RF Pulse Optimization for MR System Component Protection
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Solution Overview
Problem
In magnetic resonance systems with multiple independent radio-frequency transmission channels, the voltage limitations across channels can lead to inconsistencies in pulse sequences, resulting in reduced image quality due to phase relationships and amplitude differences, which are not accounted for during the design of pulse sequences.
Innovation Solution
A method that determines a current, component-dependent B1 field maximum value specific to the examination subject, allowing for temporal shortening and amplitude scaling of RF pulses to maintain component protection while maximizing bandwidth, thereby optimizing pulse sequences for better image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If RF pulse trains are determined with a minimum B1 field maximum value to protect components, then component protection is ensured, but pulse duration is extended and bandwidth is reduced
Solution Approach 1:
The patent applies preliminary action by determining the current component-dependent B1 field maximum value in an adjustment step before final pulse application. This allows the system to pre-assess the actual voltage limits of transmission components for the specific examination subject, then optimize RF pulse parameters accordingly. By performing this assessment beforehand, the system can set appropriate B1 field limits that protect components while avoiding excessive pulse duration extension that would reduce bandwidth.
Solution Approach 2:
The patent implements dynamics by making the B1 field maximum value adaptive rather than fixed. The system dynamically adjusts the B1 field limit based on the actual voltage conditions of transmission components during the adjustment step. This dynamic adaptation allows the pulse sequence to optimize the trade-off between component protection and bandwidth preservation according to real-time system conditions.
2Reliability
If voltage limitations are applied across multiple transmission channels, then component protection is maintained, but phase relationships and amplitude differences cause inconsistencies in pulse sequences
Solution Approach 1:
The patent applies local quality by determining individual complex scaling factors for each transmission channel based on its specific voltage limitations and B1 field characteristics. Rather than applying a uniform limit across all channels, the system optimizes each channel's RF pulse train independently according to its local properties. This ensures that each channel operates within its safe voltage limits while maintaining optimal phase relationships and amplitude consistency across the multi-channel pulse sequence.
3Reliability
If RF pulses are temporally extended to reduce maximum amplitude, then component protection is ensured, but image quality is reduced due to increased artifacts
Solution Approach 1:
The patent applies parameter changes by optimizing multiple RF pulse parameters simultaneously rather than adjusting a single parameter. The system determines complex scaling factors that modify both amplitude and phase, and temporally adjusts pulse duration, to achieve the desired flip angle while staying within voltage limits. This multi-parameter optimization allows the system to minimize pulse duration extension, thereby reducing artifacts due to chemical shift while still protecting components.
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 enables the generation of significantly better magnetic resonance image data by ensuring component protection while minimizing artifacts due to chemical shift and maintaining optimal pulse sequence timing.
Implementation Method 1
the subject to be examined is typically exposed by means of a basic field magnet system, subject to a relatively high basic magnetic field (also designated as a 'B0 field') of 3 or 7 Tesla, for example, which aligns nuclear spins in the subject with the direction of the basic magnetic field
Implementation Method 2
By means of a gradient system, a magnetic field gradient is additionally applied. By means a radio-frequency transmission system, radio-frequency excitation signals (RF signals) are then emitted by suitable antenna devices
Implementation Method 3
radio-frequency excitation signals (RF signals) are then emitted by suitable antenna devices, in order to cause the nuclear spins of specific atoms in the subject to be excited to resonance
Implementation Method 4
The radio-frequency field (also designated as a 'B1 field') has a defined flip angle relative to the magnetic field lines of the basic magnetic field that causes the nuclear spins to be deflected or 'flipped' by the flip angle
Implementation Method 5
with a spatial coding produced by the gradient field
Implementation Method 6
Upon relaxation of the nuclear spins, radio-frequency signals (known as magnetic resonance signals) are radiated that are received by means of suitable reception antennas
Data Source
AI summary
In a method for controlling a magnetic resonance system with multiple radio-frequency transmission channels, via which parallel RF pulse trains are emitted in operation, as well as a magnetic resonance system and a pulse optimization device therefor, RF pulse trains respectively include at least one radio-frequency pulse. The RF pulse trains are initially determined so that a minimum B1 field maximum value is not exceeded by the radio-frequency pulse. In an examination subject-specific adjustment step, a current component-dependent B1 field maximum value is then determined, and the radio-frequency pulse is temporally shortened, with its amplitude being increased dependent on the current component-dependent B1 field maximum value.