MRI Parallel Excitation for Neuroimaging Applications

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A Bioengineering Research Partnership (PAR-06-459) is proposed for the development of parallel excitation technology to improve functional magnetic resonance imaging (fMRI) studies in the inferior frontal cortex. This project is motivated by the need to eliminate large signal voids and image distortions caused by magnetic susceptibility differences between brain tissue and air in the nasal sinuses. These artifacts are ubiquitous in fMRI, especially for many inferior brain structures including the orbitofrontal cortex (OFC), inferior and medial temporal lobes, and brain stem structures. These parts of the brain have been implicated in neurodegenerative disorders, epilepsy, psychiatric conditions and alcohol/substance abuse disorders. Many current techniques to remove these distortions have a large cost in terms of temporal resolution or sensitivity for detection of activation. Our group has pioneered methods for reducing these artifacts, including multidimensional selective excitation, a technique that is promising, but is currently limited in the degree of correction and by the long duration of the excitation pulses. Parallel excitation is a new technology that will allow for greater flexibility in exciting specific patterns or more uniform patterns in MRI through the use of multiple independent excitation channels. For multidimensional excitation patterns, such as those used to eliminate the signal-loss artifacts in inferior brain regions in fMRI, parallel excitation should allow shorter pulses and offer more complete correction. This project is uniquely multidisciplinary in that it involves advances in parallel excitation pulse design, parallel excitation hardware, system integration, and application to studies of patients. This project will be lead by a multidisciplinary group of investigators: the Lead Investigators for this project are Douglas Noll (PI;System Integration and Software, Validation), Jeffrey Fessler (Pulse Optimization), and Stephen Taylor (Patient Studies); all from Univ. of Michigan and Steven Wright (Co-Pi; Hardware, System Integration) from Texas A&M University. This project offers novel optimization strategies to parallel excitation pulse design, unique current source technologies for driving the parallel transmit array, and important scientific investigation into the functioning of the OFC. Together, these approaches lead to valuable new methods for functional MRI that are capable of probing inferior brain structures with sensitivity equal to other structures, which will aid in the study of a variety of neuropsychiatric disorders. The parallel excitation technology developed here will also advance the general state of MRI technology for correction of excitation inhomogeneity at high magnetic fields and for many other application of multidimensional excitation in MRI.