Optoacoustic monitoring of cerebral venous blood oxygenation though intact scalp in large animals.

Monitoring (currently invasive) of cerebral venous blood oxygenation is a key to avoiding hypoxia-induced brain injury resulting in death or severe disability. Noninvasive, optoacoustic monitoring of cerebral venous blood oxygenation can potentially replace existing invasive methods. To the best of our knowledge, we report for the first time noninvasive monitoring of cerebral venous blood oxygenation through intact scalp that was validated with invasive, "gold standard" measurements. We performed an in vivo study in the sheep superior sagittal sinus (SSS), a large midline cerebral vein, using our novel, multi-wavelength optoacoustic system. The study results demonstrated that: 1) the optoacoustic signal from the sheep SSS is detectable through the thick, intact scalp and skull; 2) the SSS signal amplitude correlated well with wavelength and actual SSS blood oxygenation measured invasively using SSS catheterization, blood sampling, and measurement with "gold standard" CO-Oximeter; 3) the optoacoustically predicted oxygenation strongly correlated with that measured with the CO-Oximeter. Our results indicate that monitoring of cerebral venous blood oxygenation may be performed in humans noninvasively and accurately through the intact scalp using optoacoustic systems because the sheep scalp and skull thickness is comparable to that of humans whereas the sheep SSS is much smaller than that of humans.

Optoacoustic monitoring of cerebral venous blood oxygenation through extracerebral blood.

There is strong clinical evidence that controlling cerebral venous oxygenation (oxyhemoglobin saturation) is critically important for patients with severe traumatic brain injury as well as for patients undergoing cardiac surgery. However, the only available method for cerebral venous blood oxygenation monitoring is invasive and requires catheterization of the internal jugular vein. We designed and built a novel optoacoustic monitor of cerebral venous oxygenation as measured in the superior sagittal sinus (SSS), the large midline cerebral vein. To the best of our knowledge, optical monitoring of cerebral venous blood oxygenation through overlying extracerebral blood is reported for the first time in this paper. The system was capable of detecting SSS signals in vivo at 700, 800, and 1064 nm through the thick (5-6 mm) sheep skull containing the circulating blood. The high (submillimeter) in-depth resolution of the system provided identification of the SSS peaks in the optoacoustic signals. The SSS peak amplitude closely followed the actual SSS blood oxygenation measured invasively using catheterization, blood sampling, and "gold standard" CO-Oximetry. Our data indicate the system may provide accurate measurement of the SSS blood oxygenation in patients with extracerebral blood over the SSS.

Noninvasive monitoring of cerebral blood oxygenation in ovine superior sagittal sinus with novel multi-wavelength optoacoustic system.

Noninvasive monitoring of cerebral blood oxygenation with an optoacoustic technique offers advantages over current invasive and noninvasive methods. We report the results of in vivo studies in the sheep superior sagittal sinus (SSS), a large central cerebral vein. We changed blood oxygenation by increasing and decreasing the inspired fraction of oxygen (FiO(2)). Optoacoustic measurements from the SSS were performed at wavelengths of 700, 800, and 1064 nm using an optical parametric oscillator as a source of pulsed near-infrared light. Actual oxygenation of SSS blood was measured with a CO-Oximeter in blood samples drawn from the SSS through a small craniotomy. The amplitude of the optoacoustic signal induced in the SSS blood at lambda = 1064 nm closely followed the changes in blood oxygenation, at lambda = 800 nm was almost constant, and at lambda = 700 nm was changing in the opposite direction, all in accordance with the absorption spectra of oxy- and deoxyhemoglobin. The optoacoustically predicted oxygenation correlated well with actual blood oxygenation in sheep SSS (R(2) = 0.965 to 0.990). The accuracy was excellent, with a mean difference of 4.8% to 9.3% and a standard deviation of 2.8% to 4.2%. To the best of our knowledge, this paper reports for the first time accurate measurements of cerebral venous blood oxygenation validated against the "gold standard" CO-Oximetry method.

In vivo monitoring of blood oxygenation in large veins with a triple-wavelength optoacoustic system.

A noninvasive optoacoustic technique could be a clinically useful alternative to existing, invasive methods for cerebral oxygenation monitoring. Recently we proposed to use an optoacoustic technique for monitoring cerebral blood oxygenation by probing large cerebral and neck veins including the superior sagittal sinus and the internal jugular vein. In these studies we used a multi-wavelength optoacoustic system with a nanosecond optical parametric oscillator as a light source and a custom-made optoacoustic probe for the measurement of the optoacoustic signals in vivo from the area of the sheep neck overlying the external jugular vein, which is similar in diameter and depth to the human internal jugular vein. Optoacoustic signals induced in venous blood were measured with high resolution despite the presence of a thick layer of tissues (up to 10 mm) between the external jugular vein and the optoacoustic probe. Three wavelengths were chosen to provide accurate and stable measurements of blood oxygenation: signals at 700 nm and 1064 nm demonstrated high correlation with actual oxygenation measured invasively with CO-Oximeter ("gold standard"), while the signal at 800 nm (isosbestic point) was independent of blood oxygenation and was used for calibration.

Accurate, noninvasive measurement of total hemoglobin concentration with optoacoustic technique.

The measurement of total hemoglobin concentration is currently invasive and time consuming. The optoacoustic technique may provide accurate and noninvasive measurements of total hemoglobin concentration by probing blood vessels. We studied the influence of blood vessel diameter and lateral displacement of the optoacoustic probe on accuracy of total hemoglobin concentration measurements with this technique.

Noninvasive monitoring of glucose concentration with optical coherence tomography.

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.

Pulsed laser ablation of soft tissues, gels, and aqueous solutions at temperatures below 100 degrees C.

BACKGROUND AND OBJECTIVE: It is desirable for laser microsurgical procedures to remove tissue accurately and with minimal thermal and mechanical damage to adjacent non-irradiated tissues. Pulsed laser ablation can potentially remove biological tissue with microprecision if appropriate irradiation conditions are applied. The major goal of this study was to determine whether laser ablation is possible at temperatures below 100 degrees C. Another aim was to test thermoelastic and recoil stress magnitudes and to estimate their effects on phantom and biological tissue. STUDY DESIGN/MATERIALS AND METHODS: Pulsed laser ablation of water (aqueous solution of potassium chromate) and water containing soft tissues (collagen gel and pig liver) irradiated under confined stress conditions was studied. The ablation mechanism and stages of the ablation process were determined based on time-resolved measurements of laser-induced acoustic waves with simultaneous imaging of the ablation process by laser-flash photography. RESULTS: This study reveals the important role of tensile thermoelastic stress, which produces efficient cavitation that drives material ejection at temperatures substantially below 100 degrees C. Ablation thresholds for the aqueous solution, collagen gel, and liver were 20, 38, and 55 J/cm3, respectively, which correspond to temperature jumps of 5, 10, and 15 degrees C. Two distinct stages of material ejection were observed: (1) initial removal of small volumes of material due to the rupture of single subsurface bubbles, (2) bulk material ablation in the form of jets produced by intense hydrodynamic motions formed upon collapse of large bubbles after coalescence of smaller bubbles. The duration of material ejection upon short-pulse ablation may vary from microseconds to submilliseconds, and depended on the mechanical properties of materials and the incident laser fluence. CONCLUSION: Nanosecond laser ablation of water, gels, and soft tissue under confined-stress conditions of irradiation may occur at temperatures below 100 degrees C. This ablation regime minimizes thermal injury to adjacent tissues and involves thermoelastic stress and recoil pressure magnitudes, which may be tolerated by tissues adjacent to an ablated crater.

Effects of monochromatic low-intensity light and laser irradiation on adhesion of HeLa cells in vitro.

BACKGROUND AND OBJECTIVE: The adhesion of HeLa cells was evaluated after irradiation with monochromatic low-intensity light or laser irradiation. It is well known that the cell-cell and cell-matrix adhesion changes during wound repair. For better understanding of low-power laser light action on the wound healing process, it would be of interest to study the light action on cellular adhesion in vitro. STUDY DESIGN/MATERIALS AND METHODS: The monochomatic light was in the range 580-860 nm (bandwidth 10 nm, 5-150 J/m2 1.3 W/m2) and the He-Ne laser irradiation was 632.8 nm (100 J/m2, 10 W/m2). Cell-cell and cell-glass adhesion were evaluated after irradiation of HeLa cells. RESULTS: It was found that cell-cell and cell-glass adhesion increased following irradiation depending on the irradiation conditions (wavelength, dose) and the time elapsed after the irradiation. The cell attachment to glass surface increased after irradiation of samples of HeLa cells in suspension. CONCLUSION: The adhesion was stimulated in the wavelength ranges 600-625, 645-700, and 720-850 nm with maxima at 620, 680, 750, and 820-830 nm, respectively.

Studies of acoustical and shock waves in the pulsed laser ablation of biotissue.

Quantitative studies are conducted into the absolute pressure values of the acoustical and shock waves generated and propagating in a biotissue under pulsed (tau p = 50 ns) UV (lambda = 308 nm) laser irradiation (below and above the ablation threshold). Powerful (several hundreds of bars in pressure) high-frequency (f approximately 10(7) Hz) acoustic compression and rarefaction pulses are found to be generated in the biotissue. The amplitudes and profiles of the acoustic pulses developing in atherosclerotic human aorta tissues and an aqueous CuCl2 solution under laser irradiation are investigated as a function of the laser pulse energy fluence. The results obtained point to the absence of the cold spallation of the objects of study by rarefaction waves. Based on experimental data, the rise rates, pressure gradients, and propagation velocities of shock waves in the biotissue are calculated. The experimental data are found to agree well with the theoretical estimates.

Laser ablation of atherosclerotic blood vessel tissue under various irradiation conditions.

A quantitative analysis is presented of the destruction of normal wall and atherosclerotic plaque areas of blood vessels by laser radiation. Threshold laser radiant exposure values were measured experimentally in vitro, along with the ablation efficiency for various laser wavelengths and irradiation conditions. Correlations were found between the ablation efficiency and fluence thresholds on the one hand and the optical properties of the blood vessel tissues on the other. Fibrous plaque was demonstrated to be selectively destroyed by the second-harmonic output from a pulsed Nd:YAG laser at lambda = 532 nm.

[Inactivation of alpha VEE virus using a high intensity laser with UV-radiation]. / Inaktivatsiia al'favirusa VEE pri vysokointensivnom lazernom UF-obluchenii.

Inactivation of VEE virus with laser UV impulses of nano- and picosecond duration was investigated. It has been shown that in both cases there is a decrease of the inactivation cross-section with the rise of irradiation intensity. It points to the fact that the major lethal photoproduct in VEE is formed by a single-quantum mechanism.

UV laser induced RNA-protein crosslinks and RNA chain breaks in tobacco mosaic virus RNA in situ.

The efficiency of RNA-protein crosslink and RNA chain break formation under nanosecond or picosecond UV-laser pulse irradiation of tobacco mosaic virus was determined. It was found that on high-intensity UV-laser irradiation the quantum yields of both reactions increase considerably as compared to the usual (low-intensity) UV-irradiation. The RNA-protein crosslink quantum yield was found to be 1.8 x 10(-5) and 1.2 x 10(-4) and that of RNA chain breaks 1.7 x 10(-4) and 8.9 x 10(-4) for nanosecond and picosecond irradiation, respectively.