MRI Engineering Core

MRI 工程核心

• 批准号: 10708654
• 负责人: Alan Koretsky
• 金额: $ 191.09万
• 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/10708654
• 关键词: 3D Print; Acetone; Address; Affect; Amplifiers; Anesthesia procedures; Animals; Brain; Callithrix; Cell Nucleus; Characteristics; Chemicals; Coiled Bodies; Collaborations; Computer software; Coupling; Custom; Data; Data Reporting; Detection; Development; Devices; Electric Capacitance; Electromagnetic Fields; Electronics; Engineering; Evaluation; Feasibility Studies; Feedback; Frequencies; Functional Imaging; Functional Magnetic Resonance Imaging; Future; Generations; Glass; Goals; Head; Heating; Helium; Human; Image; Infrastructure; Institutional Review Boards; Intervention; Kidney; Laboratories; Lead; Length; Liquid substance; Liver; Magnetic Resonance Imaging; Maryland; Measurement; Measures; Mechanics; Modification; Monitor; Mus; National Institute of Mental Health; National Institute of Neurological Disorders and Stroke; Neurosciences; Operative Surgical Procedures; Optics; Patients; Performance; Perfusion Weighted MRI; Pituitary Gland; Policies; Povidone; Principal Investigator; Property; Protocols documentation; Protons; Radiology Specialty; Resolution; Rod; Safety; Schedule; Scheme; Scientist; Shapes; Source; System; Technology; Temperature; Testing; Thermometry; Tissues; Transistors; United States National Institutes of Health; Universities; Validation; Variant; Work; arterial spin labeling; base; brain magnetic resonance imaging; contrast imaging; coronavirus disease; design; experience; experimental study; human imaging; image guided; imaging facilities; imaging system; implementation cost; improved; instrumentation; interest; magnetic field; medical specialties; molecular imaging; neuroimaging; new technology; next generation; notch protein; perfusion imaging; programs; prototype; radio frequency; response; safety testing; seal; simulation; success; transmission process; tumor; voltage

NIH COVID safety policy has severely restricted experimental progress by the MRI Engineering Core. The MRI Engineering core of LFMI (EC) supports new hardware developments for the highest field MRI systems at NIH, an 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. The 11.7T system is awaiting (re-)installation to be scheduled once sufficient liquid Helium for energization is procured, while a feasibility study will be performed for possible installation of the 17.6T animal MRI. The patient table of the 11.7T MRI will need to be modified in the future to accommodate up to 64 receive channels and possibly some additional transmit channels. This requires lengthening of the extension to the table and lengthening of the track system within the magnet bore that supports this assembly. This year, a track extension assembly was completed and tested by temporarily lengthening the table with some rods. Further modifications will have to wait until installation and testing of the existing table configuration has been completed by Siemens. In particular for the 11.7T system, major technical developments are needed to allow transmission and detection of the required RF fields, a difficult and yet unresolved problem. For the initial human studies at 11.7T, we plan to use a general-purpose whole head coil for both transmission and reception. As we plan to use this coil for the initial safety testing required by the FDA, we opted for a relatively simple design that allows for accurate prediction of transmitted electro-magnetic (EM) fields and associated tissue heating from simulations and measurements. We settled on a transmit-receive type 500 MHz inductive birdcage resonator. EM field simulations were performed using commercial software and used to compare measured and simulated frequency response when transmitting and receiving at different combinations of two coupling points. Excellent correspondence between simulations and measurements was observed under various conditions, improving our confidence in our ability to predict coil performance. After additional measurements and simulations with a small spherical test object (phantom) performed last year in our small bore (animal) 11.7T system, this year we repeated these measurements and simulations on our brain phantom, which more closely matches the human head in terms of shape and dielectric and conductive properties. We constructed this phantom by filling a head-shaped glass container with polyvinylpyrrolidone (https://amri.ninds.nih.gov/cgi-bin/phantomrecipe). The evaluation will be part of the FDA IDE submission for the 11.7 T. In the past year, E&M simulations of an inductive birdcage coil and the brain phantom were developed using the Remcom xFDTD program. These simulations were used to compute the spatial variation of SAR in a uniform head phantom that was filled with a conductive dielectric material that simulated the loading of the brain. For validation, these simulations were compared to measurements on the brain phantom. As the human 11.7 T system is not yet available, the coil and phantom were placed in the bore of a 3 T magnet using a custom-built coil cradle so that MR thermometry could be performed on the phantom using the 3 T body coil right after RF heating at the 11.7 T frequency. The head phantom was also equipped with optical temperature probes to monitor selective regions of the phantom during controlled heating and cooling of the phantom. Results so far are encouraging, but it appeared the accuracy of the temperature data is hampered by the instabilities (field drift) of the 3 T scanner. To improve on this, we plan to add a reference chemical to the phantom, which will allow simultaneous measurement of both the background field and the temperature shift. Preliminary experiments with various compounds have shown acetone is the most suitable candidate. The composition of the phantom will need to be adjusted to compensate for the changes in conductivity and permittivity with the addition of acetone. For several years, our lab has been developing on-coil RF amplification technology for multi-channel transmission (also called pTX). Compared to conventional remote voltage-mode RF power amplifiers, on-coil amplification allows better B1 control, reduced load sensitivity, and reduced power losses at a lower implementation cost. In addition, this technology also allows direct sensing of coil current, information that can be used for safety monitoring and feedback. Accurate RF transmit control allows better estimation of increased tissue heating associated with high field MRI. In order to evaluate feasibility and identify potential roadblocks for on-coil pTx at 11.7T, we built an 8-channel 7T prototype using optically controlled current-source RF power amplifiers. 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. Although the crossed coil arrangement for proton and other nuclei (X-nuclei) are theoretically flux decoupled, in practice we found coupling up to -20 dB due to wiring of terminals and other factors. To minimize this coupling further we built bandpass filters for X-nuclei with low insertion loss of typically 0.1 dB and a suppression of 1-H of up to -70 dB. For the 1-H coils we utilized a notch for x with similar scatter parameter characteristics. Those filters are built into the coil, however, to save extra work we made them modular to be placed in the transmission lines and those can be used for all other coils. The loop-windings in the coils were made from either single- or multi-stranded wires that are laid into groves of a 3D printed former developed in-house. The inner bore of the coil former fits around a sealed animal holding container. Various lengths of saddle coils were manufactured to achieve more sensitivity by means of adapted filling factor. For kidney and liver studies shorter coils were utilized. A mouse head coil is also made using crossed saddle loops and is mounted directly on a holding container. Restraining of the animal, temperature control and anesthesia supply is built into that coil arrangement. We also built a mouse body coil with orthogonal loops for x- nuclei in quadrature and linear loops for 1-H. The 1-H loops are 45o rotated. The expected strong coupling was overcome by application of filters as mentioned above. For the 7T in the NMR center arterial spin labeling coils and setup were reengineered to accommodate the new Siemens TERRA system. Lastly, a dual-tuned, 13C 1H head coil for 3T has been completed and integrated into a mechanical assembly for imaging of the human head on a Philips 3T MRI. The coil and its RF interface were tested extensively to develop data for the report being prepared to obtain IRB approval.

NIH COVID安全政策已严格限制了MRI工程核心的实验进展。 LFMI（EC）的MRI工程核心支持NIH最高现场MRI系统的新硬件开发，该系统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。一旦采购足够的液体氦气，就要安排11.7T系统正在等待（重新）安装，同时将进行可行性研究以安装17.6T动物MRI。将来需要修改11.7T MRI的患者表，以容纳多达64个接收通道，并可能接收一些其他发送通道。 这需要延长桌子上的扩展，并在支持该组件的磁铁孔内延长轨道系统。今年，通过用一些杆临时延长桌子来完成轨道扩展组件并测试。进一步的修改将必须等到西门子完成了现有表配置的安装和测试。 特别是对于11.7T系统，需要进行重大的技术发展，以允许传输和检测所需的RF字段，这是一个困难但尚未解决的问题。对于最初的人类研究，我们计划使用通用的整个头圈进行传播和接收。当我们计划将此线圈用于FDA所需的初始安全性测试时，我们选择了相对简单的设计，可以准确预测传输的电磁（EM）磁场（EM）磁场以及通过模拟和测量结果进行的相关组织加热。我们定居在500型MHz电感式鸟笼谐振器上。使用商业软件进行EM场仿真，并用于在两个耦合点的不同组合传输和接收时比较测量和模拟的频率响应。在各种条件下观察到了模拟和测量之间的出色对应关系，从而提高了我们对预测线圈性能的能力的信心。 在去年在我们的小孔（动物）11.7T系统中进行的小球测试对象（Phantom）进行了其他测量和模拟之后，今年，我们在脑幻影上重复了这些测量和模拟，这与人头更紧密地匹配了人头的术语形状和介电和导电性能。我们通过用聚乙烯基吡咯烷酮（https://amri.ninds.nih.gov/cgi-bin/phantomrecipe）填充头形玻璃容器来构建该幻影。评估将是11.7 T的FDA IDE提交的一部分。 在过去的一年中，使用REMCOM XFDTD程序开发了电感鸟笼线圈和脑幻像的E＆M模拟。这些模拟用于计算均匀的头部幻影中SAR的空间变化，该模拟填充有导电介电材料，该介电材料模拟了大脑的负载。为了进行验证，将这些模拟与脑幻影的测量值进行了比较。由于尚未使用人类11.7 t系统，因此使用定制的线圈摇篮将线圈和幻影放在3 t磁铁的孔中，以便可以使用3 t身体线圈在Phantom上进行MR温度法在11.7 t频率下加热RF。幻影还配备了光学温度探针，以监测幻影的加热和冷却过程中幻影的选择性区域。到目前为止，结果令人鼓舞，但似乎3 T扫描仪的不稳定性（现场漂移）阻碍了温度数据的准确性。为了改进这一点，我们计划向幻影添加参考化学物质，这将同时测量背景场和温度变化。具有各种化合物的初步实验表明丙酮是最合适的候选者。需要调整幻影的组成，以补偿丙酮的添加电导率和介电常数的变化。 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。与传统的远程电压模式RF功率放大器相比，围墙放大可以更好地控制B1控制，降低负载敏感性以及以较低的实施成本降低功率损耗。此外，该技术还允许直接感知线圈电流，可用于安全监控和反馈的信息。准确的RF发射对照可以更好地估计与高场MRI相关的组织加热增加。为了评估可行性并确定11.7T上围栏PTX的潜在障碍，我们使用光学控制的电流源RF功率放大器构建了一个8通道7T原型。 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。 尽管质子和其他核的交叉线圈布置在理论上是通量解耦的，但实际上，由于终端和其他因素的接线，我们发现耦合至-20 dB。为了最大程度地减少这种耦合，我们为X-Nuclei构建了带通滤波器，其插入损失通常为0.1 dB，抑制1-h的抑制作用高达-70 dB。对于1-h线圈，我们使用一个凹槽，用于具有相似散点参数特征的X。这些过滤器内置在线圈中，但是为了节省额外的工作，我们使它们模块化以将其放置在传输线中，并且可以用于所有其他线圈。线圈中的循环是由单链或多链电线制成的，这些电线被放入3D印刷的前在内部发达的3D格罗夫斯。线圈的内孔适合一个密封的动物固定容器。制造各种长度的马鞍线圈，以通过适应性的填充因子来实现更高的灵敏度。用于肾脏和肝脏研究，使用了较短的线圈。 还使用交叉的马鞍环制成鼠标头线圈，并直接安装在保持容器上。限制动物，温度控制和麻醉供应置于该线圈布置中。我们还用正交环构建了一个小鼠身体线圈，用于X-核的正交和线性环，用于1-H。 1-h的回路为45o旋转。如上所述，通过应用过滤器来克服预期的强耦合。 对于NMR中心中心中的7T，重新设计了动脉自旋标记线圈和设置，以容纳新的西门子Terra系统。最后，已经完成了一个三重的13摄氏度1H头线圈，并将其集成到机械组件中，用于在飞利浦3T MRI上成像人头成像。 对线圈及其RF界面进行了广泛的测试，以开发用于获得IRB批准的报告的数据。