Dynamic B0 Field Detection Using Multichannel RF Navigators
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Solution Overview
Problem
Current methods for correcting B0 field inhomogeneities in magnetic resonance imaging systems, particularly with multichannel RF coil configurations, require lengthy scan repetitions for high-quality B0 field mapping, leading to inefficient image correction and noise handling, especially for dynamic changes caused by physiological noise and system instabilities.
Innovation Solution
Utilizing navigators from multiple channels in a multichannel RF coil configuration to generate B0 maps without the need for spatial encoding, allowing for real-time or off-line image correction by leveraging the spatial information from individual coils, enabling more efficient and rapid image data acquisition and processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple scan repetitions are used for high-quality B0 field mapping, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent divides the B0 field mapping process into multiple independent scan repetitions, where each repetition contributes a portion of the final B0 map. Instead of requiring a single long scan, the system performs multiple shorter scans (e.g., 6-10 seconds each) and combines the results, allowing parallel processing and reducing the impact of dynamic noise sources while maintaining measurement precision.
Solution Approach 2:
The patent performs preliminary B0 field mapping using navigator echoes acquired during the actual imaging sequence. By extracting B0 information from these preliminary navigators that are already being acquired for motion correction, the system obtains B0 field maps without requiring separate dedicated mapping scans, thereby reducing total acquisition time while maintaining quality.
2Measurement precision
If B0 field mapping is performed separately before imaging, then measurement precision is improved, but productivity decreases
Solution Approach 1:
The patent merges the B0 field mapping function with the primary imaging sequence by incorporating navigator echoes into the EPI or spiral imaging protocol. The same RF excitations and gradient waveforms used for imaging are also used to acquire navigators that contain B0 field information, allowing simultaneous acquisition of both imaging data and B0 maps without requiring separate scan time.
Solution Approach 2:
The navigator echoes serve multiple functions simultaneously: they provide motion correction information, enable B0 field mapping, and can be used for distortion correction. This multi-functionality eliminates the need for dedicated B0 mapping scans and improves overall imaging productivity while maintaining measurement precision.
3Manufacturing precision
If static B0 field mapping is used for correction, then manufacturing precision is improved, but adaptability decreases
Solution Approach 1:
The patent transitions from static B0 field mapping to dynamic B0 field monitoring by acquiring navigators at multiple time points during the imaging sequence. This allows the system to track and correct for time-varying B0 field changes caused by physiological processes (respiration, heartbeat) and subject motion, making the correction adaptive rather than fixed.
Solution Approach 2:
The system uses real-time B0 field measurements from navigators to provide feedback for ongoing image correction. By continuously monitoring B0 field changes and applying corrections based on these measurements, the system adapts to dynamic conditions during the scan, improving both distortion correction and handling of physiological noise.
Data Source
AI summary
In a method for calculating a B0 field map (a map of the basic magnetic field) in a magnetic resonance apparatus, a navigator pulse is emitted and navigator response resulting from the navigator pulse are detected in at least some channels of a multichannel RF coil array. Each channel of the multichannel RF coil array includes an RF coil and spatial information regarding the respective positions of the individual RF coils is made available to a processor, together with the multiple navigator signals. Using the spatial information obtained from the position of the RF coils that respectively detected the navigator response signals, a B0 field map is generated, without the need for spatial encoding the respective navigator response signals.