Portable hand-held optoacoustic system for localizing blood vessels at intermediate depths

The rapid localization of blood vessels in patients is important in various clinical applications, such as catheterization procedures. While optical techniques, including visual inspection, are limited in their effectiveness at depths below 1 mm, ultrasound and optoacoustic tomography can be used at deeper depths but require a spacer between the tissue and transducer to visualize superficial structures. In this work, we introduce a portable hand-held optoacoustic system that is capable of localizing blood vessels from the point of contact to a depth of 1 cm without the need for a spacer. The probe features a flat, lens-free ultrasound array which enables a largely depth independent response, though at the cost of reduced elevational resolution. In contrast to lens-based probes, where acoustic signals from outside the focal region are distorted, the amplitude of the signal from our probe only varies with depth, resulting in an imaging quality that is largely depth-independent within the imaged region. Additionally, to facilitate miniaturization, dark-field illumination is used, whereby light scattering from the tissue is exploited to homogenize the sensitivity field.