| 摘要 |
An MRI apparatus of the invention comprises a magnet system for producing a homogeneous magnetic field along the z axis. A plurality of wire conductors are arranged in a "bird cage" or "squirrel cage" configuration and are supplied with a circularly rotating RF field centered near the Larmor frequency omega o. The wire conductors also receive a voltage source Vp having a frequency omega p, which is less than the Larmor frequency. The voltage source Vp is rotated about the wire conductors at a frequency of omega s, which is much less than the frequency omega p, to successively apply the voltage Vp to each pair of diametrically opposed wire conductors in a manner which is ordered as a spatial cylindrical harmonic rotating at a frequency omega s. The voltage source Vp produces electric fields in the object which, in turn, generate linear magnetic field gradients in the object. The voltage source Vp phase encodes the signals detected from the object which thereby enables a transverse magnetization at each point within the object to be rapidly mapped back by projection techniques. Alternately, the transverse magnetization can be mapped back by an inverse transformation of a complex plane extending from the measured region by analytic continuation or by a linear transformation utilizing the solutions to Sommerfeld's Integral. Also, the complex permittivity or ionic mobility may be continuously measured through its effect on the transverse magnetization for analysis or process control. With the invention, an image of the object is rapidly and continuously produced without requiring the use of the conventional gradient field coils and without any mechanical moving parts. <IMAGE> |
