Multi-Spectral MR Imaging Near Metal Implants
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Solution Overview
Problem
Magnetic resonance imaging (MRI) near metal implants faces significant challenges due to artifacts and distortions caused by the magnetic properties of implants, which hinder accurate clinical diagnostics, especially in musculoskeletal diagnostics where image distortions near implant interfaces are severe and limit diagnostic access to regions of interest.
Innovation Solution
An MRI system and method that acquire multiple 3D MR data sets with distinct center transmission and reception frequency offsets, reducing artifacts and distortions by constructing a composite image from these data sets, utilizing a computer-programmed pulse sequence with RF pulses and volume selection gradients to minimize image distortions and signal pileup effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional MRI is used to image near metal implants, then the imaging system can provide standard diagnostic images, but severe artifacts and distortions occur near implant interfaces that hinder accurate clinical diagnostics
Solution Approach 1:
The imaging process is segmented into multiple frequency-offset acquisitions. Instead of acquiring a single image at the center frequency, the system acquires multiple images at different frequency offsets and combines them. This segmentation of the frequency domain allows different regions (affected and unaffected by metal artifacts) to be optimally captured and combined, reducing overall image artifacts and distortions near implant interfaces
Solution Approach 2:
The patent changes the frequency offset parameter across multiple acquisitions. By varying the center frequency of the RF pulses and corresponding receiver frequencies, the system captures signal information from different frequency bands. This parameter change allows regions distorted by metal artifacts at one frequency to be compensated by information from other frequencies, improving overall image quality near implants
2Quantity of substance
If Hahn spin-echoes are used to regain signal loss, then signal intensity is improved, but drastic distortions are produced in both readout and slice directions that are unacceptable for clinical evaluation
Solution Approach 1:
Instead of relying on Hahn spin-echo refocusing which causes spatial distortions, the patent changes the frequency offset parameter across multiple acquisitions. By acquiring images at different frequency offsets and combining them, the system regains signal information without introducing the drastic spatial distortions that spin-echo refocusing would create in readout and slice directions
3Manufacturing precision
If 2D FSE imaging with View-Angle Tilting is used, then in-plane distortions are improved, but significant image blurring occurs and slice-selection direction distortions are not addressed
Solution Approach 1:
The patent segments the frequency domain into multiple offset acquisitions rather than using spatial transformation methods like VAT. This segmentation approach corrects distortions by capturing information at different frequencies and combining them, avoiding the significant image blurring that VAT introduces while also addressing slice-selection direction distortions that VAT cannot correct
Solution Approach 2:
Instead of correcting distortions in the spatial domain (as VAT attempts to do with in-plane corrections), the patent moves to the frequency domain by acquiring images at different frequency offsets. This dimensional change from spatial to frequency domain processing allows distortion correction without the blurring effects of spatial transformation methods
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
The approach significantly reduces image artifacts and distortions near metal implants, improving clinical diagnostic access and image quality by constructing a composite image with reduced artifacts and distortions, suitable for inhomogeneous magnetic fields.
Implementation Method 1
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. A signal is emitted by the excited spins
Implementation Method 2
When utilizing these signals to produce images, magnetic field gradients (Gx, Gy, and Gz) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used
Data Source
AI summary
A system and method for multi-spectral MR imaging near metal include a computer programmed to calculate an MR pulse sequence comprising a plurality of RF pulses configured to excite spins in an imaging object and comprising a plurality of volume selection gradients and determine a plurality of distinct offset frequency values. For each respective determined offset frequency value, the computer is programmed to execute the MR pulse sequence having a central transmit frequency and a central receive frequency of the MR pulse sequence set to the respective determined offset frequency value. The computer is also programmed to acquire a three-dimensional (3D) MR data set for each MR pulse sequence execution and generate a composite image based on data from each of the acquired 3D MR data sets.