Flexible water excitation for fat‐free MRI at 3T using lipid insensitive binomial off‐resonant RF excitation (LIBRE) pulses

Abstract

A flexible water excitation method was developed that shows robust, near complete fat suppression at 3T. Magn Reson Med 79:3007-3017, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Simultaneous fat‐free isotropic 3D anatomical imaging and T2 mapping of knee cartilage with lipid‐insensitive binomial off‐resonant RF excitation (LIBRE) pulses

“…The LIBRE pulse was optimized by means of numerical simulations and was then combined with the Iso3DGRE T 2 mapping technique. The fat suppression characteristics obtained using a short 1 msec total pulse duration were consistent with previously reported results with pulse durations between 1.4 msec and 2.6 msec.…”

“…Uniform fat suppression—particularly challenging due to the complex magnetic environment that characterizes musculoskeletal imaging—was therefore achieved by using the LIBRE pulse . The LIBRE‐Iso3DGRE acquisition time was one minute longer compared with Iso3DGRE (11.1 vs. 10.1 minutes, + 10%).…”

“…This variable parameter space was exploited to achieve robust fat suppression with total pulse duration of 1 msec (ie, 2τ). When a single rectangular subpulse produces a 2π rotation of the fat magnetization vector (and thus allowing for fat signal suppression), the relation between f RF , the resonance frequency of fat (f fat ), the RF excitation angle (α), and τ can be described by: where Δf is the difference between f RF and f fat at 3T, ΔB 0 represents the local magnetic field inhomogeneity, and α is in radians. In the absence of field inhomogeneities (ΔB 0 = 0) and assuming small RF excitation angles, the optimal f RF (f RFopt ) can be straightforwardly calculated.…”

“…Recently, a novel WE RF pulse that is robust to both B 0 and B 1 inhomogeneities and that allows for a homogeneous fat suppression with a large bandwidth has been developed and validated at 3T. This lipid‐insensitive binomial off‐resonant RF excitation (LIBRE) pulse was demonstrated for a range of pulse durations from 1.4 to 2.6 msec and was shown to enable superior fat suppression compared with conventional WE and fat saturation techniques, both in terms of SNR and insensitivity to magnetic field inhomogeneities. However, the utilization of the LIBRE pulse in knee musculoskeletal applications has not been explored yet.…”

Diffusion Tensor Imaging of the Calf Muscles in Subjects With and Without Diabetes Mellitus

“…Fatty infiltration of calf muscles (especially in those with DM) results in chemical shift artifacts in EPI‐acquired data and consequently affects measurements of the DTI and fiber tracking indices . In contrast to conventional fat saturation or water excitation methods with a 1‐1 binomial pulse pair, higher‐order binomial RF pulse fashions such as 1‐2‐1 (as used here) or 1‐3‐3‐1 are considered to perform better, with broader fat suppression efficiency and uniformity . To qualitatively evaluate the effect of fat infiltration, all fat‐suppressed T 1 ‐weighted images were individually inspected for the quality of fat suppression within the studied muscles.…”