Novel encoding technology for ultrafast MRI in a limited spatial region

Abstract

A new magnetic field geometry for spatial encoding of magnetic resonance imaging (MRI) is presented. The field is given by: Bz(x, y) = gyy cos(qxx), and is called a PERL field because it is PERiodic in x and Linear in y. Both imaging pulse sequences and encoding field design are analyzed theoretically. A two-dimensional (2D) imaging sequence is shown to require a Fourier transform to resolve the x dimension and the solution of a Bessel function integral transform equation to resolve the y dimension. By examining solutions to Laplace's equation that approximate the PERL field, it is shown that the PERL field can only be produced in a limited spatial region. An unusual feature is that the number of gradient switches needed during a 2D data acquisition depends on the field of view and is fundamentally determined by the finite penetration depth δ of the PERL field into the sample. For very thin sections near the PERL coil, no gradient switching is required. To increase δ, qx is decreased. To keep the spatial resolution in y constant however, a phase θ is added: Bz(x, y) = gyy cos(qxx + θ), together with additional data acquisitions (and additional gradient switches) for different values of θ. In addition, an explicit example of a PERL coil with rectangular geometry is presented and its field plotted. © 1999 John Wiley & Sons, Inc. Int J Imaging Syst Technol 10, 216–224, 1999