HF Pulse Optimization for MRI Local Exposure Control
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Solution Overview
Problem
Magnetic resonance systems face challenges in controlling local high-frequency exposure during imaging, leading to hot spots that can result in excessive energy deposition and reduced image quality due to the need to limit overall transmit power.
Innovation Solution
A method and device for determining magnetic resonance system activation sequences that optimize multichannel pulse trains based on a predefined target magnetization, using an HF pulse optimization method to manage the setpoint deviation between local and global high-frequency exposure values, ensuring precise control of local exposure while maintaining image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multichannel pulse trains are used to improve imaging performance, then image quality is improved, but local high-frequency exposure increases causing hot spots
Solution Approach 1:
The patent applies local quality by optimizing HF pulse trains individually for each transmit channel based on local SAR distribution. The system calculates channel-specific pulse sequences that account for local exposure patterns, allowing different parts of the transmit antenna to operate with tailored pulse characteristics that prevent hot spot formation while maintaining overall imaging performance.
Solution Approach 2:
The system changes HF pulse parameters (amplitude, phase, timing) on a per-channel basis to optimize the multichannel pulse train. By adjusting these parameters according to local SAR calculations, the system redistributes HF energy to achieve better image quality without exceeding local exposure limits at any position in the examination object.
2Object-affected harmful factors
If overall transmit power is limited to reduce local exposure, then hot spots are reduced, but image quality deteriorates
Solution Approach 1:
Instead of uniformly limiting transmit power across all channels, the system applies local quality by calculating and optimizing pulse trains for each transmit channel based on its specific local SAR contribution. This allows channels contributing less to hot spots to operate at higher power levels, maintaining image quality while preventing excessive local exposure.
Solution Approach 2:
The patent segments the overall transmit power control into channel-specific optimizations. By dividing the multichannel system into individual pulse train optimizations, the system can allocate power differently across channels based on their local exposure characteristics, rather than applying a blanket power reduction that would degrade image quality.
3Reliability
If prior planning of SAR exposure is performed to avoid measurement interruption, then measurement continuity is maintained, but local exposure control becomes complex
Solution Approach 1:
The system changes the approach to SAR planning by calculating channel-specific HF pulse parameters that inherently account for local exposure limits. This parameter optimization approach integrates SAR control into the pulse sequence design itself, maintaining measurement continuity while managing complexity through automated channel-by-channel optimization.
Solution Approach 2:
The system implements self-service by automatically calculating and optimizing the multichannel pulse train parameters based on the examination object's characteristics and local SAR distribution. The automated optimization process eliminates the need for manual SAR planning complexity while ensuring measurement continuity through proactive exposure management.
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 reliable control of local high-frequency exposure, reducing hot spots and maintaining image quality by distributing transmit power effectively, thereby reducing the overall HF exposure by a factor of three while adhering to safety limits.
Implementation Method 1
the body to be examined may be exposed to a relatively high basic field magnetic field, of 3 or 7 Tesla, for example, with the aid of a basic field magnet system
Implementation Method 2
A magnetic field gradient is also applied with the aid of a gradient system
Implementation Method 3
High-frequency excitation signals (HF signals) are transmitted by way of a high-frequency transmit system using suitable antenna devices to tip the nuclear spin of certain atoms that have been excited in a resonant manner by the high-frequency field with spatial resolution through a defined flip angle
Implementation Method 4
During relaxation of the nuclear spin, high-frequency signals (e.g., magnetic resonance signals) are emitted. The high-frequency signals are received using suitable receive antennas
Data Source
AI summary
A method and a control sequence determination device for determining a magnetic resonance system activation sequence are described. The magnetic resonance system activation sequence includes a multichannel pulse train with a plurality of individual HF pulse trains to be emitted in a parallel manner by the magnetic resonance system by way of different independent high-frequency transmit channels. In this process, a multichannel pulse train is calculated with a predefined target magnetization using an HF pulse optimization method, with optimization taking place with respect to a setpoint deviation of an HF local exposure value from an HF global exposure value. A method for operating a magnetic resonance system and a magnetic resonance system with the control sequence determination device are also described.