General Electric Company

Erika Schneider

Gary H Glover

Charles L Dumoulin

Christopher Judson Hardy

Ronald Dean Watkins

Kenneth William Rohling

Harvey E Cline

Matthew A Bernstein

Anton Max Linz

Randy Otto Giaquinto

Michael R Hartley

Gregory A Repinski

Sheila Srinivasan Washburn

Xiguang Zang

An MRI system acquires NMR image data to produce real time anatomic images as an ablation device is guided into contact with target tissues in a patient to be thermally treated. The ablation device includes a resistive element at its operating end which receives alternating current from an ablation control system. The resistive element produces therapeutic heat that treats the target tissues.

RF driven resistive ablation system for use in MRI guided therapy

A 3D MR image is acquired before injection of a contrast agent and an enhanced 3D image is acquired after injection of the contrast agent. The two images are registered and then subtracted to remove background and to highlight lesion voxels. Lesion objects are identified by connecting contiguous lesion objects. Volume and surface area of any continuous lesion object in a discrete digital image are then calculated. Malignant lesions are identified by determining the ratio of volume to surface area for each lesion object. Malignant tumors are identified when this ratio drops below a preset threshold.

MR imaging of lesions and detection of malignant tumors

A magnetic resonance (MR) imaging method uses chemical shift and/or slice selective inversion pulse to create angiograms of coronary arteries. In one embodiment blood is doped with a contrast enhancement agent and a sequence of slice selective and chemical shift selective inversion pulses are applied. Detection RF pulses then generate an image signal. In another embodiment two sequential chemical shift inversion pulses are applied followed by detection RF pulses for imaging.

Arterial MRI with chemical-shift nulling

A novel breast localization and biopsy system employs a chest support for holding the patient in a slightly rotated (20.degree.-30.degree.) prone position allowing the breast tissue hang downward and fit through an opening in the chest support, while holding the other breast against the subject away from the imaging region. A pair of support plates compress the breast tissue. At least one of the support plates has a grid with reference markers for localization and windows allowing a physician access to the breast tissue. A thick biopsy plate with a plurality of holes at marked positions fits into one of the grid openings and guides an interventional device, such a biopsy needle, into a desired location in a lesion. In an alternative embodiment, both breasts fit through the chest support. There are two stabilization plate assemblies, one for each breast and two medical imaging sources. Each source points from the lateral to medial support plate to accomplish imaging of both breasts simultaneously.

Image guided breast lesion localization device

NMR images indicative of thermal changes in tissues undergoing therapy are produced using a gradient-recalled double-echo pulse sequence. A reference phase image is produced using a short echo time (TE.sub.1) and a measurement phase image is produced with a longer echo time (TE.sub.2). Temperature maps are produced during therapy using the phase difference information at corresponding pixels of the two phase images.

Real time in vivo measurement of temperature changes with NMR imaging

Radiofrequency (RF) and magnetic field gradient pulse sequences employ Time-of-Flight (TOF) strategy to selectively create transverse spin magnetization which is then maintained for a selected period of time and then imaged in order to generate a vessel selective magnetic resonance angiogram. The pulse sequence employs a spatially selective excitation pulse which is used to create transverse spin magnetization in a selected region of a subject. This region typically is made to include the root of the vessel to be imaged. After excitation, transverse magnetization is maintained with a series of refocusing RF pulses while the blood moves along the vessel. The transverse magnetization is then sampled at one or more selected times after excitation with conventional imaging strategies.

Method for magnetic resonance angiography using in-flow of transverse

A method is described which corrects magnetic field inhomogeneities in a magnetic resonance (MR) imaging system that takes into account the effects of a subject on the magnetic fields. A magnetic resonance sequence is applied to the subject to extract MR response signals from the subject indicating the magnetic field inhomogeneity over space. The changes of magnetic field inhomogeneity with a change in radial variable .rho. (or r, in a cylindrical coordinate system) are calculated. A derivative with respect to a radial variable is calculated of a generalized 3D infinite series polynomial, such as a Legendre polynomial expressed in spherical coordinates. These inhomogeneity changes are then fit to 3D polynomial derivative to result in coefficients [dI.sub.c ]. Similarly coefficients of a derivative shim coil calibration matrix [dM] are determined for each shim coil modeling the effect of each shim coil is on the magnetic field within the imaging volume. An inverse derivative matrix [dM] is calculated to result in the inverse derivative matrix [dM.sup.-1 ]. The inverse derivative matrix [dM.sup.-1 ] is multiplied by the coefficients [dI.sub.c ] to determine current coefficients [C] which define currents to be passed through each shim coil to correct the magnetic field inhomogeneities.

Method of magnet shimming

A calibration procedure for correcting geometric errors in MRI images due to gradient field non-linearities and magnetic field inhomogeneities includes performing a 3D scan on a calibration phantom. The calibration phantom contains an array of tapered rods that produce an array of spots in reconstructed slice images. Spot sizes and positions enable position errors to be measured throughout the bore of the imaging system. Corrective coefficients are produced from these 3D error measurements that enable subsequent patient images to be corrected for warping errors in object position.

Measurement of geometric distortion in MRI images

In an MRI system NMR data is acquired and an image is reconstructed based on the net phase or phase difference of spins at locations in the imaged object. The phase or phase difference image is corrected for errors caused by non-linearities in one or more of the gradient fields. The phase or phase difference image values are weighted with spin signal magnitude image values and their locations warped to reflect gradient field non-linearity. The warped values are remapped to the image pixel locations and converted back to phase values by dividing by an average spin signal magnitude. In this manner geometric distortion caused by non-uniform magnetic field gradients are corrected without loss of quantitative phase or phase difference information.

Correction of geometric distortion in MRI phase and phase difference

An NMR scanner performs a series of pulse sequences from which NMR data is acquired and used to reconstruct an image. Image contrast is enhanced by magnetization transfer from short-T.sub.2 spin species that are saturated by an off-resonance, substantially rectangular shaped RF saturation pulse applied during each pulse sequence.

MR imaging with rectangular magnetization transfer pulse

The harmonic relationship of certain chemical species is exploited to produce an MRI image of a single chemical species in the presence of at least two other chemical species with the acquisition of as few as two NMR images. If the chemical shift frequencies at a particular polarizing field strength can be approximated as the ratio of two odd integers, an evolution time can be chosen for the images acquired to cancel the contributions of two of the species in one image with a corresponding contribution in the other image. A image of the uncanceled species or of the cancelled species alone may be generated. A third image may be used to correct for inhomogeneities in the polarizing B.sub.0 field.

Selective imaging among three or more chemical species

A method of separating fat and water proton NMR images in the presence of local magnetic field inhomogeneities uses multiple images with phase shift between the water and fat signals. The phase shifts need not be multiples of .pi. and are selected so that at least two images are not 'fat opposed' and so that images are not symmetric in phase shift around a 'fat aligned' image. A switch function is developed from the argument of the combined images to unambiguously identify the predominant chemical species of each voxel. Wrap arounds in the argument resulting from the limited range of trigonometric functions are treated first by subtracting a low order polynomial, then detecting and removing wrap around discontinuities.

Robust decomposition of NMR images by chemical species

Determination of the shimming fields for a polarizing NMR magnet is performed by acquiring two NMR images with evolution times differing by .tau.. A pixel by pixel division of the images yields a third image whose phase is proportional to magnetic field inhomogeneity. Several such inhomogeneity images are acquired within a cylindrical volume and the data of the images is fit according to a set of polynomials approximating the fields of the magnet shim coils. The coefficients of this fitting procedure are used to set the current level in the corresponding shim coils. The interaction between correction fields is accommodated by an empirically derived correction matrix. This procedure may be repeated to provide more accurate shimming.

Method for rapid magnet shimming

A method of separating fat and water proton NMR images in the presence of local magnetic field inhomogeneities uses three images acquired with .pi., O, and -.pi. phase shift between the water and fat signals. A switch function is developed from the argument of the combined images to unambiguously identify the predominant chemical species of each pixel. Wrap arounds in the argument resulting from the limited range of trigonometric functions are treated first by subtracting a low order polynomial, fit to the phase image, to accentuate and remove wrap around discontinuities, and second by using trend analysis to detect and remove discontinuities caused by the wrap arounds.

Method of decomposing NMR images by chemical species

In-vivo shimming is performed by acquiring two NMR images with evolution times differing by ##EQU1## where .omega..sub.1, .omega..sub.2, are the Larmor frequencies of the dominant proton species of the imaged object. A pixel by pixel division of the image yields a third image whose phase is proportional to magnetic field inhomogeneity. The phase of the third image set has periodic discontinuities as a result of the periodicity of the arctangent function used to extract the phase from the image. These discontinuities are removed by taking the derivative of the phase and integrating the product of that derivative and a weighting function where the weighting function has zero weight at the points of discontinuity. Off-center quadratic terms in the inhomogeneity are removed prior to fitting the linear shimming gradients.

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Rexford, NY, United States of America

Erika Schneider