Ultrafast pulsed magnetomotive ultrasound imaging of sentinel lymph nodes: Small animal study

Sentinel lymph nodes (SLNs) are the first draining lymph nodes while the metastatic cancer cells are spreading. A noninvasive imaging modality for SLN identification with fine needle aspiration biopsy (FNAB) would be beneficial for staging the axillary lymph nodes without surgical intervention. Here we propose a method - ultrafast pulsed magnetomotive ultrasound (pMMUS) for noninvasive SLN identification, which leverages the MRI superparamagnetic iron oxide nanoparticles (SPIOs) and potentially offers real-time imaging capability for SLN FNAB. Ultrafast pMMUS can localize the SPIOs drained to the SLNs and thus identify the SLNs. Experiments on rats were carried out to verify the feasibility. The SLN was identified in pMMUS images which was confirmed by the methylene blue assay while it is challenging to be localized in B-mode image. Overall, we demonstrated the feasibility of the proposed ultrafast pMMUS for noninvasive SLN identification. Proper SPIO particle size, time window of imaging, and motion-tracking algorithm will be studied to further improve the performance of the proposed method.