MRI Phase Contrast Imaging Near Metal Using Frequency Offset Segmentation
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Solution Overview
Problem
Conventional magnetic resonance (MR) imaging techniques struggle to differentiate between soft tissue variations near metal implants due to substantial magnetic field perturbations caused by metal hardware, leading to image artifacts and inability to effectively use phase-contrast mechanisms.
Innovation Solution
An MRI system with gradient coils and an RF transceiver system, controlled by a pulse module, acquires 3D MR data sets using distinct central transmit and receive frequency offsets, reconstructs frequency images, and generates phase images by converting time domain data, allowing for the reduction of image artifacts near metal implants and differentiation of tissue responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional MR imaging techniques are used near metal implants, then the imaging system can operate with standard sequences, but substantial B0 perturbations cause image artifacts and prevent effective phase-contrast differentiation
Solution Approach 1:
The patent applies parameter changes by systematically varying the frequency offset across multiple 3D data acquisitions. Instead of using a single fixed frequency, the method acquires data at multiple distinct frequency offsets, then processes these acquisitions to generate phase images that are insensitive to the B0 perturbations caused by metal implants.
Solution Approach 2:
The patent segments the imaging process into multiple separate 3D data acquisitions, each performed at a different frequency offset. This segmentation allows the system to capture different aspects of the signal that can be combined through processing to eliminate the harmful B0 perturbations while preserving the desired phase contrast information.
2Measurement precision
If multiple 3D data sets are acquired at distinct frequency offsets, then phase images can be generated with reduced artifacts, but the imaging time and data processing complexity increase
Solution Approach 1:
The method efficiently uses parameter changes by varying the frequency offset across multiple acquisitions. This approach allows the system to gather the necessary information for artifact-reduced phase imaging through systematic parameter variation, which can be processed relatively efficiently compared to other artifact reduction methods.
3Measurement precision
If conventional magnitude contrast techniques are used, then the imaging process is simple, but they cannot differentiate between soft tissue variations near metal implants
Solution Approach 1:
The patent moves beyond conventional magnitude contrast by utilizing frequency offset variations to access phase information. This parameter change enables the system to differentiate between soft tissue variations that are invisible to magnitude contrast, providing enhanced diagnostic capability despite the increased sequence complexity.
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 enables the removal of B0 perturbations from metal implants, exposing finer scale phase variations and facilitating the identification of local tissue reactions, thereby improving the diagnostic capabilities of MR imaging near metal hardware.
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.
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.
Implementation Method 3
A signal is emitted by the excited spins after the excitation signal B1 is terminated and this signal may be received and processed to form an image.
Data Source
AI summary
A system and method for generating MR phase contrast images near metal include an MRI apparatus that includes an MRI system having a plurality of gradient coils and an RF transceiver system and an RF switch controlled by a pulse module to transmit RF signals to an RF coil assembly. The MRI apparatus also includes a computer programmed to acquire a plurality of three-dimensional (3D) MR data sets and to generate a plurality of frequency images based on the plurality of 3D MR data sets. Each 3D MR data set is 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. The computer is also programmed to convert the plurality of frequency images to a plurality of time domain images and to generate a phase image based on the plurality of time domain images.