20 Medical Applications of NIR Spectroscopy
465
deoxygenated hemoglobin change Hb (μmol/l) and total hemoglobin change cHb
(μmol/l). For this device, three LEDs (735 nm, 810 nm, 850 nm: nominal values) are
used. As spectral evaluation methods, the so-called SRS method (spatially resolved
spectroscopy) and MBL method (modified Beer-Lambert) are applied; for details,
see NIRO 200 NX brochure (Hamamatsu, Japan). A wide range of applications has
been reported, reaching from the management of brain oxygenation status during
surgery, over clinical studies related to muscle function [59], kidney transplant perfusion [60], and in particular to brain function and metabolism [61]. The latter review
provides a comprehensive and actual overview on different optical methods employed
in brain monitoring, with special focus on functional near-infrared spectroscopy
(fNIRS), diffuse correlation spectroscopy (DCS), photoacoustic imaging (PAI) and
optical coherence tomography (OCT). In addition, also wearable devices have been
discussed. For details on the individual measurement techniques, the reader must be
referred to the review with its extensive literature list, as otherwise this would go
beyond the scope of this chapter.
Nevertheless, a few special applications will be mentioned. Non-invasive monitoring in preterm infants in intensive care units is another important activity in
hospital care. Meanwhile, there is undeniably significant progress, although much
work remains mostly on an experimental level due to lack of standardization and
use of various algorithms for the spectral assessment. The state of the art and an
overview of past studies concerning NIRS in preterm infants were presented by
Korˇ cek et al. [62].
Human functional brain mapping applications have gained a new dimension when
looking back at the latest developments of functional near-infrared spectroscopy
(fNIRS). This technology usually refers to a point measurement of the hemodynamics
that is providing information on the tissue perfusion via blood flow as well as blood
volume changes, and oxygenation changes, marking oxygen supply. Schematics for
the instrumentation and basic principle of fNIRS are presented with Fig. 20.16. In
contrast, measurements can also be performed simultaneously at different locations
for imaging purposes of the probed area. Other descriptors such as optical topography, near-infrared imaging and diffuse optical imaging have also been in use. Its
aim is to detect simultaneous changes in the optical properties of the brain from
multiple measurement sites with according results displayed as a map or image of
the monitored area. In case of depth-resolved processing of the spectral information,
one speaks of NIR tomography, also known as diffuse optical imaging (DOI) or NIR
optical tomography.
The history and developments of fNIRS using continuous wave (CW) measurements, as well as time and frequency resolved instrumentation, have been presented
several times, but a review on the state of the art and recent advances in hardware and
signal processing from Yücel et al. [63] is worth to be mentioned. CW-based devices,
which take the great advantage of being simple and more cost-efficient, compared
with time and frequency domain instrumentation, have been applied for measurement
of brain activation induced hemoglobin concentration changes that was reviewed by
Scholkmann et al. [64]. Details on the different involved technologies, their advantages and disadvantages, cannot be given here, so that the reader is referred to the
465
deoxygenated hemoglobin change Hb (μmol/l) and total hemoglobin change cHb
(μmol/l). For this device, three LEDs (735 nm, 810 nm, 850 nm: nominal values) are
used. As spectral evaluation methods, the so-called SRS method (spatially resolved
spectroscopy) and MBL method (modified Beer-Lambert) are applied; for details,
see NIRO 200 NX brochure (Hamamatsu, Japan). A wide range of applications has
been reported, reaching from the management of brain oxygenation status during
surgery, over clinical studies related to muscle function [59], kidney transplant perfusion [60], and in particular to brain function and metabolism [61]. The latter review
provides a comprehensive and actual overview on different optical methods employed
in brain monitoring, with special focus on functional near-infrared spectroscopy
(fNIRS), diffuse correlation spectroscopy (DCS), photoacoustic imaging (PAI) and
optical coherence tomography (OCT). In addition, also wearable devices have been
discussed. For details on the individual measurement techniques, the reader must be
referred to the review with its extensive literature list, as otherwise this would go
beyond the scope of this chapter.
Nevertheless, a few special applications will be mentioned. Non-invasive monitoring in preterm infants in intensive care units is another important activity in
hospital care. Meanwhile, there is undeniably significant progress, although much
work remains mostly on an experimental level due to lack of standardization and
use of various algorithms for the spectral assessment. The state of the art and an
overview of past studies concerning NIRS in preterm infants were presented by
Korˇ cek et al. [62].
Human functional brain mapping applications have gained a new dimension when
looking back at the latest developments of functional near-infrared spectroscopy
(fNIRS). This technology usually refers to a point measurement of the hemodynamics
that is providing information on the tissue perfusion via blood flow as well as blood
volume changes, and oxygenation changes, marking oxygen supply. Schematics for
the instrumentation and basic principle of fNIRS are presented with Fig. 20.16. In
contrast, measurements can also be performed simultaneously at different locations
for imaging purposes of the probed area. Other descriptors such as optical topography, near-infrared imaging and diffuse optical imaging have also been in use. Its
aim is to detect simultaneous changes in the optical properties of the brain from
multiple measurement sites with according results displayed as a map or image of
the monitored area. In case of depth-resolved processing of the spectral information,
one speaks of NIR tomography, also known as diffuse optical imaging (DOI) or NIR
optical tomography.
The history and developments of fNIRS using continuous wave (CW) measurements, as well as time and frequency resolved instrumentation, have been presented
several times, but a review on the state of the art and recent advances in hardware and
signal processing from Yücel et al. [63] is worth to be mentioned. CW-based devices,
which take the great advantage of being simple and more cost-efficient, compared
with time and frequency domain instrumentation, have been applied for measurement
of brain activation induced hemoglobin concentration changes that was reviewed by
Scholkmann et al. [64]. Details on the different involved technologies, their advantages and disadvantages, cannot be given here, so that the reader is referred to the