"A gamma probe or a Geiger counter is used to locate the radioactive particles," Wang says, "but it gives only a rough idea of the node's location." To find the node, the surgeon must cut open the area and follow the dye visually to the sentinel lymph node.
Roughly 10 percent of the patients who undergo this procedure are found to have cancerous nodes, but 5 percent of the patients suffer a side effect, such as numbness, swelling (lymphedema) or a decreased range of motion. So the diagnostic procedure itself is not without risk.
Wang proposes instead simply to inject an optical dye that shows up so clearly in photoacoustic images that a hollow needle can be guided directly to the sentinel lymph node and a sample of tissue taken through the needle.
In the clinical trial now under way, he says, the surgeon is not taking tissue but instead deploying a tiny metal clip through the needle. The patient then undergoes lymph node dissection, the "standard of care" treatment. The dissected lymph node is X-rayed to see whether it contains the clip.
"If this technique proves accurate, we will be converting a surgical procedure into a needle biopsy possible on an outpatient basis," Wang says. "In the U.S. alone, 100,000 of these surgical biopsies are done very year, so the new procedure would spare many patients injury not to mention expense."
One exciting aspect of photoacoustic tomography is that images contain functional as well as structural information because color reflects the chemical composition and chemistry determines function.
Photoacoustic tomography, for example, can detect the oxygen saturation of hemoglobin, which is bright red when it is carrying oxygen and turns darker red when it releases it.
Almost all diseases, especially cancer and diabetes,
|Contact: Diana Lutz|
Washington University in St. Louis