Gold nanocages change lymph node biopsy, reduce radiation exposure
Information obtained from a new application of photoacoustic tomography (PAT) is “worth its weight in gold” to breast cancer patients, according to researchers at Washington University in St. Louis.

For the first time, Lihong Wang, PhD, from the department of biomedical engineering, Younan Xia, PhD, and James M. McKelvey, professor in biomedical engineering, have used gold nanocages to map sentinel lymph nodes (SLN) in a rat noninvasively using PAT.

Wang and colleagues said that their work can minimize invasive surgical lymph node biopsy procedures to determine if breast cancer has metastasized and reduce the patient's exposure to radioactivity. The nanocages also have the potential to serve as an alternative to chemotherapy to kill targeted cancers by heating them up.

PAT blends optical and ultrasonic imaging to give high-resolution images of the body that contain information about physiology or tissue function. When light is shone on the tissue, the contrast agent absorbs the light, converts it to heat and expands. This expansion is detected as sound and decoded into an image.

"Using pure optical imaging, it is hard to look deep into tissues at high resolution because light scatters. The useful photons run out of juice within 1 mm," Wang explained. "PAT improves tissue transparency by two to three orders of magnitude because sound scatters less than light. This allows us to see through the tissue by listening to the sound."

Exogenous contrast agents, like the gold nanocages developed by Xia's group, can be used to image parts of the body that even contain endogenous contrast agents. These nanocages are especially attractive because their properties can be tuned to give optimal contrast and gold is non-toxic.

"By controlling the synthesis, we can move the absorption peak for the nanocages to a region that allows them to be imaged deep in tissue. We can also attach biomolecules to the surface of the nanocages so they are targeted to cancer cells," Xia said.

The SLN, the first draining node, is often biopsied in breast cancer patients to determine if the cancer has metastasized.

Wang and Xia said the technique allows the SLN to be imaged safely without radioactivity or surgery. A piece of tissue can then be removed using a minimally invasive needle biopsy and tested for cancer.

In the future, they hope to attach molecules to the surface of the gold nanocages that will selectively bind to cancer cells, making a "smart contrast agent." Then, the nanocages will only be detected where cancer is present, eliminating the need for a needle biopsy.

The National Institutes of Health providing funding for the research.