Abstract: The present invention includes a method and apparatus to correct for gradient field distortions. The invention is particularly applicable in moving table imaging where a single extended image is desirable. The invention includes acquiring MR data in motion in the presence of gradient non-linearities, transforming the MR data acquired into the image domain, and then applying a warping correction function to the transformed MR data. The warp-corrected MR data is then corrected for motion induced during the MR acquisition. The data may be acquired point-by-point, line-by-line, or another sub-portion of the entire MR data acquired, and processed to minimize the amount of motion correction needed. Based on table velocity or acquisition sequence applied, the data is partitioned based on a common motion correction factor, and after correcting for motion, the data is accumulated to build up a final image.

Abstract: A method for the simultaneous acquisition of data from two transmit/receive “birdcage” coils is described. The coils are individually RF shielded, making them insensitive to signals generated outside of each coil's volume. Each coil is designed for imaging one leg, and when used together, both legs are imaged simultaneously. In coronal or axial orientations, a small FOV around each leg can be imaged without aliasing. This results in a two-fold scan time reduction compared to a large FOV acquisition with the same spatial resolution.

Abstract: MRA data is acquired from a large region of interest by translating the patient through the bore of the MRI system as a three-dimensional MRA data set are acquired. Patient table movement is controlled to track a bolus of contrast agent as it passes through the region of interest. Fluoroscopic images may be acquired during the scan to enable accurate bolus tracking. A seamless image of the entire region of interest is reconstructed.

Abstract: An fMRI scan is performed with an MRI system in which a series of single shot EPI pulse sequences are performed to acquire a series of images. A shim navigator pulse sequence is interleaved with the EPI pulse sequence to acquire data with which the MRI system polarizing magnetic field can be measured. Measured changes in the polarizing field during the scan are employed to calculate corrective changes in the scan parameters that offset phase errors caused by changes in the polarizing field.

Abstract: An image acquisition using a spoiled, gradient-recalled echo imaging pulse sequence is preceded by a magnetization preparation sequence which rapidly drives longitudinal magnetization to the steady-state equilibrium level established by the imaging pulse sequence. The preparation sequence includes an RF saturation pulse followed by a recovery period (Trec) whose length is determined by the scan parameters of the imaging pulse sequence.

Abstract: An MRI system performs a three-dimensional fast, gradient-recalled echo pulse sequence to acquire NMR data for both 2D and 3D images during a CE-MRA scan. The 2D images may be acquired before, during or after the 3D image acquisition. The 2D images may be reconstructed in real-time and used to control the acquisition of the high resolution 3D image.

Abstract: An MRI system performs a three-dimensional fast, gradient-recalled echo pulse sequence to acquire NMR data for both 2D and 3D images during a CE-MRA scan. The 2D images may be acquired before, during or after the 3D image acquisition. The 2D images may be reconstructed in real-time and used to control the acquisition of the high resolution 3D image.

Abstract: An MRI system produces a series of real-time images by repeatedly acquiring image data and repeatedly reconstructing images from the acquired image data. The effective latency period between acquisition of the image data and display of the reconstructed images is minimized by acquiring image data in a reverse-centric view order in which low spatial frequencies are acquired last.

Abstract: A method and apparatus for producing an imaging plane on an image of a structure of interest, such as an anatomical structure, positioned in an MRI system. An operator interactively pages through real-time, planar sections of the structure of interest. Using an input device, the operator selects three separate points in a planar section of the structure under study. Within approximately one second of selection of the third point, the method of the present invention determines the imaging plane containing the three selected points, determines the centroid of the imaging plane centered on a triangle defined by the three selected points, sends such imaging geometry and in-plane offsets of the imaging plane directly to the MRI system to generate a new imaging plane optimally positioned with respect to the selected points on the structure of interest and displaying such new imaging plane. The operator can also selectively maneuver the imaging plane on the image of the structure of interest.

Abstract: A dynamic MRA study of a subject is performed using a 3D fast gradient-recalled echo pulse sequence after the subject is injected with a contrast agent. The sampling of k-space is synchronized with the peak of the contrast enhancement profile by sampling in an inward spiral pattern during the rise in enhancement and by sampling in an outward spiral pattern after peak enhancement occurs.

Abstract: A dynamic MRA study of a subject is performed using a 3D fast gradient-recalled echo pulse sequence after the subject is injected with a contrast agent. The flip angle of an rf excitation pulse in the pulse sequence is modulated during the acquisition as a function of contrast agent concentration in the region of interest. In one embodiment the flip angle is updated by interleaving measurement pulse sequences which measure in real-time contrast agent concentration. In another embodiment the contrast concentration profile is determined in advance and a corresponding table of optimal flip angles are calculated and played out during the image acquisition.

Abstract: A bipolar, phase-encoding, pre-phaser pulse is employed in each shot of a multi-shot EPI pulse sequence to smooth the phase-encoding gradient first moment throughout the scan. The first moment of the pre-phaser pulse is calculated for each shot in the scan and is played out at the beginning of each shot after the RF excitation.

Abstract: A 3DFT NMR scan is performed by stepping two phase encoding gradients through a sequence of values to sample all locations in k-space. The gradients are stepped such that k-space is covered by sampling closer to the origin of k-space first. Two methods for ordering the k-space sample points are disclosed.

Abstract: A method for removing artifacts from NMR images in which two NMR data sets S.sub.1 and S.sub.2 for two images of the region of interest are acquired. The correlation of the two data sets S.sub. and S.sub.2 is produced as part of the Fourier transformation image reconstruction process and a corrected image is reconstructed from the result. Modulations which are different in the two NMR data sets S.sub. and S.sub.2 are removed, while common signals produced by stationary structures contribute to the image.

Abstract: In an NMR system a respiration monitor provides a visual feedback to the patient which enables the patient to perform a series of breath-holds with the patient's diaphragm positioned at the same reference point. This enables NMR data to be acquired over a series of breath-holds without introducing blurring or image artifacts. Between breath-holds a navigator pulse sequence is used to gather NMR data from which diaphragm position is measured, and during each breath-hold the pulse sequence is changed to gather NMR image data.

Abstract: An ultra-fast NMR scan includes a preparatory phase, a stabilization phase and a data acquisition phase. Image contrast is enhanced by an inversion-recovery-like preparation phase and this is followed by a set of fast pulse sequences in which magnetization is allowed to stabilize. Image data is then acquired during the final phase using a set of GRASS pulse sequences executed in a centric view order.

Abstract: A 3DFT NMR scan is performed by stepping two phase encoding gradients through a sequence of values to sample all locations in k-space. The gradients are stepped such that k-space is covered by a spiral trajectory that originates at the origin and extends to the periphery of k-space. Alternative embodiments cover k-space with a set of four or eight interleaved spiral trajectories.

Abstract: An NMR system acquires data by performing a scan using a spin echo pulse sequence. An image is produced from the acquired data using a 2DFT reconstruction method. During the scan the echo time (TE) or the repetition time (TR) is altered as a function of phase encoding value to decrease total scan time or to improve signal-to-noise.

Abstract: Near real time imaging of materials within a body is accomplished by subjecting a body area to a predetermined plurality of applications of short repetition time NMR pulse sequences and constructing an image from data corresponding thereto. The image is continuously updated by collecting data from repetitive applications of one or more short repetition time NMR pulse sequences subsequent to the plurality of applications wherein each of the applications of one or more pulse sequences consists of fewer applications than the plurality of applications of pulse sequences. The imaging data from each of the applications of one or more pulse sequences is repetitively substituted for corresponding imaging data previously used to construct the image in order to provide for continuous partial updating of the image.

Abstract: High speed selective imaging of blood vessels is accomplished by subjecting an area of interest to a plurality of short repetition time NMR pulse sequences during each high velocity period and low velocity period of a heart beat cycle for several or more heart beats. The imaging data from each NMR pulse sequence is collected and weighted according to whether it corresponds to a high velocity period or a low blood velocity period. The weighted imaging data corresponding to high blood velocity periods is then subtracted from weighted imaging data corresponding to low blood velocity periods and the resulting data used to form an image which depicts only the blood vessels of interest. Also, an imaging data processing apparatus is disclosed which operates in real time so as to permit an operator to optimize diagnostic performance.