Current four dimensional magnetic resonance imaging (4D-MRI) techniques lack sufficient temporal/spatial resolution and consistent tumor contrast. To overcome these limitations, this study presents the development and initial evaluation of a new strategy for 4D-MRI which is based on retrospective k-space reordering.
Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive neuromodulation technique that has been closely examined as a possible treatment for Parkinson disease (PD). However, results evaluating the effectiveness of rTMS in PD are mixed, mostly owing to low statistical power or variety in individual rTMS protocols.
A new phase-shifted EPI pulse sequence is described that encodes EPI phase errors due to all off-resonance factors, including B(o) field inhomogeneity, eddy current effects, and gradient waveform imperfections. Combined with the previously proposed multichannel modulation postprocessing algorithm (Chen and Wyrwicz, MRM 1999;41:1206-1213), the encoded phase error information can be used to effectively remove geometric distortions in subsequent EPI scans. The proposed EPI distortion correction technique has been shown to be effective in removing distortions due to gradient waveform imperfections and phase gradient-induced eddy current effects. In addition, this new method retains advantages of the earlier method, such as simultaneous correction of different off-resonance factors without use of a complicated phase unwrapping procedure. The effectiveness of this technique is illustrated with EPI studies on phantoms and animal subjects. Implementation to different versions of EPI sequences is also described. Magn Reson Med 45:525-528, 2001.
In this prospective, longitudinal study of young children, we examined whether a history of preschool generalized anxiety, separation anxiety, and/or social phobia is associated with amygdala-prefrontal dysregulation at school-age. As an exploratory analysis, we investigated whether distinct anxiety disorders differ in the patterns of this amygdala-prefrontal dysregulation.
Computation of B1 fields is a key issue for determination and correction of intensity nonuniformity in magnetic resonance images. This paper presents a new method for computing transmitted and received B1 fields. Our method combines a modified MRI acquisition protocol and an estimation technique based on the Levenberg-Marquardt algorithm and spatial filtering. It enables accurate estimation of transmitted and received B1 fields for both homogeneous and heterogeneous objects. The method is validated using numerical simulations and experimental data from phantom and human scans. The experimental results are in agreement with theoretical expectations.
