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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.

项目摘要/摘要该方案的目的是开发一种用于射频发射线圈工程的新设备磁共振成像和MRS射频线圈系统几十年来一直是磁共振成像领域中一个活跃而重要的研究领域。由于多频道接收器现在几乎无处不在，所以大多数站点都可以访问接收器线圈的研究。此外，一旦信号被数字化，处理(相位和幅度调整) 信号在重建过程中完成。最后，为了调谐和调整线圈本身，变容二极管提供可用于处理低功率射频信号的电压可变电容。这个案子很有说服力与发射阵列不同。由于RF所需的高电压，变容二极管通常不工作传输链。因此，移相元件通常是简单的传输线，可能用PIN交换二极管开关。调谐是固定的，也可以手动调整，也可以用开关调整。开关元件可能会很笨重，因此在离散化中，这可能不足以满足某些B1填隙应用或诸如传输应用有道理。这在传输链中特别重要，因为所有信号调整都是一次完成的，在每次传输之前--而不是在重建期间。这将发射阵列的设计限制为小得多的一组站点，主要是那些具有多个通道发射器的站点，这可能相当昂贵。而八个频道发射机在7T系统上可用，但在3T及以下的情况下，很少有超过两个通道的发射机可用。该提案旨在开发适用于大功率应用的直流可控可变电容器。该项目研究了两种方法：(1)利用MOSFET漏源电压相关的输出电容被偏置为可变电容器的晶体管以及(2)使用以下特性的直流偏置电压相关性铁电电容器。我们确定了三个具体目标。目标1将是实施独立的高使用这两种方法的供电直流控制可变电容器及其在热和射频方面的特性电压依赖性。AIM 2将使用这些器件来构建直流控制移相器和可变功率分割器。两者都将进行热和射频电平相关性测试，以及任何波形失真影响，板凳和核磁共振检查中。最后，AIM 3将构建四通道发射阵列，具有独立的幅度和每个通道上的相位控制，而不需要多个通道发射器。这一目标将再次成为 B1型花样控制稳定。第一个目标的成功实现将为MR社区提供一个调谐射频电路的新装置，并为射频发射系统的MR工程带来了新的方法借助于分立和笨重的开关电路。全面的成功既将证明建议的技术，并为MR社区的用户提供即时翻译。