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Signal‐to‐noise optimization for sodium MRI of the human knee at 4.7 Tesla using steady state
Author(s) -
Watts Alexander,
Stobbe Robert W.,
Beaulieu Christian
Publication year - 2011
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.22838
Subject(s) - flip angle , specific absorption rate , signal to noise ratio (imaging) , nuclear magnetic resonance , magnetic resonance imaging , signal (programming language) , cartilage , pulse (music) , osteoarthritis , steady state (chemistry) , materials science , biomedical engineering , image quality , noise (video) , chemistry , physics , optics , computer science , medicine , anatomy , detector , telecommunications , alternative medicine , pathology , artificial intelligence , antenna (radio) , image (mathematics) , radiology , programming language
Sodium magnetic resonance imaging of knee cartilage is a possible diagnostic method for osteoarthritis, but low signal‐to‐noise ratio yields low spatial resolution images and long scan times. For a given scan time, a steady‐state approach with reduced repetition time and increased averaging may improve signal‐to‐noise ratio and hence attainable resolution. However, repetition time reduction results in increased power deposition, which must be offset with increased radiofrequency pulse length and/or reduced flip angle to maintain an acceptable specific absorption rate. Simulations varying flip angle, repetition time, and radiofrequency pulse length were performed for constant power deposition corresponding to ∼6 W/kg over the human knee at 4.7T. For 10% agar, simulation closely matched experiment. For healthy human knee cartilage, a 37% increase in signal‐to‐noise ratio was predicted for steady‐state over “fully relaxed” parameters while a 29% ± 4% increase was determined experimentally ( n = 10). Partial volume of cartilage with synovial fluid, inaccurate relaxation parameters used in simulation, and/or quadrupolar splitting may be responsible for this disagreement. Excellent quality sodium images of the human knee were produced in 9 mins at 4.7T using the signal‐to‐noise ratio enhancing steady‐state technique. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.