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Germon, T. J.; Evans, PD; Manara, A.R.; Barnett, N. J.; Wall, P.T.; Nelson, R. J.

doi:10.1023/a:1009957032554

Cited by 46 publications

(21 citation statements)

References 26 publications

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“…The shortest source-detector separation in the pHOS is however 2 cm, a distance long enough for the detector to pick up some brain signal [48,49], and therefore using these measurements to decontaminate the 3.0 and 3.5 cm measurements would produce erroneous results. It is also acknowledged that Monte Carlo simulations in the adult head suggest an error of over 20% in the measurement of optical absorption using an FD spectrometer with source-detector spacing between 3.0 and 4.5 cm, induced by the extra-cerebral tissue [50].…”

Section: Discussionmentioning

confidence: 99%

Systematic investigation of changes in oxidized cerebral cytochrome c oxidase concentration during frontal lobe activation in healthy adults

Kolyva

Tachtsidis

Ghosh

et al. 2012

Biomed. Opt. Express

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Using transcranial near-infrared spectroscopy (NIRS) to measure changes in the redox state of cerebral cytochrome c oxidase (Δ[oxCCO]) during functional activation in healthy adults is hampered by instrumentation and algorithm issues. This study reports the Δ[oxCCO] response measured in such a setting and investigates possible confounders of this measurement. Continuous frontal lobe NIRS measurements were collected from 11 healthy volunteers during a 6-minute anagram-solving task, using a hybrid optical spectrometer (pHOS) that combines multi-distance frequency and broadband components. Only data sets showing a hemodynamic response consistent with functional activation were interrogated for a Δ[oxCCO] response. Simultaneous systemic monitoring data were also available. Possible influences on the Δ[oxCCO] response were systematically investigated and there was no effect of: 1) wavelength range chosen for fitting the measured attenuation spectra; 2) constant or measured, with the pHOS in real-time, differential pathlength factor; 3) systemic hemodynamic changes during functional activation; 4) changes in optical scattering during functional activation. The Δ[oxCCO] response measured in the presence of functional activation was heterogeneous, with the majority of subjects showing significant increase in oxidation, but others having a decrease. We conclude that the heterogeneity in the Δ[oxCCO] response is physiological and not induced by confounding factors in the measurements.

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Section: Discussionmentioning

confidence: 99%

Systematic investigation of changes in oxidized cerebral cytochrome c oxidase concentration during frontal lobe activation in healthy adults

Kolyva

Tachtsidis

Ghosh

et al. 2012

Biomed. Opt. Express

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show abstract

“…Particularly, it was shown that an increase in interoptode distance leads to an increase in the measurement sensitivity to the absorption changes in the brain. [13][14][15] It was also reported that utilization of the frequency-domain technique 16 as well as time-resolved measurements [17][18][19] allow one to discriminate information originating from the cortex and extracerebral tissues.…”

Section: Introductionmentioning

confidence: 99%

Optical system based on time-gated, intensified charge-coupled device camera for brain imaging studies

et al. 2010

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An imaging system for brain oxygenation based on a time-gated, intensified charge-coupled device camera was developed. It allows one to image diffusely reflected light from an investigated medium at defined time windows delayed with respect to the laser pulse. Applying a fast optomechanical switch to deliver the light at a wavelength of 780 nm to nine source fibers allowed one to acquire images in times as short as 4 s. Thus, the system can be applied in in vivo studies. The system was validated in phantom experiments, in which absorbing inclusions were localized at different depths and different lateral positions. Then, the decrease in absorption of the brain tissue related to increase in oxygenation was visualized in the motor cortex area during finger tapping by a healthy volunteer.

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“…Some of this skepticism comes fi-om the fact that at short distances between emitters and detectors the cortical NIR signal can be confounded by changes in oxygenation of scalp muscles (Germon et al, 1994). While such confounds are less of a concern with greater emitter-detector separation (Germon et al, 1998), increased separation decreases the overall signal-to-noise ratio and is influenced more by blood flow beneath the cortical surface. Even at some "optimal" emitter-detector separation NIR signal strength is affected by regional differences in the thicknesses of the skull and scalp tissues and in the geometry of the brain surface.…”

Section: Discussionmentioning

confidence: 99%