Systems and methods for magnetic resonance imaging
Inventors
Jeong, Eun-Kee • Parker, Dennis L • Choi, Kim Seong-Eun • Kholmovski, Evgueni G
Assignees
National Institutes of Health NIH
Publication Number
US-9770186-B2
Publication Date
2017-09-26
Expiration Date
2027-04-02
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Abstract
Methods and apparatus for operating an MRI system is provided. The disclosure provides a diffusion-prepared driven-equilibrium preparation for an imaging volume and acquiring 3-dimensional k-space data from said prepared volume by a plurality of echoplanar readouts of stimulated echoes. An excitation radio-frequency signal and first and second inversion RF signals are provided to define a field-of-view (FOV).
Core Innovation
The invention provides methods and apparatus for operating an MRI system that performs a diffusion-prepared driven-equilibrium preparation for an imaging volume and acquires three-dimensional k-space data from the prepared volume using multiple echoplanar readouts of stimulated echoes. This approach involves a single diffusion-prepared driven-equilibrium preparation and short EPI readouts to collect raw, untransformed 3D k-space data, enabling diffusion-weighted and diffusion tensor MRI imaging.
The problem addressed involves limitations in conventional two-dimensional single-shot diffusion-weighted EPI techniques, which suffer from severe distortion due to local magnetic field susceptibility changes, especially near tissue/bone or tissue/air interfaces. These distortions increase with longer data acquisition windows required for higher spatial resolution, leading to decreased image quality and limiting the clinical usefulness of such methods mainly to moderately low-resolution intracranial applications. Further, existing multishot imaging techniques suffer from phase errors due to motion, and non-EPI singleshot techniques have low signal-to-noise ratio and poor resolution along the slice direction.
To overcome these limitations, the invention introduces a three-dimensional single-shot stimulated echo planar imaging technique (3D ss-DWSTEPI) that combines diffusion-prepared driven-equilibrium preparation with short EPI readouts applying inner volume imaging to reduce readout time and susceptibility artifacts. Additionally, it offers a method for interleaved MR imaging using double inversion RF pulses immediately following excitation to define a field-of-view with slice-selective gradients that preserve magnetization within the FOV while suppressing it outside, enabling time-efficient interleaved multislab imaging with minimal signal loss.
The invention also provides a real-time motion artifact correction method during MR imaging that acquires navigation data concurrently with imaging data, determines in real time whether reacquisition is necessary due to intra- or inter-shot motion based on analysis of 2D k-space navigation echoes, and reacquires corrupted data to improve imaging quality and accuracy in diffusion-weighted and diffusion tensor imaging, functional MRI, and other multi-average single-shot EPI acquisitions.
Claims Coverage
The patent includes two independent claims covering a method and a system for interleaved magnetic resonance imaging with notable inventive features concerning the use of excitation and inversion RF pulses to define a field-of-view and multi-slice acquisition with controlled flip angles.
Method for interleaved MR imaging using excitation and inversion RF signals to define a field-of-view
The method performs a preparation sequence comprising providing an excitation RF signal, immediately followed by first and second inversion RF signals to define the FOV. This is followed by interleaved multi-slice acquisition over sequential acquisition segments where each segment applies an imaging RF pulse with a flip angle that increases over the sequence, enabling reconstruction of images from the acquired k-space data.
Use of closely timed inversion RF pulses with slice-selective gradients for FOV control
The first and second inversion RF pulses can be separated by approximately 5 milliseconds or more, or less than 5 milliseconds, with slice-selective gradients chosen so that magnetization within the FOV is preserved while magnetization external to the FOV is suppressed, allowing magnetization in multiple slices to remain substantially at equilibrium during excitation and imaging of other slices.
System configured to perform preparation, acquisition, and reconstruction with excitation and inversion RF signals
An MRI system comprising a scanner and associated computing devices configured to execute instructions for providing the excitation RF signal and closely timed inversion RF signals defining the FOV, performing interleaved multi-slice acquisition with increasing RF flip angles over sequential acquisition segments to obtain k-space data, and reconstructing images therefrom. The system further includes instructions to provide slice-selective gradients to achieve magnetization preservation within the FOV and suppression external to it.
The claims collectively cover methods and systems employing immediate sequential excitation and double inversion RF pulses with slice-selective gradients to define and limit the field-of-view, coupled with interleaved multi-slice acquisition using progressively increasing flip angles to acquire k-space data for image reconstruction. These inventive features enable efficient reduced field-of-view imaging with preserved magnetization and minimized artifacts.
Stated Advantages
Reduction of motion-induced artifacts during diffusion tensor imaging.
Significantly reduced susceptibility-induced geometric distortions compared to conventional 2D single-shot EPI.
High spatial resolution achievable in all imaging directions, including slice encoding.
Reduced scan time through efficient interleaved multislice or multislab acquisition enabled by double inversion RF pulses and inner volume imaging.
Improved image quality due to real-time detection and reacquisition of motion-corrupted data, enhancing accuracy of DTI measurements.
Documented Applications
High-resolution diffusion-weighted MRI and diffusion tensor imaging (DTI) of localized volumes such as restricted brain regions, cervical spinal cord, optic nerve, heart, and extracranial organs.
Multishot EPI-DTI imaging with motion artifact correction using real-time 2D navigators.
Functional MRI (fMRI) and other multi-average single-shot EPI techniques benefiting from real-time motion correction.
Interleaved multivolume or multislab imaging with reduced field-of-view to prevent aliasing artifacts and to enable faster, more efficient acquisitions.
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