A couple of days ago on medtechinsider, we covered research on ultrasound technology at the Lawrence Berkeley National Laboratory that potentially could lead to vastly improved resolution of ultrasound scanners. A different group of researchers at the Berkeley lab have announced similar efforts to improve the resolution of magnetic resonance imaging (MRI) systems. The scientists are exploring a new technique known as “Hyper-SAGE” that could detect ultralow concentrations of clincal targets such as lung cancer. Leading the efforts is MRI technology specialist Alexander Pines, a chemist who holds joint appointments with the Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California, Berkeley. The central concept behind the technique is the use of xenon gas that has been treated with laser light to “hyperpolarise” the atomic nuclei, aligning the spins of the majority of its atomic nuclei.
“By detecting the MRI signal of dissolved hyperpolarised 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 says. “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.”
Though MRI is a popular image modality, its application to biomedical samples, for instance, has been limited by sensitivity issues. For the past three decades, Pines has led efforts to enhance the sensitivity of MRI and nuclear magnetic resonance (NMR) spectroscopy. Hyper-SAGE, the latest development, is a significant new advance for both technologies, says Xin Zhou, a member of Pines’ research group.
A press release from the Berkeley Lab summarises the groups research:
Pines and his research group have developed numerous ways of increasing the sensitivity of MRI technology and expanding its applicability. Previous work showed 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. Pines and his group also showed 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.
The new technique, Hyper-SAGE, for “hyperpolarized xenon signal amplification by gas extraction,” offers other major advantages over conventional MRI/NMR techniques in addition to a signal that is up to 10,000 times stronger than previous signals, according to Zhou.
“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,” he 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 their PNAS paper, Zhou, Graziani and Pines describe the successful testing of the Hyper-SAGE technique on a pair of membranes that mimicked the function of the lungs. Hyper-polarized 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.
Explains Zhou, “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. 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 Berkeley Lab.Brian Buntz