Juan Mata Pavia

A review on continuous wave functional near-infrared spectroscopy and imaging instrumentation and methodology

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.

A 1 × 400 Backside-Illuminated SPAD Sensor With 49.7 ps Resolution, 30 pJ/Sample TDCs Fabricated in 3D CMOS Technology for Near-Infrared Optical Tomography

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 sensors 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.

3D near-infrared imaging based on a single-photon avalanche diode array sensor: A new perspective on reconstruction algorithms

Recently, we demonstrated the potential of single-photon imagers in diffuse optical tomography (DOT). We present the advances of a new algorithm based on optical setups using this kind of sensors.

3D near-infrared imaging based on a single-photon avalanche diode array sensor

Near-infrared light can be used to determine the optical properties (absorption and scattering) of human tissue. Optical tomography uses this principle to image the internal structure of parts of the body by measuring the light that is scattered in the tissue. An imager for optical tomography was designed based on a detector with 128x128 single photon pixels that included a bank of 32 time-to-digital converters. Due to the high spatial resolution and the possibility of performing time resolved measurements, a new contactless setup has been conceived. The setup has a resolution of 97ps and operates with a laser source with an average power of 3mW. This new setup generated an high amount of data that could not be processed by established methods, therefore new concepts and algorithms were developed to take advantage of it. Simulations show that the potential resolution of the new setup would be much higher than previous designs. Measurements have been performed showing its potential. Images derived from the measurements showed that it is possible to reach a resolution of at least 5mm.

Time Domain Near-Infrared Optical Tomography with Time-of-Flight SPAD Camera: The New Generation, Biophotonics Congress: Biomedical Optics Congress 2018 (Microscopy/Translational/Brain/OTS)

We present the first laboratory results of the new generation of time domain near-infrared optical tomography setup, which is based on a time-of-flight 32×32 SPAD camera with high photon detection probability in the NIR range.