Low-field MRI Of human lungs with hyperpolarized gas

肺的健康功能依赖于充分通畅的通气、均匀的血液灌注和有效的气体交换。不幸的是，高分辨率的肺功能空间量化被证明是困难的。超极化气体磁共振成像在肺通气和肺结构成像方面已被证明具有实用价值。最近，研究人员利用气体磁化弛豫速率（1/T1）对氧的依赖性来提取局部肺泡氧浓度。此外，在屏气期间，这种松弛率被观察到会降低，这表明血液的吸氧量。用这种技术绘制区域摄氧量图是可行的。不幸的是，低信噪比限制了他们技术的精度。由于肺部的磁不均匀性限制了横向极化时间T2到10ms，他们必须最小化每张图像中不可再生磁化损失的量。我们建议利用在低成像场（BO）下超长的横向偏振时间（T2约1秒）来提高肺部摄氧量测量的灵敏度。我们描述了一个成像序列，类似于驱动平衡傅立叶变换（DEFT），它利用全磁化进行测量，但在每个图像后将其恢复到纵向。我们估计这个序列在信号强度上提供了一个数量级的改进。新罕布什尔大学的核物理小组是生产用于核科学和核磁共振成像的超极化气体技术的先驱。我们提出了一个实用的高容量超极化氦源的新想法。我们进一步建议改进现有的内部低场成像仪，以实现体噪声在噪声系数中占主导地位。利用我们的低场成像仪，气体极化能力，我们打算绘制肺的区域摄氧量分布。我们的成像仪的开放几何结构也允许研究身体方向对肺结构、通气和摄氧量的重力影响。

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.