Comparison of optical coherence tomography, the pulsed photoacoustic technique, and the time-of-flight technique in glucose measurements <em>in vitro</em>

Abstract

<div lang="en" class="abs"><p class="abs_header">Abstract</p><p>The development of a non-invasive glucose monitoring technique is very important because it would tremendously diminish the need to puncture the skin when taking blood samples and help diabetic patients in controlling their blood glucose levels and in treating <em>Diabetes Mellitus</em>. The focus of this thesis is on measuring the effect of glucose on the light scattering properties of a tissue-simulating phantom and biological tissues <em>in vitro</em>. Optical coherence tomography (OCT), the pulsed photoacoustic (PA) technique, and the time-of-flight (TOF) technique are used in the measurements and their capabilities for detecting changes in the scattering properties are evaluated and compared with each other. The theoretical background of the techniques, light propagation and PA wave generation are briefly explained. The glucose-induced changes in light scattering are also reviewed. </p><p>The measurement results with the OCT and the PA technique from Intralipid, pig whole blood, and mouse skin tissue samples show that the glucose-induced changes are larger in the biological tissues than in the Intralipid phantom. The PA measurements show that although the PA signals are stronger at a wavelength of 532 nm than at 1064 nm, the glucose-induced change in the peak-to-peak value of the PA signal measured from pig whole blood is larger at a wavelength of 1064 nm than at 532 nm. The TOF measurements with a streak camera show that the scattering-related changes in the registered pulse shapes occur mainly in the rising part of the pulses. The utilization of fiber-optic measurement heads enabled the detection of back-scattered photons at different distances from the emitting fiber.</p><p>Although all the techniques are able to detect changes induced by large glucose concentrations (0–5000 mg/dl) in Intralipid, the effect of glucose on the scattering properties of Intralipid is so weak that the techniques failed to detect changes with lower (50–500 mg/dl) concentrations. The measurements of biological samples with the PA technique and with the OCT also demonstrate capabilities to measure glucose concentrations in the physiologically relevant range (18–450 mg/dl) as well. The results compare well with earlier literature and also confirm some earlier findings.</p></div>