It is possible, however, to oscillate the gradients so that over time each pixel is assigned a unique frequency or physically move the patient within the magnet from point to point. Both these strategies were used in the early days of MR imaging and were known as sensitive point techniques. Damadian's original field-focused nuclear magnetic resonance (FONAR) used such a method. However, sensitive point techniques are extremely slow and have largely been abandoned in modern imaging except for some limited spectroscopic applications.
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Phase-encoding can be abandoned entirely using a technique known as 3D-projection acquisition. This method was originally proposed by Lai and Lauterbur in 1981 but has only recently received renewed interest. Gradient orientations produce a set of variations in frequency along radial lines in polar coordinates. Incremental change of gradient directions alter the polar and azimuthal angles of these radial lines. Reconstruction of the 3D k-space data is accomplished by filtered back projection followed by a 3D Fourier Transform.
Damadian R. Field focusing n.m.r (FONAR) and the formation of chemical images in man. Phil Trans R Soc Lond B 1980; 289:489-500
Hinshaw WS. Image formation by nuclear magnetic resonance: the sensitive-point method. J Appl Phys 1976; 47:3709-3721.
Lai CM, Lauterbur PC. True three-dimensional image reconstruction by nuclear magnetic resonance zeugmatography. Phys Med Bio 1981; 26:851-856.
How does frequency-encoding work?