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Off-resonance Correction (off-resonance + correction)
Selected AbstractsKeyhole Dixon method for faster, perceptually equivalent fat suppressionJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2003Chris A. Flask MS Abstract Purpose To reduce the acquisition time associated with the two-point Dixon fat suppression technique by combining a keyhole in-phase (Water + Fat) k-space data set with a full out-of-phase (Water , Fat) k-space data set and optimizing the keyhole size with a perceptual difference model. Materials and Methods A set of keyhole Dixon images was created by varying the number of lines in the keyhole data set. Off-resonance correction was incorporated into the image reconstruction process to improve the homogeneity of the fat suppression. A perceptual difference model (PDM) was validated with human observer experiments and used to compare the keyhole images to images from a full two-point Dixon acquisition. The PDM was used to determine the smallest keyhole width required to obtain perceptual equivalence to images obtained from the full two-point Dixon method. Results In experimental phantom studies, the keyhole Dixon image reconstructed from 96 of 192 Water + Fat k-space lines and 192 Water , Fat k-space lines was perceptually equivalent to the full (192 + 192) two-point Dixon images, resulting in a 25% reduction in scan time. Clinical images of a volunteer's knee, orbits, and abdomen created from the smallest, perceptually equivalent keyhole width resulted in a 27%,38% reduction in total scan time. Conclusion This method improves the temporal efficiency of the conventional two-point Dixon technique and may prove especially useful for high-field systems where specific absorption rate (SAR) limits will constrain radiofrequency (RF)-based fat suppression techniques. J. Magn. Reson. Imaging 2003;18:103,112. © 2003 Wiley-Liss, Inc. [source] Transverse relaxation time (T2) mapping in the brain with off-resonance correction using phase-cycled steady-state free precession imagingJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2009Sean C.L. Deoni PhD Abstract Purpose To investigate a new approach for more completely accounting for off-resonance affects in the DESPOT2 (driven equilibrium single pulse observation of T2) mapping technique. Materials and Methods The DESPOT2 method derives T2 information from fully balanced steady-state free precession (bSSFP) images acquired over multiple flip angles. Off-resonance affects, which present as bands of altered signal intensity throughout the bSSFP images, results in erroneous T2 values in the corresponding calculated maps. Radiofrequency (RF) phase-cycling, in which the phase of the RF pulse is incremented along the pulse train, offers a potential method for eliminating these artifacts. In this work we present a general method, referred to as DESPOT2, with full modeling (DESPOT2-FM), for deriving T2, as well as off-resonance frequency, from dual flip angle bSSFP data acquired with two RF phase increments. Results The method is demonstrated in vivo through the acquisition of whole-brain, 1 mm3 isotropic T2 maps at 3T and shown to provide near artifact-free maps, even in areas with steep susceptibility-induced gradients. Conclusion DESPOT2-FM offers an efficient method for acquiring high spatial resolution, whole-brain T2 maps at 3T with high precision and free of artifact. J. Magn. Reson. Imaging 2009;30:411,417. © 2009 Wiley-Liss, Inc. [source] Novel interleaved spiral imaging motion correction technique using orbital navigatorsMAGNETIC RESONANCE IN MEDICINE, Issue 2 2003Hisamoto Moriguchi Abstract Although spiral imaging seldom produces apparent artifacts related to flow, it remains sensitive to rapid object motion. In this article, a new correction method is presented for rapid rigid body motion in interleaved spiral imaging. With this technique, an identical circular navigator k -space trajectory is linked to each spiral trajectory. Data inconsistency due to both rotation and translation among spiral interleaves can be corrected by evaluating the magnitudes and phases of the data contained in the navigator "ring." Further, it is difficult to create a frequency field map for off-resonance correction when an object moves during a scan, because there is motion-dependent misregistration between the two images acquired with different TEs. However, this difficulty can be overcome by combining the motion-correction method with a recently proposed technique (off-resonance correction using variable-density spirals (ORC-VDS)), thereby enabling both motion compensation and off-resonance correction with no additional scanning. Magn Reson Med 50:423,428, 2003. © 2003 Wiley-Liss, Inc. [source] High temporal and spatial resolution 4D MRA using spiral data sampling and sliding window reconstructionMAGNETIC RESONANCE IN MEDICINE, Issue 1 2004He Zhu Abstract Contrast-enhanced magnetic resonance angiography (CE-MRA) requires high spatial resolution to demonstrate detailed vasculature and high temporal resolution to capture the contrast bolus. Sparse bright voxels in MRA permit substantial undersampling in MRI data acquisition, allowing simultaneous high temporal and spatial resolution. We developed a time-resolved 3D MRA technique using the efficient spiral sampling trajectory, and performed off-resonance corrections using inhomogeneity field maps. View sharing and sliding window reconstruction were utilized to generate high temporal resolution. High-resolution 3D angiograms were generated at 1,2 s per frame, with a 5,8 ml gadolinium dose, in patients with vascular disease. Magn Reson Med 52:14,18, 2004. © 2004 Wiley-Liss, Inc. [source] | ||||||||||