Focused, wide-band, polymer-based optoacoustic transducers for noninvasive monitoring of total hemoglobin concentration and other blood variables

One of the most frequently performed blood tests, measurement of total hemoglobin concentration, requires invasive blood sampling. We developed an optoacoustic technique for noninvasive monitoring of total hemoglobin concentration and other blood variables by probing the radial artery or other blood vessels. Recently, we designed and built a focused, wide-band, polymer-based optoacoustic transducer for blood vessel probing with high, submillimeter lateral resolution and incorporated it into a highly portable, laser diode-based optoacoustic system. The focused optoacoustic transducer combines a fiber-optic delivery system and a wide-band piezosensor. First, we experimentally measured transducer parameters (lateral resolution, sensitivity, focal length). To test the transducer capabilities in measurement of total hemoglobin concentration and other blood parameters from blood vessels, we prepared a tissue phantom simulating strongly-scattering tissues with blood vessels of different diameters, spacing, and depths. Optoacoustic signals were acquired from blood at different hemoglobin concentration and oxygenation during transducer scanning over the phantom. In vivo experiments were performed from radial arteries and peripheral veins of different size, depth, and spacing. Submillimeter lateral resolution was obtained in the in vitro and in vivo experiments. The high resolution combined with the wide-band detection of the optoacoustic waves can be used for monitoring of blood variables in blood vessels with high accuracy, sensitivity, and specificity.