In vivo photoacoustic and ultrasonic mapping of rat sentinel lymph nodes with a modified commercial ultrasound imaging system
Sentinel lymph node biopsy (SLNB) has become the standard method for axillary staging in breast cancer patients, relying on invasive identification of sentinel lymph nodes (SLNs) following injection of blue dye and radioactive tracers. While SLNB achieves a low false negative rate (5-10%), it is an invasive procedure requiring ionizing radiation. As an alternative to SLNB, ultrasound-guided fine needle aspiration biopsy has been tested clinically. However, ultrasound alone is unable to accurately identify which lymph nodes are sentinel. Therefore, a non-ionizing and noninvasive detection method for accurate SLN mapping is needed. In this study, we successfully imaged methylene blue dye accumulation in vivo in rat axillary lymph nodes using a Phillips iU22 ultrasound imaging system adapted for photoacoustic imaging with an Nd:YAG pumped, tunable dye laser. Photoacoustic images of rat SLNs clearly identify methylene blue dye accumulation within minutes following intradermal dye injection and co-registered photoacoustic/ultrasound images illustrate lymph node position relative to surrounding anatomy. To investigate clinical translation, the imaging depth was extended up to 2.5 cm by adding chicken breast tissue on top of the rat skin surface. These results raise confidence that photoacoustic imaging can be used clinically for accurate, noninvasive SLN mapping.
Additional Information© 2010 Society of Photo-Optical Instrumentation Engineers (SPIE). This research was supported by National Institutes of Health grants U54 CA136398 (Network for Translational Research), R01 EB000712, R01 NS46214, and R01 EB008085. We thank Victor Gornstein and Adam Schleicher for their contributions to modifying the Philips iU22 ultrasound imaging system. We thank Julie Margenthaler for helpful discussions on clinical breast cancer staging and treatment. LVW has a financial interest in Microphotoacoustics, Inc. and Endra, Inc., which, however, did not support this work. TNE, JD, and LJ are employees of Philips Research.
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