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Density compensation functions for spiral MRI
Author(s) -
Hoge Richard D.,
Kwan Remi K. S.,
Bruce Pike G.
Publication year - 1997
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.1910380117
Subject(s) - cartesian coordinate system , spiral (railway) , fourier transform , fast fourier transform , transformation (genetics) , sampling (signal processing) , rotation (mathematics) , mathematical analysis , mathematics , computer science , geometry , algorithm , computer vision , filter (signal processing) , biochemistry , chemistry , gene
Abstract In interleaved spiral MRI, an object's Fourier transform is sampled along a set of curved trajectories in the spatial frequency domain ( k ‐space). An image of the object is then reconstructed, usually by interpolating the sampled Fourier data onto a Cartesian grid and applying the fast Fourier transform (FFT) algorithm. To obtain accurate results, it is necessary to account for the nonuniform density with which k ‐space is sampled. An analytic density compensation function (DCF) for spiral MRI, based on the Jacobian determinant for the transformation between Cartesian coordinates and the spiral sampling parameters of time and interleaf rotation angle, is derived in this paper, and the reconstruction accuracy achieved using this function is compared with that obtained using several previously published expressions. Various non‐ideal conditions, including intersecting trajectories, are considered. The new DCF eliminated intensity cupping that was encountered in images reconstructed with other functions, and significantly reduced the level of artifact observed when unevenly spaced sampling trajectories, such as those achieved with trapezoidal gradient waveforms, were employed. Modified forms of this function were found to provide similar improvements when intersecting trajectories made the spiral‐Cartesian transformation noninvertible, and when the shape of the spiral trajectory varied between interleaves.