Quantitative measurement oxygen consumption in the muscles is important to evaluate the effect of the exercise. Near-infrared spectroscopy (NIRS) is a noninvasive method for measuring muscle oxygenation. However, measurement results are affected by blood volume change due to changes in the blood pressure. In order to evaluate changes in blood volume and to improve measurement accuracy, we proposed a calculation method of three-wavelength measurement with considering the scattering factor and the measurement with monitoring blood flow for measuring the temporal change of the oxygen concentration more precisely. We applied three-wavelength light source (680nm, 808nm and 830nm) for the continued wave measurement. Two detectors (targeted detector and the reference detector) were placed near the target muscle and apart from it. We measured the blood flow by controlling the intravascular pressure and the oxygen consumption with the handgrip exercise in the forearm. The measured results show that the scattering factor contains the artifact at the surface and the blood flow in the artery and the vein in the same phase. The artifact and the blood flow in the same phase are reduced from the oxygenated and the deoxygenated hemoglobin densities. Thus our proposed method is effective for reducing the influence of the artifact and the blood flow in the same phase from the oxygen consumption measurement. Further, it is shown that the oxygen consumption is measured more accurately by subtracting the blood flow measured by the reference detector.
A new method for cancelling the skin blood flow in functional near-infrared spectroscopy (fNIRS) is proposed to
improve the measurement accuracy of oxygen consumption in a brain tissue. We proposed to use two kinds of
cancellation signals. One is a sharing aperture approach which uses cancellation signals detected at apertures for
irradiating the light. Another one is an additional aperture approach which uses cancellation signals detected at the
midpoint between the irradiation and detection aperture in conventional measurement. We further applied an equilateral-triangular
probe arrangement to our method. For the equilateral-triangular probe arrangement, the cancellation signal of
the sharing aperture approach is detected at apex, and the cancellation signal of the additional aperture approach is
detected at the median point of the equilateral-triangular. Simulation and experiments with a phantom were performed.
Simulation results show that the proposed method effectively detected the influence of the near-surface absorption
change, which depends on its position and size, by automatically selecting the two kinds of cancellation signal.
Diffuse reflective optical measurement is a useful approach for monitoring the oxygen consumption of living tissue such
as brain and muscle. To improve the oxygen consumption measurement accuracy, we propose a method for suppressing
the near-surface sensitivity. Diffuse reflective light is detected at the aperture used for irradiating the light and is used as
a cancellation signal for near-field sensitivity in the conventional measurement scheme. Photon fluence density
functions and positional dependences of detected light sensitivity to change in absorbance were simulated. The
sensitivity detected at the same position (aperture) as irradiation was significantly high for the near-surface region.
With our method, the near-surface sensitivity is reduced by more than 90% while keeping target sensitivity almost
constant (only 3% deterioration). The near-surface and deep-field sensitivity was measured with a phantom with light
(785 nm) modulated at 1 kHz through an optical fiber bundle. It confirmed suppressed the near-surface sensitivity by
subtracting the light detected at the same aperture from the light detected at another aperture.