T2*-WEIGHTED IMAGES OF THE HUMAN BRAIN DURING HYPEROXIA

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 高氧对比度(增加氧气的吸入分数&gt；21%)产生正对比度 脑组织T2*加权图像的增强并已用于计算大脑 并对BOLD功能磁共振实验中的信号变化进行标准化。这一增长 静脉血的氧合是由于动脉的血浆中携带了过多的溶解氧。 血液，在高氧状态下含有完全饱和的血红蛋白。虽然大家都知道 分子氧是顺磁性的，浓度的增加会显著降低 T1，在以下情况下，重T2*加权图像中的影响通常被认为可以忽略不计 与大胆对比的效果相比，尤其是在低FiO2水平下。我们在我们的 在3T的全脑EPI研究中使用高氧对比的初步研究，尽管 阳性对比度增强主宰了大部分区域，大脑的下部区域显示 强T2*加权图像中的显著负对比度增强，即使在低信号下也是如此 氧气浓度(FiO2&lt；0.6)。这些显示负对比度的区域具有相对 动脉脑血容量的高比例，因为它们包含为大脑供血的大动脉 大脑。我们认为，这种负对比至少部分是由于T2*in的缩短 动脉血中溶解在血浆中的顺磁分子氧过多。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Hyperoxic contrast (increasing the inspired fraction of oxygen >21%) produces positive contrast enhancement in T2*-weighted images in brain tissue and has been used to calculate cerebral blood volume and to standardize signal changes in BOLD fMRI experiments. The increase in venous blood oxygenation is due to excess dissolved oxygen carried in the plasma of arterial blood, which during hyperoxia contains completely saturated hemoglobin. While it is known that molecular oxygen is paramagnetic and that increased concentrations significantly reduce T1, the effect in heavily T2*-weighted images is generally considered to be negligible when compared to the effects of BOLD contrast, especially at low FiO2 levels. We have found in our preliminary studies using hyperoxic contrast in a whole brain EPI study at 3T that, although positive contrast enhancement dominates most regions, the inferior regions of the brain show significant negative contrast enhancement in strongly T2*-weighted images, even at low oxygen concentration (FiO2<0.6). These regions showing negative contrast have a relatively high fraction of arterial cerebral blood volume, since they contain large arteries that feed the brain. We believe that this negative contrast is at least in part due to the shortening of T2* in arterial blood due excess paramagnetic molecular oxygen dissolved in the plasma.