<span>Background of the invention: The present invention relates to magnetic resonance ("MR") imaging. It finds particular application in conjunction with correcting MRI motion artifacts and main field fluctuation and will be described with particular reference thereto. It will be appreciated, however, that the invention is also amenable to other like applications. Magnetic resonance imaging is a diagnostic imaging modality that does not rely on ionizing radiation. Instead, it uses strong (ideally) static magnetic fields, radio-frequency ("RF") pulses of energy and magnetic field gradient waveforms. More specifically, MR imaging is a non-invasive procedure that uses nuclear magnetization and radio waves for producing internal pictures of a subject. Three-dimensional diagnostic image data is acquired for respective "slices" of an area of the subject under investigation. These slices of data typically provide structural detail having a resolution of one (1) millimeter or better. Programmed steps for collecting data, which is used to generate the slices of the diagnostic image, are known as an MR image pulse sequence. The MR image pulse sequence includes magnetic field gradient waveforms, applied along three (3) axes, and one (1) or more RF pulses of energy. The set of gradient waveforms and RF pulses are repeated a number of times to collect sufficient data to reconstruct the slices of the image. The data for each slice </span><span>is acquired during respective excitations of the MR device. Ideally, there is little or no variations in the phase of the nuclear magnetization during the respective excitations. However, movement of the subject (caused, for example, by breathing, cardiac pulsation, blood pulsation, and/or voluntary movement) and/or fluctuations of the main magnetic field strength may change the nuclear magnetization phase from one excitation to the next. This change in the phase of the nuclear magnetization may degrade the quality of the MR data used to produce the images. A non-phase encoded additional echo signal, prior to or after the data echo used for image generation, may be used to detect view dependent global phase variations when two-dimensional Fourier transform encoding and reconstruction algorithms are used. This "Navigator" echo passes through the center of the data space (K-space) each time, while the MR image data is ordered sequentially and linearly. Then, computational methods are used to correct the undesired view-to-view phase variation, thereby eliminating a significant source of image artifacts. With reference to FIG. 1, a typical MR imaging pulse 10 includes a slice select (frequency encoding) gradient 12 and an RF pulse 14 (i.e., the actual MR image signal). The slice select gradient 12 and the RF pulse 14 define a spatial location in which the image data occurs.http://www.google.com/patents?vid=USPAT6404196</span>
