O3 Regional Oximeter Chapter 1: Technology
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Components of the Regional Oximetry System
The regional oximetery system uses a common emitter and at least two detectors that are
spaced apart from each other and are at different distances relative to the emitter. In the
case of a two-detector system, as in Figure 2, the detectors may be known as:
• Shallow detector: This detector is closer to the emitter (LEDs) and receives the
optical signal travelled through relatively superficial (shallow) section of tissue.
• Deep detector: This detector is farther from the emitter and receives optical signal
travelled deeper into the tissue, in addition to passing through superficial layers.
Figure 2: Schematic of an example of a regional oximeter sensor measuring deep tissue
oxygenation.
This geometry leads to the following relationships that allow the calculation of rSO
2
in the
deep tissue.
1. Optical signals received at the same detector have traveled the same path.
However, due to their different wavelengths, their attenuations are different, as
light absorption depends on the wavelength. (In the Beer-Lambert Law, it leads to
different µa and same Δ.)
2. Optical signals of the same wavelength received at different detectors see the
same tissue absorption coefficient, but experience different attenuation due to the
different paths they have travelled. (In the Beer-Lambert Law, it leads to same µa
and different Δ.)
Deep tissue oxygenation can therefore be calculated by subtracting the effects of shallow
tissue from deep tissue via manipulating signals received at the deep and shallow detectors.
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