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Paul Villard, a French chemist and physicist, discovered gamma rays in 1900. Like most great discoveries, it happened while studying something else—in Villard’s case, radiation emitted by radium. He was leading a beam of radiation out of a shielded container of radium salts onto a photographic plate, which was shielded by a thin layer of lead. The lead stopped alpha rays, but there were two others. One was beta, one unknown. That was the gamma ray.
These waves are generated by radioactive atoms and in nuclear explosions. Gamma rays have a number of uses, but one in particular is the ability to kill living cells, which physicians take advantage of to attack certain cancers. They have the smallest wavelengths and the most energy of any wave in the electromagnetic spectrum.
Gamma rays also are being used in other medical research. An interesting project at the University of Arizona (Tucson) uses FastSPECT III, a dedicated SPECT (single photon emission computed tomography) imager designed specifically for imaging and studying neurological pathologies—including Alzheimer’s and Parkinson’s disease—in rodent brains. It incorporates 20 Point Grey Research (Richmond, B.C. Canada) Dragonfly Express cameras that stream images to Firewire 1394b framegrabbers at up to 800 Mbps or 200 frames per second at full resolution (640 x 480).
The Firewire bus is daisy chained across computers to synchronize cameras for timing purposes in dynamic imaging studies. Each computer has an Intel Core i7 quad-core processor and two Nvidia GeForce GTX 295 cards. There are two GPUs per GTX 295 card providing a total of 960 stream processors per computer. Frame parsing with multiple detectors at 200 fps is readily achieved by parallel computing using Nvidia CUDA and OpenMP APIs. Operation of the detectors at this rate corresponds to processing 4,000 fps for the entire system or 1.23 Gpix/second. Assuming uniform illumination, more than 2:5 x 104 counts per second per detector or greater than 5 x 105 for the entire system can be processed.
The researchers use what they call BazookaSPECT detector technology (so-called because of its original appearance to a Bazooka due to a long imaging chain). “It’s a whole different type of gamma-ray detector than is used in clinics,” explains Brian Miller, a PhD candidate at the University of Arizona Center for Gamma-Ray Imaging. “This differs in that it uses CCDs and has resolution orders of magnitude higher than in clinics. These are 100 microns; in the clinic, it’s 3 or 4 millimeters.”