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:: By: Lydialyle Gibson

:: Photography Courtesy the University of Chicago Electronics Design Group

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Investigations ::

Next Generation

Flight time

Physicists aren’t the only ones interested in determining the location and velocity of subatomic particles. That same information allows physicians, for instance, to make earlier and more precise cancer diagnoses. “The electronics needs in medical imaging,” says Chicago physicist Henry Frisch, “look very closely related to the needs we have in high-energy physics.”  

Specifically, Frisch, with Chicago radiologist Chin-Tu Chen, PhD’86, and Argonne physicist Karen Byrum, is working to build microchips—like the one below, which measures 850 microns across—that would improve the speed and accuracy of “time-of-flight” PET scans, a technique offering more precise images of vital functions such as glucose metabolism, blood flow, and oxygen use. 

Conventional PET scans work by detecting the energy released after a short-lived radioactive isotope is injected into the body and absorbed into the organs. The isotope decays, giving off positrons that collide with neighboring electrons, a process that generates millions of photons—including numerous spurious signals that require intense computational analysis to filter out before the data is converted into images.
Time-of-flight PET scans, meanwhile, not only detect photons as they travel in opposite directions, but also measure the time difference between them, a calculation that helps construct clearer pictures and weed out false signals.

Commercial time-of-flight PET scanners went on the market last December, and their accuracy is still being improved. While they offer a resolution of 750 picoseconds, it takes a photon only 100 picoseconds to travel an inch. High-energy physics typically measures particle velocities with ten-picosecond accuracy, but, Chen says, raising the accuracy of time-of-flight scans to within just 30 picoseconds would mean detecting a tumor when it’s a quarter of an inch in diameter rather than half an inch, eight times larger by volume. That accuracy would, he says, “essentially eliminate the need for complex and costly image reconstruction.” For some patients, it would also mean the difference between life and death.