Limits...
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

Fast Fourier Transform-based characterization of the PA signal with a Phase-locked loop operating at 486.2 kHz and for various DVs (Left) or phase differences (Right).
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4541882&req=5

sensors-15-16358-f005: Fast Fourier Transform-based characterization of the PA signal with a Phase-locked loop operating at 486.2 kHz and for various DVs (Left) or phase differences (Right).

Mentions: To confirm these findings, we then performed an analysis of the acoustic signal detected by the transducer in the frequency domain. At this stage, we monitored a response peak at a frequency of 486.2 kHz. We first made the adjustments along the phase difference and voltage based on minimizing the PA signal. Then, we replaced the lock-in amplifier with an oscilloscope and performed decomposition of the acoustic signal in the frequency domain. Figure 5 shows the results around the fundamental frequency when the phase difference or voltage was changed from the reference point. In the graph, the 0 abscissa corresponds to the balanced configuration (two signals balanced, so no emission of an acoustic wave). This point was determined on the basis of the previously described PA procedure and, as expected, there is no signal captured at the resonance frequency.


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)

Fast Fourier Transform-based characterization of the PA signal with a Phase-locked loop operating at 486.2 kHz and for various DVs (Left) or phase differences (Right).
© Copyright Policy
Related In: Results  -  Collection

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

sensors-15-16358-f005: Fast Fourier Transform-based characterization of the PA signal with a Phase-locked loop operating at 486.2 kHz and for various DVs (Left) or phase differences (Right).
Mentions: To confirm these findings, we then performed an analysis of the acoustic signal detected by the transducer in the frequency domain. At this stage, we monitored a response peak at a frequency of 486.2 kHz. We first made the adjustments along the phase difference and voltage based on minimizing the PA signal. Then, we replaced the lock-in amplifier with an oscilloscope and performed decomposition of the acoustic signal in the frequency domain. Figure 5 shows the results around the fundamental frequency when the phase difference or voltage was changed from the reference point. In the graph, the 0 abscissa corresponds to the balanced configuration (two signals balanced, so no emission of an acoustic wave). This point was determined on the basis of the previously described PA procedure and, as expected, there is no signal captured at the resonance frequency.

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