Characteristics of Hirayama Disease in Young South Korean Soldiers.

BACKGROUND AND PURPOSE: The purpose of this study was to describe the clinical presentation and features in electrodiagnostic and imaging investigations of young South Korean males diagnosed with Hirayama disease (HD). METHODS: We reviewed the electronic medical records of South Korean enlisted soldiers who were diagnosed with HD and discharged from military service during 2011-2021. We investigated the clinical characteristics and results of electrodiagnostic and magnetic resonance imaging (MRI) investigations. We analyzed laterality and identified the involved muscles using needle electromyography (EMG). Loss of lordosis, localized cervical cord atrophy, loss of attachment between the posterior dura and subjacent lamina, asymmetric flattening of the cord, crescent-shaped mass in the posterior epidural space, and noncompressive intramedullary T2-weighted high signal intensity were investigated using neutral- or flexion-position MRI. RESULTS: Forty-two male patients aged 20.2±0.8 years (mean±standard deviation) were identified. All patients complained of hand weakness, and 10 complained of hand tremor (23.8%). Four patients (9.5%) had symptoms in both upper limbs, and five (11.9%) had sensory disturbances. Needle EMG revealed that muscles in the C7-T1 myotome were commonly involved, and C5-C6 involvement of the deltoid (10.5%) and biceps brachii (12.5%) was also observed. In cervical MRI, localized cord atrophy (90.0%) was the most characteristic finding, and cord atrophy was most severe at the C5-C6 level (58.3%). CONCLUSIONS: This is the first description of a large number of patients with HD in South Korea. The clinical presentation and features found in electrodiagnostic and imaging investigations will improve the understanding of HD in the young South Korean male population.

Efficient evaluation of a three-dimensional eye-box in a near-eye display using light-field acquisition of luminance distribution.

We propose, what we believe to be, a novel assessment methodology for evaluating three-dimensional (3D) characteristics of an eye-box volume in a near-eye display (NED) using a light-field (LF) data acquired at a single measuring distance. In contrast to conventional evaluation methods for the eye-box, where a light measuring device (LMD) changes its position in lateral and longitudinal directions, the proposed method requires an LF of the luminance distribution (LFLD) for the NEDs captured only at the single observation distance, and the 3D eye-box volume is evaluated via a simple post-analysis. We explore an LFLD-based representation for the efficient evaluation of the 3D eye-box, and the theoretical analysis is validated by simulation results using Zemax OpticStudio. As experimental verifications, we acquired an LFLD for an augmented reality NED at a single observation distance. The assessed LFLD constructed a 3D eye-box successfully over the distance range of 20 mm, which included assessment conditions where it was hard to measure the light rays' distributions directly in the conventional methodologies. The proposed method is further verified by comparing with actual observed images of the NED both inside and outside of the evaluated 3D eye-box.

Analysis on image quality of a holographic lens with a non-converging signal wave for compact near-eye displays.

We analyze an image quality of a holographic lens (HL) in order to implement compact near-eye displays using a flat-panel-type micro-display panel. The proposed method utilizes a non-converging signal wave in a fabrication process of the HL, so that it provides affordable eye-box size with minimizing the aberration due to rays in the off-Bragg condition. For analyzing and optimizing the HL based on the non-converging signal wave, we introduce a comprehensive analysis model for an assessment of the image quality in the HL. The analysis model, inspired from the conventional lens design strategy for near-eye displays, evaluates the focal spot quality for incident rays forming each pixel with considering the on- and off-Bragg diffraction. The theoretical analysis is validated by simulation results using a volume hologram model in Zemax OpticStudio. As experimental verifications, we realize a prototype system using photopolymer-based HLs in a green color with the high transmittance of 89.3%. The image quality of the HLs is analyzed, which coincides well with the proposed analysis and assessment metric. By building a compact experimental setup employing the HL and a micro-organic light emitting diode display, we present see-through images with 8.0 mm of eye-box with reduced aberrations.

Projection-type see-through near-to-eye display with a passively enlarged eye-box by combining a holographic lens and diffuser.

We propose a projection-type see-through near-to-eye display by combining two holographic optical elements (HOEs), a holographic lens with the on-axis projection configuration and a holographic diffuser. The proposed method provides an enlarged eye-box by virtue of diffusing properties of an HOE diffuser (HOED) without any temporal multiplexing methods. In this paper, a thorough analysis on imaging characteristics of an HOE lens (HOEL) according to the projection configuration is provided, so that we optimize the recording geometry of the HOEL with the passively enlarged eye-box. The theoretical analysis is validated by simulation results using a volume hologram model in OpticStudio. As experimental verifications, we realize a prototype of the proposed method using the photopolymer-based HOEs in a single color. The fabricated HOEL and HOED show high transmittance of 84.9% and 62.2%, respectively. By using the fabricated HOED with a diffusing angle over 20 ° and an angular selectivity of 8.7 °, the prototype successfully provides see-through images with the eye-box larger than 5 mm in width.

Pre-compensation method for optimizing recording process of holographic optical element lenses with spherical wave reconstruction.

We propose a pre-compensated recording process of holographic optical element (HOE) lenses, where both of reference and signal waves have spherical wavefronts, for solving a wavelength mismatch problem between the recording and displaying process. Based on a localized approximation for aperiodic volume gratings, the wavelength mismatch and shrinkage effects are pre-compensated by optimizing the recording setup of HOE lenses, so that the Bragg condition of each local grating is satisfied. In order to realize the practical implementations of recording setup, complicated wavefronts to be required for the wavelength and shrinkage compensation are approximated into spherical waves. The simulation results using the volume hologram models of OpticStudio verify that the undesirable focal shift and color breakup problems in the HOE lens due to the wavelength mismatch are compensated. Displaying experiments using a full-color HOE lens with the field of view of 30° are presented, where the maximum wavelength mismatch between the recording and displaying process is 17 nm.

Validation of Attitude and Heading Reference System and Microsoft Kinect for Continuous Measurement of Cervical Range of Motion Compared to the Optical Motion Capture System.

OBJECTIVE: To compare optical motion capture system (MoCap), attitude and heading reference system (AHRS) sensor, and Microsoft Kinect for the continuous measurement of cervical range of motion (ROM). METHODS: Fifteen healthy adult subjects were asked to sit in front of the Kinect camera with optical markers and AHRS sensors attached to the body in a room equipped with optical motion capture camera. Subjects were instructed to independently perform axial rotation followed by flexion/extension and lateral bending. Each movement was repeated 5 times while being measured simultaneously with 3 devices. Using the MoCap system as the gold standard, the validity of AHRS and Kinect for measurement of cervical ROM was assessed by calculating correlation coefficient and Bland-Altman plot with 95% limits of agreement (LoA). RESULTS: MoCap and ARHS showed fair agreement (95% LoA<10°), while MoCap and Kinect showed less favorable agreement (95% LoA>10°) for measuring ROM in all directions. Intraclass correlation coefficient (ICC) values between MoCap and AHRS in -40° to 40° range were excellent for flexion/extension and lateral bending (ICC>0.9). ICC values were also fair for axial rotation (ICC>0.8). ICC values between MoCap and Kinect system in -40° to 40° range were fair for all motions. CONCLUSION: Our study showed feasibility of using AHRS to measure cervical ROM during continuous motion with an acceptable range of error. AHRS and Kinect system can also be used for continuous monitoring of flexion/extension and lateral bending in ordinary range.

Characteristics of Dysphagia in Severe Traumatic Brain Injury Patients: A Comparison With Stroke Patients.

OBJECTIVE: To compare the swallowing characteristics of dysphagic patients with traumatic brain injury (TBI) with those of dysphagic stroke patients. METHODS: Forty-one patients with TBI were selected from medical records (between December 2004 to March 2013) and matched to patients with stroke (n=41) based on age, sex, and disease duration. Patients' swallowing characteristics were analyzed retrospectively using a videofluoroscopic swallowing study (VFSS) and compared between both groups. Following thorough review of medical records, patients who had a history of diseases that could affect swallowing function at the time of the study were excluded. Dysphagia characteristics and severity were evaluated using the American Speech-Language-Hearing Association National Outcome Measurement System swallowing scale, clinical dysphagia scale, and the videofluoroscopic dysphagia scale. RESULTS: There was a significant difference in radiological lesion location (p=0.024) between the two groups. The most common VFSS finding was aspiration or penetration, followed by decreased laryngeal elevation and reduced epiglottis inversion. Swallowing function, VFSS findings, or quantified dysphagia severity showed no significant differences between the groups. In a subgroup analysis of TBI patients, the incidence of tube feeding was higher in patients with surgical intervention than in those without (p=0.011). CONCLUSION: The swallowing characteristics of dysphagic patients after TBI were comparable to those of dysphagic stroke patients. Common VFSS findings comprised aspiration or penetration, decreased laryngeal elevation, and reduced epiglottis inversion. Patients who underwent surgical intervention after TBI were at high risk of tube feeding requirement.

Diagnosis and Clinical Course of Unexplained Dysphagia.

OBJECTIVE: To investigate the final diagnosis of patients with unexplained dysphagia and the clinical and laboratory findings supporting the diagnosis. METHODS: We retrospectively analyzed 143 patients with dysphagia of unclear etiology who underwent a videofluoroscopic swallowing study (VFSS). The medical records were reviewed, and patients with a previous history of diseases that could affect swallowing were categorized into a missed group. The remaining patients were divided into an abnormal or normal VFSS group based on the VFSS findings. The clinical course and final diagnosis of each patient were examined. RESULTS: Among the 143 patients, 62 (43%) had a previous history of diseases that could affect swallowing. Of the remaining 81 patients, 58 (72.5%) had normal VFSS findings and 23 (27.5%) had abnormal VFSS findings. A clear cause of dysphagia was not identified in 9 of the 23 patients. In patients in whom a cause was determined, myopathy was the most common cause (n=6), followed by laryngeal neuropathy (n=4) and drug-induced dysphagia (n=3). The mean ages of the patients in the normal and abnormal VFSS groups differed significantly (62.52±15.00 vs. 76.83±10.24 years, respectively; p<0.001 by Student t-test). CONCLUSION: Careful history taking and physical examination are the most important approaches for evaluating patients with unexplained swallowing difficulty. Even if VFSS findings are normal in the pharyngeal phase, some patients may need additional examinations. Electrodiagnostic studies and laboratory tests should be considered for patients with abnormal VFSS findings.

Recent progress in see-through three-dimensional displays using holographic optical elements [Invited].

The principles and characteristics of see-through 3D displays are presented. We especially focus on the integral-imaging display system using a holographic optical element (IDHOE), which is able to display 3D images and satisfy the see-through property at the same time. The technique has the advantage of the high transparency and capability of displaying autostereoscopic 3D images. We have analyzed optical properties of IDHOE for both recording and displaying stages. Furthermore, various studies of new applications and system improvements for IDHOE are introduced. Thanks to the characteristics of holographic volume grating, it is possible to implement a full-color lens-array holographic optical element and conjugated reconstruction as well as 2D/3D convertible IDHOE. Studies on the improvements of viewing characteristics including a viewing angle, fill factor, and resolution are also presented. Lastly, essential issues and their possible solutions are discussed as future work.

Viewing angle enhancement of an integral imaging display using Bragg mismatched reconstruction of holographic optical elements.

Holographic-optical-element (HOE)-based integral imaging display can be applied to augmented reality. However, a narrow viewing angle is a bottleneck for commercialization. Here, we propose a method to enhance the viewing angle of the integral imaging display using Bragg mismatched reconstruction of HOEs. The viewing angle of the integral imaging display can be enlarged with two probe waves, which form two different viewing zones. The effect of Bragg mismatched reconstruction is analyzed with simulation and experiment. In order to show feasibility of the proposed method, a display experiment is demonstrated.

Three-dimensional/two-dimensional convertible projection screen using see-through integral imaging based on holographic optical element.

We propose a 3D/2D convertible screen using a holographic optical element and angular multiplexing method of volume hologram. The proposed screen, named a multiplexed holographic optical element screen (MHOES), is composed of passive optical components, and displaying modes between 3D and 2D modes are converted according to projection directions. In a recording process, the angular multiplexing method by using two reference waves with different incidence angles enables the functions of 3D and 2D screens to be recorded in a single holographic material. Also, in order to avoid the bulky experimental setup due to adopting different projectors for the 3D and 2D modes, the projection part is realized based on a prism. The designed projection part enables the single projector to present 3D on 2D mode, where the 3D and 2D contents are simultaneously displayed in one scene, without active components. The optical characteristics of MHOES are experimentally analyzed, and displaying experiments with a full-color MHOES are presented in order to verify the 3D/2D convertibility and see-through properties.

Plasmonic cavity-apertures as dynamic pixels for the simultaneous control of colour and intensity.

Despite steady technological progress, displays are still subject to inherent limitations in resolution improvement and pixel miniaturization because a series of colours is generally expressed by a combination of at least three primary colour pixels. Here we propose a structure comprising a metal cavity and a nanoaperture, which we refer to as a cavity-aperture, to simultaneously control the colour and intensity of transmitted light in a single pixel. The metal cavity constructs plasmonic standing waves to organize the spatial distribution of amplitudes according to wavelength, and the nanoaperture permits light with a specific wavelength and amplitude to pass through it, depending on the nanoaperature's relative position in the cavity and the polarization state of the incident light. Therefore, the cavity-aperture has the potential to function as a dynamic colour pixel. This design method may be helpful in developing various photonic devices, such as micro-imaging systems and multiplexed sensors.

Space bandwidth product enhancement of holographic display using high-order diffraction guided by holographic optical element.

A space bandwidth product (SBP) enhancement method for holographic display using high-order diffraction of a spatial light modulator (SLM) is proposed. Among numerous high order diffraction terms, the plus-minus first and the zeroth are adopted and guided by holographic optical elements (HOEs) to an identical direction with the same intensity. By using a set of electro-shutters synchronized with corresponding order component, the system acts as if three SLMs are tiled in the horizontal direction. To confirm the feasibility of using HOE as the guiding optics for the system, several optical characteristics of the recording material are measured before using them. Furthermore, a computer generated hologram algorithm is proposed for compensating the wavefront distortion caused by use of the HOE. The demonstrated system achieves a three-fold increase in SBP of a single SLM. The results are verified experimentally.

Real-time depth controllable integral imaging pickup and reconstruction method with a light field camera.

In this paper, we develop a real-time depth controllable integral imaging system. With a high-frame-rate camera and a focus controllable lens, light fields from various depth ranges can be captured. According to the image plane of the light field camera, the objects in virtual and real space are recorded simultaneously. The captured light field information is converted to the elemental image in real time without pseudoscopic problems. In addition, we derive characteristics and limitations of the light field camera as a 3D broadcasting capturing device with precise geometry optics. With further analysis, the implemented system provides more accurate light fields than existing devices without depth distortion. We adapt an f-number matching method at the capture and display stage to record a more exact light field and solve depth distortion, respectively. The algorithm allows the users to adjust the pixel mapping structure of the reconstructed 3D image in real time. The proposed method presents a possibility of a handheld real-time 3D broadcasting system in a cheaper and more applicable way as compared to the previous methods.

Lamina 3D display: projection-type depth-fused display using polarization-encoded depth information.

In order to realize three-dimensional (3D) displays, various multiplexing methods have been proposed to add the depth dimension to two-dimensional scenes. However, most of these methods have faced challenges such as the degradation of viewing qualities, the requirement of complicated equipment, and large amounts of data. In this paper, we further developed our previous concept, polarization distributed depth map, to propose the Lamina 3D display as a method for encoding and reconstructing depth information using the polarization status. By adopting projection optics to the depth encoding system, reconstructed 3D images can be scaled like images of 2D projection displays. 3D reconstruction characteristics of the polarization-encoded images are analyzed with simulation and experiment. The experimental system is also demonstrated to show feasibility of the proposed method.

See-through integral imaging display using a resolution and fill factor-enhanced lens-array holographic optical element.

We report on the development of a high-resolution see-through integral imaging system with a resolution and fill factor-enhanced lens-array holographic optical element (HOE). We propose a procedure for fabricating of a lens pitch controllable lens-array HOE. By controlling the recording plane and performing repetitive recordings process, the lens pitch of the lens-array HOE could be substantially reduced, with a high fill factor and the same numerical aperture compared to the reference lens-array. We demonstrated the feasibility by fabricating a lens-array HOE with a 500 micrometer pitch. Since the pixel pitch of the projected image can be easily controlled in projection type integral imaging, the small lens pitch enhances the quality of the displayed 3D image very effectively. The enhancement of visibility of the 3D images is verified in experimental results.

Projection-type dual-view three-dimensional display system based on integral imaging.

A dual-view display system provides two different images in different directions. Most of them only present two-dimensional images for observers. In this paper, we propose a projection-type dual-view three-dimensional (3D) display system based on integral imaging. To assign directivities to the images, a projection-type display and dual-view screen with lenticular lenses are implemented. The lenticular lenses split the collimated image from the projection device into two different directions. The separated images are integrated by a single lens array in front of the screen, and full-parallax 3D images are observed in two different viewing regions. The visibility of the reconstructed 3D images can be improved by using high-density lenticular lenses and a high numerical aperture lens array. We explain the principle of the proposed method and verify the feasibility of the proposed system with simulations and experimental results.

Two-dimensional and three-dimensional transparent screens based on lens-array holographic optical elements.

Two-dimensional (2D) and three-dimensional (3D) transparent screens can be created using lens-array holographic optical elements (HOEs). Lens-array HOEs can be used to perform 2D and 3D imaging for Bragg matched images while maintaining the transparent properties of the images in the background scenes. 2D or 3D imaging on the proposed screen is determined by the relative size of an elemental-lens on the lens-array to a pixel on the projected image. The 2D and 3D displays on the lens-array HOEs are implemented by the diffusion of light on each elemental-lens and by taking advantage of reflection-type integral imaging, respectively. We constructed an HOE recording setup and recorded two lens-array HOEs having different optical specifications, permitting them to function as 2D and 3D transparent screens. Experiments regarding 2D and 3D imaging on the proposed transparent screens are carried out and the viewing characteristics in both cases are discussed. The experimental results show that the proposed screens are capable of providing 2D and 3D images properly while satisfying the see-through properties.

Solution for pseudoscopic problem in integral imaging using phase-conjugated reconstruction of lens-array holographic optical elements.

We propose an optical pseudoscopic to orthoscopic conversion method for integral imaging using a lens-array holographic optical element (LAHOE), which solves the pseudoscopic problem. The LAHOE reconstructs an array of diverging spherical waves when a probe wave with the phase-conjugated condition is imposed on it, while an array of converging spherical waves is reconstructed in ordinary reconstruction. For given pseudoscopic elemental images, the array of the diverging spherical waves integrates the orthoscopic three-dimensional images without a distortion. The principle of the proposed method is verified by the experiments of displaying the integral imaging on the LAHOE using computer generated and optically acquired elemental images.

Reflection-type integral imaging system using a diffuser holographic optical element.

A reflection-type integral imaging (InIm) system using a diffuser holographic optical element (DHOE) is proposed for improving the fill factor of displayed three-dimensional images. The DHOE performs an optical function similar to that for a conventional diffuser only for Bragg matched light, while Bragg mismatched light passes through the DHOE. Elemental images projected under Bragg matching condition are scattered by the DHOE. Meanwhile, light reflected by a concave mirror-array becomes Bragg mismatched light, and is integrated into three-dimensional images without the fill factor problem. The optical characteristics of the DHOE are examined by measuring diffraction efficiencies, and the feasibility of the fill-factor-improved InIm is verified by a concave mirror-array and DHOE.