MR B1 Field Determination Using Gradient-Modulated Stimulated Echoes
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Solution Overview
Problem
Existing MR methods using stimulated echoes to determine B1 magnetic fields often result in artifacts and incorrect phase shift measurements due to magnetization from previous sequences affecting current data acquisition.
Innovation Solution
A method involving a sequence of resonant RF pulses and magnetic field gradients is used to refocus only the longitudinal magnetization component from the current sequence, with differing gradient moments between successive repetitions to prevent adulteration of MR data and reduce image artifacts, allowing for accurate determination of the B1 magnetic field by measuring phase shifts induced by non-resonant RF pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a stimulated echo method is used to determine B1 magnetic field, then measurement speed is improved, but measurement precision deteriorates due to phase shift errors from previous sequence magnetization
Solution Approach 1:
The patent applies preliminary dephasing gradients before the stimulated echo sequence to ensure that magnetization from previous sequences is already dephased and will not contribute to the current measurement. This preliminary action prevents contamination of the phase shift measurement without requiring long waiting periods for T1 relaxation, thus maintaining both measurement speed and precision.
Solution Approach 2:
The patent extracts and eliminates the harmful component (magnetization from previous sequences) by applying specific gradient moments that dephase this unwanted magnetization while preserving the stimulated echo signal from the current sequence. This selective removal allows accurate phase shift measurement without interference.
2Loss of time
If magnetization from previous sequences is allowed to persist, then measurement time is reduced, but image quality deteriorates due to artifacts from magnetization adulteration
Solution Approach 1:
The patent applies dephasing gradients as a preliminary action before the readout sequence to eliminate unwanted magnetization from previous sequences. This allows the system to proceed immediately with the current measurement without waiting for T1 relaxation, thus reducing measurement time while preventing image artifacts.
Solution Approach 2:
The patent changes the gradient moment parameters between successive sequences to ensure that magnetization prepared in one sequence does not refocus and adulterate the next sequence. By modifying gradient moments, the patent achieves both rapid sequential measurements and high image quality without cross-contamination.
3Stability of the object's composition
If gradient moments are kept constant between successive sequences, then sequence consistency is maintained, but measurement precision deteriorates due to magnetization adulteration from previous sequences
Solution Approach 1:
The patent deliberately changes gradient moment parameters between successive sequences to prevent magnetization from one sequence from refocusing and contaminating the next. This controlled parameter change maintains sequence consistency in terms of the intended measurement protocol while preventing harmful magnetization adulteration, thus improving B1 field determination accuracy.
Solution Approach 2:
The patent applies preliminary dephasing gradients with specific moment values that are different between sequences. This preliminary action ensures that unwanted magnetization is dephased before each measurement, maintaining consistent measurement conditions while preventing cross-sequence contamination.
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 reduces systematic errors and image artifacts, enabling precise determination of the B1 magnetic field without waiting for complete T1 relaxation, thus reducing measurement time and improving accuracy.
Implementation Method 1
A dephasing first magnetic field gradient is applied after the first resonant RF pulse and before the second resonant RF pulse
Implementation Method 2
A second magnetic field gradient is applied after the third RF pulse in order to refocus a stimulated echo of a magnetization component prepared by the first gradient
Implementation Method 3
A phase shift of the nuclear spins is thereby measured, which is generated by a non-resonant RF pulse. The B1 amplitude of the B1 magnetic field generated by the non-resonant RF pulse can be calculated using the magnitude of the phase shift
Data Source
AI summary
In a method to acquire magnetic resonance (MR) data within a volume segment with a magnetic resonance system, the MR data are repeatedly acquired with a sequence that includes radiating a first resonant RF pulse, radiating a second resonant RF pulse, applying a dephasing first gradient after the first resonant RF pulse and before the second resonant RF pulse, radiating a third resonant RF pulse after the second resonant RF pulse, applying a second gradient after the third RF pulse in order to refocus a stimulated echo of a magnetization component prepared by the first gradient, and read out MR data. At least one of the first gradient and/or the second gradient is/are different in a respective repetition of the sequence and an additional repetition of the sequence that directly follows the respective repetition.