MRI Flip Angle Schedule Optimization for SAR and Signal Trade-offs
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Solution Overview
Problem
Magnetic resonance imaging (MRI) systems face challenges in determining a target flip angle schedule for refocusing RF pulses, which can lead to increased specific absorption rate (SAR) and decreased signal-to-noise ratio and contrast ratio in MR images.
Innovation Solution
A method and system for determining a target flip angle schedule by comparing an initial flip angle schedule to multiple criteria, adjusting it based on parameters such as echo train intensity and total energy, to optimize the MR signal generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If large flip angles are used in refocusing RF pulses, then the echo signal intensity is improved, but the specific absorption rate (SAR) increases
Solution Approach 1:
The patent implements dynamic adjustment of flip angles across the echo train rather than using static large flip angles. The flip angle schedule varies through the echo train, with smaller angles used later in the train, thereby reducing cumulative SAR while maintaining adequate signal intensity through optimized timing and sequence design
Solution Approach 2:
The patent changes the flip angle parameter throughout the echo train according to a predetermined schedule. By varying this critical parameter (from larger initial angles to smaller subsequent angles), the system optimizes the balance between signal intensity and SAR accumulation across multiple refocusing pulses
2Use of energy by stationary object
If variable flip angles are used in refocusing RF pulses, then the SAR is reduced, but the signal-to-noise ratio and contrast ratio decrease
Solution Approach 1:
The patent applies preliminary action by using larger flip angles at the beginning of the echo train where signal intensity is most critical for image formation, then transitions to smaller angles. This strategic sequencing ensures adequate signal-to-noise ratio and contrast in the most important echoes while reducing SAR in later, less critical echoes
Solution Approach 2:
The dynamic flip angle schedule is designed to maintain signal quality in the critical early echoes while reducing angles later, thereby preserving signal-to-noise ratio and contrast ratio where they matter most for image diagnostics while achieving overall SAR reduction
Data Source
AI summary
A method may include providing an initial flip angle schedule of refocusing radio frequency pulses, the refocusing radio frequency pulses being configured to generate an echo train; comparing the initial flip angle schedule with a first criterion, the first criterion relating to a first parameter relating to the echo train; determining, a first flip angle schedule based on the first comparison, the first flip angle schedule satisfying the first criterion; comparing the first flip angle schedule with a second criterion, the second criterion relating to a second parameter relating to the echo train; determining, a second flip angle schedule based on the second comparison, the second flip angle schedule satisfying the second criterion; and obtaining a magnetic resonance (MR) signal based on the second flip angle schedule.