BIOPHYSICAL BASIS OF FUNCTIONAL BRAIN FMRI

拟议工作的总体目的是为了更好地理解 影响BOLD(血氧)的生理因素 电平相关)在功能磁共振成像中检测到的信号 (功能磁共振成像)。功能磁共振成像是对现有方法的一个非常重要的补充 人脑的非侵入性测绘，并在临床上得到广泛的应用 医学以及认知的基础研究。虽然有一般的 关于粗体信号如何产生达成了一致，但仍有许多功能 大胆的效果是不确定的，几个因素的影响是 未知，特别是对于所谓的事件相关功能磁共振成像。这些方面的赤字 理解限制了我们定量解释fMRI数据的能力。 此外，我们还不能很好地理解是什么限制了fmri在 实践，也不是作为更高场强磁铁可能获得的收益 变得更广泛可用。在这笔赠款的下一阶段，我们将量化 改变形状和形状的几个技术和物理因素的影响 瞬时事件相关fMRI反应的幅度。在这两种动物模型中 体感激活和人类大脑皮层，我们将量化其影响 场强、脉冲序列、刺激参数和内在血液 易感性，对与事件相关的潜伏期、幅度和持续时间 响应，并验证这些响应在紧密间隔时可能会非线性相加。我们会 也量化了几个生理和药理因素的影响 在人类受试者中，与事件相关的反应通常有所不同，包括 基础血流量改变，轻度低血糖，红细胞压积降低， 血液中一氧化碳、尼古丁、咖啡因和雌激素的水平 事件相关的粗体信号的特征。为了澄清 当前用于将粗体信号与潜在信号相关联的模型的有效性 代谢和生理变化，我们将衡量两者之间的关系 渐进性高碳酸血症大鼠模型的脑血容量和脑血流 神经刺激，最后，我们将量化和表征来源 影响功能磁共振信号的噪声。我们将测量对信号的贡献 可能由心脏、呼吸、运动和血管运动引起的变异 影响，并评估这些影响如何影响不同的fMRI信号/噪声比 技术因素的选择，包括场强、脉冲序列、回波 时间和空间分辨率。这些研究将进一步推动我们的努力 更好地理解和解释fMRI提供的数据，并提供重要的 关于如何提高通过fMRI获得的信息质量的见解 在不同的领域有不同的应用。

The overall purpose of the work proposed is to better understand the physical and physiological factors that affect the BOLD (blood oxygenation level dependent) signals detected in functional magnetic resonance imaging (fMRI). FMRI is a very important addition to the methods available for non-invasive mapping of the human brain, and is being widely used in clinical medicine as well as in basic studies of cognition. Although there is general agreement about how BOLD signals originate, there are still many features of the BOLD effect that are uncertain, and the influence of several factors is unknown, especially for so-called event-related fMRI. These deficits in understanding limit our ability to interpret fMRI data quantitatively. Furthermore, we do not understand well what limits the sensitivity of fMRI in practice, nor what gains may be possible as higher field strength magnets become more widely available. In the next phase of this grant we will quantify the effects of several technical and physical factors that modify the shape and amplitude of transient event-related fMRI responses. In both a rat model of somatosensory activation and human cortex, we will quantify the effects of field strength, pulse sequence, stimulation parameters, and intrinsic blood susceptibility, on the latency, magnitude and duration of event related responses, and verify these may add non-linearly when closely spaced. We will also quantify the effects of several physiological and pharmacological factors that commonly vary in humans subjects on the event-related responses, including the effects of altered basal flow, mild hypoglycemia, reduced hematocrit, levels of blood carbon monoxide, nicotine and caffeine, and estrogen, on the characteristics of the event-related BOLD signal. In order to clarify the validity of current models that are used to relate BOLD signals to underlying metabolic and physiological changes, we will measure the relationship between cerebral blood volume and flow in a rat model with graded hypercapnia and with neural stimulation, Finally, we will quantify and characterize the sources of noise that affect the fMRI signal. We will measure the contributions to signal variance that may arise from cardiac, respiratory, movements and vasomotor effects, and assess how these affect the fMRI signal/noise ratio, for different choices of technical factors including field strength, pulse sequence, echo time, and spatial resolution. These studies will further our efforts to understand and interpret data provided from fMRI better, and provide important insights into how to improve the quality of information obtainable by fMRI in diverse applications at different field strengths.