Magnetic resonance image artifact correction using navigator echo information
First Claim
1. A method for characterizing magnet system instabilities in magnetic resonance imaging system, the method comprising the steps of:
- applying magnetic field gradients and a radio frequency excitation pulse to gyromagnetic material of a subject of interest;
applying an image echo readout gradient of a first polarity with a phase encoding gradient, followed by detecting first magnetic resonance signals from the subject;
applying a navigator echo gradient of a second polarity opposite the first polarity of the image echo readout gradient and detecting second magnetic resonance signals representative of magnet system field instabilities due to magnet system structures; and
analyzing the second magnetic resonance signals to characterize a plurality of effects of magnet system instabilities.
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Abstract
A technique is provided for characterizing and correcting for instabilities or variations in a magnet system of an MRI scanner. The technique makes use of a navigator pulse to read out navigator echo data in the absence of phase encode, or with phase encode effects rewound. The navigator data is used to characterize several potential effects of magnet system instabilities or variations, such as zeroth order phase shifts, first order (linear) phase shifts, bulk position shifts, and amplitude effects. The effects of the instabilities can be used, then, to correct image data acquired during an examination.
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Citations
35 Claims
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1. A method for characterizing magnet system instabilities in magnetic resonance imaging system, the method comprising the steps of:
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applying magnetic field gradients and a radio frequency excitation pulse to gyromagnetic material of a subject of interest;
applying an image echo readout gradient of a first polarity with a phase encoding gradient, followed by detecting first magnetic resonance signals from the subject;
applying a navigator echo gradient of a second polarity opposite the first polarity of the image echo readout gradient and detecting second magnetic resonance signals representative of magnet system field instabilities due to magnet system structures; and
analyzing the second magnetic resonance signals to characterize a plurality of effects of magnet system instabilities. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for generating magnetic resonance image data from a magnetic resonance scanner, the method comprising the steps of:
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applying readout gradient pulse of a first polarity with a phase encoding gradient, and a radio frequency pulse to a subject of interest to produce emissions from gyronmagnetic materials within the subject;
detecting the emissions and generating image data representative thereof;
applying a navigator gradient pulse to the subject of interest, the navigator gradient pulse having a second polarity opposite from the first polarity of the image readout pulse used to detect the emissions;
detecting navigator echo signals resulting from the navigator echo pulse and generating navigator echo data representative thereof;
analyzing the navigator echo data to characterize a plurality of effects of anomalies in a magnet system of the scanner due to magnet system structures; and
correcting the image data based upon the analysis to generate corrected image data. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17)
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18. A method for correcting image data in a magnetic resonance imaging system, the method comprising the steps of:
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in the presence of a primary magnetic field, applying a pulse sequence to gradient coils to generate gradient fields and to a radio frequency coil to generate emissions from a subject of interest, including a readout gradient having a first polarity and with a phase encoding gradient;
detecting the emissions and generating image data representative thereof;
applying a navigator readout pulse to the subject, the navigator readout pulse having a second polarity opposite from the first polarity of an image readout pulse used to detect the emissions;
detecting a navigator echo signal and generating navigator data representative thereof;
performing a one-dimensional Fourier transform in a readout direction on the image data and the navigator data;
analyzing the transformed navigator data to characterize effects of variations in the primary or gradient magnetic fields due to magnet system structures;
correcting the transformed image data based upon the characterized effects; and
performing a one-dimensional Fourier transform in a phase encode direction on the corrected image data. - View Dependent Claims (19, 20, 21, 22)
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23. A magnetic resonance imaging system comprising:
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a magnet configured to generate a primary magnetic field;
a set of gradient coils configured to generate gradient fields in the presence of the primary magnetic field;
a radio frequency transmitter and receiver set configured to generate radio frequency pulses and to detect radio frequency emissions from a subject of interest in response to the radio frequency pulses; and
a control system coupled to the gradient coils and to the radio frequency transmitter and receiver set, the control system being configured to apply a pulse sequence to the gradient coils and to the radio frequency transmitter and receiver set to generate image echo signals, including an image readout gradient having a first polarity and with a phase encoding gradient, and navigator echo signals in the subject of interest, the navigator echo signals resulting from a navigator echo pulse having a second polarity opposite from the first polarity of the image readout pulse used to detect the emissions, to detect the image and navigator echo signals and generate image and navigator data representative thereof, and to analyze the navigator data to characterize effects of variations in the primary magnetic field and the gradient fields during the pulse sequence. - View Dependent Claims (24, 25, 26, 27, 28)
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29. A computer program for controlling operation of a magnetic resonance imaging system having a magnet configured to generate a primary magnetic field, a set of gradient coils configured to generate gradient fields in the presence of the primary magnetic field, a radio frequency transmitter and receiver set configured to generate radio frequency pulses and to detect radio frequency emissions from a subject of interest in response to the radio frequency pulses, and a control system coupled to the gradient coils and to the radio frequency transmitter and receiver set, the computer program comprising;
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a machine readable medium configured to encode a control routine; and
a control routine stored on the machine readable medium, the routine including instructions for commanding the control system to apply a pulse sequence to the gradient coils and to the radio frequency transmitter and receiver set to generate image echo signals, including an image readout gradient having a first polarity and with a phase encoding gradient, and navigator echo signals in the subject of interest resulting from application of a navigator gradient pulse having a second polarity opposite from the first polarity of the image readout pulse, to detect the image and navigator echo signals and generate image and navigator data representative thereof, and to analyze the navigator data to characterize effects of variations in the primary magnetic field and the gradient fields during the pulse sequence. - View Dependent Claims (30, 31, 32, 33, 34, 35)
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Specification