MR in the far field: From mode transformation and holography to quasi-optics

Fundamental properties of holography such as storage, recall and matched filtering, arising out of momentum matching considerations of the propagating excitation fields, have been experimentally demonstrated for the first time in MR. As the wavelength of the MR scanner becomes commensurate or smaller than the geometrical thickness of the sample, new phenomena common in quantum optics but hitherto unknown in MR. Far field concept such as interference and diffraction, will become prevalent with the use of propagating excitation fields in MRI. This realization of holographic principles in MR can be fruitful in designing MR imaging and spectroscopic techniques such as phase conjugate imaging for correcting image distortions caused by field inhomogeneities, as well as new spatial encoding schemes based on a holographic grating encoding. In addition, it has potential to lead to new concepts for information storage and processing at MR frequencies.