Advancing the Detection of Human Disease at 7 Tesla MRI

 描述（由申请人提供）：超高场（UHF）MRI（e 7特斯拉）检测人体内人类疾病的前景持续增长[4]。然而，在较高场强下遇到的几个问题阻碍了其临床可行性。这项工作解决的这些特定UHF MRI挑战是：（1）实现磁场均匀性，（2）降低生物组织中的全局/局部比吸收率（SAR）， 不依赖于受试者，以及（3）解决了由于UHF下SAR估计的电磁模型不适当而导致多次发射实验的RF安全保证不明确的问题。这些挑战限制了7 T对人类疾病的干预和检测。这项工作的重点是解决人类头部的这个问题。这些局限性极大地阻碍了临床医生使用UHF MRI对患者的神经退行性疾病和脑损伤症状进行早期检测和干预。本工作的主要目标是通过硬件和软件为UHF MRI的临床使用提供解决方案，并掌握对其局限性的认识。本项目的具体目标是：目标1：开发解剖学详细的人体头部体模，通过7 T下的模拟和实验研究评价B1+、SAR和B1+温度标测。解剖学详细的人体头部体模设计为具有8个可再填充组织隔室，这些隔室在7 T下保持电导率、介电常数和T1测量值的电磁等效生物学特性。该模型的计算模拟是为了评估B1、SAR和B1温度++映射。最后，该模型的实验研究进行了比较，模拟和在体内B1 +映射的头部模型和人体头部的模型最初建模。目标二：设计、开发和评估非线性B1+匀场MRI并行传输（PTx）优化算法，以通过7 T下的仿真和实验研究实现B1+均匀性。射频激励脉冲的一种新方法是从并行传输（PTx）工具中产生的，以使用各种非线性算法（即粒子+群）在人体的各个区域上执行B1匀场。该系统旨在通过使用软件和硬件（即GPU）的并行计算技术来减少解决限制所需的时间。目标3：通过7 T下的仿真和实验研究，评估使用并行传输和/或B1+匀场进行B1+地图和SAR地图分析的多行收发器阵列的性能。为了实现这一点，执行针对RF线圈（8通道和16通道）内的解剖学上详细的人类头部模型（收缩/扩张和组织添加/减去）的变化的计算电磁建模。从B1匀场在一个区域中获得的新型RF激励脉冲被用于在各种人头模型的整个体积上提供可接受的局部和平均SAR。为了测试其真实的应用，我们分析并比较了所有头部模型的与每个RF阵列元件相关的B1场和SAR图。最后，我们对受试者进行可接受的RF激励脉冲的体内研究，以验证Tx阵列。在该项目完成时，我们期望从目标1、2和3收集的结果的组合将进一步促进UHF MRI社区对7 T成像的理解。这项工作的进展将使7 T MR成像能够通过产生更均匀的7 T MR图像来更好地检测人类疾病。

 DESCRIPTION (provided by applicant): Ultra-high field (UHF) MRI (e 7 Tesla) promise of detecting human disease within the human body continues to grow [4]. However, there are several issues experienced at higher field strengths that hinder its clinical feasibility. These specific UHF MRI challenges addressed by this work are: (1) achieving magnetic field homogeneity, (2) reducing the global/local specific absorption rate (SAR) in biological tissue that are not subject dependent and (3) addressing concerns regarding the unclear RF safety assurance of the multi-transmit experiment due to inappropriate electromagnetic models for the estimation of the SAR at UHF. Such challenges limit the intervention and detection of human disease for 7T. This work focuses on tackling this issue for the human head. The limitations drastically hinder clinicians from using UHF MRI for early detection and intervention of neurodegenerative diseases and symptoms of brain damage in patients. The main goal of this work is to provide solutions through hardware and software to the clinical use of UHF MRI and master the understanding of its limitations. The specific aims of this project are: Aim 1: Develop an Anatomically Detailed Human Head Phantom to Evaluate B1+, SAR, and B1+ Temperature Mapping through Simulation and Experimental Studies at 7T. An anatomically detailed human head phantom is designed to have eight (8) refillable tissue compartments that hold electromagnetically equivalent biological properties of the conductivity, permittivity, and T1 measurements at 7T. The model's computational simulations are produced to evaluate B1, SAR, and B1 temperature ++ mapping. Lastly, experimental studies of the model are compared to both the simulation and in-vivo B1 + mapping of the head phantom and the human head in which the phantom was originally modeled. Aim 2: Design, Develop and Evaluate a Nonlinear B1+ Shimming MRI Parallel Transmission (PTx) Optimization Algorithm to achieve the B1+ uniformity through Simulation and Experimental Studies at 7T. A novel method of RF excitation pulses are produced from a Parallel Transmission (PTx) tool to perform B1 shimming on various regions of the human body using various nonlinear algorithms (i.e. particle + swarm). The system is designed to reduce the required time to address the limitations though parallel computing techniques using software and hardware (i.e. GPUs). Aim 3: Evaluate the Performance of Multi-Row Transceiver Arrays using Parallel Transmission and/or B1+ Shimming for B1+ maps and SAR maps analysis through Simulation and Experimental Studies at 7T. In order that this is achieved, computational electromagnetic modeling for a variation of anatomically detailed human head models (contractions/expansions and tissue addition/subtractions) within an RF coil (8- ch and 16-ch) is performed. Novel RF excitation pulses obtained from B1 shimming in a region are used to provide acceptable local and average SAR across the entire volume of various human head models. To test its real application, we analyze and compare the B1 field and SAR maps associated with each of the RF array elements for all the head models. Lastly, we perform in-vivo studies of acceptable RF excitation pulses on subjects to validate Tx array. At the completion of this project, it is our expectation that the combination of results collected from aims 1, 2, and 3 will further the UHF MRI community's understanding of 7T imaging. Progress in this proposed work will allow 7T MR imaging to be more enhanced in its ability to detect human diseases by yielding a more uniform 7T MR image.