Research On Unilateral Nuclear Magnetic Resonance Imaging And Its Image De-nosing

The application of Nuclear Magnetic Resonance(NMR)technology has made human beings have a better understanding of their structure and function.Unilateral nuclear magnetic resonance equipment has the advantages of simple structure,small-sized,light weight,easy to detect non-invasively,etc.It can measure the nuclear magnetic resonance signal.However,since the longitudinal constant gradient field generated by the magnet always exists as a background field,traditional frequency encoding is no longer applicable,it is necessary to study a new pulse sequence to image.This paper is based on the basic principles of nuclear magnetic resonance.Given the characteristics of magnetic field produced by the unilateral nuclear magnetic resonance equipment,this paper studies the unilateral nuclear magnetic resonance imaging technology.Simulations and experiments are carried out to prove that the application of 2D phase encoding pulse sequences on unilateral nuclear magnetic resonance equipment is a proper way to obtain a two-dimensional image.The work of this paper is helpful to establish a clinical trial based on low field unilateral nuclear magnetic resonance imaging of shallow-layer skin,which is of greatly practical significance for the diagnosis of skin burns.The content includes the following parts:(1)One-dimensional NMR signal analysis.Two kinds of one-dimensional NMR signal analysis methods are studied.To begin with Bloch equation,the conventional gradient echo pulse sequence is used to obtain the magnetization vector at the end of the frequency encoding.By solving the Bloch equation or linearizing the Bloch equation to find the solution of Bloch equation to get a one-dimensional signal.Fast Fourier transform is adopted to obtain the reconstructed proton density.The possibility of one-dimensional NMR signal analysis for inhomogeneous magnetic field is also discussed.The influence of vertical gradient field on the one-dimensional signal is further discussed.(2)Two-dimensional magnetic resonance imaging technology.According to the characteristics of static magnetic field formed by unilateral magnet,two kinds of 2D phase encoding pulse sequences are studied.The constant gradient which is perpendicular to the surface of the magnet is taken as the gradient to select layer,not the frequency encoding but the 2D phase encoding pulse sequence is performed to encode the position.The use of 180°refocus pulses will continue to recover the signal,overcoming the influence of low signal to noise by cumulating.The interface of MRI software is made.(3)Unilateral nuclear magnetic resonance image de-noising.In order to improve the de-nosing effect of magnetic resonance image,a new threshold de-noising function based on traditional threshold function is proposed.The improved threshold function can overcome the shortcomings of the traditional threshold function.Experimental results demonstrate that the proposed algorithm is superior to the traditional threshold in peak signal to noise ratio and subjective visual effects.(4)Two-dimensional imaging experiments based on unilateral nuclear magnetic resonance equipment.Write the 2D phase encoding pulse sequence correctly to the sequence editing software called TNMR of Tecmag nuclear magnetic resonance spectrometer.Experiments are conducted on rubber sample,normal skin and burned skin using unilateral nuclear magnetic resonance equipment through a well-established nuclear magnetic resonance platform.Magnetic resonance signals are obtained through experiment after appropriate imaging parameters were set.The reconstructed two-dimensional images are obtained.This experiment proves the feasibility of using the 2D phase encoding pulse sequence on the unilateral nuclear magnetic equipment.