MRI of weak periodic currents using balanced Steady State Free Precession

使用平衡稳态自由进动的弱周期电流 MRI

• 批准号: 7532154
• 负责人: GIEDRIUS T BURACAS
• 金额: $ 23.18万
• 依托单位: UNIVERSITY OF CALIFORNIA, SAN DIEGO
• 依托单位国家: 美国
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-07-01 至 2010-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7532154
• 关键词: Achievement; Acoustic Stimulation; Address; Affect; Animals; Arteriogram; Blood Vessels; Brain; Brain imaging; Caffeine; Carbon Dioxide; Cardiac; Cerebrovascular Circulation; Cerebrum; Characteristics; Computer Simulation; Condition; Coupling; Data; Detection; Electromagnetics; Equilibrium; Financial compensation; Frequencies; Goals; Head; Heating; Human; Image; Magnetic Resonance Imaging; Magnetoencephalography; Measures; Metabolic; Methods; Modality; Motion; Neuromodulator; Neurons; Noise; Pattern; Phase; Physiologic pulse; Physiological; Problem Solving; Protocols documentation; Public Health; Pulse taking; Radio; Rattus; Reporting; Research; Resolution; Respiration; Scanning; Signal Transduction; Source; Spin Labels; Standards of Weights and Measures; Stimulus; Techniques; Testing; Time; Variant; Vibrissae; Visual; base; blood oxygen level dependent; blood oxygenation level dependent response; in vivo; magnetic field; relating to nervous system; research study; respiratory; response; theories

DESCRIPTION (provided by applicant): Existing functional brain MR imaging methods such as blood oxygenation level dependent (BOLD) imaging are based on vascular and metabolic responses to variations in underlying neuronal activity and thus reflect the latter only indirectly. It has been proposed (e.g. Bodurka & Bandettini, 2002) that magnetic field perturbations caused by neuronal currents in the brain in principle ought to be detectable by means of MRI. Several research groups have demonstrated the feasibility of this idea in theory, electric current phantoms and in vivo. However, relatively low signal-to-noise ratio achieved to date renders existing methods impractical. Balanced Steady State Free Precession (bSSFP, also known as TrueFISP, FIESTA) pulse sequence is unique in that it can afford the highest known SNR per unit time and thus application of bSSFP for functional neural current imaging can potentially solve the problem of low SNR. Recent studies suggest that certain SSFP sequences might be exquisitely sensitive to minute periodic perturbations of the spin phase. Thus, periodic currents locked to RF excitation pulse result in an alternating balanced steady state (ABSS) that can effectively amplify the phase offset induced by currents. Our theoretical calculations and the data acquired with bSSFP at 3T using a current phantom indicates SNR of the signal induced by periodic currents that is substantially superior to that achieved previously using standard gradient and spin echo imaging (Buracas et al., 2007). We propose to develop optimized alternating steady-state imaging protocols for imaging of periodic electric currents. First, we will optimize, analytically, in computer simulations, and current phantom experiments the sensitivity of the ABSS method to weak periodic currents and address the impact of various sources of noise on the ABSS signal. Next, we will apply this method to imaging neuronal currents in vivo (using rat whisker stimulation and human audiovisual stimulation paradigms). We will implement noise compensation for magnetic field fluctuation due to respiration and scanner drift and motion compensation. In conclusion, the current proposal will address the possibility to measure electromagnetic correlates of cerebral neuronal activity by means of ABSS and will address critical sources of noise. Accomplishment of the proposed aims has a potential of introducing a new imaging modality for functional brain imaging - high resolution MRI-based magnetoencephalography. PUBLIC HEALTH RELEVANCE: Established functional brain MR imaging methods are susceptible to factors influencing neurovascular coupling. It has been recently proposed and demonstrated that MRI can be used for imaging neuronal currents directly, but existing methods are impractical due to their low SNR. The proposed research will develop ultra- sensitive MRI methods for imaging neuronal currents using balanced Steady State Free Precession pulse sequences that possess best known SNR efficiency.

描述（由申请人提供）：现有的功能性脑磁共振成像方法，如血氧水平依赖（BOLD）成像，是基于血管和代谢对潜在神经元活动变化的反应，因此只能间接反映后者。有人提出（如Bodurka & Bandettini， 2002），原则上，大脑中由神经元电流引起的磁场扰动应该可以通过MRI检测到。几个研究小组已经在理论上、电流幻影和体内证明了这一想法的可行性。然而，迄今为止实现的相对较低的信噪比使得现有方法不切实际。平衡稳态自由进动（bSSFP，也称为TrueFISP， FIESTA）脉冲序列的独特之处在于它可以提供单位时间内已知的最高信噪比，因此将bSSFP应用于功能神经电流成像可以潜在地解决低信噪比问题。最近的研究表明，某些SSFP序列可能对自旋相的微小周期性扰动非常敏感。因此，锁定在射频激励脉冲上的周期性电流产生交流平衡稳态（ABSS），可以有效地放大电流引起的相位偏移。我们的理论计算和bSSFP在3T下使用电流幻象获得的数据表明，周期电流诱导的信号信噪比大大优于先前使用标准梯度和自旋回波成像获得的信号（Buracas等，2007）。我们建议为周期性电流的成像开发优化的交变稳态成像方案。首先，我们将在计算机模拟和电流模拟实验中分析优化ABSS方法对弱周期电流的灵敏度，并解决各种噪声源对ABSS信号的影响。接下来，我们将把这种方法应用于体内神经元电流成像（使用大鼠须刺激和人类视听刺激范例）。我们将对呼吸和扫描仪漂移引起的磁场波动进行噪声补偿和运动补偿。总之，目前的提议将解决通过ABSS测量大脑神经元活动的电磁相关性的可能性，并将解决关键的噪声源。实现所提出的目标有可能为功能性脑成像引入一种新的成像方式-高分辨率核磁共振脑磁图。公共卫生相关性：已建立的功能性脑磁共振成像方法易受影响神经血管耦合的因素影响。最近已经提出并证明MRI可以直接用于神经元电流成像，但现有方法由于其低信噪比而不切实际。提出的研究将开发超灵敏的MRI方法成像神经元电流使用平衡稳态自由进动脉冲序列，具有最知名的信噪比效率。