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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

Schematic view of the experimental setup for OPBS-based measurements.
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sensors-15-16358-f001: Schematic view of the experimental setup for OPBS-based measurements.

Mentions: Figure 1 is a schematic view of the experimental setup used to perform the PA-based study of aqueous solutions of glucose. The frequency generator (FG) (WF1948, NF, Yokohama, Japan) generates a square-wave voltage signal that triggers the SR844RF lock-in amplifier (Stanford Research System, Sunnyvale, CA, USA) and drives the two distributed feedback LDs (NTT Electronics, Yokohama, Japan) at the same modulation frequency but in the opposing phase, while the voltage levels can be adjusted independently. The two optical signals modulated in intensity are then combined through a coupler and sent to the measuring cell through a single-mode optical fiber. On the other side of the cell, the acoustic pressure sensed by the transducer (Acoustic Emission R-CAST M-204A, Fujicera, Kyoto, Japan) is first pre-amplified (Pre-Amp Unit A1002, Fujicera, Japan) before being fed into the lock-in amplifier. A computer controls all components via a MATLAB GUI interface (MATLAB R2012b, Natick, USA). This experimental system enables amplitude and phase measurements at any frequency within the bandwidth of the transducer, i.e., between 300 and 600 kHz.


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)

Schematic view of the experimental setup for OPBS-based measurements.
© Copyright Policy
Related In: Results  -  Collection

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

sensors-15-16358-f001: Schematic view of the experimental setup for OPBS-based measurements.
Mentions: Figure 1 is a schematic view of the experimental setup used to perform the PA-based study of aqueous solutions of glucose. The frequency generator (FG) (WF1948, NF, Yokohama, Japan) generates a square-wave voltage signal that triggers the SR844RF lock-in amplifier (Stanford Research System, Sunnyvale, CA, USA) and drives the two distributed feedback LDs (NTT Electronics, Yokohama, Japan) at the same modulation frequency but in the opposing phase, while the voltage levels can be adjusted independently. The two optical signals modulated in intensity are then combined through a coupler and sent to the measuring cell through a single-mode optical fiber. On the other side of the cell, the acoustic pressure sensed by the transducer (Acoustic Emission R-CAST M-204A, Fujicera, Kyoto, Japan) is first pre-amplified (Pre-Amp Unit A1002, Fujicera, Japan) before being fed into the lock-in amplifier. A computer controls all components via a MATLAB GUI interface (MATLAB R2012b, Natick, USA). This experimental system enables amplitude and phase measurements at any frequency within the bandwidth of the transducer, i.e., between 300 and 600 kHz.

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