1. Articles from brian e. applegate

    1-24 of 39 1 2 »
    1. Organ of Corti vibration within the intact gerbil cochlea measured by volumetric optical coherence tomography and vibrometry

      Organ of Corti vibration within the intact gerbil cochlea measured by volumetric optical coherence tomography and vibrometry

      There is indirect evidence that the mammalian cochlea in the low-frequency apical and the more commonly-studied high-frequency basal regions function in fundamentally different ways. Here, we directly tested this hypothesis by measuring sound-induced vibrations of the organ of Corti (OoC) at three turns of the gerbil cochlea using volumetric optical coherence tomography vibrometry (VOCTV), an approach that permits non-invasive imaging through the bone. In the apical turn, there was little frequency selectivity and the displacement-versus-frequency curves had low-pass filter characteristics with a corner frequency of ~0.5-0.9 kHz. The vibratory magnitudes increased compressively with increasing stimulus intensity at all ...

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    2. Osmotic stabilization prevents cochlear synaptopathy after blast trauma

      Osmotic stabilization prevents cochlear synaptopathy after blast trauma

      Traumatic noise causes hearing loss by damaging sensory hair cells and their auditory synapses. There are no treatments. Here, we investigated mice exposed to a blast wave approximating a roadside bomb. In vivo cochlear imaging revealed an increase in the volume of endolymph, the fluid within scala media, termed endolymphatic hydrops. Endolymphatic hydrops, hair cell loss, and cochlear synaptopathy were initiated by trauma to the mechanosensitive hair cell stereocilia and were K + -dependent. Increasing the osmolality of the adjacent perilymph treated endolymphatic hydrops and prevented synaptopathy, but did not prevent hair cell loss. Conversely, inducing endolymphatic hydrops in control mice ...

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    3. Endoscopic optical coherence tomography enables morphological and subnanometer vibratory imaging of the porcine cochlea through the round window

      Endoscopic optical coherence tomography enables morphological and subnanometer vibratory imaging of the porcine cochlea through the round window

      A highly phase stable hand-held (HH) endoscopic system has been developed for optical coherence tomography and vibrometry. Designed to transit the ear canal to the middle ear space and peer through the round window (RW), it is capable of imaging the vibratory function of the cochlear soft tissues with subnanometer scale sensitivity. A side-looking, 9 cm long rigid endoscope with a distal diameter of 1.2 mm, was able to fit within the RW niche and provide imaging access. The phase stability was achieved in part by fully integrating a Michelson interferometer into the HH device. Ex vivo imaging of ...

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    4. Contrast enhancement of pump-probe optical coherence tomography (PP-OCT) based molecular imaging using methylene blue loaded PLGA particles

      Contrast enhancement of pump-probe optical coherence tomography (PP-OCT) based molecular imaging using methylene blue loaded PLGA particles

      Atherosclerosis, a condition in which plaque accumulates on the inner wall of arteries, is often recognized as a precursor to cardiovascular diseases (CVDs), the most common causes of death in the US. Optical Coherence Tomography (OCT) is an intravascular optical diagnosis tool, which can be used to obtain high resolution morphological images of atherosclerotic plaque. However, atherosclerotic plaque components, such as macrophages, can be misclassified due to their signal similarities to fibrin accumulations, cholesterol crystals and microcalcifications. To overcome these challenges, we develop a biocompatible contrast agent to enhance molecular imaging of a Pump-Probe OCT (PPOCT) system. Methylene blue (MB ...

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    5. ELHnet: a convolutional neural network for classifying cochlear endolymphatic hydrops imaged with optical coherence tomography

      ELHnet: a convolutional neural network for classifying cochlear endolymphatic hydrops imaged with optical coherence tomography

      Detection of endolymphatic hydrops is important for diagnosing Meniere’s disease, and can be performed non-invasively using optical coherence tomography (OCT) in animal models as well as potentially in the clinic. Here, we developed ELHnet, a convolutional neural network to classify endolymphatic hydrops in a mouse model using learned features from OCT images of mice cochleae. We trained ELHnet on 2159 training and validation images from 17 mice, using only the image pixels and observer-determined labels of endolymphatic hydrops as the inputs. We tested ELHnet on 37 images from 37 mice that were previously not used, and found that the ...

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    6. Computer-aided detection and quantification of endolymphatic hydrops within the mouse cochlea in vivo using optical coherence tomography

      Computer-aided detection and quantification of endolymphatic hydrops within the mouse cochlea in vivo using optical coherence tomography

      Diseases that cause hearing loss and/or vertigo in humans such as Meniere’s disease are often studied using animal models. The volume of endolymph within the inner ear varies with these diseases. Here, we used a mouse model of increased endolymph volume, endolymphatic hydrops, to develop a computer-aided objective approach to measure endolymph volume from images collected in vivo using optical coherence tomography. The displacement of Reissner’s membrane from its normal position was measured in cochlear cross sections. We validated our computer-aided measurements with manual measurements and with trained observer labels. This approach allows for computer-aided detection of ...

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    7. Multimodal optical coherence tomography and fluorescence lifetime imaging with interleaved excitation sources for simultaneous endogenous and exogenous fluorescence

      Multimodal optical coherence tomography and fluorescence lifetime imaging with interleaved excitation sources for simultaneous endogenous and exogenous fluorescence

      Multimodal imaging probes a variety of tissue properties in a single image acquisition by merging complimentary imaging technologies. Exploiting synergies amongst the data, algorithms can be developed that lead to better tissue characterization than could be accomplished by the constituent imaging modalities taken alone. The combination of optical coherence tomography (OCT) with fluorescence lifetime imaging microscopy (FLIM) provides access to detailed tissue morphology and local biochemistry. The optical system described here merges 1310 nm swept-source OCT with time-domain FLIM having excitation at 355 and 532 nm. The pulses from 355 and 532 nm lasers have been interleaved to enable simultaneous ...

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    8. Optical Coherence Tomography to Measure Sound-Induced Motions Within the Mouse Organ of Corti In Vivo

      Optical Coherence Tomography to Measure Sound-Induced Motions Within the Mouse Organ of Corti In Vivo

      The measurement of mechanical vibrations within the living cochlea is critical to understanding the first nonlinear steps in auditory processing, hair cell stimulation, and cochlear amplification. However, it has proven to be a challenging endeavor. This chapter describes how optical coherence tomography (OCT) can be used to measure vibrations within the tissues of the organ of Corti. These experimental measurements can be performed within the unopened cochlea of living mice routinely and reliably.

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    9. Automated analysis of multimodal fluorescence lifetime imaging and optical coherence tomography data for the diagnosis of oral cancer in the hamster cheek pouch model

      Automated analysis of multimodal fluorescence lifetime imaging and optical coherence tomography data for the diagnosis of oral cancer in the hamster cheek pouch model

      It is known that the progression of oral cancer is accompanied by changes in both tissue biochemistry and morphology. A multimodal imaging approach combining functional and structural imaging modalities could therefore provide a more comprehensive prognosis of oral cancer. This idea forms the central theme of the current study, wherein this premise is examined in the context of a multimodal imaging system that combines fluorescence lifetime imaging (FLIM) and optical coherence tomography (OCT). Towards this end, in the first part of the present study, the diagnostic advantage obtained by using both fluorescence intensity and lifetime information is assessed. In the ...

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    10. High-speed spectral calibration by complex FIR filter in phase-sensitive optical coherence tomography

      High-speed spectral calibration by complex FIR filter in phase-sensitive optical coherence tomography

      Swept-laser sources offer a number of advantages for Phase-sensitive Optical Coherence Tomography (PhOCT). However, inter- and intra-sweep variability leads to calibration errors that adversely affect phase sensitivity. While there are several approaches to overcoming this problem, our preferred method is to simply calibrate every sweep of the laser. This approach offers high accuracy and phase stability at the expense of a substantial processing burden. In this approach, the Hilbert phase of the interferogram from a reference interferometer provides the instantaneous wavenumber of the laser, but is computationally expensive. Fortunately, the Hilbert transform may be approximated by a Finite Impulse-Response (FIR ...

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    11. Phase-sensitive optical coherence tomography-based vibrometry using a highly phase-stable akinetic swept laser source

      Phase-sensitive optical coherence tomography-based vibrometry using a highly phase-stable akinetic swept laser source

      Phase-sensitive Optical Coherence Tomography (PhOCT) is an emerging tool for in vivo investigation of the vibratory function of the intact middle and inner ear. PhOCT is able to resolve micron scale tissue morphology in three dimensions as well as measure picometer scale motion at each spatial position. Most PhOCT systems to date have relied upon the phase stability offered by spectrometer detection. On the other hand swept laser source based PhOCT offers a number of advantages including balanced detection, long imaging depths, and high imaging speeds. Unfortunately the inherent phase instability of traditional swept laser sources has necessitated complex user ...

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    12. Miniature, minimally invasive, tunable endoscope for investigation of the middle ear

      Miniature, minimally invasive, tunable endoscope for investigation of the middle ear

      We demonstrate a miniature, tunable, minimally invasive endoscope for diagnosis of the auditory system. The probe is designed to sharply image anatomical details of the middle ear without the need for physically adjusting the position of the distal end of the endoscope. This is achieved through the addition of an electrowetted, tunable, electronically-controlled lens to the optical train. Morphological imaging is enabled by scanning light emanating from an optical coherence tomography system. System performance was demonstrated by imaging part of the ossicular chain and wall of the middle ear cavity of a normal mouse. During the experiment, we electronically moved ...

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    13. Feature Of The Week 04/05/15: Noninvasive in vivo Imaging Reveals Differences Between Tectorial Membrane and Basilar Membrane Traveling Waves in the Mouse Cochlea

      Feature Of The Week 04/05/15: Noninvasive in vivo Imaging Reveals Differences Between Tectorial Membrane and Basilar Membrane Traveling Waves in the Mouse Cochlea

      Sound is encoded within the auditory portion of the inner ear, the cochlea, after propagating down its length as a traveling wave. For over half a century, vibratory measurements to study cochlear traveling waves have been made using invasive approaches such as laser Doppler vibrometry. While these studies have provided critical information regarding the non-linear processes within the living cochlea that increase the amplitude of vibration and sharpen frequency tuning, the data have typically been limited to point measurements of basilar membrane vibration. In addition, opening the cochlea may alter its function and affect the findings. Here we describe volumetric ...

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    14. Molecular Imaging in Optical Coherence Tomography

      Molecular Imaging in Optical Coherence Tomography

      Optical coherence tomography (OCT) is a medical imaging technique that provides tomographic images at micron scales in three dimensions and high speeds. The addition of molecular contrast to the available morphological image holds great promise for extending OCT’s impact in clinical practice and beyond. Fundamental limitations prevent OCT from directly taking advantage of powerful molecular processes such as fluorescence emission and incoherent Raman scattering. A wide range of approaches is being researched to provide molecular contrast to OCT. Here we review those approaches with particular attention to those that derive their molecular contrast directly from modulation of the OCT ...

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    15. In vivo molecular contrast OCT imaging of methylene blue

      In vivo molecular contrast OCT imaging of methylene blue

      An 830-nm spectral-domain optical coherence tomography (OCT) system with an integrated 663-nm diode pump laser has been developed to enable molecular contrast OCT imaging of methylene blue (MB), a common vital dye used clinically. The introduction of the 663-nm diode laser, which acts as the pump in this implementation of pump-probe OCT (PPOCT), represents a minor modification to an otherwise typical OCT system. A newly developed background subtraction technique completely removes all background from intensity noise at the pump modulation frequency, simplifying the interpretation of PPOCT images. These developments have enabled the first in vivo imaging of MB with PPOCT ...

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    16. Noninvasive in vivo imaging reveals differences between tectorial membrane and basilar membrane traveling waves in the mouse cochlea

      Noninvasive in vivo imaging reveals differences between tectorial membrane and basilar membrane traveling waves in the mouse cochlea

      Sound is encoded within the auditory portion of the inner ear, the cochlea, after propagating down its length as a traveling wave. For over half a century, vibratory measurements to study cochlear traveling waves have been made using invasive approaches such as laser Doppler vibrometry. Although these studies have provided critical information regarding the nonlinear processes within the living cochlea that increase the amplitude of vibration and sharpen frequency tuning, the data have typically been limited to point measurements of basilar membrane vibration. In addition, opening the cochlea may alter its function and affect the findings. Here we describe volumetric ...

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    17. Simultaneous morphological and biochemical endogenous optical imaging of atherosclerosis

      Simultaneous morphological and biochemical endogenous optical imaging of atherosclerosis

      Aims The aim of this study was to validate novel imaging technology for simultaneous morphological and biochemical endogenous optical imaging of coronary atherosclerotic plaque. Methods and results Optical coherence tomography (OCT) generates high-resolution 3D images of plaque morphology and endogenous fluorescence lifetime imaging microscopy (FLIM) characterizes biochemical composition. Both imaging modalities rely on plaque's intrinsic optical characteristics, making contrast agents unnecessary. A multimodal OCT/FLIM system was utilized to generate luminal biochemical maps superimposed on high-resolution (7 µm axial and 13 µm lateral) structural volumetric images. Forty-seven fresh postmortem human coronary segments were imaged: pathological intimal thickening (PIT, n ...

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    18. Phase-sensitive optical coherence tomography using an Vernier-tuned distributed Bragg reflector swept laser in the mouse middle ear

      Phase-sensitive optical coherence tomography using an Vernier-tuned distributed Bragg reflector swept laser in the mouse middle ear

      Phase-sensitive optical coherence tomography (PhOCT) offers exquisite sensitivity to mechanical vibration in biological tissues. There is growing interest in using PhOCT for imaging the nanometer scale vibrations of the ear in animal models of hearing disorders. Swept-source-based systems offer fast acquisition speeds, suppression of common mode noise via balanced detection, and good signal roll-off. However, achieving high phase stability is difficult due to nonlinear laser sweeps and trigger jitter in a typical swept laser source. Here, we report on the initial application of a Vernier-tuned distributed Bragg reflector (VT-DBR) swept laser as the source for a fiber-based PhOCT system. The ...

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    19. Feature of the Week 10/19/14: Automated Classification of Optical Coherence Tomography Images for the Diagnosis of Oral Malignancy in the Hamster Cheek Pouch

      Feature of the Week 10/19/14: Automated Classification of Optical Coherence Tomography Images for the Diagnosis of Oral Malignancy in the Hamster Cheek Pouch

      Most studies evaluating the potential of optical coherence tomography (OCT) for the diagnosis of oral cancer are based on visual assessment of OCT B-scans by trained experts. Human interpretation of the large pool of data acquired by modern high-speed OCT systems, however, can be cumbersome and extremely time consuming. Development of image analysis methods for automated and quantitative OCT image analysis could therefore facilitate the evaluation of such a large volume of data. We report automated algorithms for quantifying structural features that are associated with the malignant transformation of the oral epithelium based on image processing of OCT data. The ...

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    20. Automated classification of optical coherence tomography images for the diagnosis of oral malignancy in the hamster cheek pouch

      Automated classification of optical coherence tomography images for the diagnosis of oral malignancy in the hamster cheek pouch

      Most studies evaluating the potential of optical coherence tomography (OCT) for the diagnosis of oral cancer are based on visual assessment of OCT B-scans by trained experts. Human interpretation of the large pool of data acquired by modern high-speed OCT systems, however, can be cumbersome and extremely time consuming. Development of image analysis methods for automated and quantitative OCT image analysis could therefore facilitate the evaluation of such a large volume of data. We report automated algorithms for quantifying structural features that are associated with the malignant transformation of the oral epithelium based on image processing of OCT data. The ...

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    21. Feature Of The Week 2/23/14: Texas A&M University Reports on In vivo Pump-Probe Optical Coherence Tomography Imaging in Xenopus Laevis

      Feature Of The Week 2/23/14: Texas A&M University Reports on In vivo Pump-Probe Optical Coherence Tomography Imaging in Xenopus Laevis

      Currently, optical coherence tomography (OCT), is not capable of obtaining molecular information often crucial for identification of disease. To enable molecular imaging with OCT, we have further developed a technique that harnesses transient changes in light absorption in the sample to garner molecular information. A Fourier-domain Pump-Probe OCT (PPOCT) system utilizing a 532 nm pump and 830 nm probe has been developed for imaging hemoglobin. Methylene blue, a biological dye with well-known photophysics, was used to characterize the system before investigating the origin of the hemoglobin PPOCT signal. The first in vivo PPOCT images were recorded of the vasculature in ...

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    22. In vivo pump-probe optical coherence tomography imaging in Xenopus laevis

      In vivo pump-probe optical coherence tomography imaging in Xenopus laevis

      Currently, optical coherence tomography (OCT), is not capable of obtaining molecular information often crucial for identification of disease. To enable molecular imaging with OCT, we have further developed a technique that harnesses transient changes in light absorption in the sample to garner molecular information. A Fourier-domain Pump-Probe OCT (PPOCT) system utilizing a 532 nm pump and 830 nm probe has been developed for imaging hemoglobin. Methylene blue, a biological dye with well-know photophysics, was used to characterize the system before investigating the origin of the hemoglobin PPOCT signal. The first in vivo PPOCT images were recorded of the vasculature in ...

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    23. In vivo vibrometry inside the apex of the mouse cochlea using spectral domain optical coherence tomography

      In vivo vibrometry inside the apex of the mouse cochlea using spectral domain optical coherence tomography

      Sound transduction within the auditory portion of the inner ear, the cochlea, is a complex nonlinear process. The study of cochlear mechanics in large rodents has provided important insights into cochlear function. However, technological and experimental limitations have restricted studies in mice due to their smaller cochlea. These challenges are important to overcome because of the wide variety of transgenic mouse strains with hearing loss mutations that are available for study. To accomplish this goal, we used spectral domain optical coherence tomography to visualize and measure sound-induced vibrations of intracochlear tissues. We present, to our knowledge, the first vibration measurements ...

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    24. Feature Of The Week 9/23/12: MGH Researchers Demonstrate Flexible Transbronchial OCT Imaging Needles for Biopsy Guidance

      Feature Of The Week 9/23/12: MGH Researchers Demonstrate Flexible Transbronchial OCT Imaging Needles for Biopsy Guidance

      Optical coherence tomography (OCT) systems routinely use single-mode optical fibers to transfer light to and from biological samples.  The tiny cross section, low-cost, and flexibility of single-mode optical fibers have proven to be a powerful attribute that allows for a wide variety optical coherence tomography (OCT) probes to be constructed including ultra small catheters, guidewires, and endoscope to get light to and from hard to reach places in the human body.  OCT equipped fiber optic needle probes are increasingly proving to be powerful technique for guidance of needle placement (search "needle" in the search box to see some of the ...

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    1-24 of 39 1 2 »
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    1. (39 articles) Brian E. Applegate
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    Multimodality optical imaging combining optical coherence tomography (OCT) and fluorescence lifetime imaging (FLIM) for morphological and biochemical tissue characterization Fourier Domain Pump-Probe Optical Coherence Tomography Imaging of Melanin Feature Of The Week 6/20/10: Fourier Domain Pump-Probe Optical Coherence Tomography Imaging A dual-modality optical coherence tomography and fluorescence lifetime imaging microscopy system for simultaneous morphological and biochemical tissue characterization In Vivo Simultaneous Morphological and Biochemical Optical Imaging of Oral Epithelial Cancer Cornea microstructure and mechanical responses measured with nonlinear optical and optical coherence microscopy using sub-10-fs pulses Biophysical Mechanisms Underlying Hearing Loss Associated with a Shortened Tectorial Membrane Feature Of The Week 9/23/12: MGH Researchers Demonstrate Flexible Transbronchial OCT Imaging Needles for Biopsy Guidance Feature Of The Week 04/05/15: Noninvasive in vivo Imaging Reveals Differences Between Tectorial Membrane and Basilar Membrane Traveling Waves in the Mouse Cochlea Real-time detection of circulating tumor cells in living animals using functionalized large gold nanorods Macular OCT-angiography parameters to predict the clinical stage of nonproliferative diabetic retinopathy: an exploratory analysis Central perpendicular line in macular spectral-domain optical coherence tomography in five eyes