Investigation of Morphological Variations of Photoplethysmography Signal in Human Epilepsy.

The purpose of this study is to analyse the ictal variations in peripheral blood flow using photoplethysmogram (PPG) and single lead Electrocardiogram (ECG) signals. 11 subjects with 56 partial seizures were recorded with the PPG sensor worn on their left ankles. 6 different features from PPG pulse morphology related to hemodynamics were derived. The seizures were divided into two groups based on the side of the seizure activity. The investigation of ictal variations in features did not show any significant difference between the seizures' lateralizations. The analysis of latencies of ictal changes in the PPG features revealed the PPG pulse amplitude precede the variations in other PPG features including ictal heart rate variability. In addition, analysis of the effect of seizure lengths on ictal variations showed the seizures' lengths have no significant effect on the feature variation rates.Clinical relevance- Analysis of the extracted PPG features and their timing suggest an increase in vascular resistance due to increase in sympathetic tone which occurs prior to the ictal tachycardia. These variations is independent of the seizures' lengths and lateralizations.

Design and testing of a miniature broadband frequency domain photon migration instrument.

A board-level broadband frequency domain photon migration (mini-FDPM) instrument has been constructed to replace a conventional network-analyzer-based FDPM instrument. The mini-FDPM instrument with four wavelengths (681, 783, 823, and 850 nm), matches conventional FDPM instrument in performance (-88 dBm noise level, 100 dB dynamic range) and bandwidth (1 GHz), and recovers the same optical properties within about 6% in absorption and 4% in reduced scattering for liquid phantoms covering a wide range of relevant optical properties. Compared to the conventional FDPM instrument, the mini-FDPM instrument is more than 5x faster (approximately 200 ms per 401 modulation frequencies) and several orders of magnitude less in size and cost. Standard fiber-optic-based probes can be used with the mini-FDPM instrument, which increases applications in a number of clinically relevant measurement scenarios. By drastically reducing size and cost, FDPM miniaturization lowers barriers to access and will help promote FDPM in clinical research problems. The mini-FDPM instrument forms the core of a modular broadband diffuse optical spectroscopy instrument that can be used for a variety of clinical problems in imaging and functional monitoring (i.e., breast/skin cancer, brain activation, and exercise physiology).

Reducing the Computational Complexity of EEG Source Localization With Cortical Patch Decomposition and Optimal Electrode Selection.

OBJECTIVE: Real-time implementation of EEG source localization can be employed in a broad area of applications such as clinical diagnosis of neurologic diseases and brain-computer interface. However, a power-efficient, low-complexity, and real-time implementation of EEG source localization is still challenging due to extensive iterations in the solutions. In this study, two techniques are introduced to reduce the computational burden of the subspace-based MUltiple SIgnal Classification (MUSIC) algorithm. METHODS: To shrink the exhaustive search inherent in MUSIC, the cortex is parsed into cortical regions. A novel nomination procedure involving a dictionary learning step will pick a number of regions to be searched for the active sources. In addition, a new electrode selection algorithm based on the Cramer-Rao bound of the errors is introduced to pick the best set of an arbitrary number of electrodes out of the total. RESULTS: The performance of the proposed techniques were evaluated using simulated EEG signal under variation of different parameters such as the number of nominated regions, the signal to noise ratio, and the number of electrodes. The proposed techniques can reduce the computational complexity by up to $90\%$. Furthermore, the proposed techniques were tested on EEG data from an auditory oddball experiment. CONCLUSION: A good concordance was observed in the comparison of the topographies and the localization errors derived from the proposed technique and regular MUSIC. SIGNIFICANCE: Such reduction can be exploited in the real-time, long-run, and mobile monitoring of cortical activity for clinical diagnosis and research purposes.

Application of infrared scanning of the neck muscles to control a cursor in Human-Computer Interface.

The feasibility of using infrared (IR) spectroscopy of the neck muscles in controlling a cursor in a 2-dimensional screen was assessed. The proposed technique utilizes two IR photoplethysmography sensors (λ = 940nm) to monitor the morphological changes of the Scalene and Sternocleidomastoid muscles. Since the reflection of the light has valuable information about the type of contraction, the direction of the movement (right/left, up/down) can be simply derived using two sensors. A MATLAB platform was developed in which a cursor moves using the recorded signal. Three scenarios of high/low sensitivity and joystick mode were tested. The results from 4 different healthy subjects shows the feasibility of control in terms of throughput, overshoot, and path efficiency.

Automated Power Control for Mobile Laser Speckle Imaging System.

Recently, Laser Speckle Imaging (LSI) has been applied to measure blood perfusion in human skin. Attractive features of LSI are its temporal resolution and relatively simple instrumentation. The progressive reduction in the cost and size of camera technology now enables development of mobile LSI instrumentation. To reduce the size of LSI to a mobile platform, we are faced with new challenges in terms of reducing power consumption and heat without sacrificing detection accuracy. To address these challenges, we propose pulsed laser operation using a new automated power control (APC) circuit. By synchronizing the pulses to the laser diode driver with the camera shutter, the camera detects a similar raw speckle image as before while consuming only a small fraction of the power. Furthermore, the reduced power consumption in turn keeps the temperature of the case low, increasing the stability of the system. We validated our solution using simulations in Pspice, and we evaluated the operation of the circuit using a prototype APC board and a commercial camera.