We proposed to use optical coherence tomography (OCT) for continuous noninvasive blood glucose monitoring, and recently we significantly improved the sensitivity of this technique. The accuracy of OCT glucose monitoring is limited by several factors, including variation of tissue pressure exerted by the OCT probe. We studied the influence of high (>10 kPa) and low (<1 kPa) pressure levels on OCT blood glucose monitoring. We showed that controlling external pressure to <1 kPa substantially improved the accuracy and reproducibility of OCT-based glucose monitoring.
Continuous monitoring of cerebral blood oxygenation is critically important for treatment of patients with life-threatening conditions like severe brain injury or during cardiac surgery. We designed and built a novel multiwavelength optoacoustic system for noninvasive, continuous, and accurate monitoring of cerebral blood oxygenation. We use an Optical Parametric Oscillator as a light source. We successfully tested the system in vitro as well as in vivo in large animals (sheep) through thick tissues overlying blood vessels which drain venous blood out of the brain (e.g., superior sagittal sinus or jugular vein). Here we present the results of clinical tests of the system for continuous noninvasive cerebral blood oxygenation monitoring in the internal jugular vein of healthy volunteers. We applied our custom-built optoacoustic probe (which incorporated a wide-band acoustic transducer and an optical fiber) to the neck area overlying the internal jugular vein. We performed measurements with volunteers at 18 wavelengths in the near-infrared spectral range. Despite a thick layer of overlying connective tissue and low energy used in the experiments, we recorded signals with high signal-to-noise ratios for all volunteers. We found that the temporal (independent of signal amplitude) parameters of recorded profiles for different levels of blood oxygenation correlated well with the spectrum of effective attenuation coefficients of blood.
We proposed and have been developing real-time, noninvasive monitoring of blood oxygenation, total hemoglobin concentration, and thermotherapy including hyperthermia, coagulation, and cryotherapy. In this paper we propose to use the optoacoustic technique for monitoring of nanoparticle-mediated photothermal therapy (NPT) of tumors. NPT is based on heating exogenous strongly-absorbing nanoparticles selectively delivered in tumors. Real-time monitoring of NPT is necessary for precise tumor therapy with minimal damage to normal tissues. In this study we injected PEGylated and non-PEGylated carbon nanoparticles in nude mice bearing human tumors (5-15 mm) and irradiated the tumors for 10 minutes with nanosecond Nd:YAG laser pulses which produced both thermal damage to the tumors and optoacoustic signals for monitoring NPT in real time. Irradiation of tumors was performed during or after (3 or 24 hours) nanoparticle injection. Amplitude and temporal parameters of optoacoustic signals (measured with a custom-made wide-band optoacoustic probe) correlated well with nanoparticle injection, temperature rise in tumors, and tumor coagulation. Substantial thermal damage in large areas of the tumors was produced when optimal irradiation parameters were used. Monte Carlo modeling of light distribution in tumors and optoacoustic theory were applied to study kinetics of nanoparticle concentration in the tumors. Our results demonstrated that the optoacoustic technique can be used for real-time monitoring of NTP and provide precise tumor therapy with minimal damage to normal tissues.
Optical Coherence Tomography (OCT) was recently proposed by our group for noninvasive, continuous monitoring of blood glucose concentration in diabetics as well as in critically ill patients (both diabetic and nondiabetic). In our previous studies we tested OCT-based glucose sensing using one-dimensional (1-D) lateral scanning of the OCT probing beam over the tissue surface. The measured OCT signal was prone to motion artifacts and had high level of speckle noise. In this study we used two-dimensional (2-D) lateral scanning of the OCT probing beam and achieved 3.6-fold reduction of the speckle noise level. We also applied a post-processing Fourier filtration technique that resulted in an additional 2-2.5-fold suppression of noise. Our data indicate that the combination of acquisition time of 30-40s and the Fourier filtration technique may provide OCT monitoring of blood glucose concentration with a sensitivity of 1mM (18 mg/dL).
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