A Method for Reducing Power Frequency Noise of Magnetic Resonance Signals Based on Wavelet Transform Modulus Maximum Method

Abstract

The invention belongs to the field of nuclear magnetic resonance sounding signal noise reduction, and is a method for reducing power frequency noise of magnetic resonance signals based on wavelet transform modulus maximum method, comprising the following steps: observing the full-wave magnetic resonance collected by nuclear magnetic resonance groundwater detectors The signal is decomposed by n-layer wavelet, where n is 5-7; the detail coefficient d of each layer is extracted 1 ,...,d n and the last layer approximation coefficient a n ; Use the wavelet transform modulus maximum denoising algorithm to update the detail coefficients of each layer; use the reconstructed wavelet coefficients to reconstruct the signal. The invention has simple process and fast operation speed, and can realize better noise reduction effect by processing a single detection signal.

Description

technical field [0001] The invention relates to a method for reducing noise of a magnetic resonance sounding (Magnetic Resonance Sounding, MRS) signal, in particular to a processing method for reducing power frequency noise contained in a magnetic resonance signal by using a modulus maximum method based on wavelet transform. Background technique [0002] The magnetic resonance groundwater detection technology has the advantage of being able to directly invert the hydrogeological information such as the location, water content, medium porosity and electrical conductivity of the aquifer at a depth of 0-150m underground, and has been widely used in the field of groundwater exploration in my country in recent years. Drought pressure provides a reliable technical support. However, the MRS signal is very weak, only at the nanovolt level, and is extremely susceptible to interference from environmental noise, especially in cities and surrounding areas with dense power lines. Power fr...

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Problems solved by technology

[0004] The method for filtering noise of full-wave nuclear magnetic resonance signals based on independent component analysis of the above invention utilizes the digital orthogonal method to construct input channel signals other than the observation signal channel, and does not need to use additional equipment to acquire multiple input channels according to traditional ICA requirements signal, which breaks the harsh conditions of ICA application and saves a lot of manpower and material resources, but this method needs to separate the noisy signal and perform spectrum correction on the separated signal, including centering and whitening the signal, and judging the difference between the signal and the noise. Gaussian, setting the convergence conditions of the FastICA algorithm, the calculation steps are cumbersome, and it is difficult for non-professionals to control; the ICA-based NMR groundwater detection signal noise elimination method does not need to lay reference coils during the test process, and the operation is simple. When suppressing power frequency noise It will not destroy the detailed features of the signal, but this method requires at least three sets of data, and the calculation process is complicated and the calculation amount is large; the notch method is currently a common method for removing power frequency noise, but when the noise frequency and magnetic resonance signal When the frequency is close, it is easy to cause the loss of effective signal

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