Rapid Radiofrequency Field Mapping In Vivo Using Single-Shot STEAM MRI
نویسندگان
چکیده
Higher field strengths entail less homogeneous RF fields. This may influence quantitative MRI and MRS. A method for rapidly mapping the RF field in the human head with minimal distortion was developed on the basis of a single-shot stimulated echo acquisition mode (STEAM) sequence. The flip angle of the second RF pulse in the STEAM preparation was set to 60 degrees and 100 degrees instead of 90 degrees , inducing a flip angle-dependent signal change. A quadratic approximation of this trigonometric signal dependence together with a calibration accounting for slice excitation-related bias allowed for directly determining the RF field from the two measurements only. RF maps down to the level of the medulla could be obtained in less than 1 min and registered to anatomical volumes by means of the T(2)-weighted STEAM images. Flip angles between 75% and 125% of the nominal value were measured in line with other methods.
منابع مشابه
Benefits of higher magnetic fields for diffusion tensor imaging (DTI) based on single-shot STEAM MRI sequences: In vivo mouse brain studies at 2.35 T and 7 T
Introduction In theory, the NMR signal is expected to scale more than linearly with magnetic field strength [1]. On the other hand, practical MRI applications such as diffusion tensor imaging (DTI) using echo-planar imaging (EPI) are also affected by a marked reduction of T2 and T2* relaxation times, the latter referring to enhanced magnetic field inhomogeneities with corresponding geometric di...
متن کاملRadial single-shot STEAM MRI.
Rapid MR imaging using the stimulated echo acquisition mode (STEAM) technique yields single-shot images without any sensitivity to resonance offset effects. However, the absence of susceptibility-induced signal voids or geometric distortions is at the expense of a somewhat lower signal-to-noise ratio than EPI. As a consequence, the achievable spatial resolution is limited when using conventiona...
متن کاملMagnetic Resonance in Medicine 59:686–691 (2008) Radial Single-Shot STEAM MRI
Rapid MR imaging using the stimulated echo acquisition mode (STEAM) technique yields single-shot images without any sensitivity to resonance offset effects. However, the absence of susceptibility-induced signal voids or geometric distortions is at the expense of a somewhat lower signal-to-noise ratio than EPI. As a consequence, the achievable spatial resolution is limited when using conventiona...
متن کاملRapid isotropic diffusion mapping without susceptibility artifacts: whole brain studies using diffusion-weighted single-shot STEAM MR imaging.
A subsecond magnetic resonance imaging (MRI) technique for isotropic diffusion mapping is described which, in contrast to echo-planar imaging (EPI), is insensitive to resonance offsets, i.e., tissue susceptibility differences, magnetic field inhomogeneities, and chemical shifts. It combines a diffusion-weighted (DW) spin-echo preparation period and a high-speed stimulated echo acquisition mode ...
متن کاملHigh-field diffusion tensor imaging of mouse brain in vivo using single-shot STEAM MRI.
Information about the microstructural organization of cerebral white matter that is accessible by magnetic resonance diffusion tensor imaging (DTI) gains increasing importance for studies of animal brain. Particular challenges occur for in vivo conditions as well as at high magnetic fields. Here, we have employed a diffusion-weighted (DW) single-shot STEAM MRI sequence for DTI of mouse brain in...
متن کامل