201 research outputs found
Time-resolved optical spectrometer based on a monolithic array of high-precision TDCs and SPADs
We present a compact time-resolved spectrometer suitable for optical spectroscopy from 400 nm to 1 μm wavelengths. The detector consists of a monolithic array of 16 high-precision Time-to-Digital Converters (TDC) and Single-Photon Avalanche Diodes (SPAD). The instrument has 10 ps resolution and reaches 70 ps (FWHM) timing precision over a 160 ns full-scale range with a Differential Non-Linearity (DNL) better than 1.5 % LSB. The core of the spectrometer is the application-specific integrated chip composed of 16 pixels with 250 μm pitch, containing a 20 μm diameter SPAD and an independent TDC each, fabricated in a 0.35 μm CMOS technology. In front of this array a monochromator is used to focus different wavelengths into different pixels. The spectrometer has been used for fluorescence lifetime spectroscopy: 5 nm spectral resolution over an 80 nm bandwidth is achieved. Lifetime spectroscopy of Nile blue is demonstrated
Reliable Fast (20 Hz) Acquisition Rate by a TD fNIRS Device: Brain Resting-State Oscillation Studies
A high power setup for multichannel time-domain (TD) functional near infrared spectroscopy (fNIRS) measurements with high efficiency detection system was developed. It was fully characterized based on international performance assessment protocols for diffuse optics instruments, showing an improvement of the signal-to-noise ratio (SNR) with respect to previous analogue devices, and allowing acquisition of signals with sampling rate up to 20 Hz and source-detector distance up to 5 cm. A resting-state measurement on the motor cortex of a healthy volunteer was performed with an acquisition rate of 20 Hz at a 4 cm source-detector distance. The power spectrum for the cortical oxy- and deoxyhemoglobin is also provided
Effect of a thin superficial layer on the estimate of hemodynamic changes in a two-layer medium by time domain NIRS
In order to study hemodynamic changes involved in muscular
metabolism by means of time domain fNIRS, we need to discriminate in the
measured signal contributions coming from different depths. Muscles are,
in fact, typically located under other tissues, e.g. skin and fat. In this paper,
we study the possibility to exploit a previously proposed method for
analyzing time-resolved fNIRS measurements in a two-layer structure with
a thin superficial layer. This method is based on the calculation of the timedependent
mean partial pathlengths. We validated it by simulating venous
and arterial arm cuff occlusions and then applied it on in vivo
measurements
Recent Advances in Time-resolved Nir Spectroscopy for Nondestructive Assessment of Fruit Quality
Non-destructive monitoring of food internal attributes by near infrared spectroscopy (NIRS) is typically
performed by the continuous wave (CW) technique, where steady state light sources (e.g. lamp or LED with
constant intensity in time) and photodetectors (e.g. photodiode or charge coupled device camera) are used to
measure light attenuation. Indeed light scattering can largely affect light attenuation resulting in the need of
calibration for each new batch of samples. To tackle this effect time-resolved NIRS (TRS) has been proposed
to improve the classical CW approach to NIRS. The main feature of TRS is its ability to retrieve information on
photon path-length in a diffusive medium (generally much larger than the geometrical distance between
source and detector). The use of TRS in combination with proper physical models for photon migration allows
for the complete optical characterisation with the simultaneous non-destructive measurement of the optical
properties (absorption and scattering) of a diffusive medium. This can be of special interest for most fruits and
vegetables as well as for other foods (e.g. meat, fish, and cheese), because information derived by TRS refers
to the internal properties of the medium, and is not so much affected by surface features as is the case for CW
spectroscopy. In the past TRS measurements were possible only with complex laboratory instrumentation
consisting of picosecond pulsed lasers, water cooled photomultiplier tubes, and electronic chain for timecorrelated
single photon counting. In this work we present the recent advances in TRS technology (laser,
detectors and acquisition electronics) that allow the design of portable instrumentation for use in the preharvest
(i.e. in the field) and post-harvest
New frontiers in time-domain diffuse optics, a review
The recent developments in time-domain diffuse optics that rely on physical concepts (e.g., time-gating and null distance) and advanced photonic components (e.g., vertical cavity source-emitting laser as light sources, single photon avalanche diode, and silicon photomultipliers as detectors, fast-gating circuits, and time-to-digital converters for acquisition) are focused. This study shows how these tools could lead on one hand to compact and wearable time-domain devices for point-of-care diagnostics down to the consumer level and on the other hand to powerful systems with exceptional depth penetration and sensitivity
Enhanced single-photon time-of-flight 3D ranging
We developed a system for acquiring 3D depth-resolved maps by measuring the Time-of-Flight (TOF) of single photons. It is based on a CMOS 32 × 32 array of Single-Photon Avalanche Diodes (SPADs) and 350 ps resolution Time-to-Digital Converters (TDCs) into each pixel, able to provide photon-counting or photon-timing frames every 10 μs. We show how such a system can be used to scan large scenes in just hundreds of milliseconds. Moreover, we show how to exploit TDC unwarping and refolding for improving signal-to-noise ratio and extending the full-scale depth range. Additionally, we merged 2D and 3D information in a single image, for easing object recognition and tracking
Probe-hosted silicon photomultipliers for time-domain functional near-infrared spectrscopy: phantom and in vivo tests
We report the development of a compact probe for time-domain (TD) functional near-infrared spectroscopy
(fNIRS) based on a fast silicon photomultiplier (SiPM) that can be put directly in contact with the sample
without the need of optical fibers for light collection. We directly integrated an avalanche signal amplification
stage close to the SiPM, thus reducing the size of the detection channel and optimizing the signal immunity
to electromagnetic interferences. The whole detection electronics was placed in a plastic screw holder compatible
with the electroencephalography standard cap for measurement on brain or with custom probe holders. The
SiPM is inserted into a transparent and insulating resin to avoid the direct contact of the scalp with the 100-V bias
voltage. The probe was integrated in an instrument for TD fNIRS spectroscopy. The system was characterized
on tissue phantoms in terms of temporal resolution, responsivity, linearity, and capability to detect deep absorption
changes. Preliminary in vivo tests on adult volunteers were performed to monitor hemodynamic changes in
the arm during a cuff occlusion and in the brain cortex during a motor tas
A Compact Two-Wavelength Time-Domain NIRS System Based on SiPM and Pulsed Diode Lasers
This paper presents a complete, compact, and low power consumption instrument designed for time-domain near-infrared spectroscopy. It employs two custom-designed pulsed diode lasers (operating at 830 and 670 nm, with average optical power higher than 2 mW at 40 MHz repetition frequency), a single-photon detection module (based on a 1 mm2 active area silicon photomultiplier), and a custom time-to-digital converter with 10 ps time resolution. The system experimental characterization shows an instrument response function narrower than 300 ps (full-width at half maximum), with measurement stability better than ±1% over several hours of operation. The instrument, which is housed into a compact aluminum case (size 200 à 160 à 50 mm3), is specifically tailored for portability and ease of operation, hence fostering the diffusion of time-domain diffuse optics techniques. Thanks to a total power consumption lower than 10 W, this system is suitable for battery operation, thus enabling on-field measurements
Time domain functional NIRS imaging for human brain mapping
AbstractThis review is aimed at presenting the state-of-the-art of time domain (TD) functional near-infrared spectroscopy (fNIRS). We first introduce the physical principles, the basics of modeling and data analysis. Basic instrumentation components (light sources, detection techniques, and delivery and collection systems) of a TD fNIRS system are described. A survey of past, existing and next generation TD fNIRS systems used for research and clinical studies is presented. Performance assessment of TD fNIRS systems and standardization issues are also discussed. Main strengths and weakness of TD fNIRS are highlighted, also in comparison with continuous wave (CW) fNIRS. Issues like quantification of the hemodynamic response, penetration depth, depth selectivity, spatial resolution and contrast-to-noise ratio are critically examined, with the help of experimental results performed on phantoms or in vivo. Finally we give an account on the technological developments that would pave the way for a broader use of TD fNIRS in the neuroimaging community
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