Litz Wire Radiofrequency Receive Coils for Hyperpolarized Noble Gas MR Imaging of Rodent Lungs at 73.5 mT

Magnetic resonance imaging with hyperpolarized noble gases, He-3 or Xe-129, has become a promising approach for visualizing lung anatomy and function. The polarization of hyperpolarized noble gases does not depend on the magnetic field strength of the imaging system providing an opportunity to image at magnetic field strengths considerably lower than those typically used for clinical purposes (<0.1 T). At such low fields, image noise is dominated by electronic sources, particularly those originating from the radiofrequency coils. An improvement in image signal-to-noise ratio (SNR) is possible at low fields by reducing radiofrequency coil noise using Litz wire. In this work, radiofrequency coils of similar geometry were constructed with either conventional copper wire or three different types of Litz wire and compared in phantoms and in vivo in rat lungs using hyperpolarized He-3 and Xe-129 gases. The coils were tuned at either 0.866 MHz or 2.385 MHz, corresponding to the Larmor frequencies of Xe-129 and He-3 at 73.5 mT. The effect of wire spacing and number of windings was investigated. A SNR improvement of up to 131% was obtained with the Litz wire when compared with that of conventional copper wire. (C) 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 37B: 75-85, 2010