1. Field of the Invention
The present disclosure relates to a living-body component measuring apparatus that measures a component of the inner tissue of a living body by measuring reflected light of laser light having two or more wavelengths emitted from a light source, and more particularly, to a living-body component measuring apparatus that is improved to more accurately and more stably determine the quantity of a substance in the living body.
2. Description of the Related Art
For example, in a spectroscopy method of the related art using near-infrared light, when light is applied from a light source to an object to be measured, a component contained in the object exhibits an optical absorption characteristic based on the quantity of the component in a wavelength region peculiar to the component. Hence, an absorbance (light absorbance of a specific component) is calculated from measurement light such as reflected light from the object, and the component contained in the object is analyzed on the basis of the absorbance spectrum.
Japanese Unexamined Patent Application Publication No. 2008-301944 proposes a living-body component measuring apparatus that measures components of the inner tissue of the living body (e.g., various substances contained in the blood in a blood vessel or tissue fluid in the tissue of the human body and animals (the concentration of a component such as the blood sugar level)) with a wavelength tunable laser and a confocal optical system. This living-body component measuring apparatus measures components of the inner tissue of the living body serving as an object to be measured by measuring reflected light from the inner tissue of the living body and light passing through the living body, which are obtained from laser light emitted from the wavelength tunable laser and having two or more wavelengths.
More specifically, laser light having two or more wavelengths is applied onto the inner tissue of a living body serving as an object to be measured, and the absorbance spectrum is obtained from light reflected from the inner tissue of the living body and light passing through the living body. After that, components of the inner tissue of the living body are calculated by a known test, and an expression representing the correlation between the absorbance spectrum and the components of the inner tissue of the living body (hereinafter referred to as a correlation expression) is created and stored beforehand. By substituting the absorbance calculated from the reflected light from the inner tissue of the living body and the light passing through the living body into the correlation expression, a component of the inner tissue of the living body is measured.
The living-body component measuring apparatus of the above publication further includes a movement driving mechanism that three-dimensional moves the confocal optical system and the living body relative to each other. By three-dimensional moving the confocal optical system and the living body relative to each other by the movement driving mechanism, the focal position of the confocal optical system is three-dimensional moved relative to the living body, and three-dimensional data on the inner tissue of the living body is obtained, whereby a portion of the living body to be measured is reliably specified, and a component of the portion of the living body is reliably measured in a non-invasive manner.
Such a living-body component measuring apparatus of the related art can measure the concentration of a target component on the basis of a degree (absorbance) to which light applied to the living body is absorbed by the living body, by detecting reflected light from the living body and light passing through the living body, without collecting the blood by invading the living body (more specifically, without actually collecting the blood by finger stick or earlobe stick).
In the living-body component measuring apparatus of the related art, however, the change in intensity of output light from the wavelength tunable laser leads to the change in intensity of scattering light in the living body. This makes it difficult to substantially remove errors due to this change.
That is, the living-body component measuring apparatus of the related art cannot accurately measure the absorbance spectrum since the intensity of output light from the wavelength tunable laser changes.