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Enquiries: NRC-IBD
Phone: 204-983-7692
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Email: ibd.research@nrc-cnrc.gc.ca
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Diffuse Reflectance Spectroscopy
What is Diffuse Reflectance Spectroscopy?
in vivo diffuse reflectance spectroscopy, or point spectroscopy, uses fibre optic probes coupled to both a source and a spectrometer to transmit light of a particular wavelength range (700-1000nm) to the tissue surface.
near-IR spectrometer and fibre optics schematic
near-IR spectrometer
As the photons enter the tissue, some of the light is absorbed, some is reflected (scattered), and some passes through the tissue unperturbed (transmitted). Only some of the scattered photons return to the tissue surface and emerge for detection.
Since only a portion of the scattered photons are returned to the detector, the intensity of the emerging light is reduced (attenuated).
By measuring the change in the intensity of reflected light over a spectral range, relative changes of specific structures within the tissue can be determined.
How Does Diffuse Reflectance Spectroscopy Work?
Reflectance and absorption of light in skin
Light in the near infrared region (700 - 1000 nm) penetrates relatively deep into tissue when compared to visible light (450-700 nm) making the detection of deeper tissue structures, like hemoglobin, possible.
In tissue, hemoglobin, an important tissue chromophore, varies in concentration and hence absorption as a direct result of blood flow. Hemoglobin is carried by red blood cells and is responsible for transporting oxygen to our tissues.
oxy- and deoxy-hemoglobin spectra
wavelength (nm)
Since hemoglobin can exist in both an oxygenated state (HbO2) and a deoxygenated state (Hb), and since each form of the molecule has its own characteristic absorption spectrum, the identification of tissue oxygenation (HbO2) and blood volume (as total hemoglobin, thb=HbO2+Hb) is possible.
Furthermore, since oxygen (and therefore a healthy blood supply) is vital to tissue survival, the ability to detect its presence is of high clinical significance.
By spectroscopically monitoring tissue blood volume and oxygenation, changes in tissue status can be determined before they are visually apparent. The ability of the technique to make an early assessment of tissue health means that interventions aimed at saving the tissue can be applied before irreversible damage occurs.
Spectroscopic Imaging
CCD camera and liquid crystal tunable filter
By fitting a CCD camera with a liquid crystal tuneable filter (LCTF), it is possible to acquire near infrared images. Like other cameras, the "pictures" are acquired without any skin contact, which adds to the technique's appeal.
By taking a series of near infrared spectroscopic images at different wavelengths, a spectrum can be generated. The images provide the same information (tissue oxygenation and blood volume) as obtained with the point spectroscopy, but instead of providing information at a single point on the tissue (local assessment), a more global assessment of tissue health can be made.
in vivo spectrum created from multispectral burn images (shown)
A stack of images at selected wavelengths is collected at a narrow spectral band. Each pixel in the image sequence represents a point in the spectrum.
How Can Diffuse Reflectance Spectroscopy be Used?
For in vivo purposes, the technique can be used for non-invasive, real-time assessments of tissue oxygenation and blood volume. The NRC-IBD Spectroscopy Group has applied diffuse reflectance spectroscopy to numerous biomedical situations including the assessment of skin flaps, pressure damaged skin, and intestinal ischemia. It has also used to determine the severity of burn injuries and coronary artery disease.
Related Information
Read more about Diffuse Reflectance Spectroscopy:
- Non-linear Optical Microscopic Imaging
- Fluorescence Imaging
- Frequency Modulated Spectroscopy
- MRI Studies
- Bioluminescence Imaging
- Molecular Imaging - Spectroscopy
- Optical Coherence Tomography
- Raman Spectroscopy
- Speckle Imaging
- Thermal Imaging
- High Throughput Diagnostics
- Diagnostic Technologies
