Parallel Imaging for MRI Near Metallic Implants
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Solution Overview
Problem
Magnetic resonance imaging (MRI) near metallic implants faces challenges due to signal distortions and prolonged scan times, particularly with existing parallel imaging techniques like SENSE-based methods which are ineffective and computationally intensive for MAVRIC imaging.
Innovation Solution
A data-driven parallel imaging method using a computer-programmed MRI system that acquires multiple 3D MR data sets with distinct central transmit and receive frequencies, including fully-sampled calibration k-space data lines, to determine reconstruction weights and synthesize unacquired data, reducing calibration computation time and overall scan time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If SENSE-based parallel imaging techniques are applied to MAVRIC imaging, then scan time reduction is achieved, but the technique becomes ineffective due to large signal voids causing difficulties in sensitivity map estimation
Solution Approach 1:
The patent changes the fundamental parameter of the parallel imaging approach from SENSE-based (which requires sensitivity map estimation) to data-driven methods like GRAPPA and ARC that estimate reconstruction weights directly from k-space data. This parameter change bypasses the signal void problem entirely, as the weight estimation is performed in k-space rather than image space, making the technique effective for MAVRIC imaging while still achieving scan time reduction through parallel imaging acceleration.
2Reliability
If data-driven parallel imaging techniques such as GRAPPA and ARC are used, then effectiveness is maintained despite signal voids, but calibration computation time increases
Solution Approach 1:
The patent applies preliminary action by performing the computationally intensive calibration process once to establish reconstruction weights, then reusing these weights across multiple MAVRIC data sets. Instead of recalibrating for each frequency offset, the system performs a single calibration and applies the resulting weights to all subsequent reconstructions, dramatically reducing the cumulative calibration computation time while maintaining the effectiveness of data-driven parallel imaging.
3Measurement precision
If multiple 3D MR data sets are acquired with distinct frequency offsets, then image quality near implants is improved, but scan duration is prolonged to 20-25 minutes
Solution Approach 1:
The patent applies partial action by using parallel imaging acceleration to acquire only a portion of the k-space data directly, then synthesizing the remaining unacquired data using the estimated reconstruction weights. This allows the system to maintain the multiple frequency offset acquisition strategy for image quality while reducing the overall scan duration by not fully sampling all k-space points, effectively implementing a partial acquisition approach that balances quality and time.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces calibration computation time and scan duration while minimizing artifacts, enabling effective MRI imaging near metallic implants by using data-driven techniques like ARC, which are insensitive to signal voids caused by metallic implants.
Implementation Method 1
When utilizing these signals to produce images, magnetic field gradients (Gx, Gy, and Gz) are employed
Implementation Method 2
the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency
Implementation Method 3
If the substance, or tissue, is subjected to a magnetic field (excitation field B1) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, or 'longitudinal magnetization ', MZ, may be rotated, or 'tipped ', into the x-y plane to produce a net transverse magnetic moment Mt
Data Source
AI summary
A system and method for magnetic resonance imaging is disclosed, the MRI apparatus comprising a computer programmed to acquire a plurality of 3D MR data sets, each 3D MR data set acquired using a central transmit frequency and a central receive frequency set to an offset frequency value that is distinct for each 3D MR data set, wherein at least a portion of each 3D MR data set is accelerated k-space data, and wherein at least one of the plurality of 3D MR data sets comprises fully-sampled calibration k-space data lines. The computer is also programmed to determine reconstruction weights from the fully-sampled calibration k-space data lines, reconstruct an image for each 3D MR data set using the reconstruction weights from the fully-sampled calibration k-space data lines to synthesize unacquired data, and generate a composite image from the reconstructed images based on the plurality of 3D MR data sets.