MRI Engineering Core

MRI 工程核心

• 批准号: 10916074
• 负责人: Alan Koretsky
• 金额: $ 303.83万
• 依托单位: NATIONAL INSTITUTE OF NEUROLOGICAL DISORDERS AND STROKE
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/10916074
• 关键词: Address; Affect; Amplifiers; Animals; Bite; Brain; Brain imaging; Calibration; Callithrix; Cell Nucleus; Characteristics; Chemicals; Coiled Bodies; Collaborations; Development; Devices; Electric Capacitance; Electromagnetic Fields; Electromagnetics; Electronics; Engineering; Ensure; Evaluation; Frequencies; Functional Imaging; Functional Magnetic Resonance Imaging; Future; Generations; Goals; Head; Heating; Helium; Human; Image; Infrastructure; Intervention; Joints; Laboratories; Lead; MRI Scans; Magnetic Resonance Imaging; Maryland; Measurement; Mus; National Institute of Mental Health; National Institute of Neurological Disorders and Stroke; Neurosciences; Operative Surgical Procedures; Performance; Perfusion; Pituitary Gland; Principal Investigator; Procedures; Property; Protocols documentation; Radiology Specialty; Resolution; Safety; Scanning; Scheme; Scientist; Signal Transduction; Source; System; Technology; Temperature; Testing; Tissues; Transistors; United States National Institutes of Health; Universities; Work; arterial spin labeling; design; detector; experience; experimental study; imaging facilities; improved; instrumentation; interest; magnetic field; manufacture; medical specialties; molecular imaging; neuroimaging; new technology; next generation; operation; perfusion imaging; prototype; radio frequency; safety testing; simulation; success; transmission process; tumor

The MRI Engineering core of LFMI (EC) supports new hardware developments for the highest field MRI systems at NIH, and supports specialty projects for other systems. Currently, its main goal is to develop 11.7T human MRI and 17.6T animal MRI in order to perform neuroimaging with superior contrast and resolution. Energization of the 11.7T human system was waiting over two years for Helium to become available. This situation got resolved in 2023, and cool down of the system started in June. The system is expected to be at field in October 2023, when final installation of the electronics will commence. It is anticipated that the system will be ready for MRI scanning in early 2024. One of the key parts of the 11.7T human system that is under the responsibility of the Engineering Core is the RF system, including RF transmitters and detectors. Progress has been made on implementing detuning circuitry on the previously developed volume transmitter to allow it to be used in transmit receive mode. This allows joint operation with receive detector arrays that provide improved sensitivity over volume detectors. A 32-channel receiver detector is under construction, and six of its channels have been constructed and tested. Full, 32-channel capability is expected in early 2024, when it can be tested and used with the detuneable volume transmitter inside the 11.7T scanner. To allow human scanning, it must be ensured that RF transmission does not cause tissue heating more than 1 degree Celsius. As MRI at 11.7T cause highly inhomogeneous RF fields and associated tissue heating, simulations and measurements need to be performed to estimate safe operating limits. During 2023, the Engineering Core has made progress on these aspects and has developed a test phantom with electromagnetic properties similar to the human head. In addition, the phantoms chemical composition provide MRI reference signals that enable accurate estimation of temperature based on temperature-dependent resonance frequency shifts. Initial experiments will be performed at 3T using 11.7T-like RF irradadiation (i.e. 500 MHz frequency). For several years, our lab has been developing on-coil RF amplification technology for multi-channel transmission (also called pTx). This technology is important for human MRI at 11.7 T as it allows improved control over the transmission field and its associated tissue heating. A prototype system for 7T was tested in 2022. In 2023, the Engineering Core has explored the critical components for pTx at 11.7T, and characterized the effect of the magnetic field on the operational characteristic of the power transistor in the RF amplifier. This has informed on the design of an efficient prototype, which we plan to manufacture in late 2023. To adapt the 7T prototype to work at 11.7T, several issues need to be resolved that relate to the power transistor. Parasitic capacitances in the transistor lead to power loss that is exacerbated at increasing field (=RF frequency). In addition, increased magnetic field also affects transistor performance and power efficiency. To overcome these problems, we started investigating the possibility to improve transistor design beyond capabilities currently available with commercial devices. This is done in collaboration with the University of Maryland, which has experience in transistor design and manufacturing. The Engineering Core also continued its support of the various groups the use MRI at NIH. It developed a variety of mouse coils and RF filters for the Mouse Imaging Facility. Presently all mouse body coils are tuned/matched, and orthogonally arranged saddle pairs and used in transmit/receive (transceiver)-mode with the 7T, 9.4 T and 3 T Bruker systems. Resonant nuclei included 1-H, 13-C, 2-H. Substantial effort was made in testing the safety of the previously developed combined 13C-1H head coil for 3T. This required extensive RF field simulations and close examination of the safety features and RF calibration procedures on the 3T scanner. Several iterations occurred between RF testing and safety committee evaluation, and in summer 2023 the head coil received approval for human use.

LFMI（EC）的MRI工程核心支持NIH最高现场MRI系统的新硬件开发，并支持其他系统的专业项目。目前，其主要目标是开发11.7吨人类MRI和17.6T动物MRI，以进行神经影像，并具有出色的对比度和分辨率。 11.7T人类系统的能量正在等待两年以上，以便氦气可用。这种情况在2023年得到了解决，该系统的冷却始于6月。该系统预计将于2023年10月在现场进行，届时电子设备的最终安装将开始。预计该系统将在2024年初准备进行MRI扫描。 在工程核心负责的11.7T人类系统的关键部分之一是RF系统，包括RF发射器和探测器。在先前开发的音量发射器上实现引导电路方面取得了进展，以允许将其用于传输接收模式。这允许与接收检测器阵列进行联合操作，从而提高了对体积检测器的灵敏度。正在建造一个32通道接收器检测器，其六个通道已被构建和测试。预计将在2024年初进行32通道的能力，当时可以对其进行测试并与11.7T扫描仪内部的量发射机一起进行测试并使用。 为了允许人类的扫描，必须确保RF传播不会导致组织加热超过1度摄氏摄氏度。由于11.7T的MRI导致高度不均匀的RF场和相关的组织加热，因此需要进行模拟和测量，以估计安全的工作限制。在2023年期间，工程核心在这些方面取得了进展，并开发了具有类似于人头的电磁特性的测试幻影。此外，幻影化学成分提供了MRI参考信号，可以根据温度依赖性谐振频率移动来准确估算温度。最初的实验将在3T下使用11.7T样RF辐照（即500 MHz频率）进行。 几年来，我们的实验室一直在开发用于多通道传输（也称为PTX）的围栏RF扩增技术。该技术对人类MRI在11.7 T时很重要，因为它可以改善对传输场及其相关组织加热的控制。在2022年测试了7T的原型系统。2023年，工程核心在11.7T探索了PTX的关键组件，并表征了磁场对RF放大器中功率晶体管的操作特征的影响。这已经告知了一个有效原型的设计，我们计划在2023年底制造。 为了使7T原型在11.7T工作，需要解决与功率晶体管有关的几个问题。晶体管中的寄生电容会导致功率损失，这在增加场（= RF频率）处加剧。此外，增加的磁场还会影响晶体管性能和功率效率。为了克服这些问题，我们开始研究将晶体管设计改善超越商业设备可用功能的可能性。这是与马里兰大学合作完成的，该大学在晶体管设计和制造方面具有经验。 工程核心还继续支持各组的NIH使用MRI。它为小鼠成像设施开发了各种小鼠线圈和RF滤波器。目前，所有鼠标身体线圈均已调整/匹配，并与7T，9.4 T和3 t bruker Systems一起用于传输/接收器（收发器） - 模式。谐振核包括1-H，13-C，2-H。 在测试先前开发的13C-1H头线圈的3T合并组合的安全性方面做出了巨大的努力。这需要大量的RF现场模拟，并在3T扫描仪上仔细检查安全功能和RF校准程序。 RF测试和安全委员会评估之间发生了几次迭代，在2023年夏季，头盘管获得了人使用的批准。