Abstract: A method for designing non-linear phase 180° spectral-spatial radio frequency pulses that can be used for spectral editing in magnetic resonance spectroscopic imaging. A novel feature of the pulse is a symmetric sweep developed by the spectral profile from the outside edges of the spectral window towards the middle whereby coupled components are tipped simultaneously and over a short interval. Pulses have been designed for lactate editing at 1.5T and 3T. The spectral and spatial spin-echo profiles of the RF pulses can be measured experimentally and altered in an iterative manner. Spectral-spatial radio frequency (SSRF) pulses allow simultaneous selection in both frequency and spatial domains. These pulses are particularly important for clinical and research magnetic resonance spectroscopy (MRS) applications for suppression of large water and lipid resonances.

Abstract: One aspect of the invention is a method for reconstructing a moving table MR image. The method comprises receiving an input array that includes a plurality of uncorrected k-space data points. The method further comprises clearing a summation array. For uncorrected k-space data points in the input array the following steps are performed. A kernel associated with the k-space data point is obtained. Corrected data is created in response to the k-space data point, the input array and the kernel. Creating the corrected data includes correcting the uncorrected k-space data point for gradient non-linearities, where the correction is performed in k-space, and correcting the uncorrected k-space data point for table movement. The corrected data is added into the summation array. The image is reconstructed in response to the data in the summation array.

Abstract: A RF Excitation pulse for MRI applications has built-in saturation sidebands, thereby reducing the time for an excitation sequence. The pulse is created using the Shinnar-Le Roux (SLR) transform and designing beta-polynomials for a desired image slice excitation and for saturation of RF excitation such as by de-phasing in regions adjacent to the desired image slice. The beta-polynomials are combined and an inverse SLR transform creates the RF pulse from the combined beta-polynomial.

Abstract: A system and method are disclosed using continuous table motion while acquiring data to reconstruct MR images across a large FOV without significant slab-boundary artifacts that reduces acquisition time. At each table position, full z-encoding data are acquired for a subset of the transverse k-space data. The table is moved through a number of positions over the desired FOV and MR data are acquired over the plurality of table positions. Since full z-data are acquired for each slab, the data can be Fourier transformed in z, interpolated, sorted, and aligned to match anatomic z locations. The fully sampled and aligned data is then Fourier transformed in remaining dimension(s) to reconstruct the final image that is free of slab-boundary artifacts.

Abstract: Disclosed is a generalized reconstruction method that corrects for non-linear phase errors based on least-squares estimation. An approximation of the least squares estimate utilizes refocusing reconstruction in which high-resolution data is multiplied by the phase conjugate of a navigator in image-space. The multiplication rephases the unaliased signal in the high-resolution data. The high-resolution data can then be added together coherently. The multiplication can be effected in k-space as a convolution using a gridding reconstruction of the high-resolution data using the low resolution navigator.

Abstract: A modified projection on convex sets (POCS) algorithm and method for partial k-space reconstruction using low resolution phase maps for scaling full sets of reconstructed k-space data. The algorithm can be used with partial k-space trajectories in which the trajectories share a common point such as the origin of k-space, including variable-density spiral trajectories, projection reconstruction trajectories with a semicircle region acquisition, and projection reconstruction trajectories with every other spike acquired.

Abstract: A method for functional magnetic resonance imaging (fMRI) uses steady-state free precession (SSFP) to image changes in blood oxygenation between two time periods. A center frequency of the SSFP sequence is placed between the different resonant frequencies for oxyhemoglobin and deoxyhemoglobin whereby the signals have a phase difference of 180° and tend to cancel. By repeating the SSFP imaging sequence at different times, the difference in the measured signals provides a measure of change in oxyhemoglobin. RF flip angle of the SSFP sequence is chosen to maximize signal level in the frequency range from that of water in the presence of oxyhemoglobin and that of water in the presence of deoxyhemoglobin.

Abstract: Imaging time using PILS is reduced by using multiple coils with localized sensitivities with each coil having a separate demodulation channel thereby permitting parallel signal processing and image reconstruction. Images from the multiple coils are then combined to form an image with a larger field of view (FOV).

Abstract: The present invention provides a method for view-angle tilt magnetic resonance imaging of an object having a localized variation of magnetic susceptibility. The method includes the steps of: applying an RF excitation pulse and a first field gradient simultaneously to the object; applying an RF refocusing pulse and a second field gradient simultaneously to the object; and applying a tilted readout gradient to the object, where the tilt angle is selected to provide incomplete removal of the image distortion produced by the magnetic susceptibility variation. In this manner, magnetic susceptibility contrast is provided in the region of variable magnetic susceptibility. Adjustment of the tilt angle can be used to provide a desired amount of magnetic susceptibility contrast.

Abstract: One aspect of the invention is a method for reconstructing a moving table MR image. The method comprises receiving an input array that includes a plurality of uncorrected k-space data points. The method further comprises clearing a summation array. For uncorrected k-space data points in the input array the following steps are performed. A kernel associated with the k-space data point is obtained. Corrected data is created in response to the k-space data point, the input array and the kernel. Creating the corrected data includes correcting the uncorrected k-space data point for gradient non-linearities, where the correction is performed in k-space, and correcting the uncorrected k-space data point for table movement. The corrected data is added into the summation array. The image is reconstructed in response to the data in the summation array.

Abstract: A system and method are disclosed using continuous table motion while acquiring data to reconstruct MR images across a large FOV without significant slab-boundary artifacts that reduces acquisition time. At each table position, full z-encoding data are acquired for a subset of the transverse k-space data. The table is moved through a number of positions over the desired FOV and MR data are acquired over the plurality of table positions. Since full z-data are acquired for each slab, the data can be Fourier transformed in z, interpolated, sorted, and aligned to match anatomic z locations. The fully sampled and aligned data is then Fourier transformed in remaining dimension(s) to reconstruct the final image that is free of slab-boundary artifacts.

Abstract: A steady-state condition for tipped nuclear spins is accelerated or catalyzed by first determining magnetization magnitude of the steady state and the scaling magnetization along one axis (Mz) to at least approximate the determined magnetization magnitude. Then the scaled magnetization is rotated to coincide with a real-valued eigenvector extension of the tipped steady-state magnetization. Any error vector will then decay to the steady-state condition without oscillation. In one embodiment, the magnetic resonance imaging utilizes steady-state free precession (SSFP). The scaling and rotating steps are followed by the steps of applying read-out magnetic gradients and detecting magnetic resonance signals from the tipped nuclear spins. The magnetization magnitude is determined by eigenvector analysis, and the eigenvector extension is a real-valued eigenvector determined in the analysis.

Abstract: Three dimensional magnetic resonance imaging employs spiral trajectories which traverse a volume in k-space. The spiral trajectories can include interleaved planar k-space trajectories which are axially rotated as in projection-reconstruction or planar k-space trajectories which traverse parallel planar slices through the volume. The volume can be spherical, ellipsoidal, or defined by generatrices of a family of cones. The scans provide faster coverage of k-space and thus reduce total scan time.

Abstract: A fast, spectrally-selective steady-state free precession (SSFP) imaging method is presented. Combining k-space data from SSFP sequences with certain phase schedules of radiofrequency excitation pulses permits manipulation of the spectral selectivity of the image. For example, lipid and water can be rapidly resolved. The contrast of each image depends on both T1 and T2, and the relative contribution of the two relaxation mechanisms to image contrast can be controlled by adjusting the flip angle. Several applications of the technique are presented, including fast musculoskeletal imaging, brain imaging, and angiography. The technique is referred to herein as linear combination steady-state free precession (LCSSFP) and fluctuating equilibrium magnetic resonance (FEMR).

Abstract: The present invention uses spectral-spatial 180° refocusing pulses in the point resolved spectroscopy (PRESS) localization sequence. The PRESS sequence uses a series of three pulses having a tilt angle pattern of 90°-180°-180°. The first excitation pulses in the present invention is a spatially selective 90° tilt angle pulse. The following two pulses are spectral-spatial refocusing pulses which provide multi-dimensional selectivity. This feature allows for enhanced solvent suppression, reduced chemical shift induced spatial displacement and an ability to refocus weakly coupled spins. In a preferred embodiment, the spectral-spatial pulses are time-asymmetric and identical, providing for a linear phase profile by means of phase compensation between the two refocusing pulses. Alternatively, a linear phase profile can be provided by using time-symmetric refocusing pulses. The time-asymmetric feature is preferred because it results in lower applied RF power and shorter echo times.

Abstract: The present invention provides methods for adjustment of contrast of magnetic susceptibility variations where the variations cause distortions which are removed by view angle tilting. Often, magnetic susceptibility variations are caused by devices such as needles inserted into a patient. In two methods of the present invention, first and second field gradients are applied simultaneous with excitation and refocusing gradients, respectively. The first and second gradients have different amplitudes or orientations, or both. This results in fewer spins rephasing in the vicinity of the susceptibility variation than elsewhere, thereby providing contrast. In another embodiment of the invention, a spin echo is produced, and the detection time of the spin echo signal is offset from the time of the spin echo. The offset results in a phase cancellation of spins near the susceptibility variation due to the relatively large range of magnetic field strengths. Other methods of the present invention are also disclosed.

Abstract: The present invention provides methods for adjustment of contrast of magnetic susceptibility variations where the variations cause distortions which are removed by view angle tilting. Often, magnetic susceptibility variations are caused by devices such as needles inserted into a patient. In two methods of the present invention, first and second field gradients are applied simultaneous with excitation and refocusing gradients, respectively. The first and second gradients have different amplitudes or orientations, or both. This results in fewer spins rephasing in the vicinity of the susceptibility variation than elsewhere, thereby providing contrast. In another embodiment of the invention, a spin echo is produced, and the detection time of the spin echo signal is offset from the time of the spin echo. The offset results in a phase cancellation of spins near the susceptibility variation due to the relatively large range of magnetic field strengths. Other methods of the present invention are also disclosed.

Abstract: Spiral gradient design for a k-space trajectory using gradient amplifier parameters includes first determining an angle between a given gradient, g.sub.n, and the next gradient, g.sub.n+1, and then determining the magnitude of .vertline.g.sub.n+1 .vertline. based on gradient constraints represented by a circle or other shape surrounding and offset from the distal end of g.sub.n, where g.sub.n+1 extends along <g.sub.n+1 to the farthest intersection thereof with the circle.

Abstract: Flyback imaging is combined with echo planar imaging (EPI) for improved readout flow properties. For increases in imaging time of 50% or less, significant improvements in imaging are realized. The partial flyback improves partial-Fourier EPI and inside-out EPI and can be applied to any EPI trajectory.

Abstract: Time-varying error between a prescribed magnetic field and an actual magnetic field is identified from a self-encoding technique and the measurement of detected responses to various magnetic read-out gradients. The gradients can be a sinusoidal, step function, or other suitable form which enables the actual responses to be obtained from which transfer functions can be defined. In one embodiment, the data can effectively frequency sample the transfer function of the system. A gradient-recalled echo occurs each time the self-encode lobe is refocussed, and the phase of the echo peak is used to estimate the time variation of the main magnetic field, B.sub.0 (t).