Estimation of Spherical Refractive Errors Using Virtual Reality Headset.

Refractive errors are the most common visual defects in humans. They are corrected using lenses whose power is determined using expensive and bulky devices operated by trained professionals. This limits the outreach of eye- health care. We exploit commercial virtual reality (VR) setup to create a portable and inexpensive system for subjective estimation of spherical refractive errors. In doing so, we aim to keep hardware additions simple and to a minimum. We add a plain reflecting mirror in a VR headset to project optotypes on programmable focal planes at varying distances from the subject's eye. An interactive interface uses feedback from the user to estimate accommodation range and spherical refractive errors automatically. We compute the range and precision of our system, and validate them in a user trial study. The proposed setup strongly agrees with clinical subjective refraction.

GearVision: Smartphone Based Head Mounted Perimeter For Detection Of Visual Field Defects.

Automated visual field perimetry is widely used for the evaluation of visual field defects caused by ophthalmological and neurodegenerative diseases. This test is typically performed using the Humphrey Perimeter or Octopus Perimeter. However, their high cost and large footprint limit their use to the clinical setting. This in turn limits their reach especially in the context of screening in remote environments and personal setting. In this paper, we report the development and testing of GearVision, a portable, accessible and compact virtual reality based visual field perimeter. It enables regular visual field testing in a cost-effective and convenient manner. Currently, GearVision is meant to augment the existing perimetry system and hence facilitate the detection of visual field defects early and without expert supervision or the need for hospital visits. In addition to the development of standard 30-2 suprathreshold and full threshold perimetry tests, we have proposed methods to improve test reliability and compliance. These include optional rest intervals during the test to reduce errors caused by strain or fatigue and improved false positive estimation based on statistical analysis of a patient's response times. We have tested the proposed system on 21 subjects and validated its capability to detect visual field defects.

A novel method for accurate estimation of HRV from smartwatch PPG signals.

Photoplethysmography(PPG) as a non-invasive tool for monitoring various cardiovascular parameters, has become popular due to the ease of wearable integration and pervasive nature. Due to unobtrusive nature of sensor placement at wrist, smartwatches and wrist based fitness bands have gained popularity. However, any movement of the wrist along with frequent loose contacts significantly corrupts the PPG signal. Reliable peak detection from the corrupted PPG signal is essential for any further processing, as many physiological quantities such as heart rate variability (HRV) depends on the peak-to-peak distances in the PPG signal, known as the RR Series. This paper attempts to provide a robust algorithm for peak detection in noise & motion artefact corrupted PPG signals. The algorithm consists of steps to remove the baseline drift in the PPG signal using wavelet filtering and trend removal and subsequent peak detection using autocorrelation for each pseudo-periodic segment of the signal. The validation of the method is done by comparing the PPG peaks detected by the algorithm with RR series extracted from simultaneously captured ECG signal.

Wearable PPG sensor based alertness scoring system.

Quantifying mental alertness in today's world is important as it enables the person to adopt lifestyle changes for better work efficiency. Miniaturized sensors in wearable devices have facilitated detection/monitoring of mental alertness. Photoplethysmography (PPG) sensors through Heart Rate Variability (HRV) offer one such opportunity by providing information about one's daily alertness levels without requiring any manual interference from the user. In this paper, a smartwatch based alertness estimation system is proposed. Data collected from PPG sensor of smartwatch is processed and fed to machine learning based model to get a continuous alertness score. Utility functions are designed based on statistical analysis to give a quality score on different stages of alertness such as awake, long sleep and short duration power nap. An intelligent data collection approach is proposed in collaboration with the motion sensor in the smartwatch to reduce battery drainage. Overall, our proposed wearable based system provides a detailed analysis of alertness over a period in a systematic and optimized manner. We were able to achieve an accuracy of 80.1% for sleep/awake classification along with alertness score. This opens up the possibility for quantifying alertness levels using a single PPG sensor for better management of health related activities including sleep.

Cerebral oxygen metabolism of rats using injectable (15)O-oxygen with a steady-state method.

To develop a less-stressful and simple method for measurement of the cerebral metabolic rate of oxygen (CMRO(2)) in small animals, the steady-state method was applied to injectable (15)O(2)-PET ((15)O(2)-positron emission tomography) using hemoglobin-containing vesicles ((15)O(2)-HbV). Ten normal rats and 10 with middle cerebral arterial occlusion (MCAO) were studied using a small animal PET scanner. A series of (15)O-PET scans with C(15)O-labeled HbV, H(2)(15)O, and (15)O(2)-HbV were performed with 10 to 15 minutes intervals to measure cerebral blood volume (CBV), cerebral blood flow (CBF), and CMRO(2). Positron emission tomography scans were started with a tracer injection using a multiprogramming syringe pump, which provides a slowly increasing injection volume to achieve steady-state radioactivity for H(2)(15)O and (15)O(2)-HbV scans. The radioactivity concentration of (15)O rapidly achieved equilibrium in the blood and whole brain at about 2 minutes after H(2)(15)O and (15)O(2)-HbV administration, which was stable during the scans. The whole brain mean values of CBF, CBV, and CMRO(2) were 54.3±2.0 mL per 100 g per minute, 4.9±0.4 mL/100 g, and 2.8±0.2 µmoL per g per minute (6.2±0.4 mL per 100 g per minute) in the normal rats, respectively. In the MCAO model rats, all hemodynamic parameters of the infarction area on the occlusion side significantly decreased. The steady-state method with (15)O-labeled HbV is simple and useful to analyze hemodynamic changes in studies with model animals.

Sensitive diffusion tensor imaging quantification method to identify language pathway abnormalities in children with developmental delay.

OBJECTIVE: To investigate whether abnormal regional white matter architecture in the perisylvian region could be used as an easy and sensitive quantitative method to demonstrate language pathway abnormalities in children with developmental delay (DD). STUDY DESIGN: We performed diffusion tensor imaging in 15 DD subjects (age, 61.1 ± 20.9 months) and 15 age-matched typically developing (TD) children (age, 68.4 ± 19.2 months). With diffusion tensor imaging color-coded orientation maps, we quantified the fraction of fibers in the perisylvian region that are oriented in anteroposterior (AP) and mediolateral (ML) directions, and their ratio (AP/ML) was calculated. RESULTS: The AP/ML ratio was more sensitive than tractography in characterizing perisylvian regional abnormalities in DD children. The AP/ML ratio of the left perisylvian region was significantly lower in DD children compared with TD children (P = .03). The ML component of bilateral perisylvian regions was significantly higher in DD children compared with TD children (P = .01 [left] and P = .004 [right]). No significant difference was found in the AP component in the two groups. A significant negative correlation of the left ML component with Vineland communication skills was observed (r = -0.657, P = .011). CONCLUSIONS: The AP/ML ratio appears to be a sensitive indicator of regional white matter architectural abnormalities in the perisylvian region of DD children.

Can diffusion tensor imaging (DTI) identify epileptogenic tubers in tuberous sclerosis complex? Correlation with α-[11C]methyl-L-tryptophan ([11C] AMT) positron emission tomography (PET).

In this study, we determined whether diffusion tensor imaging (DTI), a more widely available imaging modality, is as effective as α-[(11)C]methyl-l-tryptophan (AMT)-positron emission tomography (PET) in localizing epileptogenic tubers in tuberous sclerosis complex. Following that, coregistration of AMT-PET and diffusion tensor imaging scans apparent diffusion coefficient (ADC) and fractional anisotropy (FA) were measured in all tubers using a region-of-interest approach and were compared with AMT-PET tuber/cortex uptake ratios, which were used to differentiate between epileptogenic and nonepileptogenic tubers. Forty-three tubers, out of a total of 320 tubers, had AMT-PET uptake ratios greater than 1 and hence were classified as potentially epileptogenic. FA in epileptogenic tubers was reduced compared with the other tubers (P = .03). A significant negative correlation was observed between AMT-PET uptake ratio of epileptogenic tubers and FA values (r = -.45; P = .003). Tubers with higher AMT-PET uptake ratios corresponded well with lower FA values in tuberous sclerosis complex patients.

A sensitive diffusion tensor imaging quantification method to detect language laterality in children: correlation with the Wada test.

Using diffusion tensor imaging tractography and color-coded anisotropy map quantification, we investigated asymmetry of the arcuate fasciculus to determine language laterality in children and compared it with the Wada test. Arcuate fasciculus volume and fractional anisotropy were measured after tractography. We also quantified the fiber orientation distribution in the arcuate fasciculus region, ie, the fraction of arcuate fasciculus fibers oriented in the anteroposterior and mediolateral directions. A Laterality Index was calculated for each of the measured parameters. Volumetric analysis of the arcuate fasciculus showed asymmetry favoring the language dominant hemisphere (P = .02), while fractional anisotropy showed no significant asymmetry (P = .07). The mean anteroposterior and mediolateral components on the language dominant side were significantly higher than on the nondominant side (P = .003 and .002, respectively). The Laterality Index values were concordant with the Wada test results except for 1 case. Fractional anisotropy also falsely lateralized language in 1 case.

Automatic labeling method for injectable 15O-oxygen using hemoglobin-containing liposome vesicles and its application for measurement of brain oxygen consumption by PET.

INTRODUCTION: The aim of this study was to develop an injectable (15)O-O(2) system using hemoglobin-containing vesicles (HbV), a type of artificial red blood cell, and to investigate the feasibility of (15)O(2)-labeled HbV ((15)O(2)-HbV) to measure cerebral metabolic rate of oxygen (CMRO(2)) in rats. METHODS: The direct bubbling method was combined with vortexing to enhance labeling efficiency of HbV with (15)O-O(2) gas. L-Cysteine was added as a reductant to protect hemoglobin molecules in HbV from oxidation at different concentrations, and labeling efficiencies were also compared. Measurement of cerebral blood flow (CBF) and CMRO(2) in five normal rats was performed using a small animal PET scanner after the injection of H(2)(15)O and (15)O(2)-HbV to evaluate the precision of hemodynamic parameters quantitatively. RESULTS: The labeling efficiency of HbV was significantly increased when vortexing and bubbling were combined compared with the simple bubbling method (P<.05). The most efficient method for labeling was bubbling of (15)O-O(2) combined with vortexing and the addition of 2.8 mM L-cysteine in HbV solution. The mean radioactivity of 214.4+/-7.8 MBq/mL HbV was obtained using this method. PET scans using (15)O(2)-HbV and H(2)(15)O yielded a mean CMRO(2) value of 6.8+/-1.4 (mL/min per 100 g) in rats with normal CBF of 51.4+/-7.9 (mL/min per 100 g). CONCLUSION: Addition of l-cysteine to HbV and simple direct bubbling of (15)O-O(2) gas combined with vortexing was the most efficient method for preparation of (15)O(2)-HbV. The present injectable system using (15)O(2)-HbV was successfully utilized to measure CMRO(2) in rats, indicating that this new method could be useful for animal models to measure oxygen metabolism in the brain.