Improved MRI by correcting static and dynamic magnetic field inhomogeneity

高质量的磁共振成像（MRI）需要高度均匀的磁场分布，其变化不超过百万分之几。与均匀性的不受控制的偏差被称为“非共振”，并导致有害的图像伪影。非共振效应可以是时不变的，例如由空气-脑组织界面处的磁化率失配产生的那些，或者是动态的，例如由大量患者运动和呼吸引起的磁场。虽然已经存在减少静态非共振伪影的方法，但是尚未实现非共振场分布的准确表征和高度局部化的不均匀磁场（特别是动态磁场）的鲁棒减少。 在这个发现补助金，我建议减轻人类大脑MRI中的非共振效应的挑战。我将特别关注颞叶和眶额皮层：这两个区域在神经系统、精神疾病和神经科学研究中非常重要，但却广泛受到非共振伪影的影响。提出了三个目标： 目标1：测量和减少人脑中的静态和动态非共振效应 除了常见的静态主磁场（B 0）不均匀性测量外，还将开发专用磁场探头，以表征由体运动和呼吸引起的动态B 0不均匀性分布的形状和强度-长时间MRI扫描中动态B 0不均匀性的两个主要来源。这些场干扰测量将用于通过后处理减少图像失真并提高信号稳定性。 目标2：使用局部匀场线圈阵列减轻静态和动态非共振效应 将开发两个多线圈（MC）匀场阵列，以在患者的颞叶和眶额皮质中提供稳健的非共振抑制。每个MC匀场阵列将具有几组线圈，以考虑群体中非共振分布的可变性。还将集成场探头，以调整匀场电流，抑制动态非共振效应，从而提供空间上更加均匀且时间上更加稳定的磁场。 目的3：通过语言处理和决策的功能性MRI（fMRI）验证该技术 作为示例性验证，MC垫片阵列和场探头将用于在执行语言和决策任务时减轻快速fMRI（每秒10个脑容量，5 mm各向同性分辨率）中的非共振效应。我们的方法有望揭示更大的激活脑区，更强的功能磁共振成像信号，以及更显着的差异，在颞叶和眶额皮质的实验条件下区分功能磁共振成像时间。 意义 在完成这项工作后，将开发新的MRI技术，为临床应用提供强大而有效的非共振伪影抑制。

High-quality magnetic resonance imaging (MRI) requires a highly homogeneous magnetic field distribution that varies by no more than a few parts-per-million. The un-controlled deviation from the homogeneity is termed “off-resonance” and causes detrimental image artifacts. Off-resonance effects can be time-invariant, such as those produced by the magnetic susceptibility mismatch at air-brain tissue interfaces, or dynamic, such as the magnetic fields caused by bulk patient motion and breathing. While there have been methods of reducing static off-resonance artifacts, accurate characterization of the off-resonance field distribution and robust reduction of highly localized inhomogeneous magnetic fields, particularly dynamic ones, have yet to be achieved. In this Discovery grant, I propose to mitigate the challenge of off-resonance effects in MRI of the human brain. I will focus specifically on the temporal lobes and the orbitofrontal cortex: two regions that are important in neurological as well as psychiatric disorders and neuroscience studies, yet suffer extensively from off-resonance artifacts. Three aims are proposed: Aim 1: Measure and reduce the static and dynamic off-resonance effects in the human brain In addition to the common static main field (B0) inhomogeneity measurement, dedicate magnetic field probes will be developed to characterize the shapes and strengths of dynamic B0 inhomogeneity distributions caused by bulk motion and breathing - two major sources of dynamic B0 inhomogeneity in lengthy MRI scans. These field disturbance measurements will be used to reduce image distortion and improve signal stability by post-processing. Aim 2: Mitigate static and dynamic off-resonance effects using localized shim coil arrays Two multi-coil (MC) shim arrays will be developed to offer robust off-resonance suppression in the temporal lobes and orbitofrontal cortex across patients. Each MC shim array will have a few sets of coils to account for the variability of the off-resonance distributions in the population. Field probes will also be integrated to adjust shim currents to suppress dynamic off-resonance effects to offer a much more spatially homogeneous and temporally stable magnetic field. Aim 3: Validation of the technology by functional MRI (fMRI) of language processing and decision making As an exemplary validation, the MC shim arrays and field probes will be used to mitigate off-resonance effects in fast fMRI (10 brain volumes per second with 5 mm isotropic resolution) when performing language and decision-making tasks. Our approach is expected to reveal larger activated brain areas, stronger fMRI signals, and more significant differences in fMRI timing to distinguish among experimental conditions at temporal lobes and orbitofrontal cortices. Significance On completion of this work, novel MRI technology will have been developed to provide robust and effective suppression of off-resonance artifacts for clinical applications.