We aim to realize non-invasive blood glucose measurements in daily life. The human body emits light with an intensity that depends on the body temperature (approximately 300 K). Mid-infrared passive spectroscopic imaging obtains component information from this radiated light. Using radiated light measurements of the arm from a distance of 600 mm, we identified the specific emission spectral peaks of glucose components at wavelengths of 9.25 μm and 9.65 μm. In addition, we determined the correlation between the intensity of radiated light at the peak wavelength and blood glucose level. From these results, we previously reported the possibility of non-invasive blood glucose measurements from a distance using mid-infrared passive spectroscopic imaging. Therefore, we developed a passive one-shot Fourier spectrometer to apply this method to wearable devices. The apparatus was designed with a numerical aperture (N.A.) of 0.77 for passive spectroscopy of the living body. The field curvature due to the increased N.A. was mitigated by combining an imaging lens with a phase shifter. Additionally, the apparatus was configured with two lenses to enhance transmission. Owing to the small object lens (diameter of 6 mm) and short optical path (axis length of approximately 14 mm), the apparatus was mountable on wearable devices. Moreover, the apparatus was equipped with a multi-slit to prevent loss of interference sharpness. The multi-slit was designed with five lines comprising aperture patterns that enabled the detection of glucose. As a result, we succeeded in detecting spectral characteristics of polypropylene using a blackbody as the background light source.
The proposed mid-infrared passive spectroscopic imager could measure blood glucose levels of internal bodies from a distance. In this report, we distinguished blood vessel areas and interstitial fluid areas in accordance with time-response differences. Freestyle Libre measures blood glucose levels in interstitial fluid. Thus, the measured value has time delay around 10 min compared with the conventional blood collection type. In accordance with correlation coefficients of radiation value, whose wavelength was 9.65μm, we identified these two areas at every pixel.
We developed a one-shot passive Fourier spectrometer to integrate with wearable devices for non-invasive blood glucose measurements. The apparatus was designed with a N.A. of 0.77 for passive spectroscopy of the living body. The field curvature due to the increased N.A. was improved by combining an imaging lens with a phase shifter. Because the apparatus was configured with two lenses, the transmission was high and the optical axis length was 14 mm. In addition, the apparatus was equipped with a multi-slit to prevent loss of interference sharpness. The multi-slit was designed with 5 lines with aperture patterns that enabled the detection of glucose. We measured a blackbody to evaluate the apparatus.
We developed a mid-infrared passive spectroscopic imaging apparatus that uses an uncooled micro-bolometer array sensor as a light-receiving device. This apparatus makes it possible to acquire component information such as that of glucose directly emitted from the skin without a light source. However, it is difficult to obtain the background for spectroscopic measurements inside the human body. In this paper, we propose a background correction method for calculating the spectral characteristics from the acquired spectral emission intensity. The proposed method estimates the emitted light through a fitting calculation using Planck’s law as a basis function.
We aim to measure the glucose concentration in the body through passive mid-infrared spectroscopy using a palm-sized imaging two-dimensional Fourier spectrometer. Radiation in the mid-infrared region (at a wavelength of approximately 10 µm) is emitted from the object surface, with the intensity of the radiated light corresponding to the object temperature. Passive spectroscopy acquires component information from the spectral intensity of the radiated light emitted from the object without a light source. Intrinsic vibrations of molecules in the object itself are detected, and the spectral characteristics are thus the emission spectrum of intrinsic vibration peaks. In contrast, conventional active spectroscopy irradiates the measurement target with light and acquires spectral characteristics from the reflected light. Molecular vibrations excited by the light source are measured, and the spectral characteristics are thus absorption spectra of the energy absorbed at the eigenfrequency of the molecule. The wavelengths that are confirmed as absorption wavelengths in active spectroscopy are confirmed as emission wavelengths in passive spectroscopy. Active spectroscopy and passive spectroscopy thus have a negative–positive relationship. The imaging-type two-dimensional Fourier spectrometer (7 to 14 µm) used in past measurement has transmission optics. Using three Ge lenses for the front lens, objective lens, and imaging lens, we constructed reflective optics using reflective mirrors for the objective and imaging lenses. The reflective mirror guarantees flatness and high spectral reflectance over a wide bandwidth (3 to 20 µm), and the measurement bandwidth is thus extended.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.