Progress toward optimizing image acquisition and other information from helium 3 MRI scans is rapid. At Johannes Gutenberg University, Hans-Ulrich Kauczor, Ernst W. Otten and their colleagues have developed special scanning techniques that can detect how quickly helium is diffusing in different parts of the lung, which could increase the ability to detect disease. And because oxygen makes hyperpolarized helium lose its spin faster, comparisons between scans made in rapid succession can reveal changes in regional oxygen concentration. That in turn should reveal the local blood flow, valuable information for doctors to know. Helium 3 is not without problems, however.
Governments extract the gas from expired tritium drained out of hydrogen bombs.
Xenon 129, in contrast, is abundant and cheap, and because it diffuses less rapidly it should ultimately yield sharper images, Johnson says. Moreover, it dissolves in blood, unlike helium, and despite its classification as an inert gas it interacts with biological chemicals, notes James R. MacFall of Duke. When xenon 129 binds to chemicals in the body, its resonances are changed, points out physicist Ronald Walsworth of Harvard-Smithsonian Center for Astrophysics . That means researchers can tweak an MRI machine to visualize, or even depolarize, xenon in specific chemical environments, so that its movements and chemical associations can be tracked. Even though xenon is harder to hyperpolarize and store than helium, Grey Morgan says Nycomed intends to bring xenon imaging up to the same level of sophistication as helium imaging.