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11.7T人体MRI和17.6T动物MRI，以进行具有卓越对比度和分辨率的神经成像。 11.7T 人体系统的供能等待了两年多的时间，氦气才可用。这种情况在 2023 年得到解决，系统从 6 月份开始冷却。该系统预计将于 2023 年 10 月投入使用，届时电子设备的最终安装将开始。预计该系统将于 2024 年初准备好进行 MRI 扫描。 工程核心负责的11.7T人体系统的关键部分之一是射频系统，包括射频发射器和探测器。在先前开发的体积发送器上实现失谐电路方面取得了进展，使其能够在发送接收模式下使用。这允许与接收探测器阵列联合操作，从而提供比体积探测器更高的灵敏度。 32通道接收探测器正在建设中，其中6个通道已经建成并进行了测试。预计将于 2024 年初实现完整的 32 通道功能，届时可以对其进行测试并与 11.7T 扫描仪内的可调谐音量发射器一起使用。 为了允许人体扫描，必须确保射频传输不会导致组织加热超过 1 摄氏度。由于 11.7T 的 MRI 会导致射频场高度不均匀以及相关的组织加热，因此需要进行模拟和测量来估计安全操作极限。 2023年期间，工程核心在这些方面取得了进展，并开发了具有与人头相似的电磁特性的测试体模。此外，模型的化学成分提供 MRI 参考信号，能够根据温度相关的共振频移准确估计温度。初始实验将在 3T 下使用类似 11.7T 的射频辐射（即 500 MHz 频率）进行。 多年来，我们的实验室一直致力于开发用于多通道传输（也称为 pTx）的线圈射频放大技术。该技术对于 11.7 T 的人体 MRI 非常重要，因为它可以改进对传输场及其相关组织加热的控制。 7T 原型系统于 2022 年进行了测试。2023 年，工程核心探索了 11.7T pTx 的关键组件，并表征了磁场对射频放大器中功率晶体管工作特性的影响。这为高效原型的设计提供了信息，我们计划在 2023 年末制造该原型。 为了使 7T 原型能够在 11.7T 下工作，需要解决与功率晶体管相关的几个问题。晶体管中的寄生电容会导致功率损耗，随着磁场（= RF 频率）的增加，功率损耗会加剧。此外，磁场的增加也会影响晶体管的性能和功率效率。为了克服这些问题，我们开始研究改进晶体管设计的可能性，使其超越目前商用器件的能力。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拥有丰富的经验。 工程核心还继续支持 NIH 使用 MRI 的各个团体。它为小鼠成像设备开发了各种小鼠线圈和射频滤波器。目前，所有鼠标体线圈均已调谐/匹配，并正交排列鞍座对，并在 7T、9.4 T 和 3 T Bruker 系统的发射/接收（收发器）模式下使用。共振核包括1-H、13-C、2-H。 我们对之前开发的 3T 组合 13C-1H 头部线圈的安全性进行了大量的测试。这需要进行广泛的射频场模拟，并对 3T 扫描仪的安全功能和射频校准程序进行仔细检查。 RF 测试和安全委员会评估之间发生了多次迭代，2023 年夏季，头部线圈获得了人类使用的批准。