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Precision Slicing of Bismuth Germanate Crystal Material Helps Fight the War Against Cancer

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, part of McGill University, has developed an innovative approach in the ongoing battle against breast cancer. The method involves positron emission mammography (PEM) 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.


Figure 1 : 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.

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 an ULTRASLICE saw from ULTRA TEC Mfg. Inc., cutting with three 0.25-mm blades ‘ganged’ diamond blades.

BGO scintillation material is extremely delicate, and requires care in precision slicing, particularly when using multiple diamond blades. The ULTRASLICE machine allows success in this application by allowing control of all parameters that optimize the slicing operation. The advanced features of the ULTRASLICE saw allow for multiple-blade cutting and alleviate edge chipping and damage to the crystalline material, which often feature with other cutting techniques.


Figure 2. The BGO Crystal Arrays. Each slice across the crystal is 2mm wide. Three blades are ganged together to optimize the process.

Unique Detectors

The four sliced 36 x 36 x 20-mm crystal blocks are then optically coupled to a 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 patient’s 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.

 

Contacts: C.J. Thompson, McGill University, Montreal; (514) 398-8505, for his work funded by the National Cancer Institute of Canada’s "Canadian Breast Cancer Research Initiative"; Tim Hazeldine,  ULTRA TEC 

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