High-speed dynamic 3D photoacoustic imaging of sentinel lymph node in a murine model using an ultrasound array
Noninvasive photoacoustic sentinel lymph node (SLN) mapping with high spatial resolution has the potential to improve the false negative rate and eliminate the use of radioactive tracers in SLN identification. In addition, the demonstrated high spatial resolution may enable physicians to replace SLN biopsy with fine needle aspiration biopsy, and thus reduce the risk of associated morbidity. The primary goal of this study is to demonstrate the feasibility of high-speed 3D photoacoustic imaging of the uptake and clearance dynamics of Evans blue dye in SLNs. The photoacoustic imaging system was developed with a 30MHz ultrasound array and a kHz repetition rate laser system. It acquires one 3D photoacousticimage of 166 B-scan frames in 1s, with axial, lateral, and elevational resolutions of 25, 70, and 200μm, respectively. With optic-fiber based light delivery, the entire system is compact and is convenient to use. Upon injection of Evans blue, a blue dye currently used in clinical SLN biopsy, SLNs in mice and rats were accurately and noninvasively mapped in vivo using our imaging system. In our experiments, the SLNs were found to be located at ∼0.65mm below the skin surface in mice and ∼1.2mm in rats. In some cases, lymph vessels and lymphatic valves were also imaged. The dye dynamics—accumulation and clearance—in SLNs were quantitatively monitored by sequential 3D imaging with temporal resolution of as high as ∼6s. The demonstrated capability suggests that high-speed 3D photoacoustic imaging should facilitate the understanding of the dynamics of various dyes in SLNs and potentially help identify SLNs with high accuracy.
Additional Information© 2009 American Association of Physicists in Medicine. Received 14 April 2009; Revised 11 June 2009; Accepted 13 June 2009; Published online 13 July 2009. This work was sponsored in part by National Institutes of Health Grant Nos. U54 CA136398 (NTR), R01 EB000712, R01 NS46214 (BRP), and R01 EB008085. One of the authors (L.V.W.) has a financial interest in Microphotoacoustics, Inc., and Endra, Inc., which, however, did not support this work. The authors are grateful to Dr. Julie Margenthaler, Junjie Yao, Song Hu, and Dr. Janet Eary for beneficial discussions.
Published - MPHYA6-000036-003724_1.pdf