| 摘要 |
<p>In an MRI scanner, the transmission and reception of RF excitation and detected signal waves is accomplished using far field excitation instead of conventional near field excitation. By superimposing two counter-propagating waves from the same source in the MRI sample interference fringes are recorded in the sample in such a way that the relative phase between the two propagation wave vectors determines the periodicity of the maxima and minima in the interference fringe pattern. The complete fringe pattern, known as a spatial hologram, contains both the phase and amplitude information of the information-bearing wave. When exposed to a replica of the original reference wave, the fringe pattern acts as a diffraction grating, reproducing the information-bearing field propagating at the same relative phase.</p> |
