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The original version of this Article contained errors in references 3, 4, 25, 36, 41 and 48, which were incorrectly given as

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 characterized in the range from the UV up to the IR wavelengths, in order to test their possible employment for probe construction in DO applications. To this purpose, measurements with Near Infrared Spectroscopy and Diffuse Correlation Spectroscopy techniques were considered. The results obtained show how the material employed for probe construction can negatively affect the quality of DO measurements.

A study on 118 subjects, performed with TD-fNIRS, demonstrated that the glaucoma has a cerebral component. The fNIRS parameters that best represent this finding are the OHB and HHB amplitudes, as revealed by PCA.

TD-NIRS allows the monitoring of tissue hemodynamics enhancing the contribution from the late (deeper) photons. After a brief review of its peculiarities, examples of its employment in clinics, on brain and muscles, will be presented

3D filament printers are nowadays used in diffuse optics for custom probes or phantoms boxes fabrication. We observed that not all the PLA filaments are suitable for NIRS and DCS applications.

We investigate the use of broadband time-domain diffuse optical spectroscopy (TD-DOS) to track in real time the changes in the optical properties of biological tissue undergoing radio frequency (RF) based thermal treatment.

Glaucoma is a multifactorial optic neuropathy characterized by progressive loss of retinal ganglion cells, changes in optic disk morphology and visual field defects; its pathophysiology is still unclear. Recently it was demonstrated that glaucoma can be associated with a degenerative effect at the level of the optic nerve and the primary visual cortex. Functional near infrared spectroscopy (fNIRS) is a non-invasive optical technique, which allows the brain hemodynamic monitoring. In particular, the Time Domain fNIRS (TD-fNIRS) allows to remove from the detected signal the contribution coming from the surface (scalp, skull and cerebral fluid) in order to obtain the brain hemodynamic activation. The aim of this preliminary study is to understand if in the glaucomatous patients, the visual cortex activation during a visual stimulus is different from the one of a control group. A total of 20 subjects took part to the study. We divided them into three groups: 7 controls, 5 ocular hypertension (HYPER), and 8 glaucoma. The hemodynamic time courses of oxy- (OHB) and deoxy- (HHB) hemoglobin were compared with a hemodynamic response function (HRF) with the adaptive HRF approach. Finally, an inference test was applied (t-student) to statistically determine the visual cortex activation (simultaneous increase in OHB and decrease in HHB). The p-value threshold was set at 0.05. The 86% of the controls and the 80% of the HYPER combinations are activated; while the 81% of the glaucoma ones are not, outlining a well-defined trend. Also the OHB and HHB show drastic differences between controls and patients.

A recent upgrade of the time domain multi-wavelength optical mammograph developed by Politecnico di Milano achieved good performance in laboratory tests [Biomed. Opt. Express 9, 755 (2018).10.1364/BOE.9.000755]. However, it proved unsatisfactory when in vivo measurements were finally performed. That led to a further upgrade, including the replacement of the time-to-digital converter with a new model, and the related set-up changes. The new instrument version offers improved laboratory performance (as assessed through established protocols: BIP and MEDPHOT) and good in vivo performance (extension of the scanned breast area, repeatability, consistency of estimated tissue composition with physiology). Besides introducing the new set-up and detailing its laboratory and in vivo performance, we highlight the importance of systematic in vivo testing before entering clinical trials.

To enhance photon harvesting and improve data quality, an 8-channel compact SiPM probe and TDC acquisition replace PMTs and TCSPC boards in a time-resolved optical mammograph still providing similar performances for optical properties estimation.

Collagen content quantified through 7-wavelength (635-1060 nm) time domain diffuse optical mammography in 200 women proved key to discriminate malignant from benign breast lesions, to measure breast density, and to estimate breast cancer risk.

We present a new technique, Frequency Offset Raman Spectroscopy (FORS), for probing deep layer Raman spectra of diffusive media. It was demonstrated on a tissue mimicking phantom, and shows potential for in vivo applications.

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.

We present a new technique, frequency offset Raman spectroscopy (FORS), to probe Raman spectra of diffusive media in depth. The proposed methodology obtains depth sensitivity exploiting changes in optical properties (absorption and scattering) with excitation wavelengths. The approach was demonstrated experimentally on a two-layer tissue phantom and compared with the already consolidated spatially offset Raman spectroscopy (SORS) technique. FORS attains a similar enhancement of signal from deep layers as SORS, namely 2.81 against 2.62, while the combined hybrid FORS-SORS approach leads to a markedly higher 6.0 enhancement. Differences and analogies between FORS and SORS are discussed, suggesting FORS as an additional or complementary approach for probing heterogeneous media such as biological tissues in depth.

Several techniques are being investigated as a complement to screening mammography, to reduce its false-positive rate, but results are still insufficient to draw conclusions. This initial study explores time domain diffuse optical imaging as an adjunct method to classify non-invasively malignant vs benign breast lesions. We estimated differences in tissue composition (oxy- and deoxyhemoglobin, lipid, water, collagen) and absorption properties between lesion and average healthy tissue in the same breast applying a perturbative approach to optical images collected at 7 red-near infrared wavelengths (635–1060 nm) from subjects bearing breast lesions. The Discrete AdaBoost procedure, a machine-learning algorithm, was then exploited to classify lesions based on optically derived information (either tissue composition or absorption) and risk factors obtained from patient’s anamnesis (age, body mass index, familiarity, parity, use of oral contraceptives, and use of Tamoxifen). Collagen content, in particular, turned out to be the most important parameter for discrimination. Based on the initial results of this study the proposed method deserves further investigation.

An 8-channel Silicon Photomultiplier probe and a Time-toDigital 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.

Diffuse optical imaging and spectroscopy of the female breast is an area of active research. We review the present status of this field and discuss the broad range of methodologies and applications. Starting with a brief overview on breast physiology, the remodeling of vasculature and extracellular matrix caused by solid tumors is highlighted that is relevant for contrast in optical imaging. Then, the various instrumental techniques and the related methods of data analysis and image generation are described and compared including multimodality instrumentation, fluorescence mammography, broadband spectroscopy, and diffuse correlation spectroscopy. We review the clinical results on functional properties of malignant and benign breast lesions compared to host tissue and discuss the various methods to improve contrast between healthy and diseased tissue, such as enhanced spectroscopic information, dynamic variations of functional properties, pharmacokinetics of extrinsic contrast agents, including the enhanced permeability and retention effect. We discuss research on monitoring neoadjuvant chemotherapy and on breast cancer risk assessment as potential clinical applications of optical breast imaging and spectroscopy. Moreover, we consider new experimental approaches, such as photoacoustic imaging and long-wavelength tissue spectroscopy.

Top 15% age-matched collagen content (estimated on 109 subjects by optical mammography) and high mammographic density identify different subgroups of high cancer occurrence, suggesting collagen is an independent breast cancer risk factor.

We present a new compact system for time-domain diffuse optical spectroscopy of highly scattering media operating in the wavelength range from 1100 nm to 1700 nm. So far, this technique has been exploited mostly up to 1100 nm: we extended the spectral range by means of a pulsed supercontinuum light source at a high repetition rate, a prism to spectrally disperse the radiation, and a time-gated InGaAs/InP single-photon avalanche diode working up to 1700 nm. A time-correlated single-photon counting board was used as processing electronics. The system is characterized by linear behavior up to absorption values of about 3.4 cm−1 where the relative error is 17%. A first measurement performed on lipids is presented: the absorption spectrum shows three major peaks at 1200 nm, 1400 nm, and 1700 nm.

The potential disturbance in the prefrontal cortex hemodynamic signal measured by functional near infrared spectroscopy (NIRS), due to forehead skin flowmotion, detected by laser Doppler flowmetry, was investigated by a standard protocol of hemodynamic challenge by Valsalva maneuver, aimed at assessing and disentangling local regulatory responses in skin vasomotion and in cerebral perfusion in presence of a strong systemic drive, and to quantify the common information in the two signals. The deep cortical NIRS signal did not appear to be affected by surface vasomotor activity, and autoregulation dynamics were dominant with respect to autonomic control of circulation. Highlights? Functional near infrared spectroscopy (fNIRS) prefrontal cortex measurements. ? Laser Doppler flowmetry (LDF) measurements of right and left temple vasomotions. ? Dynamic responses of prefrontal cortex autoregulation and skin vasomotion to a Valsalva maneuver. ? Cerebral and skin autoregulation were uncorrelated under the systemic stimulus due to Valsalva.

A review of near infrared (NIR) spectroscopy of the female breast performed using time domain broadband systems is presented, summarising the key studies performed at Politecnico di Milano. The time domain approach, based on pulsed tunable lasers and single-photon detection, makes it possible to uncouple absorption from scattering contributions and to derive tissue optical properties in vivo non-invasively. The basic tissue absorbers in the 600–1100 nm range are discussed, together with the interpretation of the scattering spectra. Inter- and intra-subject variations in breast optical properties are addressed based on in vivo measurements on different women and on the same subject as a function of the menstrual cycle phase and of the measurement geometry. Results demonstrate that a specific breast type can be identified for each woman, ultimately related to the water, lipid and collagen content and to the scattering properties. As an example of the application of spectroscopy-derived information, we discuss the non-invasive optical detection of breast density as an important risk factor for breast cancer, envisaging an attractive contribution of NIR spectroscopy to the fight against breast cancer on both a medical diagnostics and research level.

Investigations of wall paintings by Masolino da Panicale in the Baptistery of Castiglione Olona were conducted using a multi-analytical approach, based on in situ fluorescence imaging, multispectral reflectance imaging and non-destructive analysis of a historical cross-section. Fluorescence imaging of wall paintings, mainly focused on the discrimination and identification of organic compounds, has been conducted with a novel approach, which incorporates the use of spectrally-resolved and lifetime-resolved imaging devices, applied together for the first time for the analysis of paintings. Analysis of the UV-induced emissions from the surface of the paintings allowed the documentation of the selective use of a carmine-based red lake, identified using micro-Raman spectroscopy and Scanning Electron Microscopy. Visible reflectance measurements highlighted the distribution and use of different inorganic pigments. Finally, the in situ study, with the support of early 20th century photographs, provided additional information on Masolino's style and revealed details and decorative elements of the painting, which are indiscernible under standard illumination. (C) 2010 Elsevier Masson SAS. All rights reserved.

We present a novel technique for wide dynamic range optical investigations. It is based on a fast-gated silicon single-photon avalanche diode (SPAD) in time-correlated single-photon counting (TCSPC) setup. The SPAD is gated-on and off in 500 ps so as to detect photons only within a given time interval. This technique is particularly useful in applications where a large amount of unnecessary photons precede or follow the optical signal to be detected, such as in time-resolved near infrared (NIR) spectroscopy, optical mammography, and optical molecular imaging. In particular, in time-resolved reflectance spectroscopy, it is desirable to minimize the source-detector separation to improve system performance. This leads to the saturation of the detection electronics because of the huge amount of “early” photons back scattered by superficial layers. Our setup is able to reject these photons and detect only “late” photons from the sample, thus allowing an increase in the dynamic range and the injected power. We acquired diffusive curves of two phantoms with 95 ps time resolution and 107 dynamic range with a measurement time three orders of magnitude shorter than what is currently possible with a standard TCPSC setup.

Purpose: Sustained attention is one of the most important cognitive abilities for the management of everyday life, but it is often studied only at the behavioral level, while functional correlates are scarcely investigated. In this article, the authors address the topic of characterizing the dynamics of cerebral metabolism in the prefrontal cortex during a task of prolonged attention. Method: By means of multichannel time-resolved functional near-infrared spectroscopy and generalized linear model based data processing, the authors measured the hemodynamic response of the prefrontal cortex from 19 healthy subjects to a shortened version of a sustained attention task (Conners’ Continuous Performance Test), lasting for 10 min . Results: The task elicited significant brain activation, which did not remain constant for the entire task, but showed a drop not correlated with performance decay 4 min after the beginning of the task. Furthermore, oxygenated hemoglobin showed an increasing trend also during the first phase of the recovery, just after the end of the task. Conclusion: The results indicate a nontrivial dynamics of neural activation, habituation processes, and hemodynamic/metabolic coupling. These results encourage further studies about continuous stimulation of cognitive functions on both healthy and pathological subjects.

This paper discusses the spectral distortions occurring when time-resolved spectroscopy of diffusive media is performed illuminating with a wide bandpass. It is shown that the spectral region within the bandpass that exhibits the lowest absorption will dominate the resulting time-resolved curve, leading to significant underestimations of absorption as well as distortions in the spectral shape (including shifts in peak positions). Due to the nonlinear behavior of absorption, this effect becomes even more pronounced when including longer and longer photon path lengths. First, a theoretical treatment of the problem is given, and then the distortion is described by time-resolved reflectance simulations and experimental measurements of lipid and water samples. A spectrally constrained data analysis is proposed that takes into account the spectrum of the light injected into the sample, used to overcome the distortion and improve the accuracy of the estimation of chromophore concentrations from absorption spectra. Measurements on a lipid sample show a reduction of the error from 30% to 6%.

The in-vivo optical properties of the human head are investigated in the 600-1100 nm range on different subjects using continuous wave and time domain diffuse optical spectroscopy. The work was performed in collaboration with different research groups and the different techniques were applied to the same subject. Data analysis was carried out using homogeneous and layered models and final results were also confirmed by Monte Carlo simulations. The depth sensitivity of each technique was investigated and related to the probed region of the cerebral tissue. This work, based on different validated instruments, is a contribution to fill the existing gap between the present knowledge and the actual in-vivo values of the head optical properties. (C) 2015 Optical Society of America

A retrospective pilot clinical study on time domain multi-wavelength (635 to 1060 nm) optical mammography was exploited to assess collagen as a breast-cancer risk factor on a total of 109 subjects (53 healthy and 56 with malignant lesions). An increased cancer occurrence is observed on the 15% subset of patients with higher age-matched collagen content. Further, a similar clustering based on the percentage breast density leads to a different set of patients, possibly indicating collagen as a new independent breast cancer risk factor. If confirmed statistically and on larger numbers, these results could have huge impact on personalized diagnostics, health care systems, as well as on basic research.

We propose a simple and reliable solid phantom for mimicking localized absorption changes within a diffusive medium. The phantom is based on the Equivalence Relation stating that any realistic absorption inhomogeneity can be mimicked by a totally absorbing sphere of adequate volume. Applying this concept, we constructed a solid phantom holding a movable black inclusion to be positioned beneath the source-detector pair (perturbed case) or far from it (unperturbed case). Different absorption perturbations can be mimicked by changing the volume and the position of the black object both in transmittance and reflectance configuration. Time-resolved measurements of transmittance images and a lateral reflectance scan are presented.

We propose a simple and reliable solid phantom for mimicking realistic localized absorption changes within a diffusive medium. The phantom is based on a solid matrix holding a movable black inclusion embedded in a rod. Translating the rod parallel to the phantom surface, the inhomogeneity can be positioned beneath the source-detector pair (perturbed case) or far from it (unperturbed case). Examples of time-resolved transmittance measurements and time-resolved reflectance scans are shown to demonstrate the properties and the versatility of the phantom.

The aim of this chapter is to provide an overview on the applications of time-domain diffuse optics to the assessment of breast physiology and pathology. A number of different implementations to optical mammography have been evaluated ranging from lesion detection and characterisation using endogenous or exogenous contrast, to breast density assessment as strong cancer risk factor, and to monitoring during neoadjuvant chemotherapy. The time-domain approach is the common factor of all these applications, which permits to uncouple absorption from scattering contributions and to derive tissue optical properties in vivo. The Time-Correlated Single-Photon Counting (TCSPC) is the measurement technique of choice to acquire fast and weak optical signals at the picosecond time scale. For what concerns the time-resolved optical mammography with endogenous contrast, results obtained within the European project Optimamm are reported. The aim of the clinical trial was to understand the detection breast tumor capability of the developed multi-wavelength time-domain scanning systems operating in transmittance geometry on compressed breast. Results of the Berlin and Milan groups, have shown a similar detection rates for malignant breast lesions, with a high contrast at short wavelengths due to the presence of high blood volume. Regarding the optical mammography with exogenous contrast agent, a time domain optical mammography with Indocyanine Green (ICG) including also fluorescence measurements is presented. Results have shown a good sensitivity of the fluorescent optical mammography in detecting tumor. A good discrimination between healthy and tumor tissue was achieved. Concerning the optical mammography for therapy monitoring, a time-domain optical tomography system and very preliminary results were presented, showing good results on monitoring tumor response to chemotherapy using this approach. The other application presented in this chapter is based on the use of a multi-wavelength time-domain optical mammography for the assessment of breast density since it is a recognized independent risk factor for the development of breast cancer. A good correlation between optical data and mammographic breast density (provided by X-ray mammograms) was obtained, showing an increase of water and collagen in subjects with high breast density as expected from the physiological point of view and demonstrating the capability of the time-domain system to identify subjects with a high risk to develop breast cancer.

A mechanically switchable solid inhomogeneous phantom simulating localized absorption changes was developed and characterized. The homogeneous host phantom was made of epoxy resin with black toner and titanium dioxide particles added as absorbing and scattering components, respectively. A cylindrical rod, movable along a hole in the block and made of the same material, has a black polyvinyl chloride cylinder embedded in its center. By varying the volume and position of the black inclusion, absorption perturbations can be generated over a large range of magnitudes. The phantom has been characterized by various timedomain diffuse optics instruments in terms of absorption and scattering spectra, transmittance images, and reflectance contrast. Addressing a major application of the phantom for performance characterization for functional near-infrared spectroscopy of the brain, the contrast was measured in reflectance mode while black cylinders of volumes from approximate to 20 mm(3) to approximate to 270 mm(3) were moved in lateral and depth directions, respectively. The new type of solid inhomogeneous phantom is expected to become a useful tool for routine quality check of clinical instruments or implementation of industrial standards provided an experimental characterization of the phantom is performed in advance. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.

Continuous wave (CW) methods are widely diffused for postharvest fruit quality measurement. CW colorimeters and spectrometers measure the diffusely remitted intensity which is affected also by the skin colour and is determined by both the absorption and the scattering properties of the sample. The absorption coefficient (μ a ) can be discriminated from the reduced scattering coefficient (μ' s ) by Time-resolved Reflectance Spectroscopy (TRS), which explores the sample at a depth of 1-2 cm. The absorption coefficient at 670 nm, which is related to chlorophyll content, was shown to be an effective maturity index for modelling firmness decay of nectarines after harvest. However, until now the TRS instrumentation is restricted to the scientific research field. The aim of this research was to test if CW measurement could provide similar results as time-resolved measurements to model fruit softening. Nectarine fruit (cv 'Ambra' and 'Spring Bright') were measured at harvest with different optical methods: absorption coefficient at 670 nm (TRS), CIELab* (CW), reflectance spectrometry in the VIS region with a 10 nm resolution (CW). Firmness was measured during ripening at 20°C in fruit representing the whole range of maturity. The different optical measurements were used as independent variables to model fruit softening, and results were compared. The models obtained were similar, but CW methods provided lower R 2 than time-resolved method. The absorption coefficient μ a at 670 nm measured by time-resolved methods was a better maturity index to predict fruit softening during shelf life with the logistic model, than CW measurements.

We have recently developed a portable system for advanced fluorescence investigation of works of art. The system is based on the measurement of both the time dependent and spectral features of fluorescence emission, after excitation with UV laser pulses. The technique is aimed at localising and identifying organic and inorganic compounds present on the surface of artworks. The time dependence of the emission is analysed with a fluorescence lifetime imaging apparatus, which allows us to measure the map of the fluorescence lifetime, combined with a portable spectrometer for recording fluorescence spectra of selected points. The characterization of the compounds present on the art object's surfaces is carried out with analytical measurements on micro-samples collected with the assistance of the fluorescence maps. These methods have been successfully applied to characterise the fresco paintings of Filippo Lippi in the cathedral of Prato and to study the contaminants on the surface of Michelangelo's David in F...

We developed a combined procedure for the analysis of works of art based on a portable system for fluorescence imaging integrated with analytical measurements on microsamples. The method allows us to localize and identify organic and inorganic compounds present on the surface of artworks. The fluorescence apparatus measures the temporal and spectral features of the fluorescence emission, excited by ultraviolet (UV) laser pulses. The kinetic of the emission is studied through a fluorescence lifetime imaging system, while an optical multichannel analyzer measures the fluorescence spectra of selected points. The chemical characterization of the compounds present on the artistic surfaces is then performed by means of analytical measurements on microsamples collected with the assistance of the fluorescence maps. The previous concepts have been successfully applied to study the contaminants on the surface of Michelangelo's David. The fluorescence analysis combined with Fourier transform infrared (FT-IR) measurements revealed the presence of beeswax, which permeates most of the statue surface, and calcium oxalate deposits mainly arranged in vertical patterns and related to rain washing.

The first time-resolved optical mammograph operating beyond 900 nm was tested in a retrospective clinical study involving 194 patients with malignant and benign lesions, to investigate the diagnostic potential for the detection and characterization of breast lesions. For the first part of the study (101 patients with 114 lesions), the system was operated at 683, 785, 913 and 975 nm. Subsequently, to improve the spectral content of optical images, the number of wavelengths was increased (up to 7) and the spectral range was extended (637–985 nm). Late gated intensity and scattering images provide sensitivity to tissue composition (oxy- and deoxyhaemoglobin, water and lipids) and physiology (total haemoglobin content and oxygen saturation), as well as to structural changes. Tumours are typically identified because of the strong blood absorption at short wavelengths (637–685 nm), while cysts are characterized by low scattering, leading to a detection rate of approximately 80% for both lesion types, when detection is required in both cranio-caudal and oblique views. The detection rate for other benign lesions, such as fibroadenomas, is presently much lower (

In this paper, we propose a novel approach for the acquisition of time-resolved data for optical tomography. A fast gated CCD has been used as a parallel detector to acquire in one shot the light intensity exiting a phantom within a very short time slice. By using a pulsed illumination and repeating the acquisition at different delays, the time behaviour of the diffused transmittance can be recorded very quickly. Scattering inclusions embedded in a 5 cm thick phantom have been revealed by fitting a set of 120 images, delayed 50 ps from one another, with a mathematical model based on the random walk theory. Moreover, absorption inclusions have been detected in time-gated images taken at suitable delays.

The nEUROPt protocol is one of two new protocols developed within the European project nEUROPt to characterize the performances of time-domain systems for optical imaging of the brain. It was applied in joint measurement campaigns to compare the various instruments and to assess the impact of technical improvements. This protocol addresses the characteristic of optical brain imaging to detect, localize, and quantify absorption changes in the brain. It was implemented with two types of inhomogeneous liquid phantoms based on Intralipid and India ink with well-defined optical properties. First, small black inclusions were used to mimic localized changes of the absorption coefficient. The position of the inclusions was varied in depth and lateral direction to investigate contrast and spatial resolution. Second, two-layered liquid phantoms with variable absorption coefficients were employed to study the quantification of layer-wide changes and, in particular, to determine depth selectivity, i.e., the ratio of sensitivities for deep and superficial absorption changes. We introduce the tests of the nEUROPt protocol and present examples of results obtained with different instruments and methods of data analysis. This protocol could be a useful step toward performance tests for future standards in diffuse optical imaging. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.

We present the experimental implementation and validation of a phantom for diffuse optical imaging based on totally absorbing objects for which, in the previous paper [J. Biomed. Opt. 18(6), 066014, (2013)], we have provided the basic theory. Totally absorbing objects have been manufactured as black polyvinyl chloride (PVC) cylinders and the phantom is a water dilution of intralipid-20% as the diffusive medium and India ink as the absorber, filled into a black scattering cell made of PVC. By means of time-domain measurements and of Monte Carlo simulations, we have shown the reliability, the accuracy, and the robustness of such a phantom in mimicking typical absorbing perturbations of diffuse optical imaging. In particular, we show that such a phantom can be used to generate any absorption perturbation by changing the volume and position of the totally absorbing inclusion. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.

A multi-center study has been set up to accurately characterize the optical properties of diffusive liquid phantoms based on Intralipid and India ink at near-infrared (NIR) wavelengths. Nine research laboratories from six countries adopting different measurement techniques, instrumental set-ups, and data analysis methods determined at their best the optical properties and relative uncertainties of diffusive dilutions prepared with common samples of the two compounds. By exploiting a suitable statistical model, comprehensive reference values at three NIR wavelengths for the intrinsic absorption coefficient of India ink and the intrinsic reduced scattering coefficient of Intralipid-20% were determined with an uncertainty of about 2% or better, depending on the wavelength considered, and 1%, respectively. Even if in this study we focused on particular batches of India ink and Intralipid, the reference values determined here represent a solid and useful starting point for preparing diffusive liquid phantoms with accurately defined optical properties. Furthermore, due to the ready availability, low cost, long-term stability and batch-to-batch reproducibility of these compounds, they provide a unique fundamental tool for the calibration and performance assessment of diffuse optical spectroscopy instrumentation intended to be used in laboratory or clinical environment. Finally, the collaborative work presented here demonstrates that the accuracy level attained in this work for optical properties of diffusive phantoms is reliable. © 2014 Optical Society of America.

We report on a new source able to provide probe pulses in the UV visible range and on the demonstration of its application to hyperspectral (fluorescence lifetime) imaging measurements. The source is able to generate UV (down to 300 nm) and blue light exploiting high-order mode propagation in a microstructured fiber pumped by a Ti:Sapphire laser. We believe that further optimization of pump wavelength, fiber length and fiber zero-dispersion wavelength could generate light well below 300 nm using a simple and stable set-up and become a useful tool for biomedical imaging. We demonstrated its versatility using the source for FLIM-FRET measurement a 460 nm and hyperspectral FRET-FLIM measurements. © 2014 SPIE.

The optical properties of the human head in the range from 600 nm to 1100 nm have been non-invasively investigated by various research groups using different diffuse optics techniques and data analysis methods.

Intense continua of electromagnetic radiation of very brief duration are formed in the interaction of focused ultra-short terawatt laser pulses with matter. Two different kinds of experiments, which have been performed utilizing the Lund 10 Hz titanium-doped sapphire terawatt laser system are being described, where visible radiation and X-rays, respectively, have been generated. Focusing into water leads to the generation of a light continuum through self-phase modulation. The propagation of the light through tissue was studied addressing questions related to optical mammography and specific chromophore absorption. When terawatt laser pulses are focused onto a solid target with high nuclear charge Z, intense X-ray radiation of few ps duration and with energies exceeding hundreds of keV is emitted. Biomedical applications of this radiation are described, including differential absorption and gated-viewing imaging.

A solid tissue phantom made of agar, Intralipid and black ink is described and characterized. The preparation procedure is fast and easily implemented with standard laboratory equipment. An instrumentation for time-resolved transmittance measurements was used to determine the optical properties of the phantom. The absorption and the reduced scattering coefficients are linear with the ink and Intralipid concentrations, respectively. A systematic decrease of the reduced scattering coefficient dependent on the agar content is observed, but can easily be managed. The phantom is highly homogeneous and shows good repeatability among different preparations. Moreover, agar inclusions can be easily embedded in either solid or liquid matrixes, and no artefacts are caused by the solid-solid or solid-liquid interfaces. This allows one to produce reliable and realistic inhomogeneous phantoms with known optical properties, particularly interesting for studies on optical imaging through turbid media.

Summary form only given. Time-resolved diffuse optical spectroscopy (TRS) is a valuable technique for the characterization of a variety of diffusive media like biological tissues, fruit, wood and pharmaceutical tablets. The technique is based on the injection of a short pulse (~ps) on the surface of the sample. The time-of-flight distribution (TOF) of photons detected on a different location of the surface gives information about the absorption and scattering probabilities [1]. Due to the widespread application of the technique to biological tissues, where there is a low light attenuation in the 0.6-1.1 μm range, the range beyond 1.1 μm is relatively unexplored with time-resolved techniques, also because of the difficulty to combine mode-locked continuously tunable sources with detectors having a sensitivity down to the single-photon level. Nevertheless beyond 1.1 μm there are organic compounds that contribute to interesting spectral structures like collagen, lipids, hydroxyapatite, starch, glucose and lignin. In this work we explore the application of TRS beyond 1.1 μm to the characterization of a variety of samples.

In recent years, emerging applications, such as diffuse optical imaging and spectroscopy (e.g., functional brain imaging and optical mammography), in which a wide dynamic range is crucial, have turned the interest towards Single-Photon Avalanche Diode (SPAD). In these fields, the use of a fast-gated SPAD has proven to be a successful technique to increase the measurement sensitivity of different orders of magnitude. However, an unknown background noise has been observed at high illumination during the gate-OFF time, thus setting a limit to the maximum increase of the dynamic range. In this paper we describe this noise in thin-junction silicon single-photon avalanche diode when a large amount of photons reaches the gated detector during the OFF time preceding the enabling time. This memory effect increases the background noise with respect to primary dark count rate similarly to a classical afterpulsing process, but differently it is not related to a previous avalanche ignition in the detector. We discovered that memory effect increases linearly with the power of light impinging on the detector and it has an exponential trend with time constants far different from those of afterpulsing and independently of the bias voltage applied to the junction. For these reasons, the memory effect is not due to the same trapping states of afterpulsing and must be described as a different process.

Novel protocols were developed and applied in the European project “nEUROPt” to assess and compare the performance of instruments for time-domain optical brain imaging and of related methods of data analysis. The objective of the first protocol, “Basic Instrumental Performance”, was to record relevant basic instrumental characteristics in a direct way. The present paper focuses on the second novel protocol (“nEUROPt” protocol) that was devoted to the assessment of sensitivity, spatial resolution and quantification of absorption changes within inhomogeneous media. It was implemented with liquid phantoms based on Intralipid and ink, with black inclusions and, alternatively, in two-layered geometry. Small black cylinders of various sizes were used to mimic small localized changes of the absorption coefficient. Their position was varied in depth and lateral direction to address contrast and spatial resolution. Two-layered liquid phantoms were used, in particular, to determine depth selectivity, i.e. the ratio of contrasts due to a deep and a superficial absorption change of the same magnitude. We introduce the tests of the “nEUROPt” protocol and present exemplary results obtained with various instruments. The results are related to measurements with both types of phantoms and to the analysis of measured time-resolved reflectance based on time windows and moments. Results are compared for the different instruments or instrumental configurations as well as for the methods of data analysis. The nEUROPt protocol is also applicable to cw or frequency-domain instruments and could be useful for designing performance tests in future standards in diffuse optical imaging.

Optical Projection Tomography (OPT) is a three dimensional imaging technique that is particularly suitable for studying millimeter sized biological samples and organisms. Similarly to x -ray computed tomography, OPT is based on the acquisition of a sequence of images taken through the sample at many angles (projections) . A ssuming the linearity of the optical absorption process, t he projections are combined to reconstruct the 3 -D volume of the sample, typically using a filtered back -projection algorithm. OPT has been applied to in-vivo imaging of zebrafish ( Danio rerio ). The instrument and the protocol for in vivo imaging of zebrafish embryos and juvenile specimens are described. Light scattering remains a challenge for in vivo OPT , especially when samples at the upper size limit , like zebrafish at the adult stage , are under study. We describe Time -Gated Optical Projection Tomography (TGOPT), a technique able to reconstruct adult zebrafish internal structures by counteracting the scattering effects through a fast time -gate . The time gating mechanism is based on non -linear opti cal upconversion of an infrared ultrashort laser pulse and allows the detection of quasi -ballistic photons within a 100 fs temporal gate. This results in a strong improvement in contrast and resolution with respect to conventional OPT. Artifacts in the rec onstructed images are reduced as well. We show that TGOPT is suited for imaging the skeletal system and nervous structures of adult zebrafish. Keywords: Optical projection tomography , gated imaging, non -linear imaging, zebrafish

A time-domain multiwavelength (635 to 1060 nm) optical mammography was performed on 147 subjects with recent X-ray mammograms available, and average breast tissue composition (water, lipid, collagen, oxy-and deoxyhemoglobin) and scattering parameters (amplitude a and slope b) were estimated. Correlation was observed between optically derived parameters and mammographic density [Breast Imaging and Reporting Data System (BI-RADS) categories], which is a strong risk factor for breast cancer. A regression logistic model was obtained to best identify high-risk (BI-RADS 4) subjects, based on collagen content and scattering parameters. The model presents a total misclassification error of 12.3%, sensitivity of 69%, specificity of 94%, and simple kappa of 0.84, which compares favorably even with intraradiologist assignments of BI-RADS categories. © The Authors.

Presently time-resolved optical spectroscopy is applied with increasing success for non-invasive medical diagnostics mainly up to 1100 nm. We extended the investigation range beyond this limit, employing a supercontinuum fiber laser source and a Single-Photon Avalanche Diode in InGaAs/InP operated in gated mode. First in-vivo measurements were performed on the forearm and the breast of two healthy volunteers, reaching up to 1360 nm.