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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

Systematic measurement of amplitude (Left) and phase (Right) of PA signal over a wide range of DV and phase difference at FG channel 2.
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sensors-15-16358-f004: Systematic measurement of amplitude (Left) and phase (Right) of PA signal over a wide range of DV and phase difference at FG channel 2.

Mentions: To further investigate these issues, we then added the phase difference between the two channels as a parameter. Figure 3 shows the results for three different phase difference values, where “FG: 180.0” means a 180° phase difference at the frequency generator and “FG: 164.3” and “FG: 164.0” correspond to the minimum amplitude signal and the rotating phase around the amplitude minimum value, respectively. Results of a systematic investigation along the two parameters—the phase difference and the driving voltage—are shown in Figure 4.


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)

Systematic measurement of amplitude (Left) and phase (Right) of PA signal over a wide range of DV and phase difference at FG channel 2.
© Copyright Policy
Related In: Results  -  Collection

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

sensors-15-16358-f004: Systematic measurement of amplitude (Left) and phase (Right) of PA signal over a wide range of DV and phase difference at FG channel 2.
Mentions: To further investigate these issues, we then added the phase difference between the two channels as a parameter. Figure 3 shows the results for three different phase difference values, where “FG: 180.0” means a 180° phase difference at the frequency generator and “FG: 164.3” and “FG: 164.0” correspond to the minimum amplitude signal and the rotating phase around the amplitude minimum value, respectively. Results of a systematic investigation along the two parameters—the phase difference and the driving voltage—are shown in Figure 4.

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