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B0 Gradient (b0 + gradient)

Distribution by Scientific Domains
Medical Sciences100%

Selected Abstracts

Suppression of background gradients in (B0 gradient-based) NMR diffusion experiments

CONCEPTS IN MAGNETIC RESONANCE, Issue 5 2007
Gang Zheng
Abstract Artifacts arising from background gradients are very common in NMR diffusion (i.e., PGSE) experiments involving B0 gradients because of the unavoidable magnetic susceptibility differences and B0 inhomogeneity within and around the sample. This article presents the general methodology to develop PGSE sequences with background gradient suppression. Most of the available methods which can be used for the suppression of the effects of background gradients are discussed. And two newly developed methods are presented in detail: frequency analysis of spin-dephasing, which assumes the artifacts due to background gradients come from the resonance between the spin-dephasing caused by applied gradients and background gradients, and asymmetric bipolar stimulated-echo-based PGSE, which can suppress the effects of nonconstant background gradients. © 2007 Wiley Periodicals, Inc.Concepts Magn Reson Part A 30A: 261,277, 2007. [source]

Fast proton spectroscopic imaging using steady-state free precession methods

MAGNETIC RESONANCE IN MEDICINE, Issue 3 2003
Wolfgang Dreher
Abstract Various pulse sequences for fast proton spectroscopic imaging (SI) using the steady-state free precession (SSFP) condition are proposed. The sequences use either only the FID-like signal S1, only the echo-like signal S2, or both signals in separate but adjacent acquisition windows. As in SSFP imaging, S1 and S2 are separated by spoiler gradients. RF excitation is performed by slice-selective or chemical shift-selective pulses. The signals are detected in absence of a B0 gradient. Spatial localization is achieved by phase-encoding gradients which are applied prior to and rewound after each signal acquisition. Measurements with 2D or 3D spatial resolution were performed at 4.7 T on phantoms and healthy rat brain in vivo allowing the detection of uncoupled and J-coupled spins. The main advantages of SSFP based SI are the short minimum total measurement time (Tmin) and the high signal-to-noise ratio per unit measurement time (SNRt). The methods are of particular interest at higher magnetic field strength B0, as TR can be reduced with increasing B0 leading to a reduced Tmin and an increased SNRt. Drawbacks consist of the limited spectral resolution, particularly at lower B0, and the dependence of the signal intensities on T1 and T2. Further improvements are discussed including optimized data processing and signal detection under oscillating B0 gradients leading to a further reduction in Tmin. Magn Reson Med 50:453,460, 2003. © 2003 Wiley-Liss, Inc. [source]

Suppression of background gradients in (B0 gradient-based) NMR diffusion experiments

CONCEPTS IN MAGNETIC RESONANCE, Issue 5 2007
Gang Zheng
Abstract Artifacts arising from background gradients are very common in NMR diffusion (i.e., PGSE) experiments involving B0 gradients because of the unavoidable magnetic susceptibility differences and B0 inhomogeneity within and around the sample. This article presents the general methodology to develop PGSE sequences with background gradient suppression. Most of the available methods which can be used for the suppression of the effects of background gradients are discussed. And two newly developed methods are presented in detail: frequency analysis of spin-dephasing, which assumes the artifacts due to background gradients come from the resonance between the spin-dephasing caused by applied gradients and background gradients, and asymmetric bipolar stimulated-echo-based PGSE, which can suppress the effects of nonconstant background gradients. © 2007 Wiley Periodicals, Inc.Concepts Magn Reson Part A 30A: 261,277, 2007. [source]

Fast proton spectroscopic imaging using steady-state free precession methods

MAGNETIC RESONANCE IN MEDICINE, Issue 3 2003
Wolfgang Dreher
Abstract Various pulse sequences for fast proton spectroscopic imaging (SI) using the steady-state free precession (SSFP) condition are proposed. The sequences use either only the FID-like signal S1, only the echo-like signal S2, or both signals in separate but adjacent acquisition windows. As in SSFP imaging, S1 and S2 are separated by spoiler gradients. RF excitation is performed by slice-selective or chemical shift-selective pulses. The signals are detected in absence of a B0 gradient. Spatial localization is achieved by phase-encoding gradients which are applied prior to and rewound after each signal acquisition. Measurements with 2D or 3D spatial resolution were performed at 4.7 T on phantoms and healthy rat brain in vivo allowing the detection of uncoupled and J-coupled spins. The main advantages of SSFP based SI are the short minimum total measurement time (Tmin) and the high signal-to-noise ratio per unit measurement time (SNRt). The methods are of particular interest at higher magnetic field strength B0, as TR can be reduced with increasing B0 leading to a reduced Tmin and an increased SNRt. Drawbacks consist of the limited spectral resolution, particularly at lower B0, and the dependence of the signal intensities on T1 and T2. Further improvements are discussed including optimized data processing and signal detection under oscillating B0 gradients leading to a further reduction in Tmin. Magn Reson Med 50:453,460, 2003. © 2003 Wiley-Liss, Inc. [source]