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Correcting Artifacts in Magnetic Resonance Imaging Due to Magnetic Fields Caused by Slowly Oscillating Shields

IP.com Disclosure Number: IPCOM000034173D
Original Publication Date: 1989-Jan-01
Included in the Prior Art Database: 2005-Jan-26
Document File: 3 page(s) / 31K

Publishing Venue

IBM

Related People

Feig, E: AUTHOR

Abstract

A method for correcting artifacts in magnetic resonance imaging which were caused by slowly oscillating shields is provided.

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Correcting Artifacts in Magnetic Resonance Imaging Due to Magnetic Fields Caused by Slowly Oscillating Shields

A method for correcting artifacts in magnetic resonance imaging which were caused by slowly oscillating shields is provided. The method generally comprises: a) conducting a preliminary scan through K space by providing an

initial pulse and measuring at three points in time, and then

applying a spin-echo refocusing pulse and measuring while the

voltage of the magnetic resonance imaging apparatus is varied

according to Myt, where M is a gradient along the y direc

tion;

b) from the measured values, obtaining a function Dµ which is the

Fourier transform of the density function on the imaged plane;

c) conducting a magnetic resonance scan where, during the

encoding stage of each scan the phase of the signal is

observed at the three points in time corresponding to the

three points of the preliminary scan, and from the three

values, the amplitude and frequency of the interfering

oscillations are determined, and during the observation period

after a spin-echo pulse, the output is modulated by a phase

function which is obtained directly from the amplitude and

frequency of the interfering oscillations; and

d) collecting free induction decay information and constructing

an image according to known techniques. The provided technique eliminates ghosts in images which can appear when the building which shields the magnetic resonance image scanner from outside stray magnetic fields resonates and creates time-varying interference. Turning to the figure, a pulse gradient sequence for a preliminary scan which is to be conducted is set forth. At 10, an initial excitation pulse is applied, and measurements 20 are obtained at time 0, t0/2, and t0 . During the measurement time, the induced...