Neuro-behavioral Effects of Luminance Level on Visual Performance and Discomfort with High Dynamic Range Displays

High dynamic range (HDR) displays are designed to simulate the range of perceived brightness afforded by the real world. To study how visual performance and visual comfort are affected by luminance level, 34 participants with normal vision were first asked to discriminate the brightness of two circles presented on LCD and OLED screens to determine the luminance threshold for brightness discrimination. They then judge the orientation of a circular grating target alternating with a luminance circle while their visually-evoked potentials and viewing discomfort was assessed. Results show contrast ratio is more important than luminance difference in brightness discrimination. Regression model based on behavioral outcomes suggest the maximal OLED luminance (647 cd/m2) was perceived as bright as 1035 cd/m2 on LCD screen. In discerning grating orientation, the VEP signals associated with the luminance level increased along with viewing discomfort and the signals associated with the grating target decreased along the reduced accuracy of orientation discrimination. The threshold luminance for visual discrimination and discomfort is 695 cd/m2. The OLED is visually more comfortable and affords better visual performance than LCD when the screen luminance is high due to its higher contrast and more moderate luminance. These findings suggest higher contrast ratio rather than greater luminance difference is important for brightness discrimination. To reduce visual discomfort while achieving better visual performance in dynamic images, better contrast ratio and black level are more important than greater screen luminance

Digital Radiography with Computerized Conventional Monitors Compared to Medical Monitors in Vertical Root Fracture Diagnosis

Introduction: Vertical root fracture (VRF) is a complication which is chiefly diagnosed radiographically. Recently, film-based radiography has been substituted with digital radiography. At the moment, there is a wide range of monitors available in the market for viewing digital images. The present study aims to compare the diagnostic accuracy, sensitivity and specificity of medical and conventional monitors in detection of vertical root fractures. Material and Methods: In this in vitro study 228 extracted single-rooted human teeth were endodontically treated. Vertical root fractures were induced in 114 samples. The teeth were imaged by a digital charge-coupled device radiography using parallel technique. The images were evaluated by a radiologist and an endodontist on two medical and conventional liquid-crystal display (LCD) monitors twice. Z-test was used to analyze the sensitivity, accuracy and specificity of each monitor. Significance level was set at 0.05. Inter and intra observer agreements were calculated by Cohen’s kappa. Results: Accuracy, specificity and sensitivity for conventional monitor were calculated as 67.5%, 72%, 62.5% respectively; and data for medical grade monitor were 67.5%, 66.5% and 68% respectively. Statistical analysis showed no significant differences in detecting VRF between the two techniques. Inter-observer agreement for conventional and medical monitor was 0.47 and 0.55 respectively (moderate). Intra-observer agreement was 0.78 for medical monitor and 0.87 for conventional one (substantial). Conclusion The type of monitor does not influence diagnosis of vertical root fractures

Capsule endoscopy system with novel imaging algorithms

Wireless capsule endoscopy (WCE) is a state-of-the-art technology to receive images of human intestine for medical diagnostics. In WCE, the patient ingests a specially designed electronic capsule which has imaging and wireless transmission capabilities inside it. While the capsule travels through the gastrointestinal (GI) tract, it captures images and sends them wirelessly to an outside data logger unit. The data logger stores the image data and then they are transferred to a personal computer (PC) where the images are reconstructed and displayed for diagnosis. The key design challenge in WCE is to reduce the area and power consumption of the capsule while maintaining acceptable image reconstruction. In this research, the unique properties of WCE images are identified by analyzing hundreds of endoscopic images and video frames, and then these properties are used to develop novel and low complexity compression algorithms tailored for capsule endoscopy. The proposed image compressor consists of a new YEF color space converter, lossless prediction coder, customizable chrominance sub-sampler and an efficient Golomb-Rice encoder. The scheme has both lossy and lossless modes and is further customized to work with two lighting modes – conventional white light imaging (WLI) and emerging narrow band imaging (NBI). The average compression ratio achieved using the proposed lossy compression algorithm is 80.4% for WBI and 79.2% for NBI with high reconstruction quality index for both bands. Two surveys have been conducted which show that the reconstructed images have high acceptability among medical imaging doctors and gastroenterologists. The imaging algorithms have been realized in hardware description language (HDL) and their functionalities have been verified in field programmable gate array (FPGA) board. Later it was implemented in a 0.18 μm complementary metal oxide semiconductor (CMOS) technology and the chip was fabricated. Due to the low complexity of the core compressor, it consumes only 43 µW of power and 0.032 mm2 of area. The compressor is designed to work with commercial low-power image sensor that outputs image pixels in raster scan fashion, eliminating the need of significant input buffer memory. To demonstrate the advantage, a prototype of the complete WCE system including an FPGA based electronic capsule, a microcontroller based data logger unit and a Windows based image reconstruction software have been developed. The capsule contains the proposed low complexity image compressor and can generate both lossy and lossless compressed bit-stream. The capsule prototype also supports both white light imaging (WLI) and narrow band imaging (NBI) imaging modes and communicates with the data logger in full duplex fashion, which enables configuring the image size and imaging mode in real time during the examination. The developed data logger is portable and has a high data rate wireless connectivity including Bluetooth, graphical display for real time image viewing with state-of-the-art touch screen technology. The data are logged in micro SD cards and can be transferred to PC or Smartphone using card reader, USB interface, or Bluetooth wireless link. The workstation software can decompress and show the reconstructed images. The images can be navigated, marked, zoomed and can be played as video. Finally, ex-vivo testing of the WCE system has been done in pig's intestine to validate its performance

Medical Grade Displays in Radiation Oncology

In modern day medicine medical images are an integral part of clinical care. They are used in almost every clinical department from diagnosis to treatment and beyond. Medical images are viewed using electronic displays of various sizes, shapes, hardware, and software. Some clinical departments, like diagnostic radiology, require electronic displays with a large dynamic range, high contrast and high resolution. Other departments do not have any requirements and will use any commercially available display in their clinical workflow. Viewing the same medical image on different electronic displays with different hardware, software or calibration setup could influence how observers perceive and analyze these images. This occurs often when a patient is referred from diagnostic radiology to another clinical specialty department such as radiation oncology. In this case, the patient’s tumor would be diagnosed using a high-performance display while their treatment will be planned and delivered using a commercially available display. In this dissertation, at first, an experiment was design to examine and verify the visual contrast sensitivity of observers using the two types of displays used in the clinic. Observers were tasked with detecting a modulating bar pattern using each display under different background luminance levels and ambient room illumination. The luminance response of each display was also measured for proper comparison. Second, a set of visual experiments compared the image quality of both displays in the different sections of the radiation oncology workflow. Observers were tasked with comparing medical images viewed on both displays and ranking them on a rating scale. As part of the workflow, the observers used both displays to contour tumor and healthy tissue volumes, analyze and fuse two sets of images, verify and adjust patient’s treatment position in three degrees of motion. The results show a clear presence for the high-performance display over the commercial grade display in every step of the radiation oncology workflow. It was shown that better visualization of medical images can improve the accuracy and precision of treatment plan and treatment delivery of radiation oncology patients

A Neurophysiologic Study Of Visual Fatigue In Stereoscopic Related Displays

Two tasks were investigated in this study. The first study investigated the effects of alignment display errors on visual fatigue. The experiment revealed the following conclusive results: First, EEG data suggested the possibility of cognitively-induced time compensation changes due to a corresponding effect in real-time brain activity by the eyes trying to compensate for the alignment. The magnification difference error showed more significant effects on all EEG band waves, which were indications of likely visual fatigue as shown by the prevalence of simulator sickness questionnaire (SSQ) increases across all task levels. Vertical shift errors were observed to be prevalent in theta and beta bands of EEG which probably induced alertness (in theta band) as a result of possible stress. Rotation errors were significant in the gamma band, implying the likelihood of cognitive decline because of theta band influence. Second, the hemodynamic responses revealed that significant differences exist between the left and right dorsolateral prefrontal due to alignment errors. There was also a significant difference between the main effect for power band hemisphere and the ATC task sessions. The analyses revealed that there were significant differences between the dorsal frontal lobes in task processing and interaction effects between the processing lobes and tasks processing. The second study investigated the effects of cognitive response variables on visual fatigue. Third, the physiologic indicator of pupil dilation was 0.95mm that occurred at a mean time of 38.1min, after which the pupil dilation begins to decrease. After the average saccade rest time of 33.71min, saccade speeds leaned toward a decrease as a possible result of fatigue on-set. Fourth, the neural network classifier showed visual response data from eye movement were identified as the best predictor of visual fatigue with a classification accuracy of 90.42%. Experimental data confirmed that 11.43% of the participants actually experienced visual fatigue symptoms after the prolonged task

Image processing techniques for mixed reality and biometry

2013 - 2014This thesis work is focused on two applicative fields of image processing research, which, for different reasons, have become particularly active in the last decade: Mixed Reality and Biometry. Though the image processing techniques involved in these two research areas are often different, they share the key objective of recognizing salient features typically captured through imaging devices. Enabling technologies for augmented/mixed reality have been improved and refined throughout the last years and more recently they seems to have finally passed the demo stage to becoming ready for practical industrial and commercial applications. To this regard, a crucial role will likely be played by the new generation of smartphones and tablets, equipped with an arsenal of sensors connections and enough processing power for becoming the most portable and affordable AR platform ever. Within this context, techniques like gesture recognition by means of simple, light and robust capturing hardware and advanced computer vision techniques may play an important role in providing a natural and robust way to control software applications and to enhance onthe- field operational capabilities. The research described in this thesis is targeted toward advanced visualization and interaction strategies aimed to improve the operative range and robustness of mixed reality applications, particularly for demanding industrial environments... [edited by Author]XIII n.s

Radiation dose-, contrast media- and image quality optimization in computed tomography

Computed tomography (CT) was introduced to medicine in the early 1970s, which brought slice imaging into wide use for the first time. Today, CT is an essential part of radiological diagnostics, and is used for a wide range of clinical applications. One downside of CT imaging is the health risks related to the ionizing radiation. In the 80s it was believed that CT would soon be replaced completely by MRI due, in part, to the ionizing radiation required in CT. A further downside are the health risks related to the use of iodine-based contrast media. Both radiation- and contrast media dose have a trade-off with image quality. However, many technical advances have been made, and progress is still ongoing, to improve and broaden the applications of CT. Such advances necessitate a re-evaluation of imaging protocols and continued optimization of radiation dose, contrast media dose and imaging quality. This is the subject of this PhD project. Study I: The aim of this study was to evaluate the potential of low-kV dual-source (DS) and dual-energy (DE) to reduce CM-doses while maintaining soft-tissue and iodine CNR in phantoms of varying size, and to quantify the corresponding radiation dose increases. It was found that low-kV dual-source imaging could be used to reduce CM doses by 44–53% with maintained iodine-, soft tissue- and other materials CNR in a wide range of abdominal sizes, to the cost of about 20–100% increased radiation dose, depending on size. The dual-energy technique allowed a reduction of CM dose by 20% at similar radiation dose as the standard 120 kV protocol. Study II: The aim of this study was to implement and evaluate a scanning regimen, based on the results from Study I, to reduce CM-doses for patients believed to be at risk of CIN. It was concluded that the protocols from Study I could be used to reduce CM doses by 40–50%, depending on patient size, with maintained CNR in patients with a BMI-range of 15–36 kg/m2. The size-specific dose estimates increased by 70%. Study III: The aim of this study was to compare the outcome in image noise and radiation dose in the subsequent CT scan following a single anterior-posterior (AP) vs a combined lateral plus AP (LAT+AP) localizer when using automatic tube-current modulation (ATCM). The results suggested that using LAT+AP localizer yields more consistent noise and radiation dose than a single AP. The effect was small, except for a subgroup of females with laterally protruding breast tissue, which may have been overexposed by about 57% in the thorax region. Study IV: The aim of this study was to evaluate if standard-dose CT can be replaced with low-dose CT for characterization of non-specific findings bone in scintigraphy. Based on these results, sub-mSv CT seems feasible for morphological characterization of skeletal changes in areas with increased tracer uptake on bone scintigraphy, although a larger study is needed

Sensory Prioritization in Rats: Behavioral Performance and Neuronal Correlates

Operating with some finite quantity of processing resources, an animal would benefit from prioritizing the sensory modality expected to provide key information in a particular context. The present study investigated whether rats dedicate attentional resources to the sensory modality in which a near-threshold event is more likely to occur. We manipulated attention by controlling the likelihood with which a stimulus was presented from one of two modalities. In a whisker session, 80% of trials contained a brief vibration stimulus applied to whiskers and the remaining 20% of trials contained a brief change of luminance. These likelihoods were reversed in a visual session. When a stimulus was presented in the high-likelihood context, detection performance increased and was faster compared with the same stimulus presented in the low-likelihood context. Sensory prioritization was also reflected in neuronal activity in the vibrissal area of primary somatosensory cortex: single units responded differentially to the whisker vibration stimulus when presented with higher probability compared with lower probability. Neuronal activity in the vibrissal cortex displayed signatures of multiplicative gain control and enhanced response to vibration stimuli during the whisker session. In conclusion, rats allocate priority to the more likely stimulus modality and the primary sensory cortex may participate in the redistribution of resources

Automotive-Inspired Inceptors and Control Laws Designed for Simplified Piloted Flight

This thesis details the development of a simulator-based experiment in automotive- inspired controls for aircraft. The goal is to fuse the ease of drivability of a car with the flight of an aircraft. A standard automotive control hardware setup coupled with fly-by-wire control laws will allow non-pilots to fly a plane using their familiarity with driving a car. A mathematical description of the control law logic and controller implementation is presented and the human subjects\u27 performance is measured from data collected during experimental testing of the simulator. Preliminary results indicate that non-pilots improve their path-tracking performance and reduce control activity within a short span of time achieving results comparable to those achieved by trained pilots