Wearable Near-Infrared (NIR) Imaging and Applications

Noninvasive functional neuroimaging methods, like functional magnetic resonance imaging (fMRI) and electroencephalography (EEG), are vital for studying brain function and cognition in various neurological and mental health disorders. fMRI provides high spatial resolution but suffers from poor temporal resolution and high cost, alongside the requirement of large, immobile equipment, limiting its practicality in many situations. EEG, while more affordable and portable, has restricted spatial resolution.

Micro-DOT, a functional near-infrared spectroscopy (fNIRS) system with high-density, time-domain diffuse optical tomography (HD-TD-DOT) and a sophisticated volumetric reconstruction system. Micro-DOT tackles the balance between compact design and spatial resolution that has been a persistent issue in conventional fNIRS systems through a novel hardware design that places HD-TD-DOT-capable electronics directly on the tissue surface.

This is enabled by complementary-metal-oxide-semiconductor (CMOS) source-detector chiplets, which integrate the necessary optics and electronics for HD-TD-DOT, mounted on flexible polyimide packaging with a minimal footprint. Micro-DOT provides in-plane spatial resolution, depth accuracy, and localization precision comparable to fMRI, while maintaining the portability and convenience of EEG, making it a low-cost, standalone system for measuring individualized brain activity.

Selected Publications

Sajjad Moazeni, Kevin Renehan, Eric H. Pollmann, and Kenneth L. Shepard. An Integrated-Circuit Node for High-Spatiotemporal Resolution Time-Domain Near Infrared Diffuse Optical Tomography Imaging Arrays IEEE Journal of Solid-State Circuit. (Early Access) (Dec 2022)

Abstract

Next-generation brain–computer interfaces (BCIs) for healthy individuals are expected to largely rely on noninvasive functional imaging methods to record cortex-wide neural activity because of the risk associated with surgically implanted devices. In this work, we present a fully integrated 1.8 × 1.8 mm single chip that can be arrayed on a wearable patch to perform noninvasive, functional brain imaging over large cortical areas. This chip node contains two bonded vertical-cavity surfaceemitting lasers (VCSELs), an 8 × 8 single-photon avalanche diode (SPAD) array with event-driven time-to-digital converters (TDCs) per row, and a digital back-end for on-chip histogramming and time-gating. We achieved 70-ps resolution for time-of-flight (ToF) imaging at the record-high 100-MHz laser repetition rate with 80-mW total power. We showed that time-gating improves the imaging contrast by as much as 36% using a brain-skull phantom. The fully integrated and compact node presented here is the key enabler for future high-spatiotemporal-resolution timedomain diffuse optical tomography (TD-DOT) imaging arrays.
Index Terms—Diffuse optical tomography (DOT), noninvasive brain imaging, time-of-flight (ToF) imager, wearable patch.

Sajjad Moazeni, Kevin Renehan, Eric Pollmann, Kenneth Shepard. Integrated-Circuit Node for Time-Domain Near-infrared Diffuse Optical Tomography Imaging Arrays with On-chip Histogramming and Integrated VCSELs IEEE Custom Integrated Circuits Conference (CICC). (Feb 2021)

Abstract

Next-generation brain-computer interfaces (BCI) for healthy individuals largely rely on non-invasive functional imaging methods to record cortex-wide neural activity because of the risk associated with surgically implanted devices. Near-infrared (NIR) time-domain diffuse optical tomography (TD-DOT) is a promising non-invasive imaging approach which relies on reduced optical scattering and absorption of the human skull and brain tissue in the NIR spectrum [1]. In TD-DOT imaging, the time-of-flight (ToF) of scattered photons is measured, improving on continuous-wave approaches. This method has the potential to allow for direct sensing of intracellular neural activity and hemodynamics at higher spatial resolutions than electroencephalogram (EEG) and at higher temporal resolution than functional magnetic resonance imaging (fMRI), while supporting more compact and cost-effective form factors.

Wearable Near-Infrared (NIR) Imaging and Applications

Wearable Near-Infrared (NIR) Imaging and Applications

Selected Publications

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