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Photonic Technique Helps Fight the War Against Cancer

Photonics Spectra
Mar 1998
Ruth A. Mendonsa

Photonic devices and techniques such as lasers and high-tech imaging have become well-known weapons in the war against cancer, heart disease and numerous other human afflictions. A team of scientists at Montreal Neurological Institute at McGill University in Quebec has developed an approach in the ongoing battle against breast cancer that involves positron emission mammography and a radioactive form of glucose as an imaging agent. The team designed an imaging system that, unlike x-ray mammography, detects a tumor's increased metabolism rather than its density.

The high-resolution system provided images of a subject with ductal carcinoma (top) and of healthy breast tissue (bottom). The red arrow points to the tumor. Courtesy of McGill University.

The imaging technique is based on detecting the overconsumption of the glucose agent by a malignant lesion compared with a benign lesion. The system's high resolution comes from its extraordinary detectors, which consist of two bismuth germanate (BGO) crystal blocks into which a series of slits have been cut in the top and rear faces. The cuts are made in a grid pattern using a saw from Ultra Tec Mfg. Inc. Dubbed the Ultraslice 6000, the saw has three diamond-impregnated 0.25-mm blades from South Bay Technologies.

Squarely unique

The four 36 × 36 × 20-mm crystal blocks are then optically coupled to a Hamamatsu R3941 position-sensitive photomultiplier. These specially designed photomultipliers are unique because they are square; squareness is critical to this application because of the need to get close to the chest wall. The gamma ray detectors are placed on either side of the patient's breast to measure the energy and location of the gamma rays' interaction with the pixelated BGO blocks. The detectors fit into a conventional mammography unit.

Doctors at Royal Victoria Hospital in Montreal are testing the imaging system, which promises to eliminate the expensive, trauma-inducing biopsies that typically follow suspicious results from x-ray mammography. X-ray mammography techniques may fail to detect 5 to 15 percent of primary breast cancers. In addition, from 53 to 91 percent of biopsies are performed on benign tumors.

With an estimated annual mortality rate of 45,000, breast cancer is undeniably a fearsome foe. The greatest weapon in the arsenal against the disease is early detection, and this new system could catch a malignancy before it has a chance to spread.

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