Attractive new technologies for 7-wavelength time domain optical mammography

An 8-channel Silicon PhotoMultiplier (SiPM) probe and Time-to-Digital-Converter (TDC) realize a higher-throughput, cheaper and compact detection chain for time-resolved optical mammography than photomultiplier tubes (PMTs) and Time Correlated Single Photon Counting (TCSPC) boards, providing comparable estimate of optical properties with increased optical responsivity

High throughput detection chain for time domain optical mammography

A novel detection chain, based on 8 Silicon Photomultipliers (forming a wide-area custom-made detection probe) and on a time-to-digital converter, was developed to improve the signal level in multi-wavelength (635-1060 nm) time domain optical mammography. The performances of individual components and of the overall chain were assessed using established protocols (BIP and MEDPHOT). The photon detection efficiency was improved by up to 3 orders of magnitude, and the maximum count rate level was increased by a factor of 10 when compared to the previous system, based on photomultiplier tubes and conventional time-correlated single-photon counting boards. In the estimate of optical parameters, the novel detection chain provides performances comparable to the previous system, widely validated in clinics, but with higher signal level, higher robustness, and at a lower price per channel, thus targeting important requirements for clinical applications

Novel approaches to photon detection and timing for 7-wavelength time domain optical mammography

An 8-channel Silicon Photomultiplier probe and a Time-to-Digital Converter are used to build a higher-throughput, cheaper and compact detection chain for time-resolved optical mammography as compared with conventional PhotoMultiplier Tubes and Time-Correlated Single-Photon Counting boards, still providing comparable performance in the estimation of optical properties, but with higher optical responsivity

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

An innovative 8 channels system for time-resolved diffuse optical tomography based on SiPMs

We present the design of a novel 8 channels system for time resolved optical tomography based on Silicon Photomultipliers (SiPMs), therefore knocking down cost and complexity of this technique and paving the way to a widespread diffusion. We validated the system performances on phantoms

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

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 diffuse optical tomography system based on fiber-free silicon photomultipliers

Based on recent developments in both single-photon detectors and timing electronic circuits, we designed a compact and cost effective time-domain diffuse optical tomography system operated at 1 Hz acquisition rate, based on eight silicon photomultipliers and an 8-channel time-to-digital converter. The compact detectors are directly hosted on the probe in a circular arrangement around a single light injection fiber, so to maximize light harvesting. Tomography is achieved exploiting the depth sensitivity that is encoded in the arrival time of detected photons. The system performances were evaluated on simulations to assess possible the limitations arising from the use of a single injection point, and then on phantoms and in vivo to prove the eligibility of these technologies for diffuse optical tomography

Fast silicon photomultiplier improves signal harvesting and reduces complexity in time-domain diffuse optics

We present a proof of concept prototype of a time-domain diffuse optics probe exploiting a fast Silicon PhotoMultiplier (SiPM), featuring a timing resolution better than 80 ps, a fast tail with just 90 ps decay time-constant and a wide active area of 1 mm2. The detector is hosted into the probe and used in direct contact with the sample under investigation, thus providing high harvesting efficiency by exploiting the whole SiPM numerical aperture and also reducing complexity by avoiding the use of cumbersome fiber bundles. Our tests also demonstrate high accuracy and linearity in retrieving the optical properties and suitable contrast and depth sensitivity for detecting localized inhomogeneities. In addition to a strong improvement in both instrumentation cost and size with respect to legacy solutions, the setup performances are comparable to those of state-of-the-art time-domain instrumentation, thus opening a new way to compact, low-cost and high-performance time-resolved devices for diffuse optical imaging and spectroscopy

Towards next generation time-domain diffuse optics devices

Diffuse Optics is growing in terms of applications ranging from e.g. oximetry, to mammography, molecular imaging, quality assessment of food and pharmaceuticals, wood optics, physics of random media. Time-domain (TD) approaches, although appealing in terms of quantitation and depth sensibility, are presently limited to large fiber-based systems, with limited number of source-detector pairs. We present a miniaturized TD source-detector probe embedding integrated laser sources and single-photon detectors. Some electronics are still external (e.g. power supply, pulse generators, timing electronics), yet full integration on-board using already proven technologies is feasible. The novel devices were successfully validated on heterogeneous phantoms showing performances comparable to large state-of-the-art TD rack-based systems. With an investigation based on simulations we provide numerical evidence that the possibility to stack many TD compact source-detector pairs in a dense, null source-detector distance arrangement could yield on the brain cortex about 1 decade higher contrast as compared to a continuous wave (CW) approach. Further, a 3-fold increase in the maximum depth (down to 6 cm) is estimated, opening accessibility to new organs such as the lung or the heart. Finally, these new technologies show the way towards compact and wearable TD probes with orders of magnitude reduction in size and cost, for a widespread use of TD devices in real life