A(a)) mode, slope (u) of the number of neurotubules versus axoplasmic area (neurotubule packing density), fractional area of axoplasm in the nerve fiber bundle (f), mitochondrial fractional area in the nerve fiber bundle (x(m)), mitochondria-containing axon profile fraction (m(p)), and length of axonal membrane profiles per unit of nerve fiber bundle area (L(am)/A(b)). Registered PR/UD and morphologic parameters from corresponding angular sections were then correlated by using Pearson's correlation and multilevel models. RESULTS: In one eye there was a statistically significant correlation between PR/UD and rho(RNFL) (r = 0.67, P = 0.005) and between PR/UD and neurotubule packing density (r = 0.70, P = 0.002). Correlation coefficients of r = 0.81 (P = 0.01) and r = 0.50 (P = 0.05) were observed between the PR/UD and A(x) modes for each respective subject. CONCLUSIONS: Neurotubules are the primary source of birefringence in the RNFL of the primate retina.


Subject(s)
Axons/physiology , Microtubules/physiology , Nerve Fibers/physiology , Optic Disk/physiology , Retinal Ganglion Cells/physiology , Animals , Axons/ultrastructure , Birefringence , Female , Macaca fascicularis , Nerve Fibers/ultrastructure , Optic Disk/ultrastructure , Organelles , Retinal Ganglion Cells/ultrastructure , Tomography, Optical Coherence
13.
Proc SPIE Int Soc Opt Eng ; 7171: 71710X, 2009.
Article in English | MEDLINE | ID: mdl-20431701

ABSTRACT

Retinal nerve fiber layer (RNFL) thickness, a measure of glaucoma progression, can be measured in images acquired by spectral domain optical coherence tomography (OCT). The accuracy of RNFL thickness estimation, however, is affected by the quality of the OCT images. In this paper, a new parameter, signal deviation (SD), which is based on the standard deviation of the intensities in OCT images, is introduced for objective assessment of OCT image quality. Two other objective assessment parameters, signal to noise ratio (SNR) and signal strength (SS), are also calculated for each OCT image. The results of the objective assessment are compared with subjective assessment. In the subjective assessment, one OCT expert graded the image quality according to a three-level scale (good, fair, and poor). The OCT B-scan images of the retina from six subjects are evaluated by both objective and subjective assessment. From the comparison, we demonstrate that the objective assessment successfully differentiates between the acceptable quality images (good and fair images) and poor quality OCT images as graded by OCT experts. We evaluate the performance of the objective assessment under different quality assessment parameters and demonstrate that SD is the best at distinguishing between fair and good quality images. The accuracy of RNFL thickness estimation is improved significantly after poor quality OCT images are rejected by automated objective assessment using the SD, SNR, and SS.

14.
J Small Anim Pract ; 48(9): 486-96, 2007 Sep.
Article in English | MEDLINE | ID: mdl-17617166

ABSTRACT

OBJECTIVE: To evaluate the efficacy and safety of ciclosporin therapy alone or in combination with corticosteroids and/or ketoconazole in dogs with diagnosis of meningoencephalomyelitis of unknown aetiology. METHODS: Medical records of 10 dogs diagnosed with meningoencephalomyelitis of unknown aetiology and treated with ciclosporin therapy alone or in combination with corticosteroids and/or ketoconazole were reviewed at the Veterinary Medical Teaching Hospital, University of Wisconsin-Madison. Laboratory abnormalities, side effects, clinical and cerebrospinal fluid responses to treatment and association between blood ciclosporin level and response to treatment were evaluated. Histopathological diagnosis was available in three patients. RESULTS: No significant abnormalities were detected on serial complete blood count and serum chemistry panel in any of the dogs. Side effects of ciclosporin therapy included excessive shedding, gingival hyperplasia and hypertrichosis. Overall median survival time for all dogs in the study was 930 days (range, 60 to more than 1290 days). In all dogs, serial cerebrospinal fluid analysis showed a marked improvement in the inflammation. CLINICAL SIGNIFICANCE: Results suggest that ciclosporin either alone or in combination with ketoconazole may be a safe and effective treatment for meningoencephalomyelitis of unknown aetiology in dogs.


Subject(s)
Cyclosporine/therapeutic use , Dog Diseases/drug therapy , Immunosuppressive Agents/therapeutic use , Meningoencephalitis/veterinary , Adrenal Cortex Hormones/therapeutic use , Animals , Blood Cell Count/veterinary , Blood Chemical Analysis/veterinary , Cyclosporine/adverse effects , Dog Diseases/etiology , Dog Diseases/mortality , Dogs , Drug Therapy, Combination , Female , Immunosuppressive Agents/adverse effects , Ketoconazole/therapeutic use , Meningoencephalitis/drug therapy , Meningoencephalitis/etiology , Meningoencephalitis/mortality , Prognosis , Safety , Survival Analysis , Time Factors , Treatment Outcome
15.
Phys Med Biol ; 51(15): 3759-67, 2006 Aug 07.
Article in English | MEDLINE | ID: mdl-16861779

ABSTRACT

Incorporation of polarimetric sensitivity into optical coherence tomography can provide additional image contrast when structures of interest are optically anisotropic (e.g., fibrous tissue). We present a generalized technique based on polarization-sensitive optical coherence tomography to detect changes in depth-resolved fibre orientation and thus increase image contrast in multiple-layered birefringent tissues. A high contrast B-scan image of collagen fibre orientation is shown for a porcine intervertebral disc cartilage specimen that exhibited low backscattering intensity contrast. Interfaces in the annulus fibrosus identified using depth-resolved fibre orientation allowed quantification of lamellae thickness. Moreover, the technique detects changes in fibre orientation without intense processing needed to effectively quantify tissue retardation and diattenuation.


Subject(s)
Birefringence , Tomography, Optical Coherence/instrumentation , Tomography, Optical Coherence/methods , Animals , Cartilage/pathology , Humans , Intervertebral Disc/pathology , Light , Microscopy, Polarization , Scattering, Radiation , Software , Swine
16.
J Opt Soc Am A Opt Image Sci Vis ; 23(3): 679-90, 2006 Mar.
Article in English | MEDLINE | ID: mdl-16539067

ABSTRACT

Trajectory of the normalized Stokes vector on the Poincaré sphere corresponding to light propagation in anisotropic tissues with birefringence and biattenuance is derived. Analytic expressions are determined from the Serret-Frenet formulas and derivatives of arc length for five quantities including the tangent, normal, and binormal vectors with curvature and torsion. Depth variation of curvature and torsion of normalized Stokes vector trajectories corresponding to light propagating in rodent tail tendon are given. Use of analytic expressions for depth variation of curvature and torsion of the normalized Stokes vector trajectories on the Poincaré sphere is discussed for analysis of polarization-sensitive optical coherence tomography data recorded from anisotropic biological tissues with birefringence and biattenuance.


Subject(s)
Algorithms , Connective Tissue/physiology , Connective Tissue/ultrastructure , Image Interpretation, Computer-Assisted/methods , Models, Biological , Refractometry/methods , Tomography, Optical Coherence/methods , Animals , Anisotropy , Computer Simulation , Humans
17.
Exp Eye Res ; 81(1): 81-9, 2005 Jul.
Article in English | MEDLINE | ID: mdl-15978258

ABSTRACT

The purpose of this study was to measure the peripapillary retinal nerve fiber layer (RNFL) thickness, phase retardation (PR), and depth-resolved birefringence (Deltan) of the normal primate eye using Enhanced Polarization-Sensitivity Optical Coherence Tomography (EPS-OCT). Both eyes of two rhesus monkeys were imaged with EPS-OCT. A multiple incident polarization state nonlinear fitting algorithm was used to determine RNFL phase retardation. RNFL thickness (RNFLT) was determined from the corresponding EPS-OCT intensity image and phase retardation per unit depth (PR/UD, proportional to Deltan) was calculated by dividing PR by RNFLT. Peripapillary area maps consisting of pixels uniformly distributed along a radius from 0.8 to 1.8 mm from the center of the optic nervehead were constructed for RNFLT, PR, and PR/UD. Average PR/UD in the superior and inferior quadrants was 18 degrees /100 mivrom (Deltan=4.2 x 10(-4)) and average PR/UD in the nasal and temporal quadrants was 6.3 degrees /100 microm (Deltan=1.5 x 10(-4)). Relative magnitude of PR radial gradient is similar to that of RNFLT radial gradient and no radial gradient was observed for PR/UD. Polarization-dependent amplitude attenuation per unit depth (PDAA/UD) was 0.02 rad/100 microm in thick RNFL regions. RNFL birefringence was higher in the arcuate bundles compared to nasal and temporal fibers (P=0.001). Birefringence was nearly equal in nasal and temporal quadrants. No statistically significant (P=0.01) radial gradient of birefringence was observed in any quadrant. RNFL birefringence is believed to originate from anisotropic structures within the cytoskeleton of the parallel axons. Birefringence differences presented in this study cannot be explained by the known axon diameter distribution around the optic nervehead and suggest other sources of the birefringence signal including neurotubules and neurofilaments.


Subject(s)
Retinal Ganglion Cells/physiology , Algorithms , Animals , Birefringence , Female , Macaca mulatta , Nerve Fibers/physiology , Nerve Fibers/ultrastructure , Optic Nerve/anatomy & histology , Retinal Ganglion Cells/cytology , Tomography, Optical Coherence
18.
J Opt Soc Am A Opt Image Sci Vis ; 22(3): 552-60, 2005 Mar.
Article in English | MEDLINE | ID: mdl-15770994

ABSTRACT

Polarization-sensitive optical coherence tomography provides high-resolution cross-sectional characterization of birefringence in turbid media. Weakly birefringent biological tissues such as the retinal nerve fiber layer (RNFL) require advanced speckle noise reduction for high-sensitivity measurement of form birefringence. We present a novel method for high-sensitivity birefringence quantification by using enhanced polarization-sensitive optical coherence tomography (EPS-OCT) and introduce the polarimetric signal-to-noise ratio, a mathematical tool for analyzing speckle noise in polarimetry. Multiple incident polarization states and non-linear fitting of normalized Stokes vectors allow determination of retardation with +/-1 degrees uncertainty with invariance to unknown unitary polarization transformations. Results from a weakly birefringent turbid film and in vivo primate RNFL are presented. In addition, we discuss the potential of EPS-OCT for noninvasive quantification of intracellular filamentous nanostructures, such as neurotubules in the RNFL that are lost during the progression of glaucoma.


Subject(s)
Algorithms , Image Interpretation, Computer-Assisted/methods , Nephelometry and Turbidimetry/methods , Optic Disk/physiology , Optic Disk/ultrastructure , Refractometry/methods , Tomography, Optical Coherence/methods , Animals , Birefringence , Female , Macaca mulatta , Reproducibility of Results , Sensitivity and Specificity
19.
Lasers Surg Med ; 33(4): 219-25, 2003.
Article in English | MEDLINE | ID: mdl-14571445

ABSTRACT

BACKGROUND AND OBJECTIVES: Tissue response to thermal, electrical, or chemical stimuli are important in the health and survival of tissue. We report experimental results to assess tissue response to various stimuli using a low coherence differential phase interferometer. STUDY DESIGN/MATERIALS AND METHODS: The optical system utilized to measure tissue response is a novel fiber-based phase sensitive optical low coherence reflectometer (PS-OLCR). Inasmuch as the PS-OLCR works with back-reflected light, noninvasive sensing of tissue response to stimuli is possible. In addition to high lateral (approximately 10 microm) and longitudinal (approximately 10 microm) resolution, PS-OLCR can measure sub-wavelength changes in optical path-length (Angstrom/nanometer range) by extracting the phase difference between interference fringes in two channels corresponding to orthogonal polarization modes. RESULTS: When light spatially splits into two polarization states, precise analysis of surface topography or tissue surface response such as swelling or collapse are possible. Time resolved measurements of nanometer-scale path length changes in response to electrical and thermal stimuli are demonstrated using longitudinally delayed polarization channels. CONCLUSIONS: Since PS-OLCR is a useful tool to detect ultra-small path length changes, the system has potential to aid scientists in investigating important phenomena in biomaterials and developing useful diagnostic and therapeutic imaging modalities. Applications include tissue surface profilometry, measurement of tissue, and cell response to various stimuli, high-resolution intensity and phase imaging.


Subject(s)
Arteries/physiology , Cartilage/physiology , Interferometry , Animals , Arteriosclerosis/physiopathology , Electric Stimulation , Hot Temperature , In Vitro Techniques , Lasers , Light , Nanotechnology , Rabbits , Signal Processing, Computer-Assisted , Swine
20.
Article in English | MEDLINE | ID: mdl-12020654

ABSTRACT

Differential phase optical low coherence reflectometry (OLCR) was used to detect sub-wavelength displacements in the infrared-sensitive thoracic pit organ of Melanophila acuminata (Coleoptera: Buprestidae) upon absorption of infrared radiation at 3.39 microm. The displacement had more complex morphology but similar amplitude ( approximately 100 nm at 1 W cm(-2)) when compared to the displacement measured from the exocuticle in an alternate region on the beetle's body. In addition, a simplified finite difference model was developed to predict the temperature distribution and resultant thermal expansion in the pit organ tissue. The experimental and model results were interpreted to help clarify the mechanism by which the sensilla in the pit organ convert infrared radiation to neural signals. The results of this paper are discussed in relation to the photo-thermal-mechanical transduction hypothesis. This is the first experimental examination of the transduction mechanism in Melanophila acuminata.


Subject(s)
Coleoptera/physiology , Coleoptera/radiation effects , Infrared Rays , Signal Transduction/radiation effects , Animals , Fiber Optic Technology , Mechanoreceptors/metabolism , Models, Biological , Sensory Thresholds , Temperature , Thermoreceptors/metabolism , Time Factors
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