In vivo photoacoustic (PA) mapping of sentinel lymph nodes (SLNs) using carbon nanotubes (CNTs) as a contrast agent

Sentinel lymph node biopsy (SLNB), a less invasive alternative to axillary lymph node dissection (ALND), is routinely used in clinic for staging breast cancer. In SLNB, lymphatic mapping with radio-labeled sulfur colloid and/or blue dye helps identify the sentinel lymph node (SLN), which is most likely to contain metastatic breast cancer. Even though SLNB, using both methylene blue and radioactive tracers, has a high identification rate, it still relies on an invasive surgical procedure, with associated morbidity. In this study, we have demonstrated a non-invasive single-walled carbon nanotube (SWNT)-enhanced photoacoustic (PA) identification of SLN in a rat model. We have used single-walled carbon nanotubes (SWNTs) as a photoacoustic contrast agent to map non-invasively the sentinel lymph nodes (SLNs) in a rat model in vivo. We were able to identify the SLN non-invasively with high contrast to noise ratio (∼90) and high resolution (∼500 μm). Due to the broad photoacoustic spectrum of these nanotubes in the near infrared wavelength window we could easily choose a suitable light wavelength to maximize the imaging depth. Our results suggest that this technology could be a useful clinical tool, allowing clinicians to identify SLNs non-invasively in vivo. In the future, these contrast agents could be functionalized to do molecular photoacoustic imaging.