High-Power DC Controlled Variable Capacitors for MR Engineering

用于 MR 工程的高功率直流控制可变电容器

基本信息

批准号：
10595070
负责人：
Steven M Wright
金额：
$ 18.01万
依托单位：
TEXAS ENGINEERING EXPERIMENT STATION
依托单位国家：
美国
项目类别：
财政年份：
2022
资助国家：
美国
起止时间：
2022-04-01 至 2025-01-31
项目状态：
未结题

项目摘要

Project Summary/Abstract The objective of this proposal is to develop a new device for the engineering of radiofrequency (RF) transmit coil systems for MRI and MRS. RF coils have been an active and important area of research in MRI for decades. Research in receiver coils is accessible to most sites as multiple channel receivers are now nearly ubiquitous. Additionally, once the signals are digitized, processing (phase and amplitude adjustments) on the received signals are done during reconstruction. Finally, for tuning and adjusting the coils themselves, varactor diodes provide a voltage variable capacitance that can be used to manipulate low-power RF signals. The case is quite different with transmit arrays. Varactor diodes generally do not work due to the high voltages required in the RF transmit chain. Thus, phase shifting elements are often simply transmission lines, possibly switched with PIN diode switches. Tuning is fixed or adjusted manually or with switches. Switched elements can be bulky and result in discretization that may not be sufficient for some B1 shimming applications or applications such as Transmit SENSE. This is of particular importance in the transmit chain because all signal adjustments are done one time, prior to each transmission- not during reconstruction. This has limited transmit array design to a much smaller group of sites, primarily those with multiple channel transmitters, which can be quite costly. While eight channel transmitters are available on 7T systems, they are rarely available with more than two channels at 3T and below. This proposal aims to develop DC controlled variable capacitors for high-power applications. The project investigates two approaches: (1) using the drain-source voltage dependent output capacitance of MOSFET transistors that are biased off as variable capacitors and (2) using the DC bias voltage dependence of ferroelectric capacitors. We have defined three specific aims. Aim 1 will be to implement stand-alone high- powered DC controlled variable capacitors using both methods and to characterize them for thermal and RF voltage dependence. Aim 2 will use these devices to construct DC controlled phase shifters and variable power splitters. Both will be tested for thermal and RF level dependence and any waveform distortion impacts, on the bench and in MRI test. Finally, aim 3 will construct a four channel transmit array with independent amplitude and phase control on each channel without requiring multiple channel transmitters. This aim will again characterize B1 pattern control and stability. Successful implementation of the first aim will provide the MR community with a new device for tuning RF circuits, and lead to new methods to MR Engineering of RF transmit systems without resorting to discrete and bulky switching circuits. Overall success will both demonstrate the effectiveness of the proposed technology and provide immediate translation to users in the MR community.

项目概要/摘要该提案的目标是开发一种用于射频 (RF) 发射线圈工程的新设备 MRI 和 MRS 系统。几十年来，射频线圈一直是 MRI 领域活跃且重要的研究领域。由于多通道接收器现在几乎无处不在，因此大多数站点都可以进行接收器线圈的研究。此外，一旦信号被数字化，就会对接收到的信号进行处理（相位和幅度调整）信号是在重建期间完成的。最后，为了调谐和调整线圈本身，变容二极管提供可用于操纵低功率射频信号的电压可变电容。案情颇为与发射阵列不同。由于射频中需要高电压，变容二极管通常无法工作传输链。因此，相移元件通常只是传输线，可能通过 PIN 进行切换二极管开关。调谐是固定的或手动或通过开关调节。开关元件可能体积庞大，结果离散化可能不足以满足某些 B1 匀场应用或传输等应用感觉。这在传输链中尤其重要，因为所有信号调整都是一次性完成的，在每次传输之前 - 而不是在重建期间。这将发射阵列设计限制为更小的尺寸一组站点，主要是那些具有多通道发射机的站点，这可能非常昂贵。同时八通道发射机可在 7T 系统上使用，但在 3T 及以下系统上很少有超过两个通道。该提案旨在开发用于高功率应用的直流控制可变电容器。项目研究了两种方法：(1) 使用 MOSFET 的漏源电压相关输出电容作为可变电容器偏置的晶体管和（2）使用直流偏置电压依赖性铁电电容器。我们确定了三个具体目标。目标1是实现独立的高使用这两种方法供电直流控制可变电容器并表征它们的热和射频特性电压依赖性。目标 2 将使用这些器件构建直流控制移相器和可变功率分离器。两者都将进行热和射频电平依赖性以及任何波形失真影响的测试。工作台和 MRI 测试。最后，目标3将构建一个具有独立幅度和独立的四通道发射阵列。每个通道上的相位控制，无需多个通道发射器。这一目标将再次体现 B1 模式控制和稳定性。第一个目标的成功实现将为 MR 社区提供用于调谐射频电路的新设备，并带来射频发射系统 MR 工程的新方法，无需诉诸分立且庞大的开关电路。总体成功将证明该计划的有效性提出技术并为 MR 社区的用户提供即时翻译。