Abstract: A method and apparatus are disclosed for creating peripheral MR angiographic images and performing an MRA examination using an intravascular contrast agent in which MR data acquisition is optimized in the most distal stations in a multi-station acquisition. The technique includes administering a contrast agent into the blood stream of the patient, acquiring low spatial resolution MR images of the arterial vasculature, and tracking the passage of the contrast agent through the patient. The patient table is moved in response to the tracking. The technique continues to acquire low spatial resolution images at each of the proximal stations until the most distal station is reached where a high spatial resolution image data set is then acquired of preferentially arterial vascular structures. Higher spatial resolution images are then acquired in the proximal stations.

Abstract: A system and method are disclosed to acquire high temporal resolution free-breathing cardiac MR images. The technique includes monitoring heart rate of a patient just prior to image acquisition to acquire a time period of an R-R interval, and using this time period from the heart rate monitoring to prospectively estimate future R-R intervals. The acquisition of MR data can then commence at any point in an R-R interval and extend for the time period recorded. The data acquisition can be segmented and acquired in successive R-R intervals, then combined to create high temporal resolution images.

Abstract: A method and apparatus is disclosed to initially screen a patient's peripheral arterial vasculature for lesions, or stenotic vessels, using MR technology, and then grading the severity of any located stenosis. The invention includes tracking the passage of a contrast agent bolus through a patient, while acquiring a series of first MR images having low resolution. This initial examination uses flow sensitive bi-polar gradient waveforms with a gradient echo imaging pulse sequence to increase the sensitivity to lesion detectability. The bi-polar gradients generate a broad distribution of velocities in a large voxel. Relevant stenoses present in a voxel will result in intra-voxel flow dephasing in voxels immediate to and distal to the stenosis. After identifying a stenosis, a second MR image, having a higher resolution than the first, is used to grade the stenosis.

Abstract: A cardiac triggered, fast gradient-recalled echo pulse sequence is used to acquire a partial Fourier image data set during a single breath-hold. The image data is velocity encoded and a velocity image is produced by zero-filling and Fourier transforming the zero-filled data set. A separate magnitude image is produced by performing a homodyne reconstruction on the partial Fourier image data set. Anatomic information, such as artery size, is obtained from the magnitude image and combined with velocity information from the velocity image to measure blood flowing through an artery.

Abstract: A system and method for creating MR images using mask data that is copied forward for on-the-fly image subtraction for use within such techniques as MR angiography is disclosed. The invention includes acquiring an MR mask image comprised of a plurality of k-space lines, and then copying the k-space line data of the MR mask image into a number of different memory locations. The number of different memory locations corresponds to a preselected number of MR image acquisitions as set by an MR operator. The invention next includes acquiring the preselected number of MR images, each comprised of k-space line data. As the k-space line data is acquired, it is then immediately accumulated in one of the memory locations having the MR mask image k-space line data. By setting a polarity of the data stored, each acquired k-space line of an acquired MR image is subtracted from a corresponding k-space line of the MR mask image in real time. The image is then reconstructed using the subtracted k-space line data.

Abstract: A method of MR imaging using fractional MRI acquisitions to reduce total acquisition time includes the steps of: obtaining a scan-specific partial MRI kx data set fraction and a scan-specific partial MRI ky data set fraction at a first location; acquiring a partial MRI kx data set in k-space along a kx direction, the partial MRI kx data set containing the scan-specific partial MRI kx data set fraction amount of direction data; acquiring a partial MRI ky data set in k-space along a ky direction, the partial MRI ky data set containing the scan-specific partial MRI ky data set faction amount of direction; reconstructing an MR image using the partial MRI kx data set and the partial MRI ky data set; and transmitting information relating to the MR image between the first location and a second location remote from the first location.

Abstract: A method and apparatus is disclosed to rapidly assess the severity of a stenosis using MR technology. The invention includes identifying a suspected stenotic vessel and applying a phase contrast pulse sequence to the stenotic vessel in which the MR operator is allowed to control the amplitude and direction of the flow encoding gradient. Peak flow velocity is determined in the suspected stenotic vessel by correlating the flow encoding gradient with the onset of flow velocity aliasing. In a preferred embodiment, the invention utilizes a 2D fast gradient echo pulse sequence having flow sensitizing bipolar gradient waveforms. The resulting flow sensitizing gradients are substantially coincident in time, thereby allowing rotation of the resultant flow sensitizing gradient direction. The amplitude of the flow encoding gradient is increased until the observance of flow related aliasing.

Abstract: A method is disclosed for providing a time efficient and accurate measure of the absolute positional displacements of a reference structure in navigator echo MR imaging. The method comprises the steps of operating an MR system to acquire a reference navigator echo associated with the object at a specified reference position, and applying an MR sequence to the object to acquire a set of MR image data when the object is selectively displaced from the reference position. The data set includes an acquired navigator echo having a specified field of view. The method further comprises truncating the acquired navigator echo by means of a selectively positioned truncation window, calculating the difference between linear phase shifts respectively associated with acquired and reference navigator echoes, and displacing the truncation window by an amount representing or corresponding to the phase shift difference in spatial units.

Abstract: The present invention relates generally to magnetic resonance imaging (MRI), and more particularly to a method and apparatus for efficient MRI tissue differentiation using an RF pulse designed to provide a frequency response combining a magnetization transfer contrast and fat saturation simultaneously. The invention includes creating a spectrally selective suppression pulse having an RF pulse profile designed to produce a frequency response with adequate fat suppression and selecting a spectrally selective suppression amplitude to produce a magnetization transfer contrast between two different tissue types, such as between proteinated tissue and water-based tissue. The invention also includes applying the spectrally selective suppression pulse with a flip angle selected to optimize fat suppression and magnetization transfer contrast saturation simultaneously.

Abstract: A method of peripheral MR angiography is provided for imaging an artery or other vessel, wherein the vessel is of such length that MR data must be acquired at each of a plurality of scan stations spaced along the vessel. In accordance with the method, a contrast agent is intravenously injected, in order to provide a bolus which successively flows to each of the scan stations. After acquiring an initial subset of the MR data associated with a given scan station, the bolus is tracked to determine whether it has arrived at the next-following scan station. If so, at least some of the MR data associated with the next scan station are then acquired. However, if it is found that the bolus has not yet arrived at the next scan station, acquisition of further data at the given scan station is continued.

Abstract: A system and method for the acquisition of preferential arterial and venous images is disclosed. The invention includes setting a noise level in the phase image, that is proportional to the velocity encoding value, at a threshold level above the venous signal but below the arterial signal during a systolic portion of the cardiac cycle and acquiring a phase contrast MR image during the systolic portion that effectively acquires the arterial signal and suppresses the venous signal. During the diastolic portion of the same R—R interval, the velocity encoding value is then set to establish a noise threshold level in the phase image lower to a value below the venous signal but above the arterial signal to acquire the venous signal and suppress the arterial signal. In this manner, either an arterial only image or a venous only image can be displayed. Alternatively, the images can be combined to create a higher SNR arterial and venous image.

Abstract: A system and method for phase sensitive MRI reconstruction using partial k-space data to reduce either scan time or echo time, depending on whether partial echo or partial NEX MR data is acquired, that retains phase information and reduces edge blurring in a magnetic resonance image. Phase sensitive partial k-space data reconstruction improves upon the homodyne reconstruction process to estimate and correct for an edge blurring convolution error term in a partial echo or partial NEX data while preserving phase information. The phase sensitive partial k-space reconstruction includes Fourier transforming and filtering the partial k-space data through high and low-pass filters, and a linear combination of both, and estimating a blurring correction term, representative of a convolution error factor, from a portion of the filtered data set.

Abstract: A system to correct edge blurring in an image reconstructed with partial k-space data includes a magnetic resonance imaging system, a computer, and a network. The magnetic resonance imaging system has a plurality of gradient coils positioned about a bore of a magnet to impress a polarizing magnetic field and an RF transceiver system and an RF modulator controlled by a pulse control module to transmit RF signals to an RF coil assembly to acquire MR images.

Abstract: A system and method for arterial and venous discrimination in MR venography is disclosed. By setting a noise level in the phase image (that is proportional to the velocity encoding value) at a threshold level between that of the arterial signals and the venous signals during the diastole portion of the cardiac cycle and acquiring a phase contrast MR image during the diastole portion, the arterial signals are effectively suppressed and a venous only image can be reconstructed. Post-processing steps are disclosed which can alternatively provide an arterial only image. By separately reconstructing a magnitude image and a phase image map to produce a magnitude image and a phase image, a masking module can create an output displaying venous only or arterial only images based on a user selection. The present invention allows for a complete noninvasive angiography exam to be completed within approximately 30 minutes.

Abstract: A system and method is disclosed to combine both a fractional echo (k.sub.x) and a fractional NEX (k.sub.y) to reduce acquisition times and echo times in MR imaging. The method uses both zero-filling and homodyne reconstruction to construct concurrent fractional NEX and fractional echo data in a single image while minimizing any blurring effects. The system includes acquiring partial MRI data in the k.sub.x direction and acquiring partial MRI data in the k.sub.y direction. Once a partial echo and a partial NEX are acquired, the missing data is first zero-filled in the k.sub.x direction and Fourier transformed to acquire a full x direction data set. Next, the data is synthesized in the k.sub.y direction using a homodyne reconstruction technique to acquire a full data set in the k.sub.y direction. The full x,y data set can then be used to reconstruct an MR image with reduced acquisition and echo times.

Abstract: A method of peripheral MR angiography is provided for imaging an artery or other vessel, wherein the vessel is of such length that MR data must be acquired at each of a plurality of scan stations spaced along the vessel. In accordance with the method, a contrast agent is intravenously injected, in order to provide a bolus which successively flows to each of the scan stations. After acquiring an initial subset of the MR data associated with a given scan station, the bolus is tracked to determine whether it has arrived at the next-following scan station. If so, at least some of the MR data associated with the next scan station are then acquired. However, if it is found that the bolus has not yet arrived at the next scan station, acquisition of further data at the given scan station is continued.

Abstract: NMR data for imaging perfusion of blood is acquired from a series of slice locations using a cardiac gated NMR pulse sequence. Data for the slice locations are acquired by a corresponding series of data acquisition segments performed during the R--R interval of each cardiac cycle. Selective rf saturation pulses are interleaved with the data acquisition segments to uniformly condition spin magnetization in each slice location.

Abstract: A fast and computationally efficient system and method is disclosed for detecting and tracking the position of a reference structure in the body using a linear phase shift to minimize motion artifacts in magnetic resonance imaging. In one application, the system and method is used to determine the relative position of the diaphragm in the body in order to synchronize data acquisition to the same relative position with respect to the abdominal and thoracic organs to minimize respiratory motion artifacts. The system and method uses the time domain linear phase shift of the reference structure data in order to determine its spatial positional displacement as a function of the respiratory cycle. The signal from a two-dimensional rectangular or cylindrical column is first Fourier transformed to the image domain, apodized or bandwidth-limited, converted to real, positive values by taking the magnitude of the profile, and then transformed back to the image domain.

Abstract: A uniform surface current density is approximated in an RF transmitting/receiving NMR coil by employing a plurality of discrete conductors having a resonantly distributed current. Inductive and capacitive lines provide a sinusoidal current distribution with various resonant modes providing different magnetic field orientations. The distributed current reduces losses. In a second order resonant mode, decoupling of the surface coil from a transmit coil is achieved without a blocking network.