Novel encoding technology for ultrafast MRI in a limited spatial region

A new magnetic field geometry for spatial encoding of magnetic resonance im aging (MRI) is presented. The field is given by: B-z(x, y) = g(y)y cos(q(x) x), 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 theore tically. A two-dimensional (2D) imaging sequence is shown to require a Four ier transform to resolve the x dimension and the solution of a Bessel funct ion integral transform equation to resolve the y dimension. By examining so lutions 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 un usual feature is that the number of gradient switches needed during a 2D da ta acquisition depends on the field of view and is fundamentally determined by the finite penetration depth delta of the PERL field into the sample. F or very thin sections near the PERL coil, no gradient switching is required . To increase delta, q(x) is decreased. To keep the spatial resolution in y constant however, a phase theta is added: B-z(x, y) = g(y)y cos(q(x)x + th eta), together with additional data acquisitions (and additional gradient s witches) for different values of theta. In addition, an explicit example of a PERL coil with rectangular geometry is presented and its field plotted. (C) 1999 John Wiley & Sons, Inc.