NIR photoacoustic spectroscopy for non-invasive glucose measurement.

The use of near infra red (NIR) photoacoustic spectroscopy (PAS) for continuous non-invasive glucose measurement is outlined in the paper. A photoacoustic (PA) measurement apparatus was constructed and PA measurements were made on glucose solutions at multiple NIR excitation wavelengths. A variety of time and frequency domain features, including amplitude and area based features, were extracted from the PA measurements. These features were observed to be proportional to the glucose concentration of the sample. PA measurements from samples of whole blood at different glucose concentrations showed similar results. Subsequently, in vivo PA measurements made on a cohort of 30 volunteers were calibrated using a quadratic fit, and the results were compared to reference glucose concentrations made using a regular blood glucose meter. A comparison of 196 measurement pairs of predicted and reference glucose concentrations using a Clarke Error Grid gave a point distribution of 87.24% and 12.76% over zones A and B of the grid, with no measurement pairs falling in unacceptable zones C-E of the error grid. The predicted measurements had a mean absolute difference (MAD) of 12.57 ± 13.90 mg/dl and a mean absolute relative difference (MARD) of 9.61% ± 10.55%. This is an improvement over previous results obtained using PAS and other non-invasive techniques, validating the potential of PAS for continuous noninvasive glucose monitoring.