Medical Imaging With Polarized ³He

There are several other applications of polarized ³He in fundamental and applied physics. One of the most recent applications is polarized gas magnetic resonance imaging of human lungs. Whereas conventional MRI relies on the small thermal polarization of water in a strong magnetic field, polarized gas MRI uses the much higher polarizations that are produced by optical pumping. The human lung image above was obtained in collaboration with the Radiology Department at the University of Pennsylvania. To obtain this image, the subject inhaled one standard liter of polarized ³He (polarized using the Spin Exchange method) before the MRI was taken.

Another lung image was obtained using ³He gas polarized at low pressure using the Metastability Exchange optical pumping method, compressed using an apparatus at NIST, and transported to U-Penn for the MRI experiment. A 270 cm³ cell was filled to 103 kPa (1.03 bar) at 77 K in 3 hours, yielding 400 kPa (4.0 bar) at 300 K, and thus 1.1 liter at atmospheric pressure. The 15 hour lifetime of the Corning 7056 cell allowed 75 % of the initial polarization of 15 % to be available for the image, 4.5 hours after the completion of the fill. The cell was transported in an end-compensated solenoid [field = 1.3 mT (13 G) when operated from car battery] with a cylindrical magnetic shield.

Inquiries or comments: david.gilliam@nist.gov
Online: November 1998