Artifacts caused by patient motion during scanning remain a serious problem in most MRI applications. The prospective motion correction technique attempts to address this problem at its source by keeping the measurement coordinate system fixed with respect to the patient throughout the entire scan process. In this study, a new image-based approach for prospective motion correction is described, which utilizes three orthogonal two-dimensional spiral navigator acquisitions, along with a flexible image-based tracking method based on the extended Kalman filter algorithm for online motion measurement. The spiral navigator/extended Kalman filter framework offers the advantages of image-domain tracking within patient-specific regions-of-interest and reduced sensitivity to off-resonance-induced corruption of rigid-body motion estimates. The performance of the method was tested using offline computer simulations and online in vivo head motion experiments. In vivo validation results covering a broad range of staged head motions indicate a steady-state error of less than 10% of the motion magnitude, even for large compound motions that included rotations over 15 deg. A preliminary in vivo application in three-dimensional inversion recovery spoiled gradient echo (IR-SPGR) and three-dimensional fast spin echo (FSE) sequences demonstrates the effectiveness of the spiral navigator/extended Kalman filter framework for correcting three-dimensional rigid-body head motion artifacts prospectively in high-resolution three-dimensional MRI scans. Artifacts caused by patient motion during scanning remain a serious problem in most clinical and research MRI applications. In fast single-shot sequences, such as dynamic two-dimensional (2D) echo-planar imaging (EPI), between-scan motion can introduce significant motionrelated variance to the voxel-time courses and disrupt the spin excitation history of the acquisition (1,2). In multishot 2D and three-dimensional (3D) sequences, withinscan patient motion results in k-space data inconsistencies, causing artifacts such as ghosting, blurring, and ringing in the images themselves. Offline image registration can mitigate most between-scan motion artifacts in time-series data (3-5) but cannot correct for changes in the spin excitation history caused by through-plane motion. In addition, while some within-scan motion artifacts can be corrected retrospectively using knowledge of the motion history derived from either navigator scans (6,7) or overlapping k-space data (8,9), most of these methods are limited by the inability to (1) fully correct for through-plane motion in 2D sequences and (2) avoid k-space data inconsistencies caused by interpolation errors.An alternative approach to motion correction, which shares none of these drawbacks, is modify the pulsesequence online, in real-time, during the acquisition itself. Some of the first real-time prospective motion correction methods used straight-line navigators to correct for linear translations of organs in the chest (10-12). Since then, navigator...

When an objective technique is used to define MI size by CE-MRI, accurate infarct size measurements can be obtained from images obtained up to 30 min after contrast administration.

Dual-bolus MR imaging enabled accurate measurement of absolute epicardial and endocardial perfusion across a wide range of blood flow rates (0 to >5.0 mL/min/g). Use of qualitative MR imaging measures such as the contrast enhancement ratio led to substantially underestimated hyperemic blood flow measurements.

Purpose To develop and evaluate a multiphasic contrast-enhanced MRI method called DIfferential Sub-sampling with Cartesian Ordering (DISCO) for abdominal imaging. Materials and Methods A three-dimensional, variable density pseudo-random k-space segmentation scheme was developed and combined with a Dixon-based fat-water separation algorithm to generate high temporal resolution images with robust fat suppression and without compromise in spatial resolution or coverage. With IRB approval and informed consent, 11 consecutive patients referred for abdominal MRI at 3T were imaged with both DISCO and a routine clinical 3D SPGR-Dixon (LAVA FLEX) sequence. All images were graded by two radiologists using quality of fat suppression, severity of artifacts, and overall image quality as scoring criteria. For assessment of arterial phase capture efficiency, the number of temporal phases with angiographic phase and hepatic arterial phase was recorded. Results There were no significant differences in quality of fat suppression, artifact severity or overall image quality between DISCO and LAVA FLEX images (p > 0.05, Wilcoxon signed rank test). The angiographic and arterial phases were captured in all 11 patients scanned using the DISCO acquisition (mean number of phases were 2 and 3 respectively). Conclusion DISCO effectively captures the fast dynamics of abdominal pathology such as hyperenhancing hepatic lesions with a high spatio-temporal resolution. Typically, 1.1×1.5×3 mm spatial resolution over 60 slices was achieved with a temporal resolution of 4–5 seconds.

Motion artifacts pose significant problems for the acquisition and analysis of high-resolution magnetic resonance imaging data. These artifacts can be particularly severe when studying pediatric populations, where greater patient movement reduces the ability to clearly view and reliably measure anatomy. In this study, we tested the effectiveness of a new prospective motion correction technique, called PROMO, as applied to making neuroanatomical measures in typically developing school-age children. This method attempts to address the problem of motion at its source by keeping the measurement coordinate system fixed with respect to the subject throughout image acquisition. The technique also performs automatic rescanning of images that were acquired during intervals of particularly severe motion. Unlike many previous techniques, this approach adjusts for both in-plane and through-plane movement, greatly reducing image artifacts without the need for additional equipment. Results show that the use of PROMO notably enhances subjective image quality, reduces errors in Freesurfer cortical surface reconstructions, and significantly improves the subcortical volumetric segmentation of brain structures. Further applications of PROMO for clinical and cognitive neuroscience are discussed.