title: Towards a wearable near infrared spectroscopic probe for monitoring concentrations of multiple chromophores in biological tissue in vivo.
abstract: The first wearable multi-wavelength technology for functional near-infrared spectroscopy has been developed, based on a custom-built 8-wavelength light emitting diode (LED) source. A lightweight fibreless probe is designed to monitor changes in the concentrations of multiple absorbers (chromophores) in biological tissue, the most dominant of which at near-infrared wavelengths are oxyhemoglobin and deoxyhemoglobin. The use of multiple wavelengths enables signals due to the less dominant chromophores to be more easily distinguished from those due to hemoglobin and thus provides more complete and accurate information about tissue oxygenation, hemodynamics, and metabolism. The spectroscopic probe employs four photodiode detectors coupled to a four-channel charge-to-digital converter which includes a charge integration amplifier and an analogue-to-digital converter (ADC). Use of two parallel charge integrators per detector enables one to accumulate charge while the other is being read out by the ADC, thus facilitating continuous operation without dead time. The detector system has a dynamic range of about 80 dB. The customized source consists of eight LED dies attached to a 2 mm × 2 mm substrate and encapsulated in UV-cured epoxy resin. Switching between dies is performed every 20 ms, synchronized to the detector integration period to within 100 ns. The spectroscopic probe has been designed to be fully compatible with simultaneous electroencephalography measurements. Results are presented from measurements on a phantom and a functional brain activation study on an adult volunteer, and the performance of the spectroscopic probe is shown to be very similar to that of a benchtop broadband spectroscopy system. The multi-wavelength capabilities and portability of this spectroscopic probe will create significant opportunities for in vivo studies in a range of clinical and life science applications.
authors.affiliation: Department of Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, United Kingdom.
authors.forename: Danial
authors.initials: D
authors.lastname: Chitnis
authors.affiliation: Department of Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, United Kingdom.
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Airantzis
authors.affiliation: Neurocritical Care Unit, National Hospital for Neurology and Neurosurgery, University College London Hospitals, London WC1N 3BG, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Highton
authors.affiliation: Department of Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, United Kingdom.
authors.forename: Rhys
authors.initials: R
authors.lastname: Williams
authors.affiliation: Department of Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, United Kingdom.
authors.forename: Phong
authors.initials: P
authors.lastname: Phan
authors.affiliation: Department of Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, United Kingdom.
authors.forename: Vasiliki
authors.initials: V
authors.lastname: Giagka
authors.affiliation: Department of Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, United Kingdom.
authors.forename: Samuel
authors.initials: S
authors.lastname: Powell
authors.affiliation: Department of Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, United Kingdom.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Cooper
authors.affiliation: Department of Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, United Kingdom.
authors.forename: Ilias
authors.initials: I
authors.lastname: Tachtsidis
authors.affiliation: Neurocritical Care Unit, National Hospital for Neurology and Neurosurgery, University College London Hospitals, London WC1N 3BG, United Kingdom.
authors.forename: Martin
authors.initials: M
authors.lastname: Smith
authors.affiliation: Department of Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, United Kingdom.
authors.forename: Clare E
authors.initials: CE
authors.lastname: Elwell
authors.affiliation: Department of Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, United Kingdom.
authors.forename: Jeremy C
authors.initials: JC
authors.lastname: Hebden
authors.affiliation: Department of Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, United Kingdom.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Everdell
mesh_terms: D000328:Adult; D001921:Brain / Q000000981:diagnostic imaging* / Q000502:physiology*; D005260:Female; D006801:Humans; D013055:Spectrophotometry, Infrared / Q000295:instrumentation / Q000379:methods; D000076251:Wearable Electronic Devices