Yuriy Petrov

Multiwavelength optoacoustic system for noninvasive monitoring of cerebral venous oxygenation: a pilot clinical test in the internal jugular vein

A noninvasive, high-resolution optoacoustic technique is a promising alternative to currently used invasive methods of brain oxygenation monitoring. We present the results of our pilot clinical test of this technique in healthy volunteers. Multiwavelength optoacoustic measurements (with nanosecond optical parametric oscillator as a source of radiation) were performed on the area of the neck overlying the internal jugular vein, a deeply located large vein that drains blood from the brain and from extracranial tissues. Optoacoustic signals induced in venous blood were measured with high resolution and signal-to-noise ratio despite the presence of a thick layer of overlying tissue (up to 10 mm). The characteristic parameters of the signal at different wavelengths correlated well with the spectrum of the effective attenuation coefficient of blood.

Continuous, noninvasive monitoring of total hemoglobin concentration by an optoacoustic technique

Measurement of total hemoglobin concentration [Hgb] is a blood test that is widely used to evaluate outpatients, hospital inpatients, and surgical patients, especially those undergoing surgery associated with extensive blood loss, rapid fluid administration, and transfusion of packed red blood cells. Current techniques for measurement of [Hgb] are invasive (requiring blood sampling) and cannot provide real-time, continuous monitoring. We propose to use an optoacoustic technique for noninvasive and continuous monitoring of [Hgb]. The high resolution of the optoacoustic technique may provide accurate measurement of [Hgb] by detection and analysis of optoacoustic signals induced by short optical pulses in blood circulating in arteries or veins. We designed, built, and tested in vitro (in both tissue phantoms and in preliminary in vivo experiments) a portable optoacoustic system for the monitoring of [Hgb] in the radial artery. The system includes a nanosecond laser operating in the near-infrared spectral range and a sensitive optoacoustic probe designed to irradiate the radial artery through the skin and detect optoacoustic signals induced in blood. Results of our studies demonstrated that (1) the slope of optoacoustic waves induced in blood in the transmission mode is linearly dependent on [Hgb] in the range from 6.2 to 12.4 g/dl, (2) optoacoustic signals can be detected despite optical attenuation in turbid tissue phantoms with a thickness of 1 cm, and (3) the optoacoustic system detects signals induced in blood circulating in the radial artery. These data suggest that the optoacoustic system can be used for accurate, noninvasive, real-time, and continuous monitoring of [Hgb].

Optoacoustic monitoring of blood hemoglobin concentration: a pilot clinical study

The optoacoustic technique is noninvasive, has high spatial resolution, and potentially can be used to measure the total hemoglobin concentration ([THb]) continuously and accurately. We performed in vitro measurements in blood and in vivo tests in healthy volunteers. Our clinical protocol included rapid infusion of intravenous saline to simulate rapid change in the [THb] during fluid therapy or surgery. Optoacoustic measurements were made from the wrist area overlying the radial artery for more than 1 h. The amplitude of the optoacoustic signal generated in the radial artery closely followed the [THb] measured directly in concurrently collected blood samples.

Optoacoustic, Noninvasive, Real-Time, Continuous Monitoring of Cerebral Blood Oxygenation: An In Vivo Study in Sheep

Background: Current, invasive cerebral oxygenation monitors require either retrograde jugular venous bulb cannulation or intraparenchymal probe insertion. There is no accurate, noninvasive, continuous monitor of cerebral blood oxygenation. Methods: The authors designed, built, and tested novel optoacoustic instrumentation that continuously measures blood oxygenation in the superior sagittal sinus (SSS) in vivo in 12 anesthetized sheep. In this technique, laser pulses generate acoustic signals, the amplitudes and slopes of which are proportional to oxyhemoglobin saturation in the SSS. Optoacoustic signals from the SSS measured through the scalp and cranium were compared with directly measured oxyhemoglobin saturation in blood withdrawn from the cannulated SSS. Results: In the first experiments (feasibility), Fio2 changes produced rapid corresponding changes in optoacoustic signals and arterial oxygen saturation. In the second experiments (validation), the authors correlated oxyhemoglobin saturation in the SSS with optoacoustic signals and developed quantifying algorithms. In eight of nine validation experiments, the authors quantified optoacoustic signals by subtracting the temporal profile at low Fio2 (0.08–0.1) from profiles at higher Fio2 and integrating those signals in the range from 3 to 5 &mgr;s. In each validation experiment, optoacoustic signals showed tight temporal association and good linear correlation with measured oxyhemoglobin saturation (r2 0.75 to 0.99 for eight individual experiments). Conclusions: The optoacoustic system detects signals induced in the SSS and optoacoustic signals from the SSS linearly correlate with oxyhemoglobin saturation. The data suggest that the optoacoustic technique merits clinical evaluation.

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.

Optoacoustic detection of intra- and extracranial hematomas in rats after blast injury

Surgical drainage of intracranial hematomas is often required within the first four hours after traumatic brain injury (TBI) to avoid death or severe disability. Although CT and MRI permit hematoma diagnosis, they can be used only at a major health-care facility. This delays hematoma diagnosis and therapy. We proposed to use an optoacoustic technique for rapid, noninvasive diagnosis of hematomas. In this study we developed a near-infrared OPO-based optoacoustic system for hematoma diagnosis and cerebral venous blood oxygenation monitoring in rats. A specially-designed blast device was used to inflict TBI in anesthetized rats. Optoacoustic signals were recorded from the superior sagittal sinus and hematomas that allowed for measurements of their oxygenations. These results indicate that the optoacoustic technique may be used for early diagnosis of hematomas and may provide important information for improving outcomes in patients with TBI.

Clinical tests of highly portable 2-lb. laser diode-based noninvasive optoacoustic hemoglobin monitor

Existing techniques for total hemoglobin concentration [THb] monitoring are invasive and cannot be used continuously and in real time. We developed and built a novel, light-weight (2 lb), low-cost, optoacoustic system for noninvasive, accurate monitoring of [THb]. The system incorporates an optoacoustic probe designed for sensitive probing of blood vessels with high signal-to-noise ratio at low energy of laser diode pulses. We developed a new algorithm for accurate monitoring of [THb] in the radial artery with this system. We tested the system in human subjects with different [THb]. The studies confirmed the capability of the system to accurately monitor [THb].

Monte Carlo modeling of optoacoustic signals from human internal jugular veins

Monitoring of blood oxygenation, in particular, cerebral venous oxygenation, is necessary for management of a variety of life-threatening conditions. An optoacoustic technique can be used for noninvasive monitoring of blood oxygenation in blood vessels, including large veins. We calculated optoacoustic signals from a cylinder mimicking a blood vessel using a modified Monte Carlo code and analyzed their temporal profiles. The rate of decrease of the integrated optoacoustic signal at different wavelengths of incident near-infrared radiation was related to the effective attenuation coefficient of normally oxygenated venous blood. We obtained good correlation of this parameter with the blood effective attenuation coefficient in a wide spectral range that may be useful in providing an accurate and robust optoacoustic monitoring of blood oxygenation. We also estimated the accuracy of effective attenuation coefficient calculations.

Cerebral venous blood oxygenation monitoring during hyperventilationin healthy volunteers with a novel optoacoustic system

Monitoring of cerebral venous oxygenation is useful to facilitate management of patients with severe or moderate traumatic brain injury (TBI). Prompt recognition of low cerebral venous oxygenation is a key to avoiding secondary brain injury associated with brain hypoxia. In specialized clinical research centers, jugular venous bulb catheters have been used for cerebral venous oxygenation monitoring and have demonstrated that oxygen saturation < 50% (normal range is 55–75%) correlates with poor clinical outcome. We developed an optoacoustic technique for noninvasive monitoring of cerebral venous oxygenation. Recently, we designed and built a novel, medical grade optoacoustic system operating in the near-infrared spectral range for continuous, real-time oxygenation monitoring in the superior sagittal sinus (SSS), a large central cerebral vein. In this work, we designed and built a novel SSS optoacoustic probe and developed a new algorithm for SSS oxygenation measurement. The SSS signals were measured in healthy volunteers during voluntary hyperventilation, which induced changes in SSS oxygenation. Simultaneously, we measured exhaled carbon dioxide concentration (EtCO2) using capnography. Good temporal correlation between decreases in optoacoustically measured SSS oxygenation and decreases in EtCO2 was obtained. Decreases in EtCO2 from normal values (35-45 mmHg) to 20-25 mmHg resulted in SSS oxygenation decreases by 3-10%. Intersubject variability of the responses may relate to nonspecific brain activation associated with voluntary hyperventilation. The obtained data demonstrate the capability of the optoacoustic system to detect in real time minor changes in the SSS blood oxygenation.