ARTEFACT REDUCTION IN MAGNETIC RESONANCE IMAGING
A method of operating a low-field magnetic resonance imaging (MRI) system, the method comprising: obtaining an initial set of k-space phase-encoding coordinates; generating a sampling path through at least some of the k-space phase-encoding coordinates in the initial set to mitigate impact of eddy currents on operation of the low-field MRI system; and operating the low-field MRI system using a pulse sequence in accordance with the sampling path to obtain spatial frequency data for generating one or more magnetic resonance (MR) images of a subject.
1 . A method of operating a low-field magnetic resonance imaging (MRI) system, the method comprising:
obtaining an initial set of k-space phase-encoding coordinates;
generating a sampling path through at least some of the k-space phase-encoding coordinates in the initial set to mitigate impact of eddy currents on operation of the low-field MRI system; and
operating the low-field MRI system using a pulse sequence in accordance with the sampling path to obtain spatial frequency data for generating one or more magnetic resonance (MR) images of a subject.
2 . The method of claim 1 , wherein generating the sampling path comprises generating the sampling path such that substantially all k-space phase-encoding coordinates, which are neighboring along the generated sampling path, are within a threshold distance of one another, wherein the threshold distance depends on a Nyquist spatial frequency for the low-field MRI system.
3 . The method of claim 1 , wherein generating the sampling path comprises generating the sampling path such that at least 95% of k-space phase-encoding coordinates, which are neighboring along the generated sampling path, are within a threshold distance of one another, wherein the threshold distance depends on a Nyquist spatial frequency for the low-field MRI system.
4 . The method of claim 1 , wherein generating the sampling path comprises generating the sampling path such that at least 99% of k-space phase-encoding coordinates, which are neighboring along the generated sampling path, are within a threshold distance of one another, wherein the threshold distance depends on a Nyquist spatial frequency for the low-field MRI system.
5 . The method of claim 1 , wherein generating the sampling path comprises generating the sampling path such that all of k-space phase-encoding coordinates, which are neighboring along the generated sampling path, are within a threshold distance of one another, wherein the threshold distance depends on a Nyquist spatial frequency for the low-field MRI system.
6 . The method of claim 2 , wherein the threshold distance is less than or equal to C/FOV, wherein 1≤C≤5 and FOV represents a length of an imaging field of view of the low-field MRI system along a given direction.
7 . The method of claim 1 , wherein generating the sampling path comprises:
grouping the initial set of k-space phase encoding coordinates into a plurality of k-space sectors;
determining a sequence of k-space sectors, each k-space sector in the sequence being selected from among the plurality of k-space sectors; and
generating the sampling path in accordance with the sequence of k-space sectors.
8 . The method of claim 7 , wherein the sequence of k-space sectors includes at least one of the plurality of k-space sectors multiple times.
9 . The method of claim 7 , wherein generating the sampling path in accordance with the sequence of k-space sectors comprises:
generating a plurality of sector sub-paths corresponding to the plurality of k-space sectors;
generating a plurality of transition sub-paths for transitioning among the plurality of k-space sectors; and
generating the sampling path from the plurality of sector sub-paths and the plurality of transition sub-paths.
10 . The method of claim 9 , wherein generating the plurality of transition sub-paths comprises selecting neighboring k-space phase-encoding coordinates along the transition sub-paths to be within a threshold distance of one another, wherein the threshold distance depends on a Nyquist spatial frequency for the low-field MRI system.
11 . The method of claim 1 , wherein the generated sampling path comprises one or more spiral sub-paths, and wherein the generated sampling path traverses k-space phase-encoding coordinates grouped in concentric k-space sectors.
12 . The method of claim 1 , wherein the generated sampling path traverses k-space phase encoding coordinates in a sequence of radial k-space sectors, wherein at least some consecutive radial sectors in the sequence of radial k-space sectors are angled by approximately a golden angle relative to one another in k-space.
13 . The method of claim 1 , wherein the pulse sequence is a diffusion weighted imaging (DWI) sequence.
14 . The method of claim 1 , wherein the generated sampling path includes at least some coordinates not in the initial set of k-space phase encoding coordinates.
15 . The method of claim 1 ,
wherein k-space comprises a central region and at least one region outside the central region, and
wherein the generated sampling path repeatedly samples the central region.
16 . The method of claim 15 , wherein the generated sampling path includes multiple non-contiguous sub-paths containing k-space phase-encoding coordinates in the central region.
17 . The method of claim 15 , wherein the central region of k-space is a region located entirely within a threshold distance of an origin of k-space.
18 . The method of claim 15 , wherein the central region comprises a two-dimensional (2D) elliptical, circular, rectangular, and/or square region that includes an origin of k-space.
19 . The method of claim 16 , wherein the spatial frequency data comprises keyhole spatial frequency data collected using phase-encoding gradients corresponding to coordinates in the multiple non-contiguous sub-paths, the method further comprising:
correcting the spatial frequency data and/or the one or more MR images of the subject for motion artifacts by using the keyhole spatial frequency data.
20 . The method of claim 1 , further comprising: generating the one or more MR images using the spatial frequency data.
21 . A method, comprising:
obtaining an initial set of k-space phase-encoding coordinates;
generating a sampling path through at least some of the k-space phase-encoding coordinates in the initial set to mitigate impact of eddy currents on operation of the low-field MRI system, the generating comprising:
grouping the initial set of k-space phase encoding coordinates into a plurality of k-space sectors;
determining a sequence of k-space sectors, each k-space sector in the sequence being selected from among the plurality of k-space sectors; and
generating the sampling path in accordance with the sequence of k-space sectors.
22 . The method of claim 21 , further comprising:
operating the low-field MRI system using a pulse sequence in accordance with the sampling path to obtain spatial frequency data for generating one or more magnetic resonance (MR) images of a subject.
23 . A method, comprising:
performing an initial sampling of k-space;
dividing the initial sampling into a plurality of sectors; and
selecting a desired succession of sectors that minimizes a distance between phase-encoding coordinates within a sector and between sectors.
24 . The method of claim 23 , further comprising sampling a central region of the k-space multiple times using a sampling path through the desired succession of sectors.
25 . The method of claim 23 , further comprises correcting for one or more of: motion drift, phase drift, and phase errors by using spatial frequency data collected using a sampling path through the desired succession of sectors, wherein the sampling path repeatedly samples a central region of k-space.