University of Southern California

Leland Stanford Junior University

Krishna S Nayak

Robert Marc Lebel

Yi Guo

Yinghua Zhu

Jon-Fredrik Nielsen

Sajan Goud Lingala

John Mark Pauly

Brian A Hargreaves

Charles H Cunningham

Travis B Smith

Hsu-Lei Lee

KyungHyun Sung

Yannick Bliesener

Kyunghyun Sung

Tracer kinetic models are utilized as temporal constraints for highly under-sampled reconstruction of DCE-MRI data. In one embodiment, a method for improving dynamic contrast enhanced imaging. The method includes steps of administering a magnetic resonance contrast agent to a subject and then collecting magnetic resonance contrast agent from the subject. A tracer kinetic model (i.e. eTofts or Patlak) is selected to be applied to the magnetic resonance imaging data. The tracer kinetic model is applied to the magnetic resonance imaging data. Tracer kinetic maps and dynamic images are simultaneously reconstructed and a consistency constraint is applied. The proposed method allows for easy use of different tracer kinetic models in the formulation and estimation of patient-specific arterial input functions jointly with tracer kinetic maps.

Method for joint arterial input function and tracer kinetic parameter estimation in accelerated DCE-MRI using a model consistency constraint

Tracer kinetic models are utilized as temporal constraints for highly under-sampled reconstruction of DCE-MRI data. The method is flexible in handling any TK model, does not rely on tuning of regularization parameters, and in comparison to existing compressed sensing approaches, provides robust mapping of TK parameters at high under-sampling rates. In summary, the method greatly improves the robustness and ease-of-use while providing better quality of TK parameter maps than existing methods. In another embodiment, TK parameter maps are directly reconstructed from highly under-sampled DCE-MRI data. This method provides more accurate TK parameter values and higher under-sampling rates. It does not require tuning parameters and there are not additional intermediate steps. The proposed method greatly improves the robustness and ease-of-use while providing better quality of TK parameter maps than conventional indirect methods.

Method for improved dynamic contrast enhanced imaging using tracer-kinetic models as constraints

A magnetic resonance imaging system may include: a magnet; gradient coils; an RF pulse transmitter; an RF receiver that receives MR signals from tissue that has been exposed to RF pulses from the RF pulse generator, gradient fields from the gradient coils, and a magnetic field from the magnet; a system controller that controls the magnet, gradient coils, RF pulse transmitter, and RF receiver so as to generate data representative of at least a portion of the composition of an object, including controlling the gradient coils and RF receiver so as to cause MRI data to be acquired that includes information about at least one attribute of the object at different points in time and that represents an incomplete sample of a portion of k-space that is a Fourier transform of the object; and a data processing system that generates one or more images of at least a portion of the object based on the MRI data.

Dynamic 3D MRI data sampling

An MRI scanner may include one or more gradient waveform generators, gradient amplifiers, gradient coils, an RF waveform generator, an RF amplifier, an RF coil, a superconducting magnet, an RF detector; a digitizer, and a computer system that controls the one or more gradient waveform generators and the RF waveform generator so as to generate a magnetization saturation preparation pulse sequence that includes a tip-down pulse that is insensitive to RF field inhomogeneity followed by a tip-back pulse that employs a conjugate symmetry constraint in its energy spectrum.

Method for reduced field of view MRI in an inhomogeneous field with rapid outer volume suppression

Embodiments of the present disclosure are directed to systems and methods for providing tailored RF pulse trains, based on estimated B0 and B1 profiles, for uniform saturation for MRI techniques. The tailored pulse trains are optimized to minimize residual longitudinal magnetization in target tissue. The B0 and B1 profiles can be measured a priori over a desired region of a patient, e.g., the heart, and can overcome or mitigate SAR and B1 inhomogeneity constraints. In exemplary embodiments, the tailored pulse trains can include hard pulses with unequal weighting. In other embodiments, the tailored pulse trains can include BIR-4 pulse trains that are optimized to minimize residual longitudinal magnetization in target tissue. The tailored pulse train designs can improve the immunity to B1 variation while maintaining low RF power. MRI systems, methods, and controllers for providing tailored pulse trains are described.

Tailored radiofrequency pulses for uniform saturation in magnetic resonance imaging

Magnetic resonance imaging techniques are described that utilize bSSFP sequences in which two or more gradient waveforms are interleaved in a 'groupwise' fashion, i.e., each waveform is executed consecutively two or more times before switching to the other waveform, where 'N' counts the number of times each waveform is executed consecutively. As a result, embodiments of the present disclosure can mitigate steady-state signal distortions or artifacts in interleaved balanced steady-state free precession (bSSFP) caused by slightly unbalanced eddy-current fields. Related MRI systems are also described.

Eddy-current artifact reduction in balanced steady-state free precession magnetic resonance imaging

Techniques and systems for magnetic resonance imaging. In one aspect, preparatory pulse sequences precede alternating repetition time steady state free precession (ATR SSFP) pulse sequences to enable image acquisition before reaching a steady-state equilibrium. The design of the preparatory sequences is based on a two step process: First an oscillatory residue is expressed in terms of a window (e.g., a Kaiser-Bessel window) and scale parameters. Second the oscillatory residue is minimized to determine the scale parameters according to a desired application (e.g. ATR SSFP, optimized for fat, water, etc.) The preparation scheme described in this specification can be applied to arbitrary repetition times and RF phase cycling combinations.

Preparing the magnetization state of a sample for alternating repetition time steady state free precession magnetic resonance imaging

Referenceless techniques for flow imaging are described that exploit a refocusing property of balanced steady state free precession ('SSFP') magnetic resonance imaging ('MRI'), and achieve up to approximately a 50% reduction in total scan time. With the echo time set to one half of the sequence repetition time (TE=TR/2), non-flow-related image phase tends to vary smoothly across the field-of-view, and can be estimated from static tissue regions to produce a phase reference for nearby voxels containing flowing blood. These approaches produce accurate in vivo one-dimensional velocity estimates in half the scan time compared with conventional balanced SSFP phase-contrast methods. The feasibility of referenceless time-resolved 3D flow imaging (called &#x201c;7D&#x201d; flow) is demonstrated for a carotid bifurcation application from just three acquisitions. Related systems are also described. Other attributes such as blood acceleration can also be imaged with such techniques.

Fast velocity measurements using balanced SSFP magnetic resonance imaging

For in vivo magnetic resonance imaging at high field (&#x2267;3 T) it is essential to consider the homogeneity of the active Bfield (B+), particularly if surface coils are used for RF transmission. A new method is presented for highly rapid B+ magnitude mapping. It combines the double angle method with a B-insensitive magnetization-reset sequence such that the choice of repetition time (TR) is independent of Tand with a multi-slice segmented (spiral) acquisition to achieve volumetric coverage with adequate spatial resolution in a few seconds.

RF field mapping for magnetic resonance imaging

A method and system are described for compensating for non-uniformity of excitation field B1+ in magnetic resonance imaging (MRI) of an object. The variation in the RF excitation field B1+ is measured over a region of interest (ROI) in the object, the B1+ field causing nuclear spins in the object to flip at a flip angle when B1+ is applied to the object. The flip angle profile is designed to be proportional to a reciprocal of the measured variation in the excitation field B1+. One or more control parameters of the estimated flip angle profile is adjusted, in accordance with the measured variation in B1+, so as to cancel out variation in actual flip angle until a profile of the actual flip angle is achieved that is substantially uniform throughout the ROI.

Compensating for non-uniformity of excitation field in MRI

Disclosed is a wideband SSFP, wherein a standard balanced SSFP MRI sequence is played with repetition times of alternating lengths, TR and TR, where TR&#x3c;TR. The result is significantly improved tradeoff between signal bandwidth and available acquisition interval lengths. This is particularly important as it enables the combination of balanced SSFP with high field imaging for many applications such as cardiac, musculoskeletal and abdominal imaging.

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Los Angeles, CA, United States of America

Krishna S Nayak