Optimal gradient waveform design for projection imaging and projection reconstruction echoplanar spectroscopic imaging

The use of modulated B-0 projection gradient waveforms is proposed for magn etic resonance imaging (MRI) and magnetic resonance spectroscopic imaging ( MRSI) to shape the k-space sampling density function to match the profile o f an applied reconstruction window function. This allows for a time-efficie nt means of maximizing the signal-to-noise ratio when, for example, a low-p ass spatial filter, designed to reduce k-space truncation artifacts and cor responding point-spread function sidelobe energies, is implemented. Both th e two-dimensional (2D) and 3D cases are investigated. To create the project ion gradient waveforms, a design method is developed that uses nonlinear co nstrained optimization (NLCO) to minimize the variance of the reconstructio n noise. The design is subject to both equality and inequality constraints, which include the maximum gradient magnitude and slew rate. It is shown th at NLCO can also be applied to twisting the projection trajectories for pur poses of reducing the data acquisition time while still maintaining the des ired sampling density. Applications to H-1 MRSI are investigated via simula tions. Advantages and limitations of the new sampling schemes are discussed . (C) 1999 Wiley-Liss, Inc.