Giorgia Salvatori

A Measurement System for the Analysis of the Response of the Human Eye to the Light Flicker

The response of the human eye to flicker depends on the type of lamp used. Standard flickermeters measure the voltage across the lamp and assumes a 60-W incandescent lamp as a light source. When a different lamp is the light flicker source, standard flickermeters give erroneous results. This paper presents a dynamic model of the eye-brain response to flicker. The model is based on the analysis of the light emitted by the lamp. A suitable measurement system has been developed, and three different kinds of lamps have been considered. Experimental results show how the emitted light spectra and the human eye response to different colors combined to determine the level of annoyance. The uncertainty affecting such results, which arises from the hardware of the developed system, has been also estimated.

Design and performance of a wide-bandwidth and sensitive instrument for near-infrared spectroscopic measurements on human tissue

The article describes an instrument designed to perform in vivo near-infrared spectroscopic measurements on human tissues. The system integrates five continuous-wave laser diode sources emitting in the near-infrared spectral region and a low-noise detection system based on an avalanche photodiode. The optical probe is based on a compact, reliable, and low-cost fiber based system with four quantitative measuring points. The excellent sensitivity of the instrument allows one to perform quantitative assessments of the hemoglobin concentration exploiting precise absorption measurements close to the absorption peak of the water: 975 nm. Moreover, a good signal to noise ratio is obtained also at a high acquisition rate, allowing us to follow rapid changes in oxidative metabolism. The system bandwidth is selectable within the range 2.3–27 Hz, i.e., 20 channels (five chromatic and four spatial channels) can be acquired 27 times for each measuring second, whereas the system amplification can be set to measure opti...

Investigation on the Response of the Human Eye to the Light Flicker Produced by Different Lamps

The response of the human eye to flicker depends on the type of lamp used. The standard flickermeter is based on the measurement of voltage and assumes the light source to be a 60 W incandescent lamp. When a different lamp is the source of light flicker, the standard flickermeter gives erroneous results. This paper presents a dynamic model of the eye-brain response to flicker. The model is based on the analysis of the light emitted by the lamp. A suitable measurement system has been developed and three different kinds of lamps have been considered. Experimental results show how the emitted light spectra and the human eye response to different colors determine the level of annoyance

Instrumentation and calibration protocol for a continuous wave near infrared hemoximeter

Quantification of hemoglobin content in vivo using continuous wave (CW) near infrared spectroscopy requires an accurate calibration of the measuring system. The authors introduce a recently developed instrument and focus their attention on the calibration issue, proposing a calibration procedure specifically designed for their system, but which can be easily generalized for other CW near-infrared systems. In the paper, the most important calibration procedures and the results obtained are discussed in detail

Combining Near-Infrared Spectroscopy and Electroencephalography to Monitor Brain Function

We propose to embed a continuous-wave near-infrared spectroscopy system within an electroencephalography system to perform functional hemodynamic and neural response simultaneously. In this study, we present the measuring system and the results consisting in changes of oxyhemoglobin and deoxyhemoglobin derived from continuous-wave near-infrared spectroscopy data and the evoked potential responses derived from the electroencephalography recordings. A checkerboard stimulus was adopted to elicit a response signal from the visual cortex. The results collected demonstrate that near infrared spectroscopy can detect task-induced changes in homodynamic

Analysis of the Effects of Flicker on the Blood-Flow Variation in the Human Eye

Flicker annoyance measurement, regardless if it is performed by processing the supplying voltage or by evaluating the light emitted by the lamp, relies on the assumption of a proper model of the behavior of the complex eye-brain system in the presence of fluctuating light. The only experimental data available are the ones obtained, for a certain incandescent lamp, by asking several people to report their perception about the flicker to which they were subjected. In this paper, the possibility of achieving an ldquoobjectiverdquo evaluation of the flicker effects on a human subject is investigated. In particular, the increment of the blood flow in a vessel at the optic nerve is considered and taken as a possible index of annoyance due to flicker.

Synchronous phase to voltage converter for true-phase polarimeters

This paper describes a front-end electronics designed to process the signals generated by a true-phase polarimeter. The design of the network is oriented to minimize the phase angle measurement uncertainty. The circuit has been accordingly developed and tested in operation. Exploiting a precise analogue phase-to-voltage converter based on a synchronous detection scheme, the network exhibits a phase angle measurement uncertainty less than 0.35 mdeg. The circuit exhibits excellent rejection of uncorrelated noise, disturbances, offsets and harmonics.

Instrumentation and calibration protocol for a continuous wave NIRS oximeter

We describe a continuous wave near infrared oximeter and its calibration protocol. The system performs quantitative assessments exploiting precise absorption measurements close to the absorption peak of the water: 975nm. We report the procedures and the systematic in vitro tests adopted to characterize and calibrate the entire system. A final stability analysis is reported to validate the instrumentation

A true-phase polarimetric system to study bi-anisotropic media

The article describes a true-phase polarimeter designed to study bi-anisotropic media. Exploiting a simple optical setup based on two He-Ne lasers and a precise analogue phase-to-voltage converter, the measuring system exhibits high sensitivity and excellent rejection ambient light

Near-infrared oxymeter prototype for noninvasive analysis of rat brain oxygenation

The feasibility of non-invasive analysis of brain activities was studied in the attempt to overcome the major limitation of actual in vivo methodologies i.e. invasiveness. Optic fibre probes were used as optical head of a novel, highly sensitive near infrared continuous wave spectroscopy (CW-NIR) instrument. This prototype was designed for non-invasive analysis of the two main forms of haemoglobin: oxy-haemoglobin (HbO2) and deoxy-haemoglobin (Hb), chromophores present in biological tissues. It was tested in peripheral tissue (human gastrocnemius muscle) and then reset to perform measurement on rat brain. In animal studies, the optical head was firmly placed using stereotaxic apparatus upon the sagittal line of anaesthetised adult rats head, without any surgery. Then pharmacological treatments with saline (300μl s.c.) amphetamine (2mg/kg) or nicotine (0.4mg/kg) were performed. Within 10-20 min amphetamine substantially increased HbO2 and reduced Hb control levels. Nicotine produced a rapid initial increase followed by a decrease of HbO2. In contrast to amphetamine, nicotine treatment also reduced Hb and blood volume. These results support the capacity of our CW-NIR prototype to measure non-invasively HbO2 and Hb levels in the rat brain, markers of the degree of tissue oxygenation, index of blood level then of the state of brain metabolism.