Abstract: In accordance with the invention, spatially invariant B.sub.0 eddy currents induced by a slice-selection gradient, G.sub.Z in an MRI system, are compensated by phase modulating the RF excitation pulse with a compensating function. In one embodiment, the compensating function is based on a measure of the integral of the B.sub.0 eddy current. In another embodiment, a scaled copy of the excitation gradient can be used as an approximation of the compensating function.

Abstract: Multiple inversion recovery flow imaging employs at least four spin inversion pulses following saturation of static nuclei spins to null nuclei in static material having different spin-lattice relaxation times (T.sub.1) with the inversion pulses being spaced in time to substantially reduce the longitudinal magnetization of the T.sub.1 species present. The saturation of static nuclei spins includes applying a sequence of saturation pulses with adjacent pulses being separated by a diphasing gradient to avoid refocusing coherence. The detection of signals includes applying at least one RF read-out pulse near the nulling point.

Abstract: Selective RF pulses are applied for segmented k-space imaging sequences with the tip-angle profiles of the pulses varying for stabilizing the entire signal profile and reducing ghosting and blurring artifacts in slice images.

Abstract: A long RF pulse is segmented into a plurality of RF pulses segments with nuclei spin refocusing pulses provided after each RF pulse segment to maintain phase coherence off resonance and decrease nuclei spin sensitivity to magnetic field inhomogeneity. The refocusing pulses are preferably 180.degree. rectangular pulses. Magnetic gradient segments associated with the RF pulse segments have supplemental gradients at the beginning and at the end of the gradient segment to ensure that the position in k-space for the segment corresponds to the k-space position of the gradient waveform before division into segments.

Abstract: A long train of spin echoes is produced using a RARE excitation pulse sequence, and during each spin echo an annular segment of a long k-space spiral as determined by read-out magnetic gradients is detected. At the end of the echo train the entire k-space spiral will have been covered. Each of the segments can be a unique annular portion of the k-space spiral. Alternatively, fewer annular segments of the spiral can be provided, with the fewer annular segments rotated in k-space and replayed to cover interleaved paths in k-space. The imaging gradients are refocused at the time of each spin-echo pulse in order to permit the long echo pulse trains of RARE imaging. Each spiral segment is surrounded by gradient lobes that move out from the k-space origin to the beginning of the segment, and move back to the origin from the end of the segment. Advantageously, the magnetic gradient lobes can be produced concurrently with parasitic echo crusher gradients at the beginning and end of each spin-echo pulse.

Abstract: Disclosed is a method for automatically removing blur in magnetic resonance image signals introduced due to inhomogeneity in the magnetic field and variations in magnetic susceptibility of an object being imaged. Detected signals are demodulated at several different frequencies and reconstructed to create a series of base images. The amount of blur is determined by establishing a focusing measure for each point or part in each base image, and a composite image is then constructed using only the unblurred regions from each base image. Focusing criterion can include minimization of the imaginary part of the complex MRI after removal of constant and low frequency phase information.

Abstract: A new pulse sequence which uses inversion recovery for lipid suppression and a spectral-spatial refocusing pulse for water suppression in spectroscopic imaging of the brain. In contrast to methods which eliminate fat by restricting the excited volume to lie completely within the brain, inversion recovery techniques allow imaging of an entire slice without such restrictions. A spectral-spatial pulse provides water suppression insensitive to a reasonable range of B.sub.0 and B.sub.1 inhomogeneities. Metabolite maps covering large volumes of the human brain can be produced with images from single and multiple slices obtained.

Abstract: MRI Apparatus for obtaining a spin-echo signal applies a self-refocusing RF pulse with variable delay in the spin-echo signals following application of the RF pulse. The RF pulse is designed using the Shinnar-LeRoux algorithm B.sub.1 (t)=SLR.sup.-1 {A.sub.n (z), B.sub.n (z) } with A.sub.n '(z) substituted for A.sub.n (z).A.sub.n '(z) is slightly non-minimum phase and equals P(z) A.sub.n (z) where P(z) is a unit amplitude phase function chosen to compensate the phase of B.sub.n (z). The RF pulse can be designed for a specific delay, a specific power constraint, and small tip angle.

Abstract: A method of selectively exciting nuclear spins in a limited three-dimensional volume comprising the steps of applying a plurality of subpulses in the presence of three orthogonal magnetic gradients (G.sub.x, G.sub.y, G.sub.z) over a period of time to define a k-space trajectory including a plurality of stacked two-dimensional k-space spirals arranged in pairs with each pair having an outward spiral and an inward spiral, the steps of one spiral to the next spiral corresponding to gradient pulses (G.sub.z) alternately at the edge and at the origin of each k-space spiral plane. The selective three-dimensional excitation pulse can be used with a non-selective 90.degree. pulse to the volume prior to applying the plurality of RF subpulses and allowing nuclear spins in the volume to precess, then applying the plurality of RF subpulses to selectively refocus nuclear spins in the volume, and detecting and echo signal.

Abstract: Measures of a velocity component during a plurality of time frames of cyclical motion of a region of interest are obtained using contrast cine MRI techniques. Trajectories of the region of interest are calculated in a backward direction and in a forward direction. The trajectories are then combined to define a motion trajectory. The forward and backward trajectories are weighted prior to combining with the forward trajectory being more heavily weighted for early frames and the backward trajectory being more heavily weighted for late frames.

Abstract: A high resolution NMR signal is obtained for a thin slice through a body by combining signals in which excitation k-space is covered in two or more excitations. An RF excitation pulse is applied along with an oscillating (e.g. triangular, trapezoidal, sinusoidal) wave modulated magnetic gradient with the RF pulse having nulls corresponding to zero values of the gradient. The RF pulse is applied a second time with the magnetic gradient inverted NMR signals detected following the application of the RF excitation pulses are summed. Minimum phase RF pulses can be employed to reduce signal dropout and reduce artifacts.

Abstract: An NMR system acquires data for producing an image using a spin-warp burst excitation pulse sequence. RF phase and flip-angle of each RF excitation pulse in the burst is separately controlled to maximize the SNR of the corresponding set of acquired NMR echo signals. The phase and amplitude of each acquired NMR echo signal is adjusted by an amount determined by its corresponding excitation pulse before being used for image reconstruction.

Abstract: Two-dimensional selective adiabatic pulses invert magnetization from a square region in the xy plane with insensitivity to RF variations. Two-dimensional adiabatic pulses can also invert selectively in frequency and in one spatial dimension. The pulses are useful for both MR imaging and spectroscopy.

Abstract: Magnetic resonance signals for imaging species having short spin-spin relaxation times (T.sub.2) are obtained without the need for a refocusing lobe. A series of RF excitation pulses are applied to the species with magnetic resonance signals being detected after each RF excitation pulse is applied. The magnetic resonance signals are then combined to provide the imaging signals. In one embodiment, each RF excitation pulse is half of a conventional slice-selective pulse with each pulse being slewed to zero. Contrast between the imaged short T.sub.2 species and longer T.sub.2 species can be enhanced by first applying an RF signal having sufficient amplitude to excite the longer T.sub.2 species but insufficient amplitude to excite the short T.sub.2 species whereby the longer T.sub.2 species are tipped by the RF signal. A magnetic gradient can then be applied to dephase the tipped nuclei of the longer T.sub.2 species. The imaging signals are then obtained from magnetic resonance signals from the short T.sub.

Abstract: Disclosed is a method of generating a linear large tip-angle selective excitation pulse for magnetic resonance imaging using a linear Fourier transform analysis. An inherently refocused small tip-angle excitation pulse which produces a rotation about an axis is first defined. Then a sequence of the small tip-angle excitation pulses is produced and concatenated whereby the sum of the tip angles produced by the sequence of pulses results in a desired net large tip-angle. The small tip-angle pulses have a Hermitian RF weighted k-space trajectory. The tip angle is the Fourier transform of the weighted k-space trajectory.

Abstract: Magnetic resonance signals for imaging species having short spin-spin relaxation times (T.sub.2) are obtained without the need for a refocusing lobe. A series of RF excitation pulses are applied to the species with magnetic resonance signals being detected after each RF excitation pulse is applied. The magnetic resonance signals are then combined to provide the imaging signals. In one embodiment, each RF excitation pulse is half of a conventional slice-selective pulse with each pulse being slewed to zero.

Abstract: Disclosed is a method of obtaining magnetic resonance signals from a body which are spatially and spectrally selective comprising the steps of applying a static magnetic field (Bo) to said body thereby aligning nuclear spins, applying a modulated magnetic gradient (G(t)) to said body, applying an RF excitation pulse (B(t)) to said body to tip said nuclear spins, said RF excitation pulse being related to said modulated magnetic gradient whereby resulting magnetic resonance signals are spatially and spectrally dependent, and detecting said magnetic resonance signals. The steps can be repeated in a multi-slice or multi-spectral acquisition mode. The steps can be repeated in a rapid gradient echo pulse sequence.

Abstract: A method of obtaining multi-dimensional spatially-selective magnetic resonance signals from a body includes applying a static magnetic field (Bo) to said body thereby aligning nuclear spins along an axis (z), and applying one or more time-varying magnetic gradients (Gx(t), Gy(t), Gz(t)) during a time period, T. During the time period, T, an RF excitation pulse (B.sub.1) is applied to said body to tip said nuclear spins, said RF excitation pulse being related to said modulated magnetic gradients by a first spatial frequency weighting function (W(k)(t)) whereby magnetic resonance signals transmitted by said tipped nuclear spins are spatially selective in multi dimensions. The resulting magnetic resonance signals are then detected to provide the multi-dimensional spatially-selective signals.