O3® Regional Oximeter
Chapter 1: Technology
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14
Masimo
Masimo’s O3
®
Regional Oximeter consists of a light emitter and multiple detectors. By
emitting multiple wavelengths of light (LEDs), which pass through the region of interest, and
measuring them (using photo-detectors) after they have traveled through the tissue, the
system calculates attenuation experienced by each wavelength. These optical attenuations
are then mapped to rSO
2
.
* Beard P. Biomedical photoacoustic imaging. Interface Focus 2011;1:602-631.
Components of the Regional Oximetry System
The Masimo O3
®
Regional Oximetry System uses a common emitter and at least two (2)
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 traveled through relatively superficial (shallow) section of tissue.
•
Deep detector
: This detector is farther from the emitter and receives optical signal
traveled 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
µ
a 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 traveled. (In the Beer-Lambert Law, it leads to
same
µ
a
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.