Real-time Production and in vivo Imaging of Hyperpolarized 129Xe
B. Driehuys1, G. P. Cofer1, J. Pollaro1
1
Center for in vivo Microscopy, Duke University, Durham, NC, United States
Introduction: MRI using hyperpolarized 3He and 129Xe is challenging due to the non-renewable magnetization and single gas batches generally available for imaging. However, the polarization physics of 129Xe, lends itself to real-time and continuous production which could fundamentally alter the way hyperpolarized gas MRI is implemented. Continuous 129Xe polarization has been demonstrated for in vitro NMR spectroscopy applications [1]. However, in vivo imaging requires gas pressures to be stepped down to physiologic levels, and 129Xe to be polarized faster. Here, we demonstrate the capability to perform in vivo imaging using hyperpolarized 129Xe flowing directly and continuously from the polarizer to the subject. Methods: A prototype commercial polarizer (IGI.9800.Xe, MITI, Durham, NC) was modified to eliminate cryogenic accumulation, stepping down the 5atm Xe/N2/He (1% Xe) mixture flowing out of the optical cell using an all Teflon regulator (Partek, Tuscon, AZ). This gas stream took the place V V normally occupied by the hyperpolarized gas reservoir in the ventilator [2] where it was mixed with O2 and delivered V continuously to the animal. Five Fischer 344 rats (Charles River, V V Raleigh, NC) weighing 170-200g were used for imaging. Three of the rats had unilateral pulmonary fibrosis in the left (n=2) or right (n=1) lung. Rats were anesthetized with ketamine and diazepam, perorally intubated and ventilated at 60 bmp with 2 O2 ml tidal volume. Animals were imaged in a 23.639MHz linear bird cage coil (L=8cm, φ=7cm) in a 2.0T horizontal 15cm clear bore magnet (Oxford Instruments, Oxford, UK) with shielded N2 gradients (18G/cm), controlled by a GE Excite console (GE Healthcare, Milwaukee, WI). Animals were also scanned using fully concentrated hyperpolarized 129Xe (0.5 liter, P=8%) mixed Figure 1 Continuous production and animal delivery of hyperpolarized 129Xe 75/25% with O2. All studies used 83% enriched 129Xe (Spectra Gases, Alpha, NJ). Standard images were acquired at 128×128 matrix, 4cm FOV, no slice, 8kHz bandwidth, 400 radial projections, 10 views per breath, TR=20ms and a variable flip angle. Direct flow images used a 64×64 matrix, 7cm FOV, no slice, 4kHz bandwidth, 200 radial projections, 4 views per breath, TR=50ms, and variable flip angle.

下一页