Magnetic Resonance Diffusion Weighted Imaging Flip Pulse Correction
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Solution Overview
Problem
Conventional magnetic resonance diffusion weighted imaging (DWI) techniques suffer from reduced imaging quality due to magnetization intensity vectors not meeting the Carr-Purcell-Meiboom-Gill (CPMG) conditions, caused by diffusion weighting gradient pulses and patient movements, leading to phase distribution in the X-Y plane and increased RF energy deposition.
Innovation Solution
The method involves applying an excitation pulse to flip the magnetization intensity vector from the Z direction to the X-Y plane, followed by a diffusion pulse for weighting, and a flip pulse to reorient residual vectors not satisfying CPMG conditions back to the Z direction, ensuring all vectors meet CPMG conditions for improved echo stability and reduced RF energy deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If diffusion weighting gradient pulses are applied in conventional DWI, then diffusion effects can be detected, but magnetization intensity vectors develop phase distribution in the X-Y plane that does not satisfy CPMG conditions, reducing imaging quality
Solution Approach 1:
A preliminary flip pulse is applied after diffusion weighting and before data acquisition to rotate magnetization vectors that do not satisfy CPMG conditions back to the Z-axis. This preliminary correction ensures that all magnetization vectors are properly aligned before the echo train begins, eliminating phase distribution issues and improving imaging quality while preserving diffusion detection capability
Solution Approach 2:
The invention changes the temporal parameter of the pulse sequence by inserting a flip pulse at a specific time point between diffusion weighting and data acquisition. This parameter modification transforms the magnetization state from non-CPMG compliant to CPMG compliant, resolving the contradiction between diffusion detection and imaging quality
2Manufacturing precision
If refocusing pulses with large flip angles are used to maintain echo amplitude, then imaging quality can be maintained, but RF energy deposition (SAR) increases
Solution Approach 1:
By applying a preliminary flip pulse to correct magnetization vector orientation before the echo train, the system eliminates the need for large flip angle refocusing pulses to compensate for phase distribution. This allows the use of smaller flip angles while maintaining echo amplitude stability, thereby reducing RF energy deposition
Solution Approach 2:
The invention extracts and corrects the problematic component (magnetization vectors not satisfying CPMG conditions) before the main imaging process. By removing these non-compliant vectors through the preliminary flip pulse, the system avoids the need for excessive RF energy during the echo train to maintain image quality
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 enhances imaging quality by stabilizing echo amplitude and reducing the need for refocusing pulse flip angles, thereby improving image clarity and reducing RF energy deposition.
Implementation Method 1
Magnetic resonance (MR) imaging is an imaging technology involving biomagnetics and nuclear spin that uses a magnetic field and radio frequency (RF) pulses to induce oscillation of precessing hydrogen nuclei
Implementation Method 2
Diffusion-weighted imaging (diffusion-weighted MR imaging, DWI) can be performed by adding a diffusion gradient to highlight diffusion effects in any conventional MR imaging sequence
Implementation Method 3
The scanner is further operated to apply a flip pulse to a residual magnetization intensity vector which still exists in the X-Y plane after diffusion weighting in order to flip any part of that residual vector that does not satisfy the CPMG conditions back to the Z direction
Implementation Method 4
The scanner is then operated to apply a data acquisition sequence to acquire raw data from the residual magnetization intensity vector in the X-Y plane that satisfies the CPMG conditions
Data Source
AI summary
In a magnetic resonance diffusion weighted imaging method and apparatus, an excitation pulse flips a magnetization intensity vector of nuclear spins, a subject from the Z direction into the X-Y plane; and a diffusion pulse is applied to the magnetization intensity vector flipped into the X-Y plane in order to perform diffusion weighting. A flip pulse is applied to a magnetization intensity vector that does not meet Carr-Purcell-Meiboom-Gill conditions in the X-Y plane after diffusion weighting in order to flip it back to the Z direction. A data acquisition sequence is activated to acquire imaging data from a residual magnetization intensity vector meeting the Carr-Purcell-Meiboom-Gill conditions in the X-Y plane.