Improved MRI by correcting static and dynamic magnetic field inhomogeneity

通过校正静态和动态磁场不均匀性改进 MRI

• 批准号: RGPIN-2020-05927
• 负责人: Lin, FaHsuan
• 金额: $ 2.48万
• 依托单位: University of Toronto
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=760724
• 关键词: Improved; MRI; correcting; static; dynamic

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.

高质量的磁共振成像（MRI）需要高度均匀的磁场分布，其变化不超过几百万。与均匀性的非控制偏差称为“异位”，并导致有害的图像伪像。异位效应可能是时间流逝的，例如在空气脑组织接口处磁敏感性不匹配而产生的效果，例如由散装患者运动和呼吸引起的磁场。尽管已经有减少静电非谐波伪像的方法，但尚未实现高度定位的不均匀磁场，尤其是动态的磁场的准确表征以及可靠的高度局部不均匀磁场的稳健降低。在这项发现赠款中，我建议减轻人脑MRI中异振效应的挑战。我将专门关注颞叶和眶额皮质：在神经系统和精神疾病和神经科学研究中很重要的两个区域，却因非谐和文物而遭受了广泛的影响。提出了三个目标：目标1：测量和减少人脑中静态和动态的非谐振效应，除了常见的静态主场（B0）不均匀性测量，还将开发专用磁场探针以表征形状和强度由大量运动和呼吸引起的动态B0不均匀性分布 - 冗长的MRI扫描中动态B0不均匀性的两个主要来源。这些场扰动测量将用于减少图像失真并通过后处理提高信号稳定性。 AIM 2：使用局部垫片线圈阵列减轻静态和动态的非谐振效应，将开发两个多型线圈（MC）垫片阵列，以在颞叶和眶额皮质中提供强大的异位抑制。每个MC Shim阵列都会有几套线圈，以说明人口中异位分布的可变性。还将集成现场探头以调节垫片电流以抑制动态的异位效应，以提供更加均匀且暂时稳定的磁场。 目标3：通过功能性MRI（fMRI）对技术处理和决策做出做出的验证，作为模范验证，MC SHIM阵列和现场探测器将用于减轻快速fMRI中的异位效应（每秒10次大脑量执行语言和决策任务时5毫米各向同性分辨率）。我们的方法有望揭示出更大的激活大脑区域，更强的fMRI信号以及fMRI时机的更大差异，以区分颞叶和轨道额叶皮层的实验条件之间。完成这项工作的意义，将开发出新颖的MRI技术，以便为临床应用提供强大而有效的抑制异位伪像。