210 results about "Gradient echo" patented technology

In a method and apparatus for MR imaging, a data acquisition sequence is executed wherein at least two slices of an examination subject are imaged in parallel with a gradient echo method for spatially resolved quantification of the T1 relaxation time.

At least one first acquisition sequence is implemented to acquire MR data from a first slice of the examination subject and at least one second acquisition sequence is implemented to acquire MR data from a second slice of the examination subject. The acquisition sequences each include an inversion pulse and at least two successive readout steps. The first and second acquisition sequences are temporally offset from one another such that they at least partially overlap.

A method of magnetic resonance spectroscopic imaging of an object (O) including at least one chemical species to be imaged, comprising sampling of the k-space such that a plurality of N_ω first sampling trajectories through at least one k-space segment of the k-space is formed along a phase-encoding direction, each of said first sampling trajectories beginning in a central k-space region and continuing to a k-space border of the at least one k-space segment and having a duration equal to or below a spectral dwell time corresponding to the reciprocal spectral bandwidth, collecting at least one first set of gradient-echo signals obtained along said first sampling trajectories, collecting at least one second set of gradient-echo signals obtained along a plurality of N_ω second sampling trajectories, said N_ω second sampling trajectories and said N_ω first sampling trajectories being mutually mirrored relative to a predetermined k-space line in the central k-space region.

A magnetic resonance imaging diagnostic apparatus includes a generating unit which generates a slice gradient magnetic field, a phase-encode gradient magnetic field and a read-out gradient magnetic field that extend in a slice axis, a phase-encode axis and a read-out axis, respectively, a setting unit which sets a dephase amount for weighting a signal-level decrease resulting from flows in the arteries and veins present in a region of interest of a subject, with respect to at least one axis selected form the slice axis, phase-encode axis and read-out axes, and a control unit which controls the generating unit by using a pulse sequence for a gradient echo system, which includes a dephase gradient-magnetic-field pulse that corresponds to the dephase amount set by the setting unit for the at least one axis.

The MRI apparatus of the present invention performs a pulse sequence for applying successively 180° pulses 102, 103 . . . after application of a 90° pulse 101 at constant intervals and applying readout magnetic fields 111 during the interval between pairs of 180° pulses while the polarity of the magnetic field 111 is inverted several times to collect a plurality of gradient echo signals that are phase encoded differently. Here, the application of the readout gradient magnetic field is controlled such that generation of the gradient echo signals does ot coincide with generation of the spin echo signal. The image reconstruction is performed by using only T2* weighted gradient echo signals to obtain images reflecting difference in magnetic susceptibility and inhomogeneities in local magnetic fields.

A spin locked balanced steady-state free precession (slSSFP) pulse sequence combines a balanced gradient echo acquisition with an off-resonance spin lock pulse for fast MRI. The transient and steady-state magnetization trajectory is solved numerically using the Bloch equations and is shown to be similar to balanced steady-state free precession (bSSFP) for a range of T2/T1 and flip angles, although the slSSFP steady-state could be maintained with considerably lower RF power. In both simulations and brain scans performed at 7 T, slSSFP is shown to exhibit similar contrast and SNR efficiency to bSSFP, but with significantly lower power.

A method for reconstructing a sequence of magnetic resonance (MR) images of an object under investigation, includes the steps of (a) providing a series of sets of image raw data including an image content of the MR images to be reconstructed, the image raw data being collected with the use of at least one radiofrequency receiver coil of a magnetic resonance imaging (MRI) device, wherein each set of image raw data includes a plurality of data samples being generated with a gradient-echo sequence, in particular a FLASH sequence, that spatially encodes an MRI signal received with the at least one radiofrequency receiver coil using a non-Cartesian k-space trajectory, each set of image raw data includes a set of homogeneously distributed lines in k-space with equivalent spatial frequency content, the lines of each set of image raw data cross the center of k-space and cover a continuous range of spatial frequencies, and the positions of the lines of each set of image raw data differ in successive sets of image raw data, and (b) subjecting the sets of image raw data to a regularized nonlinear inverse reconstruction process to provide the sequence of MR images, wherein each of the MR images is created by a simultaneous estimation of a sensitivity of the at least one receiver coil and the image content and in dependency on a difference between a current estimation of the sensitivity of the at least one receiver coil and the image content and a preceding estimation of the sensitivity of the at least one receiver coil and the image content.

A method for generating a susceptibility (or T2*) weighted magnetic resonance (MR) image includes defining a pulse sequence having a plurality of gradient echoes and acquiring MR data for each of the plurality of gradient echoes. A weighting function is applied to image data for each gradient echo such as MR data (e.g., k-space data) or magnitude images associated with each gradient echo. A susceptibility weighted image is generated by combining the image data for each gradient echo based on at least the application of the weighting function.

In a method and apparatus for acquiring magnetic resonance (MR) data from a subject, excitation pulses and at least two refocusing pulses are applied to the subject in an MR scanner, and the MR scanner is operated to activate gradients in a readout direction that cause at least two gradient echoes to be formed between the at least two successive refocusing pulses, with a temporal distance between the at least two gradient echoes that produces a predetermined phase shift between a signal acquired from a first nuclei in the subject and a signal acquired from a second nuclei in the subject at times of the respective gradient echoes, and that include readout gradients associated respectively with a first and a last gradient echo, among said at least two gradient echoes, the readout gradients being asymmetrical.

A system for accelerated segmented magnetic resonance (MR) image data acquisition includes an RF (Radio Frequency) signal generator and a magnetic field gradient generator. The RF signal generator generates RF excitation pulses in anatomy and enabling subsequent acquisition of associated RF echo data. The magnetic field gradient generator generates magnetic field gradients for anatomical volume selection, phase encoding, and readout RF data acquisition in a three dimensional (3D) anatomical volume. The RF signal generator and the magnetic field gradient generator acquire consecutive segments of k-space line data representative of an individual image slice in a gradient echo method by adaptively varying RF excitation pulse flip angle between acquisition of the consecutive segments.

The present invention is directed to methods for chemical species signal suppression in magnetic resonance imaging procedures, wherein Dixon techniques are enhanced by continuously sampling techniques. In the invention, k-space data is acquired during the entire period of read gradient associated with a gradient echo pulse acquisition scheme. The invention utilizes a total sampling time (TST) acquisition during the entire read gradient, using three echoes of a TST data set to achieve chemical species separation in both homogenous fields as well as areas of field inhomogeneity. As an example, a continuously sampled rectilinearly FLASH pulse sequence is modified such that the time between echoes was configured to be 2.2 milliseconds, with TE selected to allow 180° phase variation in the fat magnetization between each of the three TE's (TE1, TE2, and TE3). Data collected during the dephase and rephase gradient lobes are defined as a first Dixon acquisition, with data collected by the read gradient lobe being defined as a second Dixon acquisition. Two point Dixon reconstruction techniques are used to form images for each chemical species, such as for generating water and fat images of the scanned object region. Other corrections, such as off-resonance correction may be applied on the image data.

An apparatus includes a magnetic resonance imaging system, a processor for controlling the apparatus, and a memory containing machine executable instructions and a pulse sequence. The machine executable instructions and pulse sequence cause the processor to control the apparatus to: acquire magnetic resonance data from an imaging volume, wherein the magnetic resonance data includes gradient echo data; segment the magnetic resonance data into a plurality of segments, the segments including a fat segment, a water segment, a cortical bone segment, and an air segment; and create a bulk density map of the imaging volume from the segments.

In a method and magnetic resonance system to determine multiple magnetic resonance images for respective different echo points in time, k-space is scanned on a segment-by-segment basis with at least two rectangular k-space segments, these being scanned line by line with respective k-space lines oriented parallel to one another. A short side of the rectangular k-space segments is oriented parallel to the k-space lines. First and second gradient echoes are respectively produced by a radio-frequency pulse radiated for each k-space line.

An MRI apparatus having a calibration pulse sequence, wherein a group of pulse sequences for applying test gradient magnetic fields are established from a basic pulse sequence by a gradient echo method of short TR, a group of pulse sequences not applying test gradient fields are established from the basic pulse sequence, a set of three- or four-dimensional data including a time variable is created by using echo signals collected by at least one of the groups, two data sets are created as a whole by inverting the polarity of the test gradient magnetic field, the difference between phase images thereof is determined, the magnitude and time constant of eddy current induced at the fall or rise of the gradient magnetic field are determined from the phase difference image, and the variation of the magnetic field due to eddy current induced at the rise and/or fall of the gradient magnetic field can be measured in a relatively short time with a desired time resolution even if the magnetic field variation is of a very long time constant.

A method for reconstructing a sequence of magnetic resonance (MR) images of an object under investigation, comprises the steps of (a) providing a series of sets of image raw data including an image content of the MR images to be reconstructed, said image raw data being collected with the use of at least one radiofrequency receiver coil of a magnetic resonance imaging (MRI) device, wherein each set of image raw data includes a plurality of data sampies being generated with a gradient-echo sequence, in particular a FLASH sequence, that spatially encodes an MRl signal received with the at least one radiofrequency receiver coil using a non-Cartesian k-space trajectory, each set of image raw data comprises a set of homogeneously distributed lines in k-space with equivalent spatial frequency content,; the lines of each set of image raw data cross the center of k-space and cover a continuous range of spatial frequencies, and the positions of the lines of each set of image raw data differ in successive sets of image raw data, and (b) subjecting the sets of image raw data to a regularized nonlinear inverse reconstruction process to provide the sequence of MR images, wherein each of the MR images is created by a simultaneous estimation of a sensitivity of the at least one receiver coil and the image content and in dependency on a difference between a current estimation of the sensitivity of the at least one receiver coil and the image content and a preceding estimation of the sensitivity of the at least one receiver coil and the image content.

The invention discloses an imaging method for MRI contrast enhancement. Optimized inversion pulses are utilized to replace inversion pulses of a conventional inversion recovery sequence in MRI and to restore delay time, under the precise control of the optimized pluses, spin of different tissue will be evolved towards the trend of maximization of longitudinal magnetic moment differences, and the maximum longitudinal magnetic moment difference is obtained at the end moment of the pluses; on that basis, 90-degree excitation read pluses are applied to enable the maximized magnetic moment difference among the tissue to be turned over to a transverse plane, gradient echo signals are collected to form k spatial data, and the purpose of contrast enhancement among the tissue can be finally achieved through improvement on a phase sensitive image reconstruction method. According to the imaging method, the problem of too long scanning time of the conventional inversion recovery sequence is solved, the advantages of flexibility of optimized pulse waveforms and flexibility of the phase sensitive image reconstruction method are fully utilized, use of expensive magnetic resonance contrast media can be avoided, and the imaging method is superior to an existing MRI contrast enhancement method both in performance and in cost.

A method is disclosed for determining an attenuation map for use in positron emission tomography and for the use of homogeneity information relating to the magnetic resonance magnetic field, in particular for the purpose of determining shim settings, within the scope of a single magnetic resonance image recording. In at least one embodiment of the method, a first and a second image data record are firstly recorded with a three-dimensional gradient echo sequence during a first and a second echo time, respectively, with the phase difference between the water and the fat signal amounting to zeroduring the first echo time and amounting to 180 degrees during the second echo time. The attenuation map is determined from fat/water ratios obtained from the image data records by way of a Dixon technology, in particular a 2-point Dixon technology. In at least one embodiment, all voxels with a signal intensity below a first threshold value are excluded at least for the second image data record by using a mask and only the non excluded voxels of the first and second image data record are taken into consideration in order to determine the homogeneity information from the phase differences of adjacent voxels.

The invention discloses a gradient-echo multi-echo water and fat separation method. The method includes the following steps of 1, using a three-dimensional gradient-echo N echo sequence for conductingimaging scanning on a magnetic resonance imaging region, collecting N pieces of echo data, and using a GRAPPA technology for accelerating data collection during collection, wherein N is greater thanor equal to 4; 2, using the GRAPPA technology for fitting and restoring to-be-collected phase encoding data of the N pieces of echo data within respective K spaces, and then conducting preliminary data processing to obtain complete image domain data of N echoes; 3, substituting the image domain data of the N echoes into a water and fat separation algorithm of a multi-peak water-fat model, introducing T2* variables, conducting iterative calculation, obtaining a T2* distribution map of an imaged object, and meanwhile obtaining water and fat images through calculation. According to the method, the T2* distribution can be accurately estimated, the signal attenuation between the echoes is effectively corrected, and phase changes caused by inhomogeneity of a magnetic field are reduced, so that results of the quantitative analysis images are more accurate and stable. A magnetic resonance imaging system using the method is also provided.

In a method and a magnetic resonance system to determine the T1 time of water and the T1 time of fat in a predetermined volume segment of an examination subject, magnetic field gradients are activated to generate multiple gradient echoes. First echoes are acquired at at least two different echo times based on RF pulses with a first flip angle. A first water magnetization and a first fat magnetization are determined for each voxel of the volume segment from the first echoes, according to the Dixon method. Second echoes are acquired at at least two different echo times based on RF pulses with a second flip angle. A second water magnetization and a second fat magnetization are determined for each voxel of the volume segment depending on the second echoes according to the Dixon method. The T1 time of water and the T1 time of fat for each voxel are determined depending on the first water magnetization of the respective voxel, the first fat magnetization of the respective voxel, the first flip angle, the second water magnetization of the respective voxel, the second fat magnetization of the respective voxel, and the second flip angle.

The inventors have established design principles for phased-array MRI coils from the considerations of the target region of the anatomy being evaluated and physical anatomy of the patients. Accordingly, the inventors have demonstrated shape-optimized phased array coils with dense packing of 32 channels for posterior-head imaging exhibiting the SNR gains required to realize not only sub-millimeter fMRI BOLD imaging but also allowing single-shot Gradient Echo-EPI imaging to be performed upon general 3 T MRI instruments. At the same time the design techniques address ergonomic considerations of the patient and designing shape-optimized phased-array MRI coils and patient supports that account for variations within the human population arising from factors such as race, gender, etc.

Measurements of functional, hemographic, and blood flow parameters use a multiple echo or spin echo gradient pulse sequence whereby an early echo is acquired near the beginning of the pulse sequence which avoids saturation effects and a later echo near the end of the pulse sequence which can provide information with more sensitivity to a contrast agent for a susceptibility weighted image.

The invention provides a lower limb deep venous thrombus magnetic resonance imaging method and device. On the premise that no contrast media are used, injuries to a patient are avoided, and meanwhile the imaging effect is improved. The method includes the steps that blood flow signals of lower limb deep veins are suppressed, blood vessel wall and thrombus signals of the lower limb deep veins are retained, and preprocessed signals of the lower limb deep veins are obtained; the preprocessed signals of the lower limb deep veins are sampled through a variable-turning-angle spin echo sequence or a fast small-angle gradient echo sequence; according to sampled data, a lower limb deep venous thrombus magnetic resonance image is acquired. By means of the technical scheme, on one hand, blood vessel walls, blood flow and thrombi of the lower limb deep veins can be accurately differentiated, and whether thrombi exist in blood vessels or not can be visually displayed; on the other hand, the lower limb deep venous thrombus magnetic resonance image obtained through the method and device can display whether thrombi exist in the lower limb deep veins or not and the distribution positions of the thrombi, the thrombi can be preliminarily staged, and practical and effective information is provided for clinical treatment.