MR Fingerprinting Flip Angle Modulation for RF Overload
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Solution Overview
Problem
Magnetic resonance systems face overloading issues during MR fingerprinting, particularly with two-dimensional data acquisition, leading to reduced maximum flip angles and pulse-clipping, which affects spectral properties and image quality.
Innovation Solution
The method involves simultaneous multi-slice excitation with varying flip angles to optimize power usage within the RF power amplifier's limits, ensuring that the power limits are not exceeded and maintaining uniform power demand, thereby preventing overloading and pulse-clipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two-dimensional MR fingerprinting data acquisition is used with short repetition times and large flip angles, then quantitative parameter measurement capability is improved, but the RF power amplifier becomes overloaded causing pulse-clipping and degraded spectral properties
Solution Approach 1:
The patent implements dynamic adjustment of flip angles across multiple slices, where the flip angle for each slice is varied over time according to a predefined pattern. This dynamic modulation allows the system to achieve effective T1 and T2 mapping while keeping the instantaneous power demand within amplifier limits, preventing overload and pulse-clipping
Solution Approach 2:
The patent transitions from conventional single-slice or simple multi-slice imaging to simultaneous multi-slice imaging with independent flip angle modulation for each slice. By adding the dimension of slice-specific temporal modulation, the system achieves quantitative parameter mapping in multiple slices simultaneously without exceeding power constraints
2Measurement precision
If maximum flip angles are used to improve signal evolution contrast, then measurement accuracy is improved, but the RF power amplifier operates at or beyond its power limits causing overloading
Solution Approach 1:
The patent changes the temporal pattern of flip angle application, using modulated flip angles that vary over time according to specific patterns (e.g., sinusoidal or triangular modulation). This parameter modulation achieves the necessary signal evolution for quantitative mapping while distributing the power demand over time, preventing peak power overload
Solution Approach 2:
The patent employs periodic modulation of flip angles across multiple excitation cycles, where the flip angle for each slice follows a periodic pattern. This periodic action allows the system to accumulate the necessary signal evolution information while maintaining average power within amplifier limits, avoiding continuous overload
3Ease of operation
If uniform flip angles are applied to all slices, then system operation is simplified, but the RF power amplifier may still be overloaded and cannot optimize power distribution
Solution Approach 1:
The patent assigns different flip angle modulation patterns to different slices, allowing each slice to have optimized flip angle characteristics. This local differentiation enables better power distribution across slices, preventing any single slice from causing amplifier overload while maintaining overall system efficiency
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 accurate and efficient acquisition of quantitative physical parameters without overloading the RF power amplifier, ensuring high-quality MR images and maintaining spectral properties by adjusting flip-angle characteristics based on tissue types and power limits.
Implementation Method 1
magnetic resonance system
Implementation Method 2
radio frequency (RF) pulses to excite nuclear spins
Implementation Method 3
spatially encode the MR signals from different slices
Data Source
AI summary
The disclosure relates to techniques to acquire at least one quantitative physiological parameter using a magnetic resonance system by means of MR fingerprinting. In this process, a plurality of slices are excited simultaneously using different imaging parameters to produce MR signal evolutions in each of the plurality of slices, and the MR data from the plurality of slices is then acquired simultaneously. For the simultaneous excitation of the plurality of slices, a flip angle (FW) that is used to excite one of the plurality of slices differs from a flip angle (FW) that is used to excite another of the plurality of slices.