Corum Curtis A, Idiyatullin Djaudat, Snyder Carl J, Garwood Michael
Center for Magnetic Resonance Research, Department of Radiology, Medical School, University of Minnesota, Minneapolis, Minnesota, USA.
Magn Reson Med. 2015 Feb;73(2):677-82. doi: 10.1002/mrm.25141. Epub 2014 Feb 24.
SWIFT (SWeep Imaging with Fourier Transformation) is a non-Cartesian MRI method with unique features and capabilities. In SWIFT, radiofrequency (RF) excitation and reception are performed nearly simultaneously, by rapidly switching between transmit and receive during a frequency-swept RF pulse. Because both the transmitted pulse and data acquisition are simultaneously amplitude-modulated in SWIFT (in contrast to continuous RF excitation and uninterrupted data acquisition in more familiar MRI sequences), crosstalk between different frequency bands occurs in the data. This crosstalk leads to a "bulls-eye" artifact in SWIFT images. We present a method to cancel this interband crosstalk by cycling the pulse and receive gap positions relative to the un-gapped pulse shape. We call this strategy "gap cycling."
We carry out theoretical analysis, simulation and experiments to characterize the signal chain, resulting artifacts, and their elimination for SWIFT.
Theoretical analysis reveals the mechanism for gap-cycling's effectiveness in canceling interband crosstalk in the received data. We show phantom and in vivo results demonstrating bulls-eye artifact free images.
Gap cycling is an effective method to remove bulls-eye artifact resulting from interband crosstalk in SWIFT data.
SWIFT（傅里叶变换扫描成像）是一种具有独特特征和功能的非笛卡尔磁共振成像（MRI）方法。在SWIFT中，射频（RF）激发和接收几乎同时进行，通过在频率扫描RF脉冲期间在发射和接收之间快速切换来实现。由于在SWIFT中发射脉冲和数据采集都同时进行幅度调制（与更常见的MRI序列中连续RF激发和不间断数据采集形成对比），数据中会出现不同频段之间的串扰。这种串扰会导致SWIFT图像中出现“靶心”伪影。我们提出了一种通过循环脉冲和相对于无间隙脉冲形状的接收间隙位置来消除这种带间串扰的方法。我们将这种策略称为“间隙循环”。
我们进行理论分析、模拟和实验，以表征SWIFT的信号链、产生的伪影及其消除方法。
理论分析揭示了间隙循环在消除接收数据中带间串扰方面有效性的机制。我们展示了体模和体内结果，证明了无靶心伪影的图像。
间隙循环是一种有效方法，可消除SWIFT数据中带间串扰导致的靶心伪影。
