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].

This paper is devoted to comparison new optoacoustic tomography with conventional breast tumors diagnostic techniques such as ultrasonography and X-ray radiography. Experiments were performed in phantoms simulating breast with tumors. The fundamental harmonic of Q-switched Nd:YAG laser (2 = 1064 nm) was used to generate optoacoustic pressure waves. Laser induced pressure waves were detected by a wide-band acoustic transducer. Digital oscilloscope controlled by PC was used to store and process optoacoustic signals. Gelatin phantoms with controlled optical parameters were prepared to simulate breast with tumors. Absorbing volumes colored with naphthol green and hemoglobin were embedded in the gelatin phantoms to model the breast tumors with increased optical absorption. Optoacoustic pressure waves from the phantoms were detected at different angles and 2D images were reconstructed. Comparison of optoacoustic images with images obtained with ultrasound and X-ray techniques proved that optoacoustic method has substantially higher contrast and resolution. Obtained results confirm that laser optoacoustic imaging technique can be an important tool for early breast cancer detection with tumors less than 5 mm in diameter.

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