MR Dephasing Gradient Calculation for Coherence Pathway Suppression
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Solution Overview
Problem
Existing MR imaging techniques face challenges in suppressing undesired signal coherence pathways, particularly in twice-refocused spin echo sequences, which limits flexibility in gradient switching and is sensitive to temporal variations, restricting their application beyond diffusion measurements.
Innovation Solution
A method that involves determining dephasing gradients based on preparation gradients and undesired signal coherence pathways, allowing for flexible switching of preparation gradients and independent calculation of gradient moments to reduce undesired signal components, applicable in various MR imaging sequences including diffusion and spectroscopy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If phase cycles are used to suppress undesired coherence pathways, then signal suppression is achieved, but the method becomes very sensitive to temporal variations and instabilities
Solution Approach 1:
The patent applies preliminary action by calculating dephasing gradients before the actual signal recording based on the preparation gradients and desired dephasing. This pre-calculation allows the system to compensate for temporal variations by having the dephasing gradients ready to be applied at the optimal moment, thereby suppressing undesired coherence pathways without being sensitive to temporal instabilities during the recording process
2Adaptability or versatility
If multiple RF pulses are used to generate desired image contrast, then imaging capability is improved, but the number of coherence pathways increases leading to more interfering signals
Solution Approach 1:
The patent converts the harmful effect of multiple coherence pathways into a beneficial approach by using the preparation gradients (which create the harmful pathways) as the basis for calculating the dephasing gradients. The dephasing gradients are specifically designed to target and suppress the undesired coherence pathways while preserving the desired signal, thereby transforming the problem of multiple pathways into a solution for selective suppression
3Object-generated harmful factors
If dephasing gradients are applied with higher gradient amplitudes or longer pulse durations to suppress signal pathways, then suppression effectiveness is improved, but the complexity and time requirements increase
Solution Approach 1:
The patent applies parameter changes by calculating dephasing gradients based on the effective size of preparation gradient moments rather than using fixed high amplitudes or durations. The dephasing gradient moments are determined by the relationship between preparation gradient moments (e.g., Mspoil = |M1 - 2*M0| for diffusion), allowing optimization of suppression effectiveness while minimizing gradient complexity and time requirements through adaptive parameter adjustment
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 suppresses undesired signal coherence pathways, providing temporal flexibility in gradient switching and expanding the applicability beyond diffusion measurements, while ensuring robustness against temporal instabilities.
Implementation Method 1
Phase dispersion along the slice normals can be cancelled simply by the use of two suitable adiabatic pulses
Implementation Method 2
After each RF pulse, gradients are switched with moments that are, for example, effective for contrast generation or preparation or for spatial encoding
Implementation Method 3
A special sequence is the twice-refocused spin echo sequence, also known as double spin echo sequence, that has one RF excitation pulse and two RF refocusing pulses
Data Source
AI summary
In a method and apparatus for recording MR signals with an image-recording sequence with which preparation gradients for preparing the MR signals are switched before the signal readout and readout gradients, in order to predominantly record the MR signal components with a desired signal coherence pathway in the readout segment, the signal components with an undesired signal coherence pathway are suppressed by dephasing gradients. The dephasing gradients are determined independently of the time intervals in which the preparation gradients are switched, and only in dependence on the effective size of the gradient moments of the preparation gradients.