The Network for Translational Research

Photoacoustic/Optical/Ultrasonic Imaging of Sentinel Lymph Nodes and Metastases

The primary goal for the Washington University NTR Center is to develop an imaging technology for real-time, noninvasive, in vivo sentinel lymph node (SLN) mapping and axillary staging, which would be a highly useful clinical tool for patients with breast cancer and clinically negative axillae. Sentinal lymph node biopsy (SLNB) has become the standard method of axillary staging, but our novel imaging tool would enable the clinician to identify the SLN so that noninvasive diagnostic methods (e.g., fine needle aspiration biopsy and reverse transcription polymerase chain reaction) could be used to stage the axillae without the morbidity of an operative procedure.

Figure 1c
Photoacoustic image of a sentinel lymph node (SLN) 18 mm below the laser-illumination surface acquired with a 5-MHz photoacoustic macroscope. Axial resolution: 144 µm. Penetration limit: 30 mm.
Figure 1b
Photoacoustic image of a melanoma and the surrounding blood vessels acquired with a 50-MHz photoacoustic microscope. M: melanoma. Axial resolution: 15 µm. Penetration limit: 3 mm.
Figure 1a
Photoacoustic image of the vasculature, including capillaries, acquired with an optical-resolution photoacoustic microscope. Lateral resolution: 5 µm. Penetration limit: 0.7 mm.

The proposed imaging tool, photoacoustic tomography, is a hybrid technology that can be used in combination with conventional ultrasound imaging. Unlike ultrasound, photoacoustic imaging is highly sensitive to methylene blue dye; therefore the primary project will test the hypothesis that photoacoustic imaging can reliably map human SLN using the methylene blue contrast.

We will also enhance photoacoustic imaging with additional capabilities, including molecular imaging. Incorporation of molecular contrast agents will enhance the sensitivity and specificity and provide a strategy for multimodal validation.