Multiphotodiode Array Research Articles

A wireless, skin-interfaced biosensor for cerebral hemodynamic monitoring in pediatric care

The standard of clinical care in many pediatric and neonatal neurocritical care units involves continuous monitoring of cerebral hemodynamics using hard-wired devices that physically adhere to the skin and connect to base stations that commonly mount on an adjacent wall or stand. Risks of iatrogenic skin injuries associated with adhesives that bond such systems to the skin and entanglements of the patients and/or the healthcare professionals with the wires can impede clinical procedures and natural movements that are critical to the care, development, and recovery of pediatric patients. This paper presents a wireless, miniaturized, and mechanically soft, flexible device that supports measurements quantitatively comparable to existing clinical standards. The system features a multiphotodiode array and pair of light-emitting diodes for simultaneous monitoring of systemic and cerebral hemodynamics, with ability to measure cerebral oxygenation, heart rate, peripheral oxygenation, and potentially cerebral pulse pressure and vascular tone, through the utilization of multiwavelength reflectance-mode photoplethysmography and functional near-infrared spectroscopy. Monte Carlo optical simulations define the tissue-probing depths for source-detector distances and operating wavelengths of these systems using magnetic resonance images of the head of a representative pediatric patient to define the relevant geometries. Clinical studies on pediatric subjects with and without congenital central hypoventilation syndrome validate the feasibility for using this system in operating hospitals and define its advantages relative to established technologies. This platform has the potential to substantially enhance the quality of pediatric care across a wide range of conditions and use scenarios, not only in advanced hospital settings but also in clinics of lower- and middle-income countries.

Measuring pulse wave velocity with a novel, simple sensor on the finger tip: a feasibility study in healthy volunteers

Objective: The speed of pressure pulses traveling through the blood, the pulse wave velocity (PWV), is a metric that provides substantial information about the passive and active elasticity of the blood vessels. Therefore, PWV is a valuable parameter in the diagnosis of cardiovascular and vessel-related neurological diseases. The purpose of this study was to investigate whether a novel, simple, easy-to-use, photoplethysmography-based Multi Photodiode Array (MPA) provides PWV measurements that agree with measurements done with more complicated and harder-to-use systems currently used in clinical practice. Methods: An often-used vascular perturbation that changes the conduit artery vasomotor tone during reactive hyperemia was imposed on thirty healthy volunteers. The MPA was used alongside and its results compared to those of a commonly used measurement device, the Biopac-system, during flow-mediated dilation (FMD). This way it was investigated if measurements with these systems, measuring over two different, but partly overlapping vessel trajectories agree. Results: The baseline absolute PWV values were significantly lower for the MPA as compared to the Biopac-system. Additionally, Bland-Altman plots and Pearson’s correlation tests suggested good agreement between the two PWV measurement techniques during the FMD. Conclusion: Measuring PWV with the MPA in clinical practice is feasible and provides reliable data. Significance: The MPA may substantially simplify PWV measurements and may enable long-term PWV monitoring as long as one is aware of the relation between PWV and the vascular trajectory over which it is measured.

Design and Functional Testing of a Novel Blood Pulse Wave Velocity Sensor

The multiphotodiode array (MPA) is a novel transmission photoplethysmography (PPG) sensor to measure pulse wave velocity (PWV) in the finger. To validate the MPA, a setup was built to generate a red laser dot traveling over the MPA with known and constant scanning velocities. These scanning velocities were chosen to include speeds at least twice as high as those found in the normal range of PWV in healthy populations and were set at 12.9, 25.8, 36, or 46.7 m/s. The aim of this study was to verify the functionality of the MPA: performing local noninvasive PWV measurements. To illustrate the applicability of the MPA in clinical practice, an in vivo pilot study was conducted using the flow-mediated dilation (FMD) technique. The in vitro accuracy of the MPA was ±0.2%, 0.3%, 0.5%, and 0.6% at the applied scanning velocities. The MPA can measure PWVs with a maximum deviation of 3.0%. The in vivo pilot study showed a PWV before the FMD of 1.1±0.2 m/s. These results suggest that this novel MPA can reliably and accurately measure PWV within clinically relevant ranges and even well beyond.

A Multi-photodiode Array-based Retinal Implant IC with On/off Stimulation Strategy to Improve Spatial Resolution

We propose a novel multi-photodiode array (MPDA) based retinal implant IC with on/off stimulation strategy for a visual prosthesis with improved spatial resolution. An active pixel sensor combined with a comparator enables generation of biphasic current pulses when light intensity meets a threshold condition. The threshold is tuned by changing the discharging time of the active pixel sensor for various light intensity environments. A prototype of the 30-channel retinal implant IC was fabricated with a unit pixel area of 0.021㎟, and the stimulus level up to 354 μA was measured with the threshold ranging from 400 lx to 13120 lx.

A Simple Portable Colour Identification and Matching Instrument Using AVR Microcontroller and a Provotech Sensor

The identification of colours of objects is a much felt need in textiles, paint industries, cosmetics and so on. The complexity of identifying colour and its matching among several objects has been a requirement for common consumer outlets also. The paper discusses the principles of identifying and matching coloured objects. It uses a multi photo diode array based white balanced sensor from Provotech (India). We have been able to identify among twenty three different colours based on the Chromaticity co-ordinates precisely. The apparatus described is based on a simple embedded controller and the unit has its LCD display to indicate colour, hue and purity so that exact matching of coloured objects can be easily done.

Development of First Production Flaw Detecting System for On-Demand Repair of Large-Scale Circuit

To realize an efficient high-mix low-volume production, improving the yield rate by reducing production flaws is an important technique. Manufacturing touch panel displays with large-scale wiring boards is a typical example of the high-mix low-volume production. The National Institute of Advanced Industrial Science and Technology (AIST) has proposed a laser assisted ink-jet printing (LIJ) technology, which can repair the flaws of circuits by a silver nanoparticle ink. To establish an in-process repairing system for a touch panel display, a first production flaw detecting system is necessary in combination with LIJ technology. Therefore, the aim of this study is to develop a new first production flaw detecting system, which detects flaws in a large-scale circuit quickly. In this report, we have covered the basic concept of the proposed system, and the details of some preliminary experiments conducted using the developed measurement system. The performance requirements for the first production flaw detecting system are discussed. The basic concept of the detecting system and optical set-up was finalized. A preliminary first production flaw detecting system with galvano-scanner and multi-photodiode array was developed to confirm its ability to detect flaws and pattern profile. Some basic experiments were conducted to check the performance of this system. A flaw was intentionally created by making a scratch on a circuit pattern; the experimental results showed that this flaw could be detected by the equipment. The height detection technique for this system and preliminary experiments conducted using the developed system are also covered in this report. By using the laser trigonometry method, the displacement of profile height was detected with sufficient accuracy.

Spatial Resolution and Perception of Patterns Mediated by a Subretinal 16-Electrode Array in Patients Blinded by Hereditary Retinal Dystrophies

The perception of 11 persons blinded by hereditary retinal degeneration elicited by a subretinally implanted 16-electrode array used for light-independent direct stimulation of the retina is described. This device is part of the Tübingen retina implant, which also employs a light-sensitive, multiphotodiode array (MPDA). The ability to reliably recognize complex spatial percepts was investigated. Eleven blind volunteers received implants and participated in standardized psychophysical tests investigating the size and shape of perceptions elicited by single-electrode activation, multiple-electrode activation, and activation of compound patterns such as simplified letters. Visual percepts were elicited reliably in 8 of 11 patients. On single-electrode activation, percepts were generally described as round spots of light of distinguishable localization in the visual field. On activation of a pattern of electrodes, percepts matched that pattern when electrodes were activated sequentially. Patterns such as horizontal or vertical bars were identified reliably; the most recent participant was able to recognize simplified letters presented on the 16-electrode array. The smallest distance between sites of concurrent retinal stimulation still yielding discernible spots of light was assessed to be 280 μm, corresponding to a logMAR of 1.78. Subretinal electric stimulation can yield reliable, predictable percepts. Patterned perception is feasible, enabling blind persons to recognize shapes and discriminate different letters. Stimulation paradigms must be optimized, to further increase spatial resolution, demanding a better understanding of physical and biological effects of single versus repetitive stimulation (ClinicalTrials.gov number, NCT00515814).