  Ultrasound-switchable fluorescence (USF) imaging was recently developed to
overcome the limitation of the poor spatial resolution of the conventional
fluorescence imaging in centimeter-deep tissue. However, in vivo USF imaging
has not been achieved so far because of the lack of stable near-infrared
contrast agents in a biological environment and the lack of data about their
biodistributions. In this study, for the first time, we achieved in vivo USF
imaging successfully in mice with high resolution. USF imaging in porcine heart
tissue and mouse breast tumor via local injections were studied and
demonstrated. In vivo and ex vivo USF imaging of the mouse spleen via
intravenous injections was also successfully achieved. The results showed that
the USF contrast agent adopted in this study was very stable in a biological
environment, and it was mainly accumulated into the spleen of the mice. All the
results of USF imaging were validated by a commercial micro-CT.
