Magnetic Resonance Navigator Signal Separation Using Temporal Offsets
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Solution Overview
Problem
Simultaneous magnetic resonance imaging of multiple slices leads to challenges in identifying slice-specific phase errors due to superimposed navigator signals, requiring high computational efforts and additional acquisition time for reference data.
Innovation Solution
A modified magnetic resonance sequence with a second partial sequence that acquires additional data with lower spatial resolution, using time offsets for slice-specific refocusing pulses and gradient pulses to suppress other slice signals, allowing for independent readout of navigator data and reducing computational demands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If simultaneous acquisition of multiple slices is performed using standard parallel imaging techniques, then the total acquisition time is reduced, but the navigator signals from different slices superimpose making slice-specific phase error identification difficult
Solution Approach 1:
The patent divides the navigator signal acquisition into slice-specific segments by applying temporal offsets to the refocusing pulses for each slice. This segmentation allows the navigator signals from different slices to be separated in time, enabling independent evaluation of slice-specific phase errors while maintaining simultaneous multi-slice imaging.
Solution Approach 2:
The patent introduces dynamic temporal offsetting of refocusing pulses for different slices during the navigator signal acquisition. By dynamically adjusting the timing of refocusing pulses slice-by-slice, the system enables temporal separation of navigator signals without requiring separate acquisitions for each slice, thus resolving the phase error identification problem while maintaining fast imaging.
2Measurement precision
If slice-specific additional data are acquired with high spatial resolution, then the quality of reference data is improved, but the acquisition time and computational load increase significantly
Solution Approach 1:
The patent applies partial action by acquiring navigator data with reduced spatial resolution compared to the full imaging data. The navigator signals are acquired with lower resolution in the phase-encoding direction, which is sufficient for detecting phase errors and motion but reduces the acquisition time and computational requirements for processing these reference data.
Solution Approach 2:
The patent changes the spatial resolution parameter for the navigator signal acquisition. By using a reduced field of view or lower matrix size for navigator data compared to the diagnostic imaging data, the system obtains adequate phase error detection capability while minimizing the time and computational resources required for acquiring and processing these additional reference data.
3Ease of operation
If standard refocusing pulses are used for all slices simultaneously, then the acquisition process is simple, but slice-specific phase errors cannot be distinguished from each other
Solution Approach 1:
The patent applies preliminary action by introducing temporal offsets in the refocusing pulse timing before the navigator signal readout occurs. This preliminary temporal differentiation of slice-specific refocusing pulses ensures that when the navigator signals are acquired, they are already separated in time, making it straightforward to identify and correct slice-specific phase errors without complex post-processing.
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 efficient and real-time evaluation of movement information and correction of phase errors, reducing acquisition time and computational expense while providing robust reference data for reconstruction algorithms.
Implementation Method 1
method for acquiring magnetic resonance data with a magnetic resonance system using a magnetic resonance sequence
Implementation Method 2
radio-frequency pulses and readout processes are activated in a slice-specific manner through a time offset
Implementation Method 3
slight temporal offsets between slice-specific excitation and refocusing pulses are used to achieve temporal offsets between the echoes of each individual slice
Implementation Method 4
the resulting echoes can be scanned separately so that the resulting magnetic resonance signals can be assigned to the correct slice
Implementation Method 5
The GRAPPA technique is a frequently used version of such parallel imaging
Implementation Method 6
the magnetic resonance signals of several acquisition (receiving) coils are acquired and evaluated
Data Source
AI summary
In a method for acquiring magnetic resonance data with a magnetic resonance system using a magnetic resonance sequence, the sequence has a first partial sequence in which magnetic resonance data are acquired for multiple slices that have to be acquired simultaneously, from which image data for the individual slices are calculated by a reconstruction algorithm. The sequence also has a second partial sequence for determining additional data, which are used to evaluate and/or assess the magnetic resonance data, and which have a spatial resolution that is lower than the magnetic resonance data, in which radio-frequency pulses and readout processes take place in a slice-specific manner through a time offset within a single measuring process, in which a single continuous excitation period with the radio-frequency pulses and a single continuous readout period with the readout processes follow one another, so that separate additional data are directly determined for each slice.