O-space imaging: highly efficient parallel imaging using complementary nonlinear encoding gradient fields and receive coil geometries

Abstract

In MRI by excitation of nuclear spins and measurement of RF signals induced by these spins in the presence of spatially-varying encoding magnetic fields, signal localization is performed through recombination of measurements obtained in parallel by each coil in an encircling array of RF receiver coils. Through the use of magnetic gradient fields that vary both as first-order and second-order Z2 spherical harmonics with position, radially-symmetric magnetic encoding fields are created that are complementary to the spatial variation of the encircling receiver coils. The resultant hybrid encoding functions comprised of spatially-varying coil profiles and gradient fields permits unambiguous localization of signal contributed by spins. Using hybrid encoding functions in which the gradient shapes are thusly tailored to the encircling array of coil profiles, images are acquired in less time than is achievable from a conventional acquisition employing only first-order gradient fields with an encircling coil array.