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Miller says this new generation of detectors has stirred excitement in the gamma-ray imaging community, particularly in the context of small-animal SPECT. These detectors offer sub-100 μm resolutions, an order-of-magnitude higher than conventional scintillation-based gamma cameras. His responsibility includes prototype detector design and development, acquisition and processing software development, and imaging aperture design and fabrication.
“It’s the first of its kind,” he explains. “What’s novel is the image intensifier. It amplifies low light levels. At the end, it gives you [better] resolution.
“We take a radioactive atom, attach it to a protein or drug and inject it. It gets trapped in the body and is a non-invasive way of seeing. In the case of cancer, it goes to the tumor. The tumor processes the cell and the cell emits gamma rays. They’re like x-rays that come from the body. We can see if the tumor absorbs it. We have to be able to form images—radioactive forms—so we use pinholes to form the image. We block all the gamma rays except through the pinhole. Gamma rays are basically high-energy lights.”
SPECT imaging needs an array of pinholes as small as 200 microns, which are made of platinum. The holder needs to be made of a very dense metal, like lead, to block all the pinholes except those needed for a particular experiment. The Arizona lab uses tungsten and an epoxy to reach the density of lead. The custom molds are created with a 3D printer. The process allows multiple parts to be fabricated from a single mold.
In addition to small-animal SPECT imaging with the BazookaSPECT detector, Miller and his colleagues have investigated methods and applications that take advantage of the detector’s superb intrinsic resolution. This had led to development of a gamma-ray microscope based on micro-coded apertures. In pinhole imaging, ultimately the limiting factor in system resolution is the pinhole diameter. A smaller pinhole will result in higher resolution but at the expense of collection efficiency. It has been shown that near-field coded aperture imaging, with applications in small-animal SPECT, can be used to provide high-spatial resolution imaging with high collection efficiency. The team implemented near-field coded aperture techniques, scaled to utilize the resolution of BazookaSPECT, and demonstrated planar reconstructions having resolutions of 30μm; an unprecedented resolution for gamma-ray imaging. This experiment was achieved with the use of a platinum disk having 480 25 μm diameter pinholes.