462
H. M. Heise
for wavelength dispersion, optics for homogenous wide-field transmission illumination, an inverted microscope and further detection by a thermoelectrically cooled
InGaAs camera for wavelengths between 900 and 1500 nm. Abnormal skin samples
including melanoma, nodular basal-cell carcinoma and squamous-cell carcinoma
were acquired from dermatology and studied to distinguish healthy from diseased
tissue regions, illustrating the potential for cancer diagnostics.
There are also developments dealing with molecular beacons (dyes), which
have been suggested as endogenous chromophores for providing more contrast in
NIR imaging applications. Such substances have recently received much attention
and actual developments are described in the last section on NIR-fluorescence in
biomedicine.
20.4.2 Monitoring of Blood-Tissue Oxygenation
and Cytochrome Redox Status
Within the NIR region, the wavelength interval of 650–1100 nm, also called “optical
window” in tissue, is rather transparent for NIR radiation in scattering soft tissues.
When discussing the photon penetration depth for non-invasive blood glucose monitoring (see also Fig. 20.13), this information is clearly displayed. The penetration
depth was calculated by using optical absorption and scattering parameters of skin.
Besides the determination of blood glucose, there are further special biomolecules
of great interest for monitoring deviations from homeostasis in the body. Natural
pigments such as hemoglobin as major component in the red blood cells, myoglobin
in muscle, as well as cytochromes generally found in tissues, have characteristic
absorbance spectra within the visible and the SW-NIR spectral range. Their spectra
are dependent on the degree of oxygenation of the hemoproteins and the redox state of
the cytochromes. Therefore, spectroscopy can provide information about the in vivo
state of tissue oxygen supply.
In Fig. 20.14, absorptivities of hemoglobin in its oxy- and deoxygenated state
are shown, illustrating the possibilities for quantitative spectroscopy within several
spectral ranges from the visible up to the SW-NIR regime. Figure 20.15 provides a
blow-up of the SW-NIR region with a linear scale and different oxygenation degrees
of hemoglobin with a spectral isosbestic point around 805 nm. In particular, noninvasive continuous measuring techniques are of special interest. Many applications
are found in cerebral monitoring with its successful advent in special clinics for
neonatal intensive care or for monitoring during labor. In the past, great interest had
also been in muscle oxygenation studies.
NIR spectroscopy of skin has been subject of many investigations, e.g., in skin
transplantation as in plastic and reconstructive surgery or burn injury treatment and
wound healing [52, 53]. Regional and temporal variations in skin tissue oxygenation
are of special interest and can be assessed continuously using NIR spectroscopy.
Especially, the research group around Michael Sowa has a long-time engagement
H. M. Heise
for wavelength dispersion, optics for homogenous wide-field transmission illumination, an inverted microscope and further detection by a thermoelectrically cooled
InGaAs camera for wavelengths between 900 and 1500 nm. Abnormal skin samples
including melanoma, nodular basal-cell carcinoma and squamous-cell carcinoma
were acquired from dermatology and studied to distinguish healthy from diseased
tissue regions, illustrating the potential for cancer diagnostics.
There are also developments dealing with molecular beacons (dyes), which
have been suggested as endogenous chromophores for providing more contrast in
NIR imaging applications. Such substances have recently received much attention
and actual developments are described in the last section on NIR-fluorescence in
biomedicine.
20.4.2 Monitoring of Blood-Tissue Oxygenation
and Cytochrome Redox Status
Within the NIR region, the wavelength interval of 650–1100 nm, also called “optical
window” in tissue, is rather transparent for NIR radiation in scattering soft tissues.
When discussing the photon penetration depth for non-invasive blood glucose monitoring (see also Fig. 20.13), this information is clearly displayed. The penetration
depth was calculated by using optical absorption and scattering parameters of skin.
Besides the determination of blood glucose, there are further special biomolecules
of great interest for monitoring deviations from homeostasis in the body. Natural
pigments such as hemoglobin as major component in the red blood cells, myoglobin
in muscle, as well as cytochromes generally found in tissues, have characteristic
absorbance spectra within the visible and the SW-NIR spectral range. Their spectra
are dependent on the degree of oxygenation of the hemoproteins and the redox state of
the cytochromes. Therefore, spectroscopy can provide information about the in vivo
state of tissue oxygen supply.
In Fig. 20.14, absorptivities of hemoglobin in its oxy- and deoxygenated state
are shown, illustrating the possibilities for quantitative spectroscopy within several
spectral ranges from the visible up to the SW-NIR regime. Figure 20.15 provides a
blow-up of the SW-NIR region with a linear scale and different oxygenation degrees
of hemoglobin with a spectral isosbestic point around 805 nm. In particular, noninvasive continuous measuring techniques are of special interest. Many applications
are found in cerebral monitoring with its successful advent in special clinics for
neonatal intensive care or for monitoring during labor. In the past, great interest had
also been in muscle oxygenation studies.
NIR spectroscopy of skin has been subject of many investigations, e.g., in skin
transplantation as in plastic and reconstructive surgery or burn injury treatment and
wound healing [52, 53]. Regional and temporal variations in skin tissue oxygenation
are of special interest and can be assessed continuously using NIR spectroscopy.
Especially, the research group around Michael Sowa has a long-time engagement