3D MRI Distortion Correction Near Metallic Implants
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Solution Overview
Problem
Magnetic resonance imaging (MRI) is severely limited by image artifacts caused by metallic implants, leading to distortion, misplacement, and scaling issues, which hinder accurate imaging of tissues near these implants.
Innovation Solution
The implementation of a 3D MRI method using slice-direction distortion correction through selective cross-section excitation with RF pulses, refocusing pulses, and phase encoding, combined with view angle tilting and additional phase encoding techniques, such as SEPI-VAT and EPSI-VAT, to resolve and correct distortions, enabling distortion-free imaging near metallic implants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MRI is used near metallic implants, then imaging can be performed, but image artifacts including distortion, misplacement, and scaling issues occur
Solution Approach 1:
The patent applies view angle tilting (VAT) as a preliminary action before image acquisition. By tilting the slice selection gradient relative to the readout gradient, the method proactively compensates for susceptibility-induced frequency shifts before they cause artifacts, preventing distortion and misplacement of spins near metallic implants
Solution Approach 2:
The patent changes the orientation parameter of the slice selection gradient by applying a tilt angle relative to the readout gradient. This parameter change transforms the frequency-encoding direction, allowing spins that would normally appear at incorrect positions due to susceptibility effects to be correctly localized through the tilted encoding scheme
2Measurement precision
If distortion correction through additional phase encoding is applied, then imaging accuracy improves, but scan time increases
Solution Approach 1:
The patent applies partial Fourier transformation to reconstruct the image from partially sampled k-space data. By acquiring only a portion of the required phase-encoding lines and using mathematical reconstruction, the method achieves the necessary position resolution for distortion correction while reducing scan time compared to fully sampling k-space
Solution Approach 2:
The patent uses parallel imaging techniques where multiple receiver coils simultaneously acquire data from different spatial locations. The reconstruction process combines these parallel measurements to form a complete image, effectively copying and combining partial information from multiple sources to achieve full image resolution with reduced scanning
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 effectively eliminates both in-plane and through-slice distortions, providing clear and accurate MRI images of tissues near metallic implants, even in clinically feasible scan times, by precisely resolving the position of spins and correcting frequency shifts caused by metallic implants.
Implementation Method 1
nuclear magnetic moments are excited at specific spin precession frequencies that are proportional to the local magnetic field
Implementation Method 2
nuclear magnetic moments are excited at specific spin precession frequencies that are proportional to the local magnetic field
Implementation Method 3
A refocusing pulse is applied to form a spin echo
Implementation Method 4
phase encoding along a third axis, wherein the data along the phase encoded first and third axes is acquired with an under sampling scheme
Data Source
AI summary
A method for 3D magnetic resonance imaging (MRI) with slice-direction distortion correction is provided. One or more selective cross-sections with a thickness along a first axis are excited using a RF pulse with a bandwidth, wherein a selective cross-section is either a selective slice or selective slab. A refocusing pulse is applied to form a spin echo. One or more 2D encoded image signals are acquired with readout along a second axis and phase encoding along a third axis, wherein the data long the phase encoded first and third axes is acquired with an under sampling scheme. Slice-direction distortion is corrected by resolving the position by using phase encoding.