Laudon M K, Webster J G, Frayne R, Grist T M
Department of Electrical and Computer Engineering, University of Wisconsin-Madison 53706, USA.
IEEE Trans Biomed Eng. 1998 Feb;45(2):160-4. doi: 10.1109/10.661264.
Magnetic resonance imaging (MRI) allows a physician to obtain images of internal organs noninvasively. Imaging a moving organ such as the heart requires a trigger so that successive scans can be synchronized. In the case of cardiac imaging this trigger is the electrocardiogram (ECG). When a patient is in an MRI scanner he/she is subjected to both static and dynamic magnetic fields which can cause interference in the ECG. The dynamic fields consist of 8- to 64-MHz radio frequency (RF) pulses and low-frequency magnetic gradient pulses with frequency components below 100 Hz. Conventional bandpass filters are only moderately effective because the passband allows magnetic gradient-induced interference to be superimposed on the ECG, causing distortion of the signal. This paper describes a technique which can be used to remove induced MRI gradient interference from an ECG recorded on a patient inside the bore of a MRI scanner. Induced signal from an external loop is subtracted from the ECG to minimize the low-frequency interference. The gradient induced low-frequency interference was reduced to approximately 20% of its magnitude when using conventional ECG amplifiers.
磁共振成像（MRI）使医生能够无创地获取内部器官的图像。对心脏等运动器官进行成像需要一个触发信号，以便后续扫描能够同步。对于心脏成像而言，这个触发信号就是心电图（ECG）。当患者处于MRI扫描仪中时，他/她会受到静态和动态磁场的影响，这些磁场会对心电图产生干扰。动态磁场由8至64兆赫兹的射频（RF）脉冲和频率成分低于100赫兹的低频磁梯度脉冲组成。传统的带通滤波器效果一般，因为其通带会使磁梯度引起的干扰叠加在心电图上，导致信号失真。本文描述了一种可用于从在MRI扫描仪孔腔内的患者记录的心电图中去除MRI梯度感应干扰的技术。从心电图中减去来自外部回路的感应信号，以将低频干扰降至最低。使用传统心电图放大器时，梯度感应的低频干扰降低到其幅度的约20%。
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