Abstract: A method is presented for correcting Maxwell term error artifacts produced by an NMR system during the production of either a phase contrast angiogram or a complex difference angiogram. Phase corrections are made to the reconstructed phase image to eliminate the artifacts. Correction coefficients calculated from the flow encoding magnetic gradient waveforms of the phase contrast pulse sequence are used in a polynomial to calculate a set of phase error corrections. These corrections are then used to adjust the phase at each pixel of the angiogram image.

Abstract: A method is disclosed to remove the image artifacts produced by Maxwell terms arising from the imaging gradients in an echo planar imaging pulse sequence. The frequency and phase errors caused by the Maxwell terms are calculated on an individual slice basis. During the subsequent data acquisition these errors are compensated by dynamically adjusting the receiver frequency and phase.

Abstract: Signal fall-off in axial EPI images as well as its variations is corrected by compensating the EPI pulse sequence with gradient pulses that serve to balance the phase dispersion caused by Maxwell terms. Four embodiments are described which employ the slice-selection gradient to compensate the EPI pulse sequence and a fifth embodiment employs the readout gradient.

Abstract: Artifacts in NMR images produced by Maxwell terms during non-rectilinear scans, such as spiral scans, are reduced or eliminated. Phase corrections for in-plane and through-plane blurring are used to offset Maxwell terms errors.

Abstract: A method for correcting Maxwell field induced distortion, ghosting, and blurring artifacts in non-axially oriented EPI images is disclosed. In one embodiment phase corrections are calculated and used to offset Maxwell term errors during the image reconstruction process, and in another embodiment corrections are made after the image is reconstructed.

Abstract: A phase unwrapping method is provided comprising a post-processing MR operation for an array of phase-related MR data elements. The method includes the steps of defining a Region of Interest, of comparing each data element with the first and second data elements which are adjacent thereto in the array, in order to generate respectively corresponding first and second gradient values. A subset of the data elements is constructed, wherein a data element is assigned to the subset only if its corresponding first and second gradient values are less than a selected threshold value VENC/2. The data element subset is employed to generate a fitted phase function having a value at the position of each data element in the array, and the value of the fitted function thereof, for a given data element, is subtracted from the measured value thereof.

Abstract: A method for correcting MR data elements acquired in the presence of an imperfectly linear gradient field, each element comprising nominal first and second quadrature components. The quadrature components are multiplied by an artifact correction factor to provide respective first and second quantities. A Gradwarp geometric correction operation is applied to respective quantities to provide a corrected first and second quadrature component, corresponding to each data element. For a given data element, the arctangent function is applied to the result obtained by dividing the first corrected component by the second corrected component to provide a corrected phase component for use in forming an image.

Abstract: A system is provided for MR imaging wherein a volume within an imaging subject positioned with respect to the system contains both water molecules and fat tissue proximate to one another. The water molecules and fat tissue are selectively saturated by first determining whether application of a first RF excitation pulse of a first RF frequency to the volume, in association with a gradient magnetic field having a selected polarity with respect to an axis, would saturate fat tissue in a band lying closer to or farther from a selected location than a band of saturated water molecules. The first frequency comprises the sum of a center frequency and a first offset frequency having a magnitude and polarity determined by the gradient magnetic field.

Abstract: Flow encoded NMR pulse sequences are employed to acquire data sets from which a set of angiographic images can be reconstructed depicting blood flow at successive phases during the cardiac cycle. The number of angiographic images is increased by selecting views from adjacent data sets to form interpolated data sets that are employed to reconstruct angiographic images depicting blood flow at cardiac phases between the successive phases.

Abstract: A method for providing an indication of the limits of available functional gradient power when MRI equipment is used to obtain oblique MRI images calculates a "maximum absolute row sum" of a rotational matrix defining the degree obliquity of the image. This maximum absolute row sum provides one or more target functional gradient values based on the limitations of the physical gradients of the system.

Abstract: An NMR scanner performs a series of pulse sequences from which NMR data is acquired and used to reconstruct an image. Image contrast is enhanced by magnetization transfer from short-T.sub.2 spin species that are saturated by an off-resonance, substantially rectangular shaped RF saturation pulse applied during each pulse sequence.

Abstract: T*.sub.2 contrast in images reconstructed from fast NMR pulse sequences is improved by increasing the gradient recalled echo time TE. The pulse repetition time TR is minimized to maintain high temporal resolution by asymmetrically acquiring the echo signal with its peak disposed bear the end of the acquisition window.

Abstract: An NMR angiogram is produced from two data sets acquired using a fast pulse sequence. One data set is acquired with a readout gradient having a first moment of zero at each refocusing pulse and a first value at each acquired echo signal. A second data set is acquired with a readout gradient having a first moment of zero at each refocusing pulse and a second value at each acquired echo signal. Signals from stationary tissues are suppressed with a dephasing gradient pulse in the slice select direction applied after each refocusing pulse, and a corresponding rewinder gradient pulse is applied after each acquired echo signal.

Abstract: An NMR system produces an angiogram using the complex-difference method. Artifacts caused by system phase errors are reduced by calculating a corrected phase angle using the acquired NMR data sets and using the corrected phase angle in calculating the complex difference in the corresponding elements of the image domain NMR data sets.

Abstract: A steady-state free procession fast NMR pulse sequence includes a readout gradient waveform which refocuses the transverse magnetization to produce an S- NMR signal during the subsequent pulse sequence. A partial echo signal acquisition is acquired which enables the pulse sequence to be shortened and enables the S+ NMR signal to be displaced from the data acquisition window without disturbing the flow compensation. View reordering is used in combination with phase cycling to suppress the S+ NMR signal.

Abstract: A steady-state free precession fast NMR pulse sequence includes a readout gradient waveform which refocuses the transverse magnetization to produce an S- NMR signal during the subsequent pulse sequence. This readout gradient waveform is shaped to null the gradient first moment and to thereby suppress flow and motion artifacts. In an alternative embodiment, crusher pulses employed in the phase encoding or slice select gradients are also flow compensated.