Pradeep K. W. Abeygunawardhana

Proposal of one-shot-type spectroscopic-tomography for non-invasive medical-measurement

The one-shot-type spectroscopic-tomography is proposed to develop the medical-patient-condition monitoring systems. The optical-setup is configured with the relative-inclined phase-shifter for improving the time resolution and the phase-shift array for improving visibility. We obtained the line-spectroscopic imaging and could recognize the Hg bright-line-spectrum that is a component of the light-source. The realization of the optical stethoscope for early diagnosis of cancer can be expected by obtaining the 2-dimensional spectroscopic distribution with rotating interferometer.

Enhanced interference-pattern visibility using multislit optical superposition method for imaging-type two-dimensional Fourier spectroscopy.

A solution is found for the problem of phase cancellation between adjacent bright points in wavefront-division phase-shift interferometry. To this end, a design is proposed that optimizes the visibility of the interference pattern from multiple slits. The method is explained in terms of Fraunhofer diffraction and convolution imaging. Optical simulations verify the technique. The final design can be calculated using a simple equation.

Wide-field spectroscopic imaging of biological-substance distributions on entire faces by measuring middle infrared lights emitted from human bodies itself

We are aiming at the realization of the measurement technology for the biological-substance distributions, such as sebum, on entire faces at the daily-life environment. We proposed the imaging-type 2-dimensional Fourier spectroscopy [1] that is the palmtop-size portable measurement apparatus and has the strong robustness for mechanical vibrations. And the proposed method can measure the wide-field 2-dimensional middle-infrared spectroscopic-imaging of radiation lights emitted from human bodies itself without light sources. In the proposed method, we install the phase-shifter, that can give an arbitrary phase difference for the half-flux of objective beams, at the optical Fourier transform plane of the infinity corrected optical system. The near-common-path interferometer that is a phase-shift interferometer between objective beams can be realized. In this proposed method, the emitted rays from each single-bright-point on measurement surfaces can interfere with each other. Thus, even if the middle infrared-lights from human bodies are the spatially incoherent light, we can acquire the interferograms at each pixel on an imaging array-device in accordance with the amount of phase shift as the 2-dimensional image-intensity changes. We demonstrated the feasibility of the middle infrared spectroscopic imaging of whole human faces without active illuminations.

Quantitative measurement of biological substances in daily-life environment with the little-finger-size one-shot spectroscopic tomography

In daily-life environment, the quantitative measurement of biological substances, such as the blood glucose level in the human skin, is strongly required to realize the non-invasive healthcare apparatus. Fourier-spectroscopic-tomography of the little-finger-size with high time-resolution and with the strong robustness for mechanical vibrations is proposed. The proposed method is a kind of near-common-path interferometer with spatial phase-shift method. We install the transmission-type relative-inclined phase-shifter on the optical Fourier transform plane of the infinity corrected optical system. The phase shifter is constructed with the cuboid and wedge prisms to give the relative phase-shift spatially between each half-flux of the objective beams. The interferograms from each single-bright-point on an objective surface in a line are formed as fringe patterns on 2-dimensional imaging array devices. And because the proposed method is based on the imaging optics, only emitted rays from a focal plane can contribute forming of interferograms. Thus, the measurement plane can be limited onto the focal plane only. From the spectroscopic tomography, only at a localized vessel area in human skins, we can get the pinpointed near-infrared spectroscopic data. And we can expect the improvement of the determination precision, because a Fourier spectroscopic-character is acquired from multiple intensity data in accordance with amount of phase-shift. From the statistical point of view, the gradation of detector is improved with the square root of sample number, based on t-distribution. We constructed the statistical model to assure the determination accuracy, and demonstrated the feasibility of the glucose sensor using liquid cells.

Novel algorithm for background correction of the quantitative spectroscopic tomography of the biogenic-substances

The non-invasive blood sugar sensor by using imaging-type 2-dimensional Fourier spectroscopy is to be realized in this work. The spectroscopic imaging, that observes the biological tissue by the dark-field image, can measure the biogenic substance quantitatively such as the glucose concentration. For the quantitative analysis with high accuracy, the correction of the background such as the light-source fluctuation and the phase-shift uncertainty is inevitable issue. Thus, the quantitative band-pass plate on which the grating is locally formed has been already proposed by [1]. In that paper, the diffractive light, whose diffraction angle depends on the wavelength, has been used as the reference light. Object lens is used to narrow down the reference light and narrowed band pass diffraction light is obtained. The changes of imaging intensities with interference phenomenon on whole area of the observation image can be confirmed using the quantitative band pass filter. This paper proposed background correction method of the interferogram in spectroscopic tomography. Correction algorithm mainly contained two parts as light source fluctuation error correction and phase shift error correction.

Measurement of the mid-infrared Fourier spectroscopic imaging of whole human face by portable apparatus (size: 50*50 mm, weight: 200 g)

In the daily living space, measurement of the biological-substance distributions such as sebum can be realized by the proposed method of imaging-type 2-dimensional Fourier spectroscopy. This method has the strong robustness for mechanical vibrations. So, the spectrometer (size: 50*50mm, weight: 200g) can be produced without anti-vibration mechanism. Moreover, the phase shifter is a core part of the spectrometer, and it is constructed by the low-price bimorph type actuator which is depending on the vibration control of the piezoceramic in proposed method. It is appropriate as the actuator of the phase shifter from the evaluation results of the actuator straightness and position accuracy in the midinfrared region. As we know, the Fourier spectroscopy has a high light utilization efficiency. Therefore, the low price microbolometer can be used as the imaging sensor. So, the low-price (10,000 U.S. dollars), compact and high portability spectrometer can be produced. Furthermore, the much higher position accuracy in the short wavelength region is requested as we know, the phase shift correction method has been proposed. In this paper, high performance evaluations of the portable spectroscopy apparatus have been discussed by using the CO2 laser spectroscopy results in the midinfrared region. Then, the phase shift correction method was explained. At the end, we demonstrated the feasibility of the mid-infrared imaging of whole human faces without active illuminations.

Proposal of AAA-battery-size one-shot ATR Fourier spectroscopic imager for on-site analysis: Simultaneous measurement of multi-components with high accuracy

For simultaneous measurement of multi-components on-site like factories, the ultra-compact (diameter: 9[mm], length: 45[mm], weight: 200[g]) one-shot ATR (Attenuated Total Reflection) Fourier spectroscopic imager was proposed. Because the proposed one-shot Fourier spectroscopic imaging is based on spatial-phase-shift interferometer, interferograms could be obtained with simple optical configurations. We introduced the transmission-type relativeinclined phase-shifter, that was constructed with a cuboid prism and a wedge prism, onto the optical Fourier transform plane of infinity corrected optical systems. And also, small light-sources and cameras in the mid-infrared light region, whose size are several millimeter on a side, are essential components for the ultra-compact spectroscopic configuration. We selected the Graphite light source (light source area: 1.7×1.7[mm], maker: Hawkeye technologies) whose radiation factor was high. Fortunately, in these days we could apply the cost-effective 2-dimensional light receiving device for smartphone (e.g. product name: LEPTON, maker: FLIR, price: around 400USD). In the case of alcoholic drinks factory, conventionally workers measure glucose and ethanol concentrations by bringing liquid solution back to laboratories every day. The high portable spectroscopy will make it possible to measure multi-components simultaneously on manufacturing scene. But we found experimentally that absorption spectrum of glucose and water and ethanol were overlapped each other in near infrared light region. But for mid-infrared light region, we could distinguish specific absorption peaks of glucose (@10.5[μm]) and ethanol (@11.5[μm]) independently from water absorption. We obtained standard curve between absorption (@9.6[μm]) and ethanol concentration with high correlation coefficient 0.98 successfully by ATR imaging-type 2-dimensional Fourier spectroscopy (wavelength resolution: 0.057[μm]) with the graphite light source (maker: Hawkeye technologies, type: IR-75).

Spectroscopic imaging of blood vessels only near the skin surface for non-invasive blood glucose measurement

To realize the non-invasive blood glucose measurement, it will be effective to acquire the spectroscopic imaging of blood vessels only near the skin surface for eliminating other biological-component’s disturbances. Our proposed imaging-type 2-dimensional Fourier spectroscopic imaging can limit the measuring depth into focal plane with high light detection sensitivity. Thus, the proposed method will be suitable for measuring only near the skin surface with detecting weak reflected light from inner biomembrane. But reflectance of skin surface is more than 1000 times larger than inner skin’s reflectance. Paying attention on Fresnel reflection, fingers what were illuminated by p-polarized beam from Brewsters angle were observed with crossed-Nicol dark field optics. We successfully acquired spectroscopic characteristics of hemoglobin at vein area near the skin surface.

Spectrum correction considering light source fluctuation for non-invasive blood glucose sensing

The purpose of this study is to correct baseline shift in absorbance spectrums caused by light source fluctuation. To improve quantitative evaluation performance of blood glucose level, baseline shift is corrected by multiple scatter correction (MSC). Moreover, to increase the effect of the MSC, water vapor absorbance is subtracted, and relative glucose absorbance are calculated by dividing with hemoglobin absorbance at 1544 [cm-1]. In order to verify the effectiveness of the proposed spectrum correction method, light source fluctuation is simulated on the Fourier transform infrared spectroscopy (FT-IR), and we apply the proposed method to the spectrums measured by FT-IR. From the simulation results, the baseline shift was successfully reduced by proposed method.

Quantitative spectroscopic tomography for the non-invasive measurement of the biogenic-substances

The non-invasive blood sugar sensor by using imaging-type 2-dimensional Fourier spectroscopy is to be realized in this work. The spectroscopic imaging, that observes the biological tissue by the dark-field image, can measure the biogenic substance quantitatively such as the glucose concentration. For the quantitative analysis with high accuracy, the correction of the background such as the light-source fluctuation and the phase-shift uncertainty is inevitable issue. Thus, the quantitative bandpass plate on which the grating is locally formed has been proposed in this paper. Here, the diffractive light, whose diffraction angle depends on the wavelength, has been used as the reference light Object lens is used to narrow down the reference light and narrowed band pass diffraction light is obtained. The changes of imaging intensities with interference phenomenon on whole area of the observation image can be confirmed using the quantitative band pass filter. Thus, the light-source fluctuation from the amplitude of the reference light intensity and the phase-shift uncertainly from the interference-phase can be corrected respectively. In this paper, the theoretical accuracy of Fourier spectroscopy calculated with the numerical simulation and the background correction method of the spectral-absorption-index image by the diffraction grating type quantitative bandpass plate are presented.