  Various morphological and functional parameters of peripheral nerves and
their vascular supply are indicative of pathological changes due to injury or
disease. Based on recent improvements in optoacoustic image quality, we explore
the ability of multispectral optoacoustic tomography, in tandem with ultrasound
imaging (OPUS), to investigate the vascular environment and morphology of
peripheral nerves in vivo in a pilot study on healthy volunteers. We showcase
the unique ability of optoacoustic imaging to visualize the vasa nervorum by
observing intraneurial vessels in healthy nerves in vivo for the first time. In
addition, we demonstrate that the label-free spectral optoacoustic contrast of
the perfused connective tissue of peripheral nerves can be linked to the
endogenous contrast of haemoglobin and collagen. We introduce metrics to
analyze the composition of tissue based on its optoacoustic contrast and show
that the high-resolution spectral contrast reveals specific differences between
nervous tissue and reference tissue in the nerve's surrounding. We discuss how
this showcased extraction of peripheral nerve characteristics using
multispectral optoacoustic and ultrasound imaging can offer new insights into
the pathophysiology of nerve damage and neuropathies, for example, in the
context of diabetes.
