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Digital filter banks in MR measurement of gradient magnetic fields

机译：MR梯度磁场测量中的数字滤波器组

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摘要

The sensitivity of spectroscopic methods based on nuclear magnetic resonance (MR) is limited, in particular by the magnitude of noise in the signal being measured. In MR tomography and, above all, in localized spectroscopy and spectroscopic MR imaging, this problem becomes even more pronounced. When gradient magnetic fields are used, it cannot be fully ruled out that there will be a change in the basic magnetic field due to the eddy currents in conducting materials in the neighborhood of the sample being measured. This results in a local change in instantaneous frequency of the resonance of nuclei and in a distortion of spectral lines or MR image. For methods that eliminate this distortion and for an accurate calculation of the constants of (in particular long) preemphasis filters, techniques have been developed and experimentally tested that are based on measuring the instantaneous frequency of the signal detected with a very low signal-to-noise ratio. Adaptive filtering methods and filtering based on filter banks have been developed to reduce the level of noise. Results of these two types of filtering are described in the paper. The filtering techniques developed can be used also in other applications and thus contribute to increasing quality of methods for examining the properties of biological and chemical substances.
机译：基于核磁共振（MR）的光谱方法的灵敏度受到限制，特别是受到所测量信号中噪声的大小的限制。在MR层析成像中，尤其是在局部光谱学和光谱MR成像中，这个问题变得更加明显。当使用梯度磁场时，不能完全排除由于要测量的样品附近的导电材料中的涡流而引起的基本磁场的变化。这导致原子核共振的瞬时频率局部变化，并导致谱线或MR图像变形。对于消除这种失真的方法，以及为了精确计算（特别是长的）预加重滤波器的常数，已经开发并进行了实验测试，这些技术基于测量以极低信噪比检测到的信号的瞬时频率。噪声比。已经开发了自适应滤波方法和基于滤波器组的滤波以降低噪声水平。本文介绍了这两种类型的过滤结果。开发的过滤技术也可用于其他应用，因此有助于提高检查生物和化学物质特性的方法的质量。

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