The General Hospital Corporation

Massachusetts Institute of Technology

Siemens Aktiengesellschaft

Massachusetts General Hospital Corporation

Siemens Healthcare Gmbh

The Brigham and Women's Hospital, Inc.

Elfar Adalsteinsson

Lawrence Leroy Wald

Kawin Setsompop

Vivek K Goyal

Bastien Guerin

Adam C Zelinski

Markus Vester

Vijayanand Alagappan

Luca Daniel

Borjan Aleksandar Gagoski

Zohaib Mahmood

Hans-Peter Fautz

Matthias Gebhardt

Bruce R Rosen

Carolyn Mountford

Joerg Ulrich Fontius

Alma Gregory Sorensen

Saadallah Ramadan

A Gregory Sorensen

Ovidiu Andronesi

Divya S Bolar

Boris Keil

Joonsung Lee

Vijay Alagappan

Adam Charles Zelinski

Lawrence L Waid

Berkin Bilgic

A method of determining a decoupling matrix of a decoupling system for an array of coils of a parallel transmission magnetic resonance imaging (MRI) system includes obtaining impedance matrix data for the array of coils without the decoupling system, determining, based on the impedance matrix data for the array of coils, an objective function representative of deviation from a decoupled operating condition for the array of coils in which the array of coils are decoupled via the decoupling system, and defining, with a processor, a decoupling matrix representative of a set of impedances of the decoupling system with an iterative procedure that optimizes elements of the decoupling matrix to minimize the objective function and reach the decoupled operating condition.

Decoupling of parallel transmission arrays in magnetic resonance imaging

A magnetic resonance imaging (MRI) system includes a plurality of transmitters to generate a parallel transmission radio frequency (RF) pulse, an array of coils coupled to the plurality of transmitters to apply the parallel transmission RF pulse to a subject, and a decoupling system connected to the plurality of transmitters and the array of coils. The decoupling system includes a plurality of hybrid couplers, each hybrid coupler of the plurality of hybrid couplers being coupled to a respective pair of the plurality of transmitters and to a respective pair of the array of coils. The plurality of hybrid couplers are configured to diagonalize an impedance matrix of the plurality of coils.

Described here are a system and method for designing radio frequency ('RF') pulses for parallel transmission ('pTx') applications, and particularly pTx applications in multislice magnetic resonance imaging (&#x201c;MRI&#x201d;). The concept of &#x201c;SAR hopping&#x201d; is implemented by framing the concept between slice-selective excitations as a constrained optimization problem that attempts designing multiple pulses simultaneously subject to an overall local SAR constraint. This results in the set of RF waveforms that yield the best excitation profiles for all pulses while ensuring that the local SAR of the average of all pulses is below the regulatory limit imposed by the FDA. Pulses are designed simultaneously while constraining local SAR, global SAR, and peak power, and average power explicitly.

Local SAR reduction in multi-slice pTx via SAR-hopping between excitations

A method for reconstructing multiple images of a subject depicting multiple different contrast characteristics from medical image data acquired with a medical imaging system is provided. Multiple image data sets are acquired with one or more medical imaging systems and the image data sets used to estimate hyperparameters drawn from a prior distribution, such as a prior distribution of image gradient coefficients. These hyperparameters and the acquired image data sets are utilized to produce a posterior distribution, such as a posterior distribution of image gradients. From this posterior distribution, multiple images with the different contrast characteristics are reconstructed. The medical imaging system may be a magnetic resonance imaging system, an x-ray computed tomography imaging system, an ultrasound system, and so on.

Multi-contrast image reconstruction with joint bayesian compressed sensing

A system and method for accurately producing MR images of selected vascular compartments includes employing a control scan and a tag scan, each including velocity selective modules that suppress signal from blood flowing faster than a given cutoff velocity, to acquire control and tag sets of NMR data that may be subtracted to produce a compartment-specific MR image that is substantially free of information from stationary tissues and blood outside the selective vascular compartments. Accordingly, physiological parameters, such as oxygen saturation (SaO), oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen (CMRO), can be generated from the compartment-specific images. Further still, kinetic curves of oxygen exchange can be created, thus providing detailed insight into oxygen exchange dynamics.

System and method to analyze blood parameters using magnetic resonance imaging

In a magnetic resonance apparatus and operating method therefor, and in a processor that is programmed to design RF pulses for operating such a magnetic resonance apparatus, the RF pulses are designed to mitigate off-resonance effects caused by inhomogeneity of the basic (B0) magnetic field in the magnetic resonance apparatus. The RF pulses of a parallel transmit array are designed with different spatial phase distributions, that deviate from a constant phase from pulse-to-pulse, with the absolute value of the difference between respective spatial phase distributions of any two successively radiated RF pulses corresponding to the off-resonance that is caused by B0-inhomogeneity during the time between the radiation of the successive pulses. Additionally, or separately, currents supplied to the shim coils can be taken into account in the design of the RF pulses as an additional degree of freedom, with the shimming of the basic magnetic field produced by the shim currents deviating from shim currents designed to ideally produce a homogenous B0 field.

Method and processor and magnetic resonance apparatus for designing RF pulses to mitigate off-resonance effects

Methods for low-power in vivo localized multi-dimensional correlated magnetic resonance spectroscopy ('MRS') are provided. Low-power adiabaticity is achieved, generally, using gradient-modulated radio frequency pulses for localization and mixing. The provided pulse sequences also provide a mechanism for longitudinal mixing, which significantly increases the efficiency of magnetization transfer and thereby increases signal-to-noise ratio.

Method for two-dimensional correlation magnetic resonance spectroscopy

A method of designing a parallel transmission radio frequency (RF) pulse for a magnetic resonance imaging (MRI) system includes compressing a model for a subject to be scanned by the MRI system into a plurality of voxel clusters, each voxel cluster defining a virtual observation point with a peak sensitivity to local specific absorption rate (SAR) for the voxel cluster, and defining the parallel transmission RF pulse based on an approximation of a minimization criterion having a local SAR component based on the peak sensitivity of each virtual observation point, the approximation comprising a weighted sum of the local SAR values for each virtual observation point.

Parallel transmission RF pulse design with local SAR constraints

A system and method is provided for simultaneously designing a radiofrequency ('RF') pulse waveform and a magnetic field gradient waveform in a magnetic resonance imaging ('MRI') system. The method includes determining a desired pattern of RF excitation and determining, from the desired pattern of RF excitation, a plurality of k-space locations indicative of the magnetic field gradient waveform and a plurality of complex weighting factors indicative of RF energy deposited at each k-space location. The method also includes calculating, from the determined k-space locations, the magnetic field gradient waveform and calculating, from the complex weighting factors, the RF pulse waveform that will produce the desired pattern of RF excitation when produced with the calculated magnetic field gradient.

Method for joint sparsity-enforced k-space trajectory and radiofrequency pulse design

A method for reducing maximum local specific absorption rate ('SAR') in a magnetic resonance imaging ('MRI') system is disclosed. More specifically, a plurality of candidate radio frequency (&#x201c;RF&#x201d;) pulses are designed and the manner in which they are applied to a subject is determined such that the maximum local SAR is substantially reduced relative to applying the candidate RF pulse that produces the lowest maximum local SAR alone. Put another way, this &#x201c;time-multiplexing&#x201d; of a set of RF pulses that each produce approximately the same excitation pattern yields a lower maximum local SAR than does transmitting the individual RF pulse having the lowest local SAR over many repetition times (&#x201c;TRs&#x201d;). A convex optimization method is utilized to determine the manner in which the RF pulses are multiplexed in time such that a substantially lower maximum local SAR is achieved.

Method for reducing maximum local specific absorption rate in magnetic resonance imaging

A method for target-dependent, sparsity-enforced selection for choosing a substantially optimal connection of radiofrequency ('RF') transmitters to the elements of the RF coil array is provided. In particular, a method is provided that selects the linear combinations of the 'N' spatial mode profiles of a transmission RF coil array, such that the k-space trajectory and pulse duration acceleration capabilities of the array are advantageously utilized. A sparsity-enforcement method that determines a subset of the available spatial modes for a parallel transmission RF coil array is employed to this end. In this manner, the utilization of the encoding power of a highly-parallel N-mode coil array in a system with only &#x201c;P&#x201d; available excitation channels is enabled.

Coil array mode compression for parallel transmission magnetic resonance imaging

A method for producing a spatially and spectrally selective radiofrequency ('RF') excitation pulse includes establishing a desired spatial RF excitation pattern and establishing a desired spectral RF excitation pattern. The method also includes estimating an RF transmission profile map indicative of the transmission characteristics of an RF coil and determining, from the desired spatial and spectral excitation patterns and the estimated RF transmission profile map, at least one magnetic field gradient waveform indicative of locations in k-space to which RF energy is to be deposited. The method further includes determining, from the established spatial and spectral excitation patterns, the estimated RF transmission profile map, and the determined at least one gradient waveform, at least one RF excitation pulse waveform that will produce the desired spatial and spectral excitation patterns.

Method for producing spectral-spatial parallel RF excitation pulses for magnetic resonance imaging

A system and method for producing an image indicative of characteristics of a radiofrequency ('RF') coil with a magnetic resonance imaging ('MRI') system is disclosed. The method includes acquiring MR signals while performing a pulse sequence with the MRI system and driving the RF coil at a selected transmission power. This process is repeated a plurality of times to drive the RF coil at a different transmission powers during each repetition. A plurality of images are reconstructed from the acquired MR signals and an image indicative of RF reception characteristics of the RF coil is produced from the reconstructed images. Subsequently, an image indicative of RF transmission characteristics of the RF coil is produced using the image indicative of the RF receiver response. More specifically, only one data acquisition is necessary for each RF coil element to produce the image indicative of the RF transmission characteristics for that coil element.

Method for fast magnetic resonance radiofrequency coil transmission profile mapping

Waveforms for radio-frequency (RF) excitations pulses used in magnetic resonance imaging are designed according to a Least Squares QR (LSQR) algorithm or a Conjugate Gradient Least Squares (CGLS) algorithm, to solve the linear system of equations that arises in a multi-channel RF transmit arrangement. Better management of SAR and other factors is achieved with RF pulses designed according to these algorithms, compared to the conventionally employed singular value decomposition (SVD) algorithm.

Growing community of inventors

Belmont, MA, United States of America

Elfar Adalsteinsson