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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

OPBS-based sensor response to aqueous glucose concentration for 180-phase difference set at the FG (red) and the fiber coupler (green), and their corresponding linear regression fitting.
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sensors-15-16358-f008: OPBS-based sensor response to aqueous glucose concentration for 180-phase difference set at the FG (red) and the fiber coupler (green), and their corresponding linear regression fitting.

Mentions: Figure 8 summarizes the results with a comparison of the two responses. To estimate the measurement accuracy (error bars in Figure 8), a value of ±4 mV was used for all the data points. In the case of the 180° phase difference at the fiber coupler, this value includes a ±2 mV error due to the fact that measurements were performed in a region characterized by low signal levels and therefore by a low SNR for several points in the vicinity of the measured absolute minimum. Furthermore, it also accounts for the error in the phase difference, which can introduce an overall shift of the V-shape response as can be seen in Figure 3. In the case of the 180° phase difference at FG, the resolution is higher due to linear regression around the 0-phase point, but any error in phase difference still impacts the final measurement accuracy. As a result, the error of ±4 mV used in Figure 8 represents an overestimate of the actual resolution for both methods, but it provides valuable information for further comparison of the two sets of data.


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)

OPBS-based sensor response to aqueous glucose concentration for 180-phase difference set at the FG (red) and the fiber coupler (green), and their corresponding linear regression fitting.
© Copyright Policy
Related In: Results  -  Collection

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

sensors-15-16358-f008: OPBS-based sensor response to aqueous glucose concentration for 180-phase difference set at the FG (red) and the fiber coupler (green), and their corresponding linear regression fitting.
Mentions: Figure 8 summarizes the results with a comparison of the two responses. To estimate the measurement accuracy (error bars in Figure 8), a value of ±4 mV was used for all the data points. In the case of the 180° phase difference at the fiber coupler, this value includes a ±2 mV error due to the fact that measurements were performed in a region characterized by low signal levels and therefore by a low SNR for several points in the vicinity of the measured absolute minimum. Furthermore, it also accounts for the error in the phase difference, which can introduce an overall shift of the V-shape response as can be seen in Figure 3. In the case of the 180° phase difference at FG, the resolution is higher due to linear regression around the 0-phase point, but any error in phase difference still impacts the final measurement accuracy. As a result, the error of ±4 mV used in Figure 8 represents an overestimate of the actual resolution for both methods, but it provides valuable information for further comparison of the two sets of data.

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