Assessing Brain Tissue Viability after TBI: A Susceptibility Mapping Approach

 描述(申请人提供)：创伤性脑损伤(TBI)在美国是导致死亡和残疾的主要原因。原发损伤后，脑缺血/缺氧是主要的破坏性并发症。早期发现有脑缺血和缺氧风险的脑组织是预防继发性损伤的关键。核医学还表明，脑代谢异常，以脑氧代谢率(CMRO2)衡量，与脑损伤患者的慢性萎缩和不良预后有关。然而，脑血流动力学是区域性的；颅内和脑灌注压正常的患者仍可出现区域性缺氧。到目前为止，还没有非侵入性的工具来评估重症监护下局部脑组织的不可逆脑缺血/缺氧损伤。为了完整地了解大脑的血流动力学，需要同时测量动脉灌注和静脉氧合，以计算局部脑血流量(CBF)，这是一种衡量缺血的指标；脑组织氧合，一种衡量缺氧的指标；以及CMRO2，。最近，我们团队开发了一系列灌注加权成像(PWI)技术来确定动脉输入功能，并进一步比以前更准确地量化绝对CBF。我们进一步开发了一种称为磁化率加权成像和磁化率成像(SWIM)的定量磁化率图技术，以评估主要静脉的血氧含量，作为引流组织氧合的标志。与临床上基于导管的氧合监测仪不同，SWIM使用大脑的主要静脉，就像嵌入的导管一样，检测引流组织的氧合情况。更重要的是，它是非侵入性的，内在的，在整个大脑中都是丰富的。局部缺氧的风险将使其引流静脉在游泳图上具有更强的敏感性，表明低氧。利用动脉CBF和静脉氧合之间的关系，我们可以确定CMRO2，这是衡量脑组织活力的关键指标。我们建议同时使用SWIM和PWI来评估30例中重度颅脑损伤患者的脑组织活性及其预后价值，并与30名人口学上匹配的对照组进行比较。我们将首先使用血气分析仪来验证和校准所有对照组手臂静脉血氧饱和度的游泳值。然后，我们将测定脑外伤患者急性期的局部脑血流量、静脉血氧分压和全脑的CMRO2水平。我们将进一步确定急性期局部血流动力学对脑萎缩介导的脑损伤患者伤后6个月神经和神经心理转归的预测价值。该项目的成果将是一套用于评估脑外伤后脑组织生存能力的非侵入性成像技术。脑血流动力学的阐明将使医生能够识别有风险的脑组织 局部缺血/缺氧，适当治疗。该项目首次将SWIFE技术应用于脑外伤和脑血流动力学的非侵入性评估。

 DESCRIPTION (provided by applicant): Traumatic brain injury (TBI) is a leading cause of death and disability in the United States. After primary injury, cerebral ischemia/hypoxia are major devastating complications. Early detection of brain tissue at risk for cerebral ischemia and hypoxia is the key to preventing secondary injury. Nuclear medicine also suggests that abnormal brain metabolism, measured as cerebral metabolic rate of oxygen (CMRO2), is associated with TBI patients' chronic atrophy and poor outcome. However, cerebral hemodynamics is region-specific; patients with normal intracranial and cerebral perfusion pressures can still have regional hypoxia. To date, there are no non- invasive tools to assess regional brain tissue for irreversible ischemic/hypoxia damage in critical care. In order to painta complete picture of the brain's hemodynamics, one needs to measure both arterial perfusion and venous oxygenation to calculate local cerebral blood flow (CBF), a measure for ischemia; brain tissue oxygenation, a measure for hypoxia; and CMRO2,. Recently, our group has developed an array of perfusion-weighted imaging (PWI) techniques to determine the arterial input function and further quantify absolute CBF more accurately than before. We further developed a quantitative susceptibility mapping technique, known as susceptibility weighted imaging and mapping (SWIM), to estimate blood oxygenation in major veins as a marker of draining tissue oxygenation. Unlike clinical catheter-based oxygenation monitor, which is invasive and restricted to one region, SWIM uses the major veins of the brain like embedded catheters to detect draining tissue oxygenation. More importantly, it is non-invasive, intrinsic, and abundant throughout the brain. A risk of regional hypoxia will render its draining veins with enhanced susceptibility on the SWIM map, indicative of low oxygenation. Using the relationship between arterial CBF and venous oxygenation, we can determine CMRO2, a key measure of brain tissue viability. Using both SWIM and PWI, we propose assessing brain tissue viability and its prognostic value in a cohort of 30 moderate to severe TBI patients in comparison with 30 demographically matched controls. We will first use a blood gas analyzer to validate and calibrate the SWIM estimation of blood oxygenation in an arm vein in all controls. Then, we will determine regional CBF, venous oxygenation, and CMRO2 levels throughout the brain at the acute stage in TBI patients. We will further determine the predictive value of regional hemodynamics at the acute stage for TBI patients' neurological and neuropsychological outcome at 6 months after injury, mediated by brain atrophy. The deliverable of this project will be a set of non-invasive imaging techniques for assessing brain tissue viability after TBI. The elucidation of cerebral hemodynamics will allow physicians to identify the brain tissue at risk for regional ischemia/hypoxia for proper treatment. This project is novel for its first time use of SWIM in TBI and non-invasive assessment of brain hemodynamics.