MRI Polarity Determination Using Reference Signal Phase Correction
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Solution Overview
Problem
In magnetic resonance imaging (MRI) using an inversion recovery (IR) sequence, existing methods struggle to accurately determine the polarities of signals from different tissues, leading to contrast inconsistency in images due to individual differences and varying inversion times among tissues.
Innovation Solution
A method that generates an inversion recovery image, processes it to create a real part image, and determines the polarity by analyzing a phase-corrected signal line from a reference image without inversion recovery, ensuring accurate polarity determination without relying on specific image or scan parameter assumptions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a 180° inversion RF pulse is applied to excite tissue, then the longitudinal magnetization vector deflects by 180° to a direction opposite to the main magnetic field, but the recovery time for the longitudinal magnetization vector to completely recover to the original state is prolonged
Solution Approach 1:
The patent applies a 180° inversion pulse before the main imaging sequence to pre-deflect the longitudinal magnetization vector. This preliminary action allows subsequent small flip angle excitations to occur during the recovery phase, enabling T1 weighting without requiring long recovery times after each excitation pulse.
Solution Approach 2:
The patent uses periodic RF pulse sequences where a 180° inversion pulse is followed by multiple small flip angle excitation pulses at regular intervals. This periodic structure allows the magnetization to recover partially between excitations, maintaining steady-state conditions while achieving T1 contrast.
2Measurement precision
If different tissues have different inversion times TI, then polarities of signals collected from different tissues may be different at the same inversion time, but this leads to contrast inconsistency in image reconstruction
Solution Approach 1:
The patent employs a feedback mechanism where the polarity of the signal from a reference tissue (e.g., CSF or scalp fat) is determined first, and then this polarity information is used to correctly interpret the polarities of all other tissues in the image. The system adjusts the phase or polarity of the reconstructed image based on this feedback to ensure contrast consistency.
Solution Approach 2:
The patent introduces a reference tissue as an intermediary to mediate the polarity determination process. By selecting a tissue with known or predictable signal characteristics (such as CSF in FLAIR imaging or scalp fat in STIR imaging), the system uses this reference to establish the correct polarity for the entire image, thereby ensuring consistent contrast representation across all tissues.
3Device complexity
If real part imaging is performed based on IR sequence without pre-scan, then image processing is simplified, but polarity ambiguity cannot be eliminated and contrast consistency cannot be ensured
Solution Approach 1:
The patent enables the imaging system to automatically determine tissue polarity using intrinsic signal characteristics from the image data itself, without requiring external pre-scan calibration. The method identifies reference tissues based on their expected signal properties and uses their polarities to correct the entire image, making the system self-sufficient and eliminating the need for additional calibration scans.
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 method reliably and accurately determines the polarity of real part images for all tissues, ensuring consistent contrast in MRI images by specifically acquiring a signal line of a reference image and determining the sign of its real parts, thereby correcting polarity ambiguities.
Implementation Method 1
when a radio frequency (RF) pulse with a frequency that is the same as a procession frequency of protons is applied on processional protons in a main magnetic field, the protons may resonate
Implementation Method 2
the higher the energy of the RF pulse is, the larger the deflection angle of the macroscopic magnetization vector may be
Implementation Method 3
When a tissue is excited by a 180° RF pulse, the macroscopic longitudinal relaxation vector of the tissue may deflect by 180°, which indicates that the macroscopic longitudinal relaxation vector of the tissue may deflect to a direction opposite to the main magnetic field
Implementation Method 4
the higher the energy of the RF pulse is, the larger the deflection angle of the macroscopic magnetization vector may be, the higher the energy that the protons in an excited tissue absorb may be, the higher the energy that the protons need to release may be after the RF pulse is no longer applied to the processional protons, and the longer the longitudinal relaxation time of the excited tissue may be
Data Source
AI summary
The method for magnetic resonance imaging described in the present disclosure may include generating an inversion recovery image by scanning an object using an inversion recovery sequence. The method may also include generating a real part image corresponding to the inversion recovery image by processing the inversion recovery image. The method may also include obtaining a signal line of a reference image without inversion recovery, the reference image corresponding to the real part image. The method may also include determining a phase-corrected signal line of the reference image by performing a phase correction on the signal line of the reference image. The method may also include determining a polarity of the real part image based on the phase-corrected signal line of the reference image.