This paper details the potential of cetuximab (C225) labeled microbubbles(MBs) to improve ultrasound (US) imaging of head and neck squamous cellcarcinoma (HNSCC). C225 is a therapeutic monoclonal antibody to the epidermalgrowth factor receptor (EGFR) and currently approved for the treatment ofrecurrent HNSCC. Conjugating C225 to the surface of US MBs produces a targetedcontrast agent that selectively binds to over-expressed EGFR on the tumorendothelium to improve visualization and therapeutic monitoring. Analysis oftargeted MB binding in vitro was performed using SCC-1 and normal dermalfibroblasts (NDF) cell lines. Cells were incubated with MBs conjugated to eitherC225 or IgG isotype control antibodies. Light microscopy was used to quantifyMB receptor binding. Attached MB were normalized by cell count and recorded foreach group. To evaluate C225-labeled MBs in an animal model, SCC-1 cells wereimplanted in the flank of nude athymic mice (N=8). MBs labeled with C225 orcontrol antibodies were administered via a bolus tail vein injection and tumorswere examined using a MB sensitive harmonic imaging mode. For each tumor, USimages from the targeted and control groups were paired and assessed by ablinded reviewer to determine greatest degree of intratumoral contrastenhancement. MBs labeled with C225 exhibited significantly higher SCC-1 cellattachment levels relative to control group measurements (p=0.001).Specifically, the mean number of attached MBs per cell was 3.6±0.7 and0.7±0.1 for the C225-and control antibody-labeled groups, respectively,yielding nearly a 6-fold difference. Given presentation of paired animal data,it was determined that 75% (6 of 8) of the US images from the C225-labeled MBexperimental day exhibited increased enhancement compared to the same animalsadministered control MBs. This study demonstrates feasibility of targeted USimaging of HNSCC using cetuximab-labeled MBs.