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/摘要该提案的目的是开发一种用于射频工程（RF）传输线圈的新设备 MRI和MRS的系统。数十年来，RF线圈一直是MRI的积极研究领域。大多数站点都可以访问接收器线圈，因为多个通道接收器现在几乎无处不在。此外，一旦将信号数字化后，对接收到的处理（相位和振幅调整）信号是在重建过程中完成的。最后，为了调整和调整线圈本身，变体二极管提供电压可变电容，可用于操纵低功率RF信号。案件很与传输阵列不同。变体二极管通常由于RF所需的高电压而无法工作传输链。因此，相移元素通常是简单的传输线，可能用销钉切换二极管开关。调整是固定或手动调整或使用开关进行调整。切换元素可能很大，结果在离散化中可能不足感觉。这在发送链中尤其重要，因为所有信号调整均已完成一次，在每个传输之前 - 不是在重建过程中。这有限地传输阵列设计到一个小得多一组站点，主要是具有多个频道发射器的站点，这可能很昂贵。而八个频道在7T系统上可用发射器，很少有两个以上的频道在3T及以下可用。该建议旨在为高功率应用开发直流控制的可变电容器。项目研究两种方法：（1）使用MOSFET的漏极电压输出电容偏置为可变电容器的晶体管和（2）使用直流偏置电压依赖性铁电容器。我们定义了三个具体目标。目标1将是实施独立的高级使用这两种方法的动力DC控制可变电容器，并将其表征为热和RF 电压依赖性。 AIM 2将使用这些设备来构建直流控制的相位变速器和可变功率分裂器。两者都将测试热和RF水平依赖性和任何波形失真影响，对板凳和MRI测试。最后，AIM 3将构建具有独立振幅的四个通道传输阵列，并且每个通道上的相位控制，而无需多个通道发射器。这个目标将再次描述 B1模式控制和稳定性。成功实施第一个目标将为MR社区提供调整RF电路的新设备，并为无需RF传输的MR工程提供新方法诉诸离散和笨重的开关电路。整体成功都将证明拟议的技术，并立即向MR社区的用户进行翻译。