Background,Motivation and Objective We have previously developed a frequency and phase tracking algorithm which is able to detect superparamagnetic iron oxide nanoparticles(SPIO NPs) using magnetomotive ultrasound imaging,with our primary aim being to detect sentinel lymph nodes(SLNs) in breast cancer surgery.Recently we have shown detection of SPIO laden rat SLNs in situ(IEEE T-UFFC,61:1276-1283).Here we present the feasibility of in vivo detection of SLNs in rats and how the signal-to-clutter-ratio is affected by magnetic coil excitation.