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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

(a) PA amplitude signal versus normalized phase difference and voltage with (b) the corresponding raw data.
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sensors-15-16358-f006: (a) PA amplitude signal versus normalized phase difference and voltage with (b) the corresponding raw data.

Mentions: Then, changing the phase difference or DV of ch2 yields a contribution at the excitation frequency (Figure 5). The intensity, or height, of the peak also increases as we go further away from the 0-reference point. However, despite a similar trend in both results, the amplitude seems higher when the phase difference is changed. In order to compare the two phenomena, the raw data obtained from the peak height in the frequency domain (Figure 6b) were normalized. A 100% normalized phase difference corresponds to a 180° phase shift, while the equivalent in DV corresponds to a shift by the difference between DV at the balance level and the threshold voltage of the LDs. The results are shown in Figure 6.


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)

(a) PA amplitude signal versus normalized phase difference and voltage with (b) the corresponding raw data.
© Copyright Policy
Related In: Results  -  Collection

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

sensors-15-16358-f006: (a) PA amplitude signal versus normalized phase difference and voltage with (b) the corresponding raw data.
Mentions: Then, changing the phase difference or DV of ch2 yields a contribution at the excitation frequency (Figure 5). The intensity, or height, of the peak also increases as we go further away from the 0-reference point. However, despite a similar trend in both results, the amplitude seems higher when the phase difference is changed. In order to compare the two phenomena, the raw data obtained from the peak height in the frequency domain (Figure 6b) were normalized. A 100% normalized phase difference corresponds to a 180° phase shift, while the equivalent in DV corresponds to a shift by the difference between DV at the balance level and the threshold voltage of the LDs. The results are shown in Figure 6.

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