464
H. M. Heise
in developing technology for skin viability testing, using also instrumentation with
liquid-crystal tunable filters for spectroscopic imaging in the visible and near-IR
spectral range.
Some delicate wound healing processes need intensive management, so that
people have to consult hospitals with experienced dermatologists. This may be the
case, for example, for people with insufficiently treated diabetes mellitus or for
some elderly immunocompromised patients. Such treatment can be challenging and
costly as the healing process may require longer times. Phases of wound healing are
described in the review by Sowa et al. [53], providing an overview on NIR spectroscopic methods including alternative technology. Among the applied methods
so far, including laser speckle contrast imaging, NIR imaging is still one of the
most promising technologies, but the established indocyanine green fluorescence
angiography method is competing for a successful objective wound assessment
during the entire healing process. The evaluation of the pulsatile signals from NIR
tissue oximetry, as described above for photoplethysmography, can provide further
information, for example, by assessing arterial sufficiency.
Oximetry in the visible spectral range had found many applications and a study
on the evaluation of reflection spectra from hemoglobin-free perfused heart tissue is
given as an example of such investigations [54]. Visible spectra of myoglobin (oxyand deoxygenated form) and several cytochromes with their different redox states
can be found in the latter publication. Another study, focusing on the development of
instrumentation for breast cancer screening based on hemoglobin spectroscopy, has
been carried out by us, using two or three specially selected laser wavelengths mainly
within the SW-NIR range for optical mammography [55]. In a recently published
study, the method of opto-acoustic imaging of relative blood oxygen saturation and
total hemoglobin has been applied for breast cancer diagnosis. Here, the measurements were done at a wavelength of 757 nm and 1064 nm, respectively, with prepared
phantoms that were mimicking breast tissue for mapping oxygen saturation differences in vessels with a depth reaching down to about 50 mm [56]. A more complex
assessment of tissue compounds was performed by Chen et al., who studied an NIR
tomographic imaging system with several wavelengths between 633 and 980 nm in
continuous wave mode for a quantification of four analytes, i.e., oxy- and deoxyhemoglobin, water and lipids, in addition to a scattering factor [57]. They came up with
an optimum of seven wavelengths, which were adapted to chromophore concentrations as found for breast tissues of young and elderly women; the recommended laser
diodes had wavelengths of 650, 690, 705, 730, 870/880, 915 and 937 nm.
As pointed out in the previous sections, NIR spectroscopy (NIRS) is able to
measure oxygenation in human tissues, but statements can be found that it suffers
lack of quantification. Methods had been developed for measuring optical pathlengths
in tissue, initially enabling the detection of changes in concentrations to be quantified, and subsequently, methods for absolute quantification of HbO 2 and Hb were
developed; for details, see also Ref. [58]. Commercially available monitors such as
the NIRO 200 NX, which is used in clinics, can measure the following parameters: Tissue oxygenation index TOI (%), normalized tissue hemoglobin index nTHI
(absolute value in arbitrary unit), oxygenated hemoglobin change, HbO 2 (μmol/l),
H. M. Heise
in developing technology for skin viability testing, using also instrumentation with
liquid-crystal tunable filters for spectroscopic imaging in the visible and near-IR
spectral range.
Some delicate wound healing processes need intensive management, so that
people have to consult hospitals with experienced dermatologists. This may be the
case, for example, for people with insufficiently treated diabetes mellitus or for
some elderly immunocompromised patients. Such treatment can be challenging and
costly as the healing process may require longer times. Phases of wound healing are
described in the review by Sowa et al. [53], providing an overview on NIR spectroscopic methods including alternative technology. Among the applied methods
so far, including laser speckle contrast imaging, NIR imaging is still one of the
most promising technologies, but the established indocyanine green fluorescence
angiography method is competing for a successful objective wound assessment
during the entire healing process. The evaluation of the pulsatile signals from NIR
tissue oximetry, as described above for photoplethysmography, can provide further
information, for example, by assessing arterial sufficiency.
Oximetry in the visible spectral range had found many applications and a study
on the evaluation of reflection spectra from hemoglobin-free perfused heart tissue is
given as an example of such investigations [54]. Visible spectra of myoglobin (oxyand deoxygenated form) and several cytochromes with their different redox states
can be found in the latter publication. Another study, focusing on the development of
instrumentation for breast cancer screening based on hemoglobin spectroscopy, has
been carried out by us, using two or three specially selected laser wavelengths mainly
within the SW-NIR range for optical mammography [55]. In a recently published
study, the method of opto-acoustic imaging of relative blood oxygen saturation and
total hemoglobin has been applied for breast cancer diagnosis. Here, the measurements were done at a wavelength of 757 nm and 1064 nm, respectively, with prepared
phantoms that were mimicking breast tissue for mapping oxygen saturation differences in vessels with a depth reaching down to about 50 mm [56]. A more complex
assessment of tissue compounds was performed by Chen et al., who studied an NIR
tomographic imaging system with several wavelengths between 633 and 980 nm in
continuous wave mode for a quantification of four analytes, i.e., oxy- and deoxyhemoglobin, water and lipids, in addition to a scattering factor [57]. They came up with
an optimum of seven wavelengths, which were adapted to chromophore concentrations as found for breast tissues of young and elderly women; the recommended laser
diodes had wavelengths of 650, 690, 705, 730, 870/880, 915 and 937 nm.
As pointed out in the previous sections, NIR spectroscopy (NIRS) is able to
measure oxygenation in human tissues, but statements can be found that it suffers
lack of quantification. Methods had been developed for measuring optical pathlengths
in tissue, initially enabling the detection of changes in concentrations to be quantified, and subsequently, methods for absolute quantification of HbO 2 and Hb were
developed; for details, see also Ref. [58]. Commercially available monitors such as
the NIRO 200 NX, which is used in clinics, can measure the following parameters: Tissue oxygenation index TOI (%), normalized tissue hemoglobin index nTHI
(absolute value in arbitrary unit), oxygenated hemoglobin change, HbO 2 (μmol/l),