Low-field MRI Of human lungs with hyperpolarized gas

University Of New Hampshire, Durham NH

Investigators

Abstract

Healthy function of lungs relies on full and unobstructed ventilation, distributed blood perfusion, and efficient gas exchange. High-resolution spatial quantification of lung function has unfortunately proven difficult. Hyperpolarized gas magnetic resonance imaging has demonstrated utility in imaging lung ventilation and structure. More recently, the dependence of the gas magnetization relaxation rate (1/T1) on oxygen was exploited to extract local alveolar oxygen concentration. Furthermore, this relaxation rate was observed to decrease during a breath hold, revealing oxygen uptake by the blood. Regional maps of oxygen uptake are feasible with this technique. Unfortunately low signal-to-noise limits the precision of their technique. Because magnetic inhomogeneities in lungs limit transverse polarization time T2 to 10 ms, they must minimize the amount of non-renewable magnetization lost in each image. We propose to improve the sensitivity of measurements of oxygen uptake in lungs by exploiting the extraordinarily long transverse polarization time (T2 approximately 1 second) available at low imaging field (BO). We describe an imaging sequence, similar to driven Equilibrium Fourier transform (DEFT), which utilizes the full magnetization for measurements, but restores it to the longitudinal direction after each image. We estimate this sequence provides an order of magnitude improvement in signal strength. The Nuclear Physics Group at the University of New Hampshire is a pioneer in the technology for production of hyperpolarized gas for nuclear science and MRI. We propose to implement new ideas for a practical high-volume source for hyperpolarized helium. We further propose to improve our existing in-house low-field imager to achieve body-noise in dominance in the noise figure. With our low-field imager, gas polarization capability, we intend to map the regional oxygen uptake distribution in lungs. The open geometry of our imager also allows studies of gravitational effects of body orientation on lung structure, ventilation, and oxygen uptake.