Abstract: A method to separate two chemically-shifted components of water (w) and fat (f) signals by: (i) estimating the field inhomogeneity ? through a treatment of the residuals of the Moore-Penrose solution of the following equations: cos(?n?)*w+cos [?n(1+?)]*f=real (In) and sin(?n?)*w+sin [?n(1+?)]*f=imaginary (In), and (ii) using the estimated ? to determine the resulting solution for w and f from the original input signals In.

Abstract: A magnetic resonance imaging method and apparatus gathers NMR image data over a sequence of measurement cycles. First magnetic gradient pulses are superimposed on a nominally static magnetic field to selectively address NMR RF excitations for at least one predetermined volume and second magnetic gradient pulses are superimposed on the static magnetic field at other times in a measurement cycle. At least one further of the measurement cycles is performed during which at least one of the second gradient pulses is omitted so as to produce calibration data representative of the magnetic field then existing in the predetermined volume. The calibration data is used to produce MRI data compensated for phase angle errors which otherwise would be present due to undesirable changes with respect to time in the magnetic field actually present in said predetermined volume.

Abstract: An asymmetric spin-echo (ASE) sequence having a variable asymmetry (&Dgr;TE) with respect to the RF pulse is used for imaging paramagnetic, diamagnetic or ferromagnetic instruments within tissues during interventional MRI procedures. The degree of asymmetry introduced determines an apparent size of the imaged instrument. In one embodiment of the invention, the amount of asymmetry is varied as a function of the phase encoding gradient steps. In this manner, the sequence is made sensitive to local gradients in the magnetic field but left insensitive to large scale variations such as those introduced by main magnetic field inhomogeneities.