title: Signal-to-noise optimization for sodium MRI of the human knee at 4.7 Tesla using steady state.
abstract: 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 4.7 T. 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 4.7 T using the signal-to-noise ratio enhancing steady-state technique.
authors: Department of Biomedical Engineering, University of Alberta, Edmonton, Canada.
authors: Alexander
authors: A
authors: Watts
authors: Robert W
authors: RW
authors: Stobbe
authors: Christian
authors: C
authors: Beaulieu
mesh_terms: D000328:Adult; D002358:Cartilage, Articular / Q000378:metabolism* / Q000473:pathology; D003198:Computer Simulation; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007719:Knee Joint / Q000378:metabolism* / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D020370:Osteoarthritis, Knee / Q000175:diagnosis / Q000378:metabolism; D019047:Phantoms, Imaging; D012964:Sodium / Q000378:metabolism*; D013582:Synovial Fluid / Q000378:metabolism*
chemical_list: D012964:Sodium