This year marks the 20th anniversary of functional near-infrared spectroscopy and imaging (fNIRS/fNIRI). As the vast majority of commercial instruments developed until now are based on continuous wave technology, the aim of this publication is to review the current state of instrumentation and methodology of continuous wave fNIRI. For this purpose we provide an overview of the commercially available instruments and address instrumental aspects such as light sources, detectors and sensor arrangements. Methodological aspects, algorithms to calculate the concentrations of oxy-and deoxyhemoglobin and approaches for data analysis are also reviewed. From the single-location measurements of the early years, instrumentation has progressed to imaging initially in two dimensions (topography) and then three (tomography). The methods of analysis have also changed tremendously, from the simple modified Beer-Lambert law to sophisticated image reconstruction and data analysis methods used today. Due to these advances, fNIRI has become a modality that is widely used in neuroscience research and several manufacturers provide commercial instrumentation. It seems likely that fNIRI will become a clinical tool in the foreseeable future, which will enable diagnosis in single subjects. This year marks the 20th anniversary of functional near-infrared spectroscopy and imaging (fNIRS/fNIRI). As the vast majority of commercial instruments developed until now are based on continuous wave technology, the aim of this publication is to review the current state of instrumentation and methodology of continuous wave fNIRI. For this purpose we provide an overview of the commercially available instruments and address instrumental aspects such as light sources, detectors and sensor arrangements. Methodological aspects, algorithms to calculate the concentrations of oxy-and deoxyhemoglobin and approaches for data analysis are also reviewed. From the single-location measurements of the early years, instrumentation has progressed to imaging initially in two dimensions (topography) and then three (tomography). The methods of analysis have also changed tremendously, from the simple modified Beer-Lambert law to sophisticated image reconstruction and data analysis methods used today. Due to these advances, fNIRI has become a modality that is widely used in neuroscience research and several manufacturers provide commercial instrumentation. It seems likely that fNIRI will become a clinical tool in the foreseeable future, which will enable diagnosis in single subjects. Contents

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A 1 × 400 array of backside-illuminated SPADs fabricated in 130 nm 3D IC CMOS technology is presented. Sensing is performed in the top tier substrate and time-to-digital conversion in the bottom tier. Clusters of eight pixels are connected to a winner-take-all circuit with collision detection capabilities to realise an efficient sharing of the time-to-digital converter (TDC). The sensor's 100 TDCs are based on a dual-frequency architecture enabling 30 pJ per conversion at a rate of 13.3 ms/s per TDC. The resolution (1 LSB) of the TDCs is 49.7 ps with a standard deviation of 0.8 ps across the entire array; the mean DNL is ±0.44 LSB and the mean INL is ±0.47. The chip was designed for use in near-infrared optical tomography (NIROT) systems for brain imaging and diagnostics. Measurements performed on a silicon phantom proved its suitability for NIROT applications. Index Terms-Near-infrared optical tomography (NIROT), near-infrared spectroscopy (NIRS), optical tomography (OT), single-photon avalanche diode (SPAD), single-photon imaging, time correlated single photon counting (TCSPC), time-of-flight imaging, time-resolved imaging, time-to-digital converter (TDC).

Single-photon avalanche diode (SPAD) imagers typically have a relatively low fill factor, i.e. a low proportion of the pixel's surface is light sensitive, due to in-pixel circuitry. We present a microlens array fabricated on a 128×128 single-photon avalanche diode (SPAD) imager to enhance its sensitivity. The benefits and limitations of these light concentrators are studied for low light imaging applications. We present a new simulation software that can be used to simulate microlenses' performance under different conditions and a new non-destructive contact-less method to estimate the height of the microlenses.Results of experiments and simulations are in good agreement, indicating that a gain >10 can be achieved for this particular sensor. Abstract: Single-photon avalanche diode (SPAD) imagers typically have a relatively low fil factor, i.e. a low proportion of the pixel's surface is light sensitive, due to in-pixel circuitry. We present a microlens array fabricated on a 128x128 single-photon avalanche diode (SPAD) imager to enhance its sensitivity. The benefit and limitations of these light concentrators are studied for low light imaging applications. We present a new simulation software that can be used to simulate microlenses' performance under different conditions and a new non-destructive contact-less method to estimate the height of the microlenses. Results of experiments and simulations are in good agreement, indicating that a gain >10 can be achieved for this particular sensor.