Magnetic Resonance Control Sequence for Gradient Delay Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Magnetic resonance tomography systems face challenges in achieving a precise, rotationally symmetrical excitation profile due to gradient delay times, which cause deviations in the intended gradient shape and RF pulse alignment, leading to distortion and deviation from the desired excitation volume during two-dimensional selective excitation.
Innovation Solution
A magnetic resonance control sequence is determined with a pulse arrangement that includes multiple partial RF pulses on concentric ring trajectories in k-space, with coordinated gradient pulses to ensure RF energy delivery on circular transmission trajectories, maintaining constant amplitude during each ring trajectory passage, thereby compensating for gradient delay times and achieving robust spatial localization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional gradient pulses and RF pulses are used for two-dimensional selective excitation, then spatial encoding is achieved, but gradient delay times cause deviation from the desired excitation volume
Solution Approach 1:
The invention applies preliminary action by designing gradient pulses with pre-compensated timing parameters before the actual excitation sequence. The gradient pulse sequences are calculated in advance to account for and counteract the known gradient delay times, ensuring that the effective gradient application aligns with the intended RF pulse timing despite system delays.
Solution Approach 2:
The invention changes parameters by adjusting gradient pulse amplitudes, durations, and timing parameters based on measured or characterized gradient delay times. The control sequence determination device modifies gradient parameters dynamically to compensate for delays, transforming the standard gradient waveform parameters into corrected values that achieve the desired spatial encoding despite system imperfections.
2Device complexity
If gradient delay times are present in the system, then hardware simplicity is maintained, but excitation volume distortion occurs
Solution Approach 1:
The invention introduces an intermediary element: the control sequence determination device that acts as a mediator between the gradient system and RF pulse sequence. This intermediary calculates and determines corrected control sequences that account for gradient delays without requiring hardware modification. The control device translates the desired excitation parameters into adjusted gradient and RF pulse parameters that compensate for the delay effects.
3Ease of operation
If standard pulse sequences are used, then system operation is simple, but spatial localization accuracy deteriorates due to gradient delays
Solution Approach 1:
The invention applies segmentation by dividing the excitation process into multiple partial RF pulses, each associated with specific gradient pulses. The control sequence is segmented into discrete, calculable units that can be individually optimized for delay compensation. This segmentation allows precise control over the timing and amplitude of each gradient-RF pair, enabling accurate spatial localization despite gradient delays while maintaining operational simplicity through automated sequence generation.
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 allows for a robust and precise excitation profile, minimizing the impact of gradient delay times and maintaining the desired excitation volume, even with system imperfections, and can be used for calibration and adjustment of the magnetic resonance system.
Implementation Method 1
A magnetic field gradient is additionally applied by a gradient system
Implementation Method 2
Radio-frequency excitation signals (RF signals, or also called RF excitation pulses or just RF pulses) are then emitted by suitable antenna devices via a radio-frequency transmission system, which causes the nuclear spins of specific atoms to be excited to resonance by a defined 'flip angle'
Implementation Method 3
Upon relaxation of the nuclear spins, RF signals (magnetic resonance signals) are radiated that are received by suitable reception antennas
Data Source
AI summary
A magnetic resonance control sequence with a pulse arrangement that acts selectively in at least two spatial directions in order to excite a limited rotationally symmetrical excitation profile within an examination subject has an RF excitation pulse formed as a sequence of multiple partial RF pulses, and gradient pulses in the two spatial directions that are coordinated with the partial RF pulses so that the RF energy introduction of different partial RF pulses in transmission k-space occurs on circular k-space transmission trajectories that are concentric to one another. The amplitude of the RF envelope of the partial RF pulses is constant during the duration of a traversal of each circular k-space trajectory. The control sequence can also be used in a calibration of a magnetic resonance system.