Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey.
National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey.
Magn Reson Med. 2021 Sep;86(3):1746-1758. doi: 10.1002/mrm.28782. Epub 2021 Mar 26.
In simultaneous transmission and reception (STAR) MRI, along with the coupling of the excitation pulse to the received signal, noise, and undesired distortions (spurs) coming from the transmit chain also leak into the acquired signal and degrade image quality. Here, properties of this coupled noise and its relationship with the transmit amplifier gain, transmit chain noise density, isolation performance, and imaging bandwidth are analyzed. It is demonstrated that by utilizing a recently proposed STAR technique, the transmit noise can be reduced. The importance of achieving high isolation and careful selection of the corresponding parameters are demonstrated.
A cancellation algorithm, together with a vector modulator, is used for transmit-receive isolation. The scanner is modeled as a pipeline of blocks to demonstrate the noise contribution from each block. With higher isolation, coupled transmit noise can be reduced to the point that the dominant noise source becomes acquisition noise, as in the case for pulsed MRI. Amplifiers with different gain and noise properties are used in the experiments to verify the derived noise-transmit parameter relation.
With the proposed technique, more than 80 dB isolation in the analog domain is achieved. The leakage noise and the spurs coupled from the transmit chain, are reduced. It is shown that the transmit gain plays the most critical role in determining sufficient isolation, whereas the amplifier noise figure does not contribute as much.
The transmit noise and the spurs in STAR imaging are analyzed and mitigated by using a vector modulator.
在同步发射和接收（STAR）MRI 中，随着激励脉冲与接收信号的耦合，来自发射链的噪声和不需要的失真（spur）也会泄漏到采集信号中，从而降低图像质量。本文分析了这种耦合噪声的特性及其与发射放大器增益、发射链噪声密度、隔离性能和成像带宽的关系。结果表明，通过利用最近提出的 STAR 技术，可以降低发射噪声。结果表明，通过利用最近提出的 STAR 技术，可以降低发射噪声。还证明了实现高隔离度和仔细选择相应参数的重要性。
采用了一种消除算法和矢量调制器来实现收发隔离。采用流水线模块对扫描仪进行建模，以演示每个模块对噪声的贡献。随着隔离度的提高，耦合的发射噪声可以降低到采集噪声成为主要噪声源的程度，就像脉冲 MRI 一样。在实验中使用了具有不同增益和噪声特性的放大器来验证推导的噪声-发射参数关系。
采用所提出的技术，在模拟域中实现了超过 80dB 的隔离度。降低了泄漏噪声和从发射链耦合的spur。结果表明，发射增益在确定足够的隔离度方面起着最关键的作用，而放大器噪声系数的贡献不大。
采用矢量调制器分析和减轻了 STAR 成像中的发射噪声和spur。
