Hedlund L W, Möller H E, Chen X J, Chawla M S, Cofer G P, Johnson G A
Center for In Vivo Microscopy, Box 3302 Duke University Medical Center, Durham, NC 27710, USA.
NMR Biomed. 2000 Jun;13(4):202-6. doi: 10.1002/1099-1492(200006)13:4<202::aid-nbm645>3.0.co;2-j.
Hyperpolarized helium (HP (3)He) is useful for direct MR imaging of the gas spaces of small animal lungs. Previously, breaths of 100% HP (3)He were alternated with breaths of air to maximize helium signal in the lungs and to minimize the depolarizing effects of O(2). However, for high-resolution imaging requiring many HP (3)He breaths (hundreds) and for pulmonary disease studies, a method was needed to simultaneously deliver O(2) and HP (3)He with each breath without significant loss of polarization. We modified our existing computer-controlled ventilator by adding a plastic valve, additional relays and a controller. O(2) and HP (3)He are mixed at the beginning of each breath within the body of a breathing valve, which is attached directly to the endotracheal tube. With this mixing method, we found that T(1) relaxation of HP (3)He in the guinea pig lung was about 20 s compared to 30 s with alternate air/HP (3)He breathing. Because imaging times during each breath are short (about 500 ms), the HP (3)He signal loss from O(2) contact is calculated to be less than 5%. We concluded that the advantages of mixing HP (3)He with O(2), such as shorter imaging times (reduced T(1) losses in reservoir) and improved physiologic stability, outweigh the small signal loss from the depolarizing effects of oxygen on HP (3)He.
超极化氦气（HP (3)He）可用于小动物肺部气体空间的直接磁共振成像。此前，100%的HP (3)He呼吸与空气呼吸交替进行，以最大化肺部的氦信号，并最小化氧气的去极化效应。然而，对于需要多次（数百次）HP (3)He呼吸的高分辨率成像以及肺部疾病研究，需要一种方法在每次呼吸时同时输送氧气和HP (3)He，且极化损失不显著。我们通过添加一个塑料阀、额外的继电器和一个控制器对现有的计算机控制呼吸机进行了改进。氧气和HP (3)He在直接连接到气管插管的呼吸阀体内每次呼吸开始时混合。通过这种混合方法，我们发现豚鼠肺部HP (3)He的T(1)弛豫时间约为20秒，而空气/HP (3)He交替呼吸时为30秒。由于每次呼吸期间的成像时间很短（约500毫秒），计算得出氧气接触导致的HP (3)He信号损失小于5%。我们得出结论，将HP (3)He与氧气混合的优点，如更短的成像时间（储液器中T(1)损失减少）和更好的生理稳定性，超过了氧气对HP (3)He去极化效应导致的小信号损失。
