Digital Filter Banks in MR Measurement of Gradient Magnetic Fields

článek v časopise ve Web of Science, Jimp

angličtina

The sensitivity of spectroscopic methods based on nuclear magnetic resonance 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 neighbourhood 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) pre-emphasis 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 efficiently the level of noise. Results of the 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 the quality of methods for examining the properties of biological and chemical substances.

Digital filter, bank of filters, NMR, instantenous frequency

GESCHEIDTOVÁ, E.; KUBÁSEK, R.; SMÉKAL, Z.; BARTUŠEK, K.

2008

1. 5. 2008

Springer

Wien

0937-9347

Applied Magnetic Resonance (IF 0,665)

33

4

Rakouská republika

399

417

19