This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. This an added subproject to Acquisition Core, Project 1. This subproject is a direct collaboration with Dr. Schuff to develop high-resolution structural MRI sequences.
The specific aim of this subproject """"""""High resolution spiral MPRAGE"""""""" is to provide a novel implementation of an MPRAGE sequence using a spiral-based k-space acquisition scheme.MPRAGE (magnetization-prepared rapid gradient echo) is an MR imaging technique used to acquire structural brain images. Expected advantages of a spiral readout implementation are improved T1 contrast and signal-to-noise ratio with high image resolution due to the time-efficient data acquisition. A further advantage is the possibility to realize extremely short echo times, which minimizes additional transverse T2 and T2* relaxation effects. This is especially important for high field systems because of the short transverse relaxation times. With additional oversampling in the k-space center, motion artifacts can be greatly reduced. Also, because of negligible gradient moments at the k-space center, the sequence is robust to flow artifacts. All these advantages make the spiral MPRAGE a formidable basic tool for advanced structural brain imaging research. The subcontract covers the development of a spiral MPRAGE sequence for a Bruker MedSpec 4 Tesla MR scanner system, running Siemens Syngo software version VA25. MPRAGE sequences start with a preparatory rf pulse to prepare the longitudinal magnetization. After a certain inversion time, T1 weighted signal can be acquired. This is done by several excitation or alpha pulses which prepare part of the magnetization for readout. After each alpha pulse, exactly one line of k-space is encoded and read out. In the case of spiral MPRAGE, each line acquisitions is replaced by the acquisition of one spiral readout segment by the switching of sinusoidal gradients. The use of a spiral k-space readout brings up the advantages stated above. Difficulties which arise with this approach are: extension of the sequence flexibility regarding spiral segmentation;optimization of the spiral gradient shape and timing;the need for regridding of the raw data before further processing;correction of off-resonance effects. All these topics are addressed in the scope of the subcontract.
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