  Medical imaging plays an important role in diagnosis and treatment of
multiple diseases. It is a field under continuous development which seeks for
improved sensitivity and spatiotemporal resolution to allow the dynamic
monitoring of diverse biological processes that occur at the micro- and
nanoscale. Emerging technologies for targeted diagnosis and therapy such as
nanotherapeutics, micro-implants, catheters and small medical tools also need
to be precisely located and monitored while performing their function inside
the human body. In this work, we show for the first time the real-time tracking
of moving single micro-objects below centimeter thick tissue-mimicking
phantoms, using multispectral optoacoustic tomography (MSOT). This technique
combines the advantages of ultrasound imaging regarding depth and resolution
with the molecular specificity of optical methods, thereby facilitating the
discrimination between the spectral signatures of the micro-objects from those
of intrinsic tissue molecules. The resulting MSOT signal is further improved in
terms of contrast and specificity by coating the micro-objects surface with
gold nanorods, possessing a unique absorption spectrum, which will allow their
discrimination from surrounding biological tissues when translated to in vivo
settings.
