Improving optical contact for functional near-infrared brain spectroscopy and imaging with brush optodes
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Date
2012-05-01Author
Khan, Bilal
Wildey, Chester
Francis, Robert
Tian, Fenghua
Delgado, Mauricio R.
Liu, Hanli
MacFarlane, Duncan
Alexandrakis, George
Metadata
Show full item recordAbstract
A novel brush optode was designed and demonstrated to
overcome poor optical contact with the scalp that can occur during
functional near infrared spectroscopy (fNIRS) and imaging due to light
obstruction by hair. The brush optodes were implemented as an attachment
to existing commercial flat-faced (conventional) fiber bundle optodes. The
goal was that the brush optodes would thread through hair and improve
optical contact on subjects with dense hair. Simulations and experiments
were performed to assess the magnitude of these improvements. FNIRS
measurements on 17 subjects with varying hair colors (blonde, brown, and
black) and hair densities (0–2.96 hairs/mm2
) were performed during a finger
tapping protocol for both flat and brush optodes. In addition to reaching a
study success rate of almost 100% when using the brush optode extensions,
the measurement setup times were reduced by a factor of three.
Furthermore, the brush optodes enabled improvements in the activation
signal-to-noise ratio (SNR) by up to a factor of ten as well as significant
(p < 0.05) increases in the detected area of activation (dAoA). The
measured improvements in SNR were matched by Monte Carlo (MC)
simulations of photon propagation through scalp and hair. In addition, an
analytical model was derived to mathematically estimate the observed light
power losses due to different hair colors and hair densities. Interestingly, the
derived analytical formula produced excellent estimates of the experimental
data and MC simulation results despite several simplifying assumptions.
The analytical model enables researchers to readily estimate the light power
losses due to obstruction by hair for both flat-faced fiber bundles and
individual fibers for a given subject.