Design and validation of a mechanically flexible and ultra-lightweight high-density diffuse optical tomography system for functional neuroimaging of newborns

Abstract

Significance: Neonates are a highly vulnerable population. The risk of brain injury is greater during the first days and weeks after birth than at any other time of life. Functional neuroimaging that can be performed longitudinally and at the cot-side has the potential to improve our understanding of the evolution of multiple forms of neurological injury over the perinatal period. However, existing technologies make it very difficult to perform repeated and/or long-duration functional neuroimaging experiments at the cot-side.Aim: We aimed to create a modular, high-density diffuse optical tomography (HD-DOT) technology specifically for neonatal applications that is ultra-lightweight, low profile and provides high mechanical flexibility. We then sought to validate this technology using an anatomically accurate dynamic phantom.Approach: An advanced 10-layer rigid-flexible printed circuit board technology was adopted as the basis for the DOT modules, which allows for a compact module design that also provides the flexibility needed to conform to the curved infant scalp. Two module layouts were implemented: dual-hexagon and triple-hexagon. Using in-built board-to-board connectors, the system can be configured to provide a vast range of possible layouts. Using epoxy resin, thermochromic dyes, and MRI-derived 3D-printed moulds, we constructed an electrically switchable, anatomically accurate dynamic phantom. This phantom was used to quantify the imaging performance of our flexible, modular HD-DOT system.Results: Using one particular module configuration designed to cover the infant sensorimotor system, the device provided 36 source and 48 detector positions, and over 700 viable DOT channels per wavelength, ranging from 10 to ∼45 mm over an area of approximately 60 cm 2 . The total weight of this system is only 70 g. The signal changes from the dynamic phantom, while slow, closely simulated real hemodynamic response functions. Using difference images obtained from the phantom, the measured 3D localization error provided by the system at the depth of the cortex was in the of range 3 to 6 mm, and the lateral image resolution at the depth of the neonatal cortex is estimated to be as good as 10 to 12 mm. Conclusions:The HD-DOT system described is ultra-low weight, low profile, can conform to the infant scalp, and provides excellent imaging performance. It is expected that this device will make functional neuroimaging of the neonatal brain at the cot-side significantly more practical and effective.

Optical imaging and spectroscopy for the study of the human brain: status report

“…While fiber-based systems have thus far set the standard regarding specifications 2 , 6 , 10 (including detectivity, dynamic range, crosstalk, frame rate, optode-scalp coupling, and modulation/demodulation strategies for encoding source illuminations 4 ), several research groups have been demonstrating fiberless implementations of HD-DOT. 11 – 15 Although technical issues are still to be worked out, we expect HD-DOT systems to transition to mostly fiberless implementations over the next five years, removing a main barrier to their use instead of sparse NIRS devices.…”

MOCA: a systematic toolbox for designing and assessing modular functional near-infrared brain imaging probes

“…In addition, the performance metrics output by MOCA are currently based on a 2D probe layout and do not account for changes in SDS if the probe is wrapped on the 3D surface of a head. 34 Consequently, 2D derived metrics may underestimate the number of channels when a probe is made to conform to the scalp. This may result in an increase in the number of total inter-module channels for a probe.…”

“…With such dense coverage, complex encoding strategies such as frequency 28 multiplexing become a necessity for obtaining high-density data acquisition to achieve sufficient spatial and temporal resolution. Finally, while previously reported modular fNIRS systems often employ daisy-chain communication protocols to connect multiple modules on a single bus, 29 – 33 the design of physical inter-module connections, 34 the synchronization method between modules, 24 and the transfer of acquired data become increasingly complex with high module counts and branching connections.…”

Investigation of effect of modulation frequency on high-density diffuse optical tomography image quality

“…The availability of CW-HD-DOT systems is increasing rapidly for both adult and pediatric studies owing to the demonstrated improvements in image quality obtained with HD arrays. 1 , 12 , 13 , 55 – 62 Most research groups still utilize CW systems for wide-field optical imaging of human brain function as these systems are significantly less expensive than FD and TD systems. However, recent studies have highlighted a renewed focused on HD arrangements of FD measurements due to the value in incorporating the additional phase measurements to realize the potential for improved image quality and potential access to absolute oxygenation concentration.…”