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Xenon-Based Technique Could Give Great Boost to MRI Sensitivity
November 3, 2009
4 Min Read
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A Hyper-SAGE image of xenon dissolved in water flowing through a phantom lung shows the intensity of an MRI signal 23 seconds into the process. The warm colors represent a stronger signal than the cool colors. (Image courtesy of Xin Zhou.)
A team of researchers at the Lawrence Berkeley National Laboratory (Berkeley, CA) are working to improve the resolution of magnetic resonance imaging (MRI) systems. Known as hyperpolarized xenon signal amplification by gas extraction (Hyper-SAGE), the scientists' new technique uses xenon gas that has been treated with laser light to hyperpolarize the atomic nuclei, aligning the spins of the majority of its atomic nuclei. The researchers think that by dramatically boosting MRI sensitivity, the technology could enable doctors to detect ultralow concentrations of diseases such as lung cancer.Led by MRI technology specialist Alexander Pines, a chemist at the Berkeley Lab and the University of California, Berkeley, the team has high hopes for its innovative approach. "By detecting the MRI signal of dissolved hyperpolarized xenon after the xenon has been extracted back into the gas phase, we can boost the signal's strength up to 10,000 times," Pines explains. "It is absolutely amazing because we're looking at pure gas and can reconstruct the whole image of our target. With this degree of sensitivity, Hyper-SAGE becomes a highly promising tool for in vivo diagnostics and molecular imaging."
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Although widely used for medical imaging applications, MRI has been limited by sensitivity issues, especially in such areas as biomedical sampling. For the past three decades, Pines has led efforts to enhance the sensitivity of MRI and nuclear magnetic resonance (NMR) spectroscopy. Hyper-SAGE represents a significant advance for both technologies, remarks Xin Zhou, a member of Pines's research group.The team has developed a variety of ways to increase the sensitivity of MRI technology and expand its applicability. Previous work has shown that xenon, an inert gas whose nuclei naturally feature a tiny degree of spin polarization, can be hyperpolarized with laser light to produce a population of xenon atoms in which nearly five out of every 10 nuclei--instead of one out of every 100,000--produce an MRI signal. The team has also shown that xenon can be incorporated into a biosensor and linked to specific proteins or other biological molecules to produce spatial images of a chosen molecular or cellular target."Xenon gas has an intrinsically long relaxation time, greater than 45 minutes, which means the signal lasts long enough for us to collect all the encoded information, which in turn can enable us to detect specific targets, such as cancer-related proteins, at micromolar or parts per million concentrations," Zhou says. "Also, Hyper-SAGE utilizes remote detection, meaning the signal encoding and detection processes are physically separated and carried out independently. This is a plus for imaging the lung, for example, where the signal of interest would occupy only a small portion of the traditional MRI signal receiver."In a paper published in Proceedings of the National Academy of Sciences titled "Hyperpolarized Xenon NMR and MRI Signal Amplification by Gas Extraction," Zhou, Pines, and coauthor Dominic Grazianitheir describe the successful testing of the Hyper-SAGE technique on a pair of membranes that mimicked the function of the lungs. Hyperpolarized xenon was dissolved in solution in one membrane to mimic inhalation and was then extracted as a gas for detection from the other membrane to represent exhalation."In a clinical setting, a patient would inhale the hyperpolarized xenon gas which would be dissolved in the blood and allowed to flow into the body and brain," Zhou says. "The exhaled xenon gas would then be collected and its MRI signal would be detected. Used in combination with a target-specific xenon biomolecular sensor, we should be able to study the gas-exchange in the lung and detect cancerous cells at their earliest stage of development."More information on the research is available from the Lawrence Berkeley National Laboratory.You May Also Like
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