To improve the safety and efficacy of thermal therapy, it is necessary to map tissue temperature in real time with submillimetre spatial resolution. Accurate temperature maps may provide the necessary control of the boundaries of the heated regions and minimize thermal damage to surrounding normal tissues. Current imaging modalities fail to monitor tissue temperature in real time with high resolution and accuracy. We investigated a non-invasive optoacoustic method for accurate, real-time monitoring of tissue temperature during thermotherapy. In this study, we induced temperature gradients in tissue and tissue-like samples and monitored the temperature distribution using the optoacoustic technique. The fundamental harmonic of a Q-switched Nd : YAG laser (λ = 1064 nm) was used for optoacoustic wave generation and probing of tissue temperature. The tissue temperature was also monitored with a multi-sensor temperature probe inserted in the samples. Good agreement between optoacoustically measured and actual tissue temperatures was obtained. The accuracy of temperature monitoring was better than 1°C, while the spatial resolution was about 1 mm. These data suggest that the optoacoustic technique has the potential to be used for non-invasive, real-time temperature monitoring during thermotherapy.

We have proposed a tested in tissue phantoms and in vivo a novel sensor based on optical coherence tomography (OCT) for noninvasive and continuous monitoring of blood glucose concentration. OCT images were obtained from pig and rabbit skin before and after glucose administration. Slopes of OCT signals decreased substantially (~40% in tissues in vivo) and linearly with the increase of blood glucose concentration from 4 to 30 mM, typical for normal and diabetic subjects. Phantom studies demonstrated 1% accuracy of scattering-coefficient measurement. Our theoretical and experimental studies suggest that glucose concentration can potentially be measured noninvasively with high sensitivity and accuracy with OCT systems.

Replacement of invasive monitoring of cerebral venous oxygenation with noninvasive techniques offers great promise in the management of life-threatening neurologic illnesses including traumatic brain injury. We developed and built an optoacoustic system to noninvasively monitor cerebral venous oxygenation; the system includes a nanosecond Nd:YAG laser and a specially designed optoacoustic probe. We tested the system in vitro in sheep blood with experimentally varied oxygenation. Our results demonstrated that (1) the amplitude and temporal profile of the optoacoustic waves increase with blood oxygenation in the range from 24% to 92%, (2) optoacoustic signals can be detected despite optical and acoustic attenuation by thick bone, and (3) the system is capable of real-time and continuous measurements. These results suggest that the optoacoustic technique is technically feasible for continuous, noninvasive monitoring of cerebral venous oxygenation.

Abstract. Studying hemodynamic changes during early mammalian embryonic development is critical for further advances in prevention, diagnostics, and treatment of congenital cardiovascular ͑CV͒ birth defects and diseases. Doppler optical coherence tomography ͑OCT͒ has been shown to provide sensitive measurements of blood flow in avian and amphibian embryos. We combined Doppler swept-source optical coherence tomography ͑DSS-OCT͒ and live mouse embryo culture to analyze blood flow dynamics in early embryos. SS-OCT structural imaging was used for the reconstruction of embryo morphology and the orientation of blood vessels, which is required for calculating flow velocity from the Doppler measurements. Spatially and temporally resolved blood flow profiles are presented for the dorsal aorta and a yolk sac vessel in a 9.5-day embryo. We demonstrate that DSS-OCT can be successfully used for structural analysis and spatially and temporally resolved hemodynamic measurements in developing early mammalian embryos.

In this paper we have applied the laser optoacoustic technique for real time noninvasive monitoring of thermal damage in tissues. Changes in tissue optical properties during coagulation were detected by measuring and analysing amplitude and temporal characteristics of optoacoustic signals. Coagulation of liver, myocardium and prostate was induced by interstitial continuous wave Nd : YAG laser irradiation of the samples or by conductive heating. Real time detection of thermally-induced changes in optical properties was performed with sensitive wide-band acoustic transducers. Combination of optoacoustic and diffuse reflectance technique was applied for determination of tissue optical properties: effective attenuation, total diffuse reflectance, reduced scattering coefficient and absorption coefficient. The optical properties did not change up to temperature of coagulation (about 53°C) and sharply increased during heating up to 70°C. Monitoring of the expansion of interstitial coagulation front within freshly excised canine tissues was performed in real time with spatial resolution of about 0.6 mm. The results of our study suggest that this technique can potentially be used for real time precise thermotherapy of malignant and benign lesions at depths of the order of the centimetre.