Adaptive method for reducing motion and flow artifacts in NMR images
First Claim
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1. An NMR system, the combination comprising:
- means for generating a polarizing magnetic field;
excitation means for generating an RF excitation magnetic field which produces transverse magnetization in nuclei subjected to the polarizing magnetic field;
receiver means for sensing the NMR signal produced by the transverse magnetization and producing digitized in-phase (I) and quadrature (Q) samples of the NMR signal;
first gradient means for generating a first magnetic field gradient to impart a first phase component into the NMR signal which is indicative of the location of the transversely magnetized nuclei along a first coordinate axis;
second gradient means for generating a second magnetic field gradient to impart a second phase component into the NMR signal which is indicative of the location of the transversely magnetized nuclei along a second coordinate axis;
pulse control means coupled to the excitation means, first and second gradient means, and receiver means, said pulse control means being operable to conduct a scan in which a series of pulse sequences are conducted in which the second magnetic field gradient is stepped through a series of discrete values and a corresponding series of NMR signals are sensed and digitized to form an NMR data set; and
processor means for storing the NMR data set and for reconstructing an image array for a display from the stored NMR data set by;
(a) Fourier transforming the NMR data set along one of its dimensions to create hybrid-space data arrays I'"'"' and Q'"'"';
(b) producing a correction data array using the data in the hybrid-space data arrays I'"'"' and Q'"'"' by calculating the magnitude of the transformed sampled NMR signals in the hybrid-space data arrays I'"'"' and Q'"'"' to produce a modulus array, and correlating each row of the modulus array to produce a corresponding shift value for the correction data array;
(c) applying the data in the correction data array to the NMR data set to reduce motion effects; and
(d) Fourier transforming the corrected NMR image data set to produce the image array.
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Abstract
An NMR data set which is acquired with applied phase encoding and read-out gradients is corrected to reduce motion artifacts and increase image sharpness. The acquired NMR data set is examined to detect bulk displacements of the object being imaged and phase displacements caused by motion. This information is employed to produce correction operators which are applied to the NMR image data set. One or more navigator signals may also be acquired during the scan to produce an NMR data set from which the corrective operators can more readily be derived.
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Citations
14 Claims
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1. An NMR system, the combination comprising:
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means for generating a polarizing magnetic field; excitation means for generating an RF excitation magnetic field which produces transverse magnetization in nuclei subjected to the polarizing magnetic field; receiver means for sensing the NMR signal produced by the transverse magnetization and producing digitized in-phase (I) and quadrature (Q) samples of the NMR signal; first gradient means for generating a first magnetic field gradient to impart a first phase component into the NMR signal which is indicative of the location of the transversely magnetized nuclei along a first coordinate axis; second gradient means for generating a second magnetic field gradient to impart a second phase component into the NMR signal which is indicative of the location of the transversely magnetized nuclei along a second coordinate axis; pulse control means coupled to the excitation means, first and second gradient means, and receiver means, said pulse control means being operable to conduct a scan in which a series of pulse sequences are conducted in which the second magnetic field gradient is stepped through a series of discrete values and a corresponding series of NMR signals are sensed and digitized to form an NMR data set; and processor means for storing the NMR data set and for reconstructing an image array for a display from the stored NMR data set by; (a) Fourier transforming the NMR data set along one of its dimensions to create hybrid-space data arrays I'"'"' and Q'"'"'; (b) producing a correction data array using the data in the hybrid-space data arrays I'"'"' and Q'"'"' by calculating the magnitude of the transformed sampled NMR signals in the hybrid-space data arrays I'"'"' and Q'"'"' to produce a modulus array, and correlating each row of the modulus array to produce a corresponding shift value for the correction data array; (c) applying the data in the correction data array to the NMR data set to reduce motion effects; and (d) Fourier transforming the corrected NMR image data set to produce the image array. - View Dependent Claims (2, 4)
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3. An NMR system, the combination comprising:
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means for generating a polarizing magnetic field; excitation means for generating an RF excitation magnetic field which produces transverse magnetization in nuclei subjected to the polarizing magnetic field; receiver means for sensing the NMR signal produced by the transverse magnetization and producing digitized in-phase (I) and quadrature (Q) samples of the NMR signal; first gradient means for generating a first magnetic field gradient to impart a first phase component into the NMR signal which is indicative of the location of the transversely magnetized nuclei along a first coordinate axis; second gradient means for generating a second magnetic field gradient to impart a second phase component into the NMR signal which is indicative of the location of the transversely magnetized nuclei along a second coordinate axis; pulse control means coupled to the excitation means, first and second gradient means, and receiver means, said pulse control means being operable to conduct a scan in which a series of pulse sequences are conducted in which the second magnetic field gradient is stepped through a series of discrete values and a corresponding series of NMR signals are sensed and digitized to form an NMR data set; and processor means for storing the NMR data set and for reconstructing an image array for a display from the stored NMR data set by; (a) Fourier transforming the NMR data set along one of its dimensions to create hybrid-space data arrays I'"'"' and Q'"'"'; (b) producing a correction data array using the data in the hybrid-space data arrays I'"'"' and Q'"'"' by calculating the phase of the transformed sampled NMR signals in the hybrid-space data arrays I'"'"' and Q'"'"' to produce a two-dimensional phase array, and determining the difference in phase between elements in a reference row of the phase array and elements in the same column of the phase array to produce the values for the correction data array; (c) applying the data in the correction data array to the NMR data set to reduce motion effects; and (d) Fourier transforming the corrected NMR image data set to produce the image array.
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5. An NMR system, the combination comprising:
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means for generating a polarizing magnetic field; excitation means for generating an RF excitation magnetic field which produces transverse magnetization in nuclei subjected to the polarizing magnetic field; receiver means for sensing the NMR signal produced by the transverse magnetization and producing digitized in-phase (I) and quadrature (Q) samples of the NMR signal; first gradient means for generating a first magnetic field gradient to impart a first phase component into the NMR signal which is indicative of the location of the transversely magnetized nuclei along a first coordinate axis; second gradient means for generating a second magnetic field gradient to impart a second phase component into the NMR signal which is indicative of the location of the transversely magnetized nuclei along a second coordinate axis; pulse control means coupled to the excitation means, first and second gradient means, and receiver means, said pulse control means being operable to conduct a scan in which a series of pulse sequences are conducted in which the second magnetic field gradient is stepped through a series of discrete values and a corresponding series of NMR signals are sensed and digitized to form an NMR data set; and processor means for storing the NMR data set and for reconstructing an image array for a display from the stored NMR data set by; (a) Fourier transforming the NMR data set along one of its dimensions to create hybrid-space data arrays I'"'"' and Q'"'"'; (b) producing a correction data array using the data in the hybrid-space data arrays I'"'"' and Q'"'"'; (c) applying the data in the correction data array to the NMR data set to reduce motion effects; and (d) Fourier transforming the corrected NMR image data set to produce the image array; and in which the NMR data set acquired during the scan includes NMR navigator data which has been subjected to one of said two magnetic field gradients and NMR image data which has been subjected to both of said two magnetic field gradients, and steps (a) and (b) are performed with the NMR navigator data and step (c) is performed on the NMR image data.
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6. In an NMR system which performs a scan to acquire an NMR data set from which an image array is reconstructed, the improvement comprising:
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transforming an NMR data set produced by the NMR system to create a hybrid-space data array by performing a Fourier transformation on the NMR data set along one of its dimensions; producing a correction data array using the data in the hybrid-space data array by calculating the magnitude of each element of the hybrid-space data array to produce a corresponding modulus array, and correlating each row of the modulus array to produce a corresponding shift value for the correction data array; applying the data in the correction data array to an NMR data set produced by the NMR system to reduce artifacts caused by motion in the acquired NMR data set; and producing an image array from the corrected NMR data set. - View Dependent Claims (7, 9, 10, 11)
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8. In an NMR system which performs a scan to acquire an NMR data set from which an image array is reconstructed, the improvement comprising:
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transforming an NMR data set produced by the NMR system to create a hybrid-space data array by performing a Fourier transformation of the NMR data set along one of its dimensions; producing a correction data array using the data in the hybrid-space data array by calculating the phase of each element of the hybrid-space data array to produce the corresponding elements of a two-dimensional phase data array, and determining the difference in phase between elements in a reference row of the phase data array and elements in the same column of the phase data array; applying the data in the correction data array to an NMR data set produced by the NMR system to reduce artifacts caused by motion in the acquired NMR data set; and producing an image array from the corrected NMR data set.
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12. An NMR system, the combination comprising:
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means for generating a polarizing magnetic field; excitation means for generating an RF excitation magnetic field which produces transverse magnetization in nuclei subjected to the polarizing magnetic field; receiver means for sensing the NMR signal produced by the transverse magnetization and producing digitized in-phase (I) and quadrature (Q) samples of the NMR signal; first gradient means for generating a first magnetic field gradient to impart a first phase component into the NMR signal which is indicative of the location of the transversely magnetized nuclei along a first coordinate axis; second gradient means for generating a second magnetic field gradient to impart a second phase component into the NMR signal which is indicative of the location of the transversely magnetized nuclei along a second coordinate axis; pulse control means coupled to the excitation means, first and second gradient means, and receiver means, said pulse control means being operable to conduct a scan in which a series of pulse sequences are conducted in which the second magnetic field gradient is stepped through a series of discrete values and a corresponding series of NMR signals are sensed and digitized to form an NMR data set; and processor means for storing the NMR data set and for reconstructing an image array for a display from the stored NMR data set by; (a) producing a phase array from the NMR data set which indicates the phase of the digitized NMR signals; (b) producing correction data using the data in the phase array; (c) applying the correction data to the NMR data set to reduce motion effects; and (d) Fourier transforming the corrected NMR image data set to produce the image array.
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13. An NMR system, the combination comprising:
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means for generating a polarizing magnetic field; excitation means for generating an RF excitation magnetic field which produces transverse magnetization in nuclei subjected to the polarizing magnetic field; receiver means for sensing the NMR signal produced by the transverse magnetization and producing digitized in-phase (I) and quadrature (Q) samples of the NMR signal; first gradient means for generating a first magnetic field gradient to impart a first phase component into the NMR signal which is indicative of the location of the transversely magnetized nuclei along a first coordinate axis; second gradient means for generating a second magnetic field gradient to impart a second phase component into the NMR signal which is indicative of the location of the transversely magnetized nuclei along a second coordinate axis; pulse control means coupled to the excitation means, first and second gradient means, and receiver means, said pulse control means being operable to conduct a scan in which a series of pulse sequences are conducted in which the second magnetic field gradient is stepped through a series of discrete values and a corresponding series of NMR signals are sensed and digitized to form an NMR data set; and processor means for storing the NMR data set and for reconstructing an image array for a display from the stored NMR data set by; (a) producing a phase array from the NMR data set which indicates the phase of the digitized NMR signals; (b) producing an altered phase array by subtracting phase components produced by stationary spins from each value in the phase array; (c) producing correction data using the data in the altered phase array; (d) applying the correction data to the NMR data set to reduce motion effects; and (e) transforming the corrected NMR image data set to produce the image array. - View Dependent Claims (14)
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Specification