Alessandro Torricelli

• PhD Physics
• Full Professor at Politecnico di Milano

Significance A shared understanding of terminology is essential for clear scientific communication and minimizing misconceptions. This is particularly challenging in rapidly expanding, interdisciplinary domains that utilize functional near-infrared spectroscopy (fNIRS), where researchers come from diverse backgrounds and apply their expertise in fi...

The term diffusive media refers to all the media for which the photon diffusion equation provides an accurate description of light propagation. Indeed, this is the case for a plethora of natural media, such as biological tissues and agricultural products, when illuminated by red and near-infrared light. Diffuse Optics (DO) is the branch of Optics t...

A non-contact time-resolved reflectance spectroscopy (TRS) laboratory prototype is presented, which noninvasively probes highly scattering media, retrieving their bulk absorption and reduced scattering coefficients. The performance of the prototype was assessed according to an established procedure for the characterization of diffuse optics devices...

Recently, skin pigmentation has been shown to affect the performance of pulse oximeters and other light-based techniques like photo-acoustic imaging, tissue oximetry, and continuous wave near-infrared spectroscopy. Evaluating the robustness to changes in skin pigmentation is therefore essential for the proper use of optical technologies in the clin...

Significance Anemia is a common problem in preterm neonates, and red blood cell transfusion (RBCT) is used to improve oxygen delivery. However, RBCT is associated with complications, although an increase in cerebral oxygenation has been documented, and no universally accepted biomarker for the need for transfusion (i.e., the concentration of hemogl...

Significance A shared understanding of terminology is essential for clear scientific communication and minimizing misconceptions. This is particularly challenging in rapidly expanding, interdisciplinary domains that utilize functional near-infrared spectroscopy (fNIRS), where researchers come from diverse backgrounds and apply their expertise in fi...

We have designed and built an improved system for combined Time-Domain Near-Infrared Spectroscopy (TD NIRS) and Diffuse Correlation Spectroscopy (DCS) measurements. The system features two independent channels, enabling TD NIRS and DCS acquisition at short and long source-detector distances to enhance depth sensitivity in layered tissues. Moreover,...

Significance Reference cerebral near-infrared spectroscopy (NIRS) data on the pediatric population are scarce, and in most cases, only cerebral oxygen saturation (SO2) measured by continuous wave spatially resolved spectroscopy NIRS is reported. Absolute data for baseline optical and hemodynamic parameters are missing. Aim We aimed at collecting b...

Mango fruit is a rich source of bioactive compounds such as carotenoids, phenolics, and ascorbic acid. This research aimed at predicting the content of these bioactive compounds in ‘Tommy Atkins’ mangoes using optical properties, i.e., the absorption coefficients related to chlorophylls (µa630, µa650, µa670, µa690) and carotenoids (µa540), and the...

Aim Current non‐invasive near‐infrared spectroscopy (NIRS) tissue oximetry suffers from suboptimal reproducibility over probe repositioning, hindering clinical threshold establishment. Time Domain‐NIRS (TD‐NIRS) offers higher precision but lacks sufficient paediatric data, preventing effective clinical application. We aimed to establish reference r...

Background Sarcopenia is a muscle disorder causing a progressive reduction of muscle mass and strength, but the mechanism of its manifestation is still partially unknown. The three main parameters to assess are: muscle strength, muscle volume or quality and low physical performance. There is not a definitive approach to assess the musculoskeletal c...

Recently, skin pigmentation has been shown to affect the performance of pulse oximeters and other light-based techniques like photoacoustic imaging, tissue oximetry, and continuous wave near infrared spectroscopy. Evaluating the robustness to changes in skin pigmentation is therefore essential for the proper use of optical technologies in the clini...

The limits of applicability of scaling relations to generate new simulations of photon migration in scattering media by re-scaling an existing Monte Carlo simulation are investigated both for the continuous wave and the time domain case. We analyzed the convergence properties in various scenarios by numerical methods, trying to derive practical gui...

Significance: We explore the feasibility of using time-domain (TD) and continuous-wave (CW) functional near-infrared spectroscopy (fNIRS) to monitor brain hemodynamic oscillations during resting-state activity in humans, a phenomenon that is of increasing interest in the scientific and medical community and appears to be crucial to advancing the u...

This publisher’s note contains a correction to Biomed. Opt. Express 14(11), 5994 (2023)10.1364/BOE.502618.

We present numerical results for the probability density function f(z) and for the mean value of photon maximum penetration depth ‹z max › in a two-layer diffusive medium. Both time domain and continuous wave regime are considered with several combinations of the optical properties (absorption coefficient, reduced scattering coefficient) of the two...

A large cohort of pediatric subjects has been studied to define percentile distribution of oxygen saturation and hemoglobin concentration in prefrontal cortex and upper arm via time-domain near-infrared spectroscopy. Results on the first 240 subjects are presented.

We study the statistics of scattering events occurring along the trajectories travelled by photons in a diffuse media: insight is gained about the possibility of scattering scaling in Monte Carlo simulations.

The assessment of concentration of oxygenated hemoglobin is a crucial parameter for oximetry application. We explore the possibility of using 1064 nm wavelength to assess the concentration of oxygenated, discussing possible advantages and issues.

Absolute values of resting-state muscle hemodynamic parameters of 62 volunteers were measured using Time-Domain Near-Infrared Spectroscopy. Significant variations are observed with gender, likely related to adipose tissue thickness, while no differences are found with age.

We present preliminary in-vivo validation of VASCOVID device, a hybrid diffuse optical platform designed for automatized microvasculature health assessment in the intensive care. The in-vivo validation was run on more than hundred subjects.

Tissue oximeters may show measurements bias and reduced accuracy related to diverse skin pigmentations. The possibility to overcome this issue with time-domain near-infrared spectroscopy is assessed in-vivo, on a large cohort of pediatric subjects.

The assessment of concentration of oxygenated hemoglobin is a crucial parameter for oximetry application. We explore the possibility of using 1064 nm wavelength to assess the concentration of oxygenated, discussing possible advantages and issues.

We study the applicability of scaling relations for Monte Carlo simulations, presenting concrete cases of use in the biomedical field. We retrieve a practical criterion to define their range of efficiency, mainly focusing on scattering.

We assessed in 14 healthy volunteers and one septic patient low and very low frequency oscillations in hemodynamic parameters of muscles by studying their power spectra density exploiting time domain near-infrared and diffuse correlation spectroscopies.

While standard optical oximetry systems make use of two/more wavelengths across the isosbestic point of oxy/deoxy-hemoglobin and between 650 and 900 nm, this work explores the possibility to use only light at 1064 nm wavelength to detect the absolute oxyhemoglobin concentration in tissues using time-domain diffuse optics. Furthermore, the possibili...

Monte Carlo (MC) is a powerful tool to study photon migration in scattering media, yet quite time-consuming to solve inverse problems. To speed up MC-simulations, scaling relations can be applied to an existing initial MC-simulation to generate a new data-set with different optical properties. We named this approach trajectory-based since it uses t...

Time-resolved reflectance spectroscopy (TRS), a nondestructive technique, can help the industry to provide high-quality fruit to encourage pear consumption. The absorption coefficient measured by TRS at 670 nm (μa670) represents a maturity index for pear fruit, with less mature pears high μa670 and more mature low μa670. The aim of this work was to...

In this work, we used a hybrid time domain near-infrared spectroscopy (TD-NIRS) and diffuse correlation spectroscopy (DCS) device to retrieve hemoglobin and blood flow oscillations of skeletal muscle microvasculature. We focused on very low (VLF) and low-frequency (LF) oscillations (i.e., frequency lower than 0.145 Hz), that are related to myogenic...

Long periods of bed rest for elderly population, due to a femur fracture event, can cause a deterioration in the muscular capacity. Therefore, monitoring of the muscle oxidative capacity in this fragile population is necessary to define the muscular oxidative metabolism state before and after a rehabilitation period. The time-domain near-infrared s...

Significance Critically ill newborns are at risk of brain damage from cerebrovascular disturbances. A cerebral hemodynamic monitoring system would have the potential role to guide targeted intervention. Aim To obtain, in a population of newborn infants, simultaneous near-infrared spectroscopy (NIRS)-based estimates of cerebral tissue oxygen satura...

Biosensors applied in veterinary medicine serve as a noninvasive method to determine the health status of animals and, indirectly, their level of welfare. Near infrared spectroscopy (NIRS) has been suggested as a technology with this application. This study presents preliminary in vivo time domain NIRS measurements of optical properties (absorption...

Time-domain diffuse correlation spectroscopy (TD-DCS) has been introduced as an advancement of the “classical” continuous wave DCS (CW-DCS) allowing one to not only to measure depth-resolved blood flow index (BFI) but also to extract optical properties of the measured medium without using any additional diffuse optics technique. However, this metho...

Background Motor disorders are one of the world’s major scourges, and neuromotor rehabilitation is paramount for prevention and monitoring plans. In this scenario, exercises and motor tasks to be performed by patients are crucial to follow and assess treatments’ progression and efficacy. Nowadays, in clinical environments, quantitative assessment o...

Significance: Continuous wave near infrared spectroscopy (CW-NIRS) is widely exploited in clinics to estimate skeletal muscles and brain cortex oxygenation. Spatially resolved spectroscopy (SRS) is generally implemented in commercial devices. However, SRS suffers from two main limitations: the a priori assumption on the spectral dependence of the...

Measuring muscle fatigue and resistance to fatigue is a topical theme in many clinical research studies. Multi-domain approaches, including electromyography (EMG), are employed to measure fatigue in rehabilitation contexts. In particular, spectral features, such as the reduction in the median frequency, are accepted biomarkers to detect muscle fati...

The aim of this work was to explore the feasibility of time-resolved reflectance spectroscopy (TRS) in determining the ripening degree and the quality of orange-fleshed melons. Sixty ‘Honey Moon’ melons were measured by TRS in the 540-1064 nm range and classified as less (LeM), medium (MeM), and more (MoM) mature according to increasing values of μ...

Non-destructive techniques could help mango growers to pick fruit at the proper maturity degree and to monitor fruit quality during storage and marketing to satisfy the consumer expectations. The absorption coefficient non-destructively measured at 540 nm (μa540) by time-resolved reflectance spectroscopy (TRS) was shown to be a maturity index for m...

le varietà economicamente più importanti. Lo scopo di questo lavoro è stato quello di valutare l'effetto della conservazione, del trattamento con 1-MCP e del grado di maturazione determinato in modo non distruttivo alla raccolta mediante spettroscopia di riflettanza risolta nel tempo (TRS) sul profilo sensoriale di pere 'Abate Fetel' e 'Conference'...

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...

This report is the second part of a comprehensive two-part series aimed at reviewing an extensive and diverse toolkit of novel methods to explore brain health and function. While the first report focused on neurophotonic tools mostly applicable to animal studies, here, we highlight optical spectroscopy and imaging methods relevant to noninvasive hu...

Significance: Multi-laboratory initiatives are essential in performance assessment and standardization-crucial for bringing biophotonics to mature clinical use-to establish protocols and develop reference tissue phantoms that all will allow universal instrument comparison. Aim: The largest multi-laboratory comparison of performance assessment in...

Significance: Tissue-like solid phantoms with identical optical properties, known within tolerant uncertainty, are of crucial importance in diffuse optics for instrumentation assessment, interlaboratory comparison studies, industrial standards, and multicentric clinical trials. Aim: The reproducibility in fabrication of homogeneous solid phantom...

Time-domain diffuse correlation spectroscopy (TD-DCS) is an emerging optical technique that enables noninvasive measurement of microvascular blood flow with photon path-length resolution. In TD-DCS, a picosecond pulsed laser with a long coherence length, adequate illumination power, and narrow instrument response function (IRF) is required, and sat...

Il progetto ESPERA (Regione Lombardia) mira al miglioramento della gestione della filiera della pera IGP del Mantovano mediante l’implementazione di innovative soluzioni tecnologiche, di processo e organizzative, per limitare gli sprechi e valorizzare gli scarti. Il progetto prevede la determinazione di un indice di maturazione non distruttivo da u...

In this paper, we used time-domain functional near infrared spectroscopy (TD-fNIRS) to evaluate the haemodynamic response function (HRF) in the occipital cortex following visual stimulation in glaucomatous eyes as compared to healthy eyes. A total of 98 subjects were enrolled in the study and clinically classified as healthy subjects, glaucoma pati...

The interest for Fused Deposition Modelling (FDM) in the field of Diffuse Optics (DO) is rapidly increasing. The most widespread FDM materials are polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS), thanks to their low cost and easiness-to-print. This is why, in this study, 3D printed samples of PLA and ABS materials were optically cha...

The absorption coefficient of fruit flesh at 670 nm (μa670) non-destructively measured at harvest by time-resolved reflectance spectroscopy (TRS) was shown to be a maturity index for various fruit. In apples μa670 decreased during fruit growth and ripening, with high μa670 fruit (less mature) having lower mass and higher pulp hue at harvest and hig...

In this research, the relationship between scattering properties, texture sensory profile and Water Matrix Coordinates (WAMACs) during shelf life was studied on ‘Braeburn’ apples. In this regard, 20 fruit samples kept at 20°C were selected at 0, 2, 4, 6, 8, 10, 14 and 21 days and measured non-destructively by TRS for bulk μ’s estimation, and by a M...

Biomarkers of microcirculation dysfunction may help in the study of cerebral small vessel disease (CSVD). Time-Domain Near-Infrared spectroscopy (TD-NIRS), estimating the oxygenation of microcirculation of cerebral outer layers, might indirectly correlate with CSVD. We retrospectively evaluated TD-NIRS data from healthy subjects with age ≥ 55 years...

We assessed the accuracy of homogenous (semi-infinite, spherical) photon diffusion models in estimating absolute hemodynamic parameters of the neonatal brain in realistic scenarios (ischemia, hyperoxygenation, and hypoventilation) from 1.5 cm interfiber distance TD NIRS measurements. Time-point-spread-functions in 29- and 44-weeks postmenstrual age...

Performance assessment and standardization are indispensable for instruments of clinical relevance in general and clinical instrumentation based on photon migration/diffuse optics in particular. In this direction, a multi-laboratory exercise was initiated with the aim of assessing and comparing their performances. 29 diffuse optical instruments bel...

Time-domain fNIRS facilitates the elimination of the influence of extracerebral, systemic effects on measured signals since it contains time-of-flight information that is related to the penetration depth. Employing perturbation and Monte-Carlo simulations, we quantitatively characterized and compared the performance of measurands based on moments a...

Significance: This study is a preliminary step toward the identification of a noninvasive and reliable tool for monitoring the presence and progress of gaiting dysfunctions. Aim: We present the results of a pilot study for monitoring the motor cortex hemodynamic response function (HRF) in freely walking subjects, with time-domain functional near-in...

Time (or path length) resolved speckle contrast optical spectroscopy (TD-SCOS) at quasi-null (2.85 mm) source-detector separation was developed and demonstrated. The method was illustrated by in vivo studies on the forearm muscle of an adult subject. The results have shown that selecting longer photon path lengths results in higher hyperemic blood...

[This corrects the article DOI: 10.1117/1.NPh.8.1.012101.].

In this work, we present a new multi-distance diffuse correlation spectroscopy (DCS) device integrated with a compact state-of-the-art time domain near infrared spectroscopy (TD-NIRS) device. The hybrid DCS and TD-NIRS system allows to retrieve information on blood flow, tissue oxygenation, and oxygen metabolic rate. The DCS device performances wer...

Fast time-gated single-photon detectors demonstrated high depth sensitivity in the detection of localized absorption perturbations inside scattering media, but their use for in vivo clinical applications—such as functional imaging of brain activation—was impaired by their small ( ${\lt}{0.04}\;{\rm{mm}}^2$ ) active area. Here, we demonstrate, both...

The application of functional near-infrared spectroscopy (fNIRS) in the neurosciences has been expanding over the last 40 years. Today, it is addressing a wide range of applications within different populations and utilizes a great variety of experimental paradigms. With the rapid growth and the diversification of research methods, some inconsisten...

Bulkiness and complexity of current Time-Domain (TD) NIRS systems have strongly limited the spread of this technique in biomedical research and clinical applications. We present an instrument developed to overcome those limitations, making TD-NIRS more accessible to non-experts and adaptable to any measurement condition, paving the way to muscle an...

We propose a standardized approach for performance assessment and quality-control of the novel VASCOVID system based on optical phantoms. This approach is tailored to meet the requirements of the Medical Device Regulation, and is extendable to other biophotonics devices.

We assessed the sensitivity of 1D and 2D homogeneous photon diffusion models for Time Domain NIRS in estimating preterm and term neonates’ cerebral hemodynamic parameters simulated by Monte Carlo methods on realistic 3D anatomical meshes.

We propose a quantitative and systematic investigation of the differential pathlength factor (DPF) behavior for skeletal muscles and its dependence on different factors, such as the subcutaneous adipose tissue thickness (ATT), the variations of the tissue absorption (µa) and reduced scattering (µ′s) coefficients, and the source-detector distance. A...

The effect of sustained fatigue during an upper limb isometric exercise is presented to investigate a group of healthy subjects with simultaneous time-domain (TD) NIRS and surface electromyography (sEMG) recordings on the deltoid lateralis muscle. The aim of the work was to understand which TD-NIRS parameters can be used as descriptors for sustaine...

Two main bottlenecks prevent time-domain diffuse optics instruments to reach their maximum performances, namely the limited light harvesting capability of the detection chain and the bounded data throughput of the timing electronics. In this work, for the first time to our knowledge, we overcome both those limitations using a probe-hosted large are...

Bulk optical properties, in terms of absorption (μa) and reduced scattering coefficients (μ′s), can be used for the non-destructive monitoring of fruit quality during ripening. In this study, the performance of time-resolved (TRS) and spatially-resolved (SRS) spectroscopy were compared by analyzing ‘Braeburn’ apples over a 21 d period of ripening....