Journal of magnetic resonance imaging : JMRI
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J Magn Reson Imaging · May 2009
Comparative StudyComparison of spiral imaging and SENSE-EPI at 1.5 and 3.0 T using a controlled cerebrovascular challenge.
To quantitatively compare spiral imaging and sensitivity-encoded-echo-planar-imaging (SENSE-EPI) methods for blood oxygen level-dependent (BOLD) imaging using controlled changes in the end-tidal partial pressure of CO(2) (PetCO(2)) to provide a global BOLD response. Specifically, we examined susceptibility-field-gradient effects on the BOLD sensitivity throughout the brain. ⋯ The results at 3.0 T suggest that, compared with spiral imaging, SENSE-EPI reduces signal loss associated with susceptibility field gradients in affected regions without affecting BOLD sensitivity. This study also demonstrates a unique application of controlled PetCO(2) changes to quantitatively compare BOLD techniques, which may be useful for the design of future fMRI studies.
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J Magn Reson Imaging · May 2009
Slice offset frequency and shim adjustment for interactive steady-state free-precession (SSFP) imaging.
To devise a method allowing real-time optimization of center frequency (CF) and shim for an interactive steady-state free-precession (SSFP) sequence by reformatting a previously acquired field map in the same orientation as the interactive acquisition. ⋯ The proposed method demonstrates how CF and shim can be optimized for any interactively positioned slice, resulting in reduced off-resonance artifacts.
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J Magn Reson Imaging · May 2009
Non-contrast-enhanced MR portography with time-spatial labeling inversion pulses: comparison of imaging with three-dimensional half-fourier fast spin-echo and true steady-state free-precession sequences.
To compare and evaluate images acquired with two different MR angiography (MRA) sequences, three-dimensional (3D) half-Fourier fast spin-echo (FSE) and 3D true steady-state free-precession (SSFP) combined with two time-spatial labeling inversion pulses (T-SLIPs), for selective and non-contrast-enhanced (non-CE) visualization of the portal vein. ⋯ Both 3D half-Fourier FSE and true SSFP scans with T-SLIPs enabled selective non-CE visualization of the portal vein. Half-Fourier FSE was considered appropriate for intrahepatic portal vein visualization, and true SSFP may be preferable when visualization of the MPV is required.
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J Magn Reson Imaging · May 2009
3D diffusion tensor MRI with isotropic resolution using a steady-state radial acquisition.
To obtain diffusion tensor images (DTI) over a large image volume rapidly with 3D isotropic spatial resolution, minimal spatial distortions, and reduced motion artifacts, a diffusion-weighted steady-state 3D projection (SS 3DPR) pulse sequence was developed. ⋯ A true 3D DTI pulse sequence with high isotropic spatial resolution was developed for whole brain imaging in under 20 minutes. To minimize the effects of brain motion, a cardiac synchronized, multiecho, DW-SSFP pulse sequence was implemented. Motion artifacts were further reduced by a combination of linear phase correction, corrupt projection detection and rejection, sampling density reweighting, and parallel imaging reconstruction. The combination of these methods greatly improved the quality of 3D DTI in the brain.