title: Sodium imaging of the human knee using soft inversion recovery fluid attenuation.
abstract: Sodium signal strength in MRI is low when compared with (1)H. Thus, image voxel volumes must be relatively large in order to produce a sufficient signal-to-noise ratio (SNR). The measurement of sodium in cartilage is hindered by conflation with signal from the adjacent fluid spaces. Inversion recovery can be used to null signal from fluid, but reduces SNR. The purpose of this work was to optimize inversion recovery sodium MRI to enhance cartilage SNR while nulling fluid. Sodium relaxation was first measured for knee cartilage (T1=21±1 ms, T(2 fast)(∗)=0.8±0.2 ms, T(2 slow)(∗)=19.7±0.5 ms) and fluid (T1=48±3 ms, T2(∗)=47±4 ms) in nine healthy subjects at 4.7 T. The rapid relaxation of cartilage in relation to fluid permits the use of a lengthened inversion pulse to preferentially invert the fluid components. Simulations of inversion pulse length were performed to yield a cartilage SNR enhancing combination of parameters that nulled fluid. The simulations were validated in a phantom and then in vivo. B0 inhomogeneity was measured and the effect of off-resonance during the soft inversion pulse was assessed with simulation. Soft inversion recovery yielded twice the SNR and much improved sodium images of cartilage in human knee with little confounding signal from fluid.
authors.affiliation: Department of Biomedical Engineering, University of Alberta, Canada.
authors.forename: Rebecca E
authors.initials: RE
authors.lastname: Feldman
authors.forename: Robert
authors.initials: R
authors.lastname: Stobbe
authors.forename: Alexander
authors.initials: A
authors.lastname: Watts
authors.forename: Christian
authors.initials: C
authors.lastname: Beaulieu
mesh_terms: D000328:Adult; D002358:Cartilage, Articular / Q000033:anatomy & histology / Q000098:blood supply / Q000473:pathology; D003198:Computer Simulation; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D007091:Image Processing, Computer-Assisted; D007717:Knee / Q000033:anatomy & histology* / Q000473:pathology*; D007719:Knee Joint / Q000033:anatomy & histology / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010003:Osteoarthritis / Q000473:pathology; D019047:Phantoms, Imaging; D012039:Regional Blood Flow / Q000502:physiology; D015203:Reproducibility of Results; D012964:Sodium / Q000737:chemistry; D055815:Young Adult
chemical_list: D012964:Sodium
keywords: Cartilage; Inversion recovery; Knee; SIRFLA; Sodium; Soft inversion recovery; TPI; Twisted projection imaging