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Dynamic range compression in MRI by means of a nonlinear gradient pulse
Author(s) -
Wedeen Van J.,
Chao YongSheng,
Ackerman Jerome L.
Publication year - 1988
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.1910060306
Subject(s) - pulse sequence , amplitude , spin echo , nuclear magnetic resonance , dynamic range , nonlinear system , pulse (music) , phase (matter) , physics , magnitude (astronomy) , flip angle , range (aeronautics) , signal (programming language) , magnetic resonance imaging , computer science , optics , materials science , medicine , quantum mechanics , astronomy , detector , composite material , radiology , programming language
Abstract In current magnetic resonance imaging (MRI), valuable information must often be discarded because the NMR signal has greater dynamic range than the analog‐to‐digital converter (ADC) hardware. Typically, a small set of high‐intensity data points near the center of the spin echo is responsible for most of the MRI data dynamic range. We predict that it is possible to reduce the dynamic range of the MRI spin echo by incorporating an identical nonlinear gradient pulse into each repetition of the imaging pulse sequence, prior to data sampling. This pulse converts the phase distribution of the subject, ordinarily a linear function of image coordinates, into a nonlinear function. A nonlinear phase distribution can have a negligible impact on image magnitude and yet a profound impact on spin‐echo magnitude. Given a nonlinear phase distribution, there will no longer be a single data point at which all of the protons have an identical phase (the echo center). Instead, the protons become phase coherent on a piecemeal basis, the echo peak is smoothed out, and its maximum amplitude and dynamic range are greatly diminished. Using gradient pulses of quadratic spatial variation, we estimate that maximum echo amplitude and dynamic range can be reduced in most cases by an order of magnitude. © 1988 Academic Press, Inc.