University of California

Toshiba America Mri, Inc.

Toshiba Medical Systems Corporation

David M Kramer

Leon Kaufman

Weiguo Zhang

James D Hale

Joseph W Carlson

Christine Hawryszko

David M Goldhaber

John M Coleman

Mitsuaki A Arakawa

Lawrence E Crooks

Hsu Chang

Andrew Li

Barry M McCarten

Hector E Avram

Ching Yao

Ilya Simovsky

Kingman Yee

Kristen Hake

Heckor Avram

Joel Wummer

Ricardo Guzman

In preferred embodiments, a fast spin echo imaging technique is provided that is insensitive to violations of the Carr Purcell Meiboom Gill (CPMG) condition. Diffusion gradients disrupt the CPMG condition, and, hence, the present fast spin echo method is compatible with diffusion measurements and diffusion weighted imaging. The preferred embodiments of the present technique involve splitting of spin echoes into echo pairs. Spin echoes are split by adjustment (in magnitude or duration) of an initial readout gradient pulse. A train of echo pairs is captured. A first image is constructed using the first echoes of each pair. Also, a second image is constructed using the second echoes of each pair. Hybrid radial Cartesian methods are used for constructing the first and second images. The first and second images are constructed independently of one another. Independent image construction renders the method insensitive to violation of the CPMG condition. Finally, the two images are combined to form a final image.

Fast spin echo MRI method compatible with CPMG violation

A method and a system for acquiring diffusion magnetic resonance images with compensation of the effects of eddy currents induced by the diffusion weighting (DW) gradient pulses. Prescan data are first acquired using the same DW sequence to be used for imaging. The prescan data are used to obtain eddy current parameters that model the effects of DW-induced eddy currents under the exact conditions under which DW images are to be acquired. The DW imaging sequence is then slightly modified according to the eddy current parameters and used to acquire DW image data with the effects of DW-induced eddy currents compensated.

Method and apparatus for diffusion magnetic resonance imaging with the effects of eddy currents compensated

A magnetic resonance imaging (MRI) method is disclosed for generating and identifying water and fat separated MR images. Image data is first acquired to obtain two echo images with the water and fat signals orthogonal in the first echo image, and parallel/anti-parallel in the second echo image. The effect of background field inhomogeneties are removed, and water and fat images are separated from each other. The separated water and fat images are identified according to the difference of their precessing frequencies.

Separation and identification of water and fat MR images at mid-field strength with reduced T2/T2* weighting

A method and apparatus for producing water-dominant and fat-dominant MR signal data for use in constructing separate images from single-scan single-point Dixon MRI sequences is disclosed. The effects of field inhomogeneities are removed by quantitating the signal phase by taking the argument of the MR signal multiplied by itself. A region-growing algorithm guided by a polynomial model is used to unwrap the phase which is then used to separately generate water-pixel data and fat-pixel data for producing separate images. The invention can be used for constructing images from both 2-D and 3-D spin-echo and/or field-echo acquisitions.

Method and apparatus for providing separate water-dominant and fat-dominant images from single scan single point dixon MRI sequences

A method and apparatus for obtaining three MRI image data in a single data acquisition TR interval for use in constructing separate water and fat images by appropriate processing of the three images data is disclosed. The three image data are obtained in one exemplary embodiment by sandwiching a spin echo between two field echoes. The invention can also be used for multiple-echo and multiple-slice 3D scans.

Method and apparatus for providing separate fat and water MRI images in

Methods and apparatus for correcting image artefacts caused by variations in the main magnetic field of an MRI system are disclosed, particularly for MRI with steady-state spin precession. For field correction in MRI with steady-state spin precession, the effects of the field changes can be corrected by quantifying the time course of the field drifts by repeated acquisition of the zero k-space lines. The change in the phase between consecutive zero k-space lines is used as an indicator of field variation and for correction of associated image artifacts. By using for field correction the zero k-space lines acquired using the imaging sequence itself, the steady-states of spin precession are undisturbed throughout the MRI data acquisition.

Correction for field variation in steady-state MRI by repeated

At least one imaging parameter (e.g., the repetition interval TR or the initial nutation angle .theta.) is varied during the course of a single MR image sequence. This variation in at least one imaging parameter is preferably controlled so as to increase the contrast and signal-to-noise ratio of lower spatial frequency image components. For example, by using longer TR intervals (or smaller initial nutation angle .theta.) during lower spatial frequency phase encoding sub-sequences, relatively more signal is gathered from NMR nuclei having long T1 parameters thus providing a resultant image with many characteristics of a much longer overall sequence (e.g., one using uniform relatively long TR intervals for all spatial frequency phase encoding sub-sequences).

MRI using variable imaging parameter(s) within a single image sequence

Continuously updated real-time magnetic resonance imaging processes are used to display an MR image volume to an operator and/or patient co-located with the MRI magnet, viewing console and other elements of an MRI system within the same shielded gantry room. A CRT display may be used for lower field MRI systems while liquid crystal displays may be necessary for higher field MRI systems since the viewing console is to be co-located within the shielded gantry room near the MRI magnet assembly. Suitable RF shielding is provided to RF-isolate the viewing console and its related power and video signal cables from the MRI RF coils being used to monitor relatively weak NMR signals emanating from the image volume within the magnet assembly. When used with open access MRI magnet assemblies, such real-time viewing of the image volume within the gantry room permits performance of simultaneous patient procedures guided by real-time visual feedback to the patient and/or doctor, nurse, patient attendant and the like while located within the gantry room and having direct access to the patient anatomy within the image volume.

Real-time MR imaging inside gantry room

A measure of magnetic field inhomogeneity along a phase-encoded (e.g. y-axis) dimension is derived in k-space from previously acquired MRI phase-encoded projection data. From this, a measure of MRI data skewing caused by such inhomogeneity is obtained and used to compensate therefor. Since the MRI data is to be multi-dimensionally Fourier Transformed in most instances anyway, a transform in the relevant phase encoded dimension (e.g., y-axis) is taken followed with phase shifting each digitized data point by an amount proportional to the measured magnitude of inhomogeneity and to the datum coordinate in the read-out dimension (e.g., x-axis) and to the datum coordinate in each phase-encode dimension (e.g., y-axis) before the data is further Fourier Transformed with respect to the read-out dimension (e.g., x-axis). If two-dimensional phase encoding is employed (e.g., as in 3DFT), then a second level of similar inhomogeneity compensation can be had in the third dimension (e.g., z-axis) as well.

Method and apparatus for compensating magnetic field inhomogeneity

Positioning of interventional devices within the patient image volume of an MRI system is performed while viewing real-time fluoroscopic MR images of such devices superimposed upon a saved prior image ('ghost') of patient anatomy that was earlier located within the same image volume. After such interventional medical procedure is thoroughly planned using the earlier acquired three-dimensional ghost image, the patient anatomy is relocated within the image volume and the final selected trajectory for the interventional device or medical procedure is then performed (preferably while real time MRI fluoroscopy is used to monitor the actual interventional procedure within the real patient anatomy).

Method and apparatus for performing interventional medical procedures

Techniques for rapidly and accurately calibrating RF transmitter parameters in a Nuclear Magnetic Resonance (NMR) magnetic resonance imaging (MRI) system obtain an estimate of flip (nutation) angle by determining a ratio of plural echo responses to a plural (e.g., three) RF pulse sequence. The ratio may be selected to be independent of relaxation times T.sub.1 and T.sub.2 so no relaxation waiting time between successive iterations is required. Accurate RF transmitter level calibration can be performed within on the order of three to five seconds. The techniques are robust and can discriminate flip angles over a wide range.

Rapid calibration of nutation angles in MRI

Static B.sub.o field strength is measured during each TR interval of an MRI sequence providing field calibration data used to compensate for rapid variations in B.sub.o during the MRI sequence.

MRI compensated for spurious rapid variations in static magnetic field

Variable voxel shifts required for shifting a 3D structure into a common oblique or contoured slice volume based on an existing 3D image are achieved by effecting variable f(x,y) phase shifts in corresponding frequency domain data parallel to a selected axis dimension and then reconstructing a new three-dimensional image having the 3D structure all located within a common oblique or otherwise contoured slice volume such that it may viewed in a single planar image display without loss of volume resolution. Equivalent convolution processes withing the spatial domain may also be empolyed. Oblique or curved reconstructions can thus be made using either originally acquired frequency domain data (used to construct the original image) or frequency domain data obtained by inverse Fourier transforming the available spatial domain data of the images themselves.

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San Rafael, CA, United States of America

David M Kramer