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Phase Difference Optimization of Dual-Wavelength Excitation for the CW-Photoacoustic-Based Noninvasive and Selective Investigation of Aqueous Solutions of Glucose.

Camou S - Sensors (Basel) (2015)

Bottom Line: However, operating with optical wavelengths in the near-infrared (NIR) region ensures deep penetration inside human soft-tissue, but also leads to two serious issues: strong background level noise from water molecules in this wavelength range and small differences between the absorbance spectra of diluted compounds.The process of maintaining the phase quadrature of the two optical signals is demonstrated in real time through an analysis of the PA signal and therefore does not require any additional equipment.Finally, a comparison of aqueous glucose solution characterizations at high concentration levels with the two methods was performed and consistent results were obtained.

View Article: PubMed Central - PubMed

Affiliation: NTT Device Technology Laboratories, NTT Corporation, Atsugi 243-0198, Japan. camou.serge@lab.ntt.co.jp.

ABSTRACT
Towards the noninvasive and continuous monitoring of blood glucose levels, we chose the continuous-wave photoacoustic (CW-PA) technique and developed the optical power balance shift (OPBS) method. However, operating with optical wavelengths in the near-infrared (NIR) region ensures deep penetration inside human soft-tissue, but also leads to two serious issues: strong background level noise from water molecules in this wavelength range and small differences between the absorbance spectra of diluted compounds. To resolve them, the OPBS method relies on simultaneous optical excitation at two wavelengths for differential measurements. However, the first validation in vitro with calibrated aqueous solutions of glucose and albumin revealed strong dependence on the phase difference between the two lights sources. In this paper, we report a systematic investigation of this parameter, from PA-based measurements over a wide range of phase differences and an extensive characterization in the frequency domain. The process of maintaining the phase quadrature of the two optical signals is demonstrated in real time through an analysis of the PA signal and therefore does not require any additional equipment. Finally, a comparison of aqueous glucose solution characterizations at high concentration levels with the two methods was performed and consistent results were obtained.

No MeSH data available.


Related in: MedlinePlus

Experimental amplitude (a,b) and phase (c,d) results for 180-phase difference set at the fiber coupler (a,c) and FG (b,d) for aqueous glucose solutions with high concentration levels.
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sensors-15-16358-f007: Experimental amplitude (a,b) and phase (c,d) results for 180-phase difference set at the fiber coupler (a,c) and FG (b,d) for aqueous glucose solutions with high concentration levels.

Mentions: To estimate the benefit of including the phase difference adjustment in the measurement protocol, we measured an aqueous solution of glucose at a concentration of several grams per deciliter with and without the phase adjustment described above. The raw results are displayed in Figure 7, with the amplitude (top) and phase signal (bottom) for the protocol with the phase adjustment (left) and the one with the constant phase difference of 180° set at the FG (right). For both series, we performed measurements at several DVs and phase differences around the balanced point to assess the overall shape of the sensor response.


Phase Difference Optimization of Dual-Wavelength Excitation for the CW-Photoacoustic-Based Noninvasive and Selective Investigation of Aqueous Solutions of Glucose.

Camou S - Sensors (Basel) (2015)

Experimental amplitude (a,b) and phase (c,d) results for 180-phase difference set at the fiber coupler (a,c) and FG (b,d) for aqueous glucose solutions with high concentration levels.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4541882&req=5

sensors-15-16358-f007: Experimental amplitude (a,b) and phase (c,d) results for 180-phase difference set at the fiber coupler (a,c) and FG (b,d) for aqueous glucose solutions with high concentration levels.
Mentions: To estimate the benefit of including the phase difference adjustment in the measurement protocol, we measured an aqueous solution of glucose at a concentration of several grams per deciliter with and without the phase adjustment described above. The raw results are displayed in Figure 7, with the amplitude (top) and phase signal (bottom) for the protocol with the phase adjustment (left) and the one with the constant phase difference of 180° set at the FG (right). For both series, we performed measurements at several DVs and phase differences around the balanced point to assess the overall shape of the sensor response.

Bottom Line: However, operating with optical wavelengths in the near-infrared (NIR) region ensures deep penetration inside human soft-tissue, but also leads to two serious issues: strong background level noise from water molecules in this wavelength range and small differences between the absorbance spectra of diluted compounds.The process of maintaining the phase quadrature of the two optical signals is demonstrated in real time through an analysis of the PA signal and therefore does not require any additional equipment.Finally, a comparison of aqueous glucose solution characterizations at high concentration levels with the two methods was performed and consistent results were obtained.

View Article: PubMed Central - PubMed

Affiliation: NTT Device Technology Laboratories, NTT Corporation, Atsugi 243-0198, Japan. camou.serge@lab.ntt.co.jp.

ABSTRACT
Towards the noninvasive and continuous monitoring of blood glucose levels, we chose the continuous-wave photoacoustic (CW-PA) technique and developed the optical power balance shift (OPBS) method. However, operating with optical wavelengths in the near-infrared (NIR) region ensures deep penetration inside human soft-tissue, but also leads to two serious issues: strong background level noise from water molecules in this wavelength range and small differences between the absorbance spectra of diluted compounds. To resolve them, the OPBS method relies on simultaneous optical excitation at two wavelengths for differential measurements. However, the first validation in vitro with calibrated aqueous solutions of glucose and albumin revealed strong dependence on the phase difference between the two lights sources. In this paper, we report a systematic investigation of this parameter, from PA-based measurements over a wide range of phase differences and an extensive characterization in the frequency domain. The process of maintaining the phase quadrature of the two optical signals is demonstrated in real time through an analysis of the PA signal and therefore does not require any additional equipment. Finally, a comparison of aqueous glucose solution characterizations at high concentration levels with the two methods was performed and consistent results were obtained.

No MeSH data available.


Related in: MedlinePlus