Alberto Dalla Mora

Diffuse optics measurements performed in the time domain provide the highest information level, but are plagued by a low spatial resolution and significant sensitivity to superficial regions (e.g., extracerebral changes). Here we compare the two main analysis methods (namely, statistical moments and time-windowing of the photon time-of-flight distribution) with the recently introduced dual-slope method. Both in-silico and phantom studies are performed. Our results show that time-windowing, although not previously applied in this context, maximizes the advantages of a dual-slope approach while also maximizing the depth selectivity. Furthermore, for time-windowing, a triple-slope approach is proposed, demonstrating superior rejection of superficial changes.

Optical phantoms are widely used to characterize diffuse optical setups and data analysis methods for in-vivo/ex-vivo measurements. Coconut oil is an interesting compound to use in phantoms, because it could be used to model lipidic tissues, such as the one in breast tissue. In this paper, we measure the absorption and scattering spectra of coconut oil from 600 to 1600 nm, encompassing the so-called “therapeutic window”. To cover the entire range, we exploit a supercontinuum pulsed laser and a superconducting nanowire single photon detector operating in the time domain. Finally, we demonstrate the use of a homogeneous coconut oil phantom to characterize a hyperspectral continuous-wave (CW) setup.

Fluorescence microscopy is nowadays one of the most diffused techniques to study photophysical processes and molecular interactions in both biomedical and material science fields. Since each fluorophore is characterized by a specific emission spectrum and lifetime, it is essential not only to spatially localize its position but also to measure its spectral and temporal properties with a multispectral fluorescence lifetime imaging microscope (λFLIM). Moreover, to study rapidly evolving samples, a measurement system capable of fast acquisitions is needed. λFLIM systems are currently limited on acquisition speed and cannot reach high throughput. In this work, we propose a novel wide-field multispectral fluorescence lifetime imaging microscope based on a 16-channel silicon photomultiplier (SiPM) array. Our system, thanks to the SiPM technology along with the single pixel camera and compress sensing approaches is able to acquire multidimensional measurements (space, spectrum, and time) at high frame rate. We validate the system on moving fluorescent samples capturing snapshots at a frame rate of up to 13 fps. The developed system could enable enhanced specificity in real-time fluorescence imaging in biological and biosensing applications.

Bioresorbable fibers are an exciting prospect as probes and implants to provide optical access to the human body. In this work, we demonstrate interstitial spectroscopy with bioresorbable fibers at null distance, using time-domain diffuse optics that disentangles absorption from scattering properties and probes the tissues up to a depth of a few cm around the fiber tips. We exploit a fast-gated single-photon avalanche diode with > 55 dB of dynamic range to overcome the burst of ‘early’ photons hiding the information of absorption from deep tissues. We tested the absorption linearity—retrieving the water spectrum in the 700–950 nm range with > 85% accuracy over two decades of absorption change—and verified the hypothesis of a scattering-independent absorption retrieval. Further, we were able to detect spectral changes at a distance of 1 cm from an inclusion embedded in a biological tissue. Time-domain diffuse optical spectroscopy with bioresorbable fibers could detect spectral changes without being affected by blood extravasation at the fiber tips and could help for long-term monitoring in tissue healing, thermal treatment, photodynamic therapy and ultimately, towards minimally invasive medical procedures.

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 possibility to exploit a 1064 nm wavelength coupled with wavelengths of classical approaches is also discussed. Our findings demonstrate a reasonable overlap of the new approaches as compared to the standard one, with confined discrepancies potentially linked to a not established agreement in the scientific community on the exact value of extinction coefficients of tissue constituents beyond 1000 nm, as well as to an increased penetration depth in the tissue at 1064 nm due to a lower scattering coefficient as compared to the visible range. These findings open the way to further studies in the field, also given the increasing advancements in lasers and detectors at 1064 nm.

Thyroid vascularization and hemodynamics become altered in thyroid pathologies and could thus inform diagnostics, therapy planning, and follow-up. However, the current non-invasive monitoring methods available in clinics lack the necessary sensitivity and/or are impractical for large-scale deployment. As a step towards proposing a new modality, we applied the first platform, to our knowledge, designed to do simultaneous measurements of neck anatomy and thyroid microvascular hemodynamics and metabolism in a single probe placement, integrating state-of-the-art near-infrared spectroscopy techniques and clinical ultrasound. A rich dataset was formed with sixty-five subjects (forty-eight females), including eighteen healthy volunteers and forty-seven patients with thyroid nodules, characterizing thyroid tissue and the effects of demographic and anatomical variables while preserving the standard clinical workflow. We have found marked reductions with age and body mass index in thyroid total hemoglobin concentration (THC), tissue oxygen saturation (StO₂), and blood flow index (BFi), among others. Patients showed lower THC and BFi than healthy subjects, and the limited sample of malignant nodules showed a higher StO₂ than the benign. These findings support the need for personalized clinical approaches.

This work introduces a novel compact Time-Domain Diffuse Optics (TD-DO) system based on CMOS integrated circuits for being potentially used in non-invasive tissue characterization and physiological monitoring. The system incorporates a ~800 nm emitting laser diode and a 256-channel Single-Photon Avalanche Diode (SPAD) line sensor, offering high-throughput data acquisition. It offers remarkable capabilities for non-invasive investigations of diffusive media for biological and non-biological applications. To enhance system performance, an alignment method of the TD curves based on cross-correlation maximization is proposed and validated under internationally agreed protocols, such as MEDPHOT and nEUROPt. Finally, fast oscillations in optical properties corresponding to the heartbeat have been detected, showcasing the potential of the system for real-time physiological tracking. The results display the potential of the proposed compact TD-DO system, paving the way for the implementation of wearable instruments capable of non-invasively tracking fast physiological dynamics with high accuracy and robustness.

Fluorescence lifetime imaging microscopy (FLIM) is a powerful technique for studying biological processes. There exists a growing interest in developing strategies to enhance throughput and reduce acquisition time of FLIM systems, which commonly employ laser scanning excitation and time-correlated single-photon counting (TCSPC) detection. In this work, we propose a wide-field FLIM microscope based on compressive sensing and high photon rate detection (beyond pile-up limit) based on a high-efficiency silicon photomultiplier detector as a single-pixel camera. We experimentally validate the capabilities of this design achieving 20 frames per second FLIM images on free-moving green algae sample.