Interleaved Water Reference Scan for MRS Phase Correction
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Solution Overview
Problem
The existing methods for magnetic resonance spectroscopy (MRS) require a separate non-water suppressed scan for phase and B0 correction, which increases the total scan time and can be affected by system instability, leading to inaccurate corrections due to phase distortion and B0 drift.
Innovation Solution
A magnetic resonance sequence is implemented with a low flip-angle excitation pulse for the reference sub-sequence, minimizing delay and using the recovering water signal as a reference, allowing for faster acquisition and more accurate phase and B0 correction with a reduced total repetition time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a separate non-water suppressed scan is performed for phase and B0 correction, then correction accuracy is improved, but total scan time increases
Solution Approach 1:
The patent combines the water reference scan and MRS scan into a single interleaved sequence, where the water reference scan is performed between MRS excitations. This merging eliminates the need for a separate non-water suppressed scan while maintaining correction accuracy, as the water reference signal is acquired immediately before and after the MRS signal under identical conditions.
Solution Approach 2:
The water reference scan is performed preliminarily between MRS excitations, capturing the reference signal while the system is still stable. By acquiring the water reference data during the MRS sequence itself rather than separately, the correction is based on the most recent system state, reducing the impact of drift.
2Measurement precision
If a separate non-water suppressed scan is performed for phase and B0 correction, then correction data is obtained, but system instability causes phase distortion and B0 drift
Solution Approach 1:
By interleaving the water reference scan with the MRS scan, both signals are acquired in close temporal proximity under identical system conditions. This eliminates the time gap that allows system instability to manifest, ensuring that the reference signal and MRS signal experience the same B0 field and phase characteristics.
Solution Approach 2:
The water reference scan is continuously performed between MRS excitations without interruption, maintaining a continuous record of system stability. This continuous acquisition ensures that any phase distortion or B0 drift is captured and corrected in real-time, rather than allowing it to accumulate over a longer separate scan.
3Loss of time
If a low flip-angle excitation pulse is used for the reference sub-sequence, then total repetition time is reduced, but signal intensity may be affected
Solution Approach 1:
The patent uses a low flip-angle (e.g., 10 degrees) for the water reference excitation pulse instead of a standard 90-degree pulse. This parameter change reduces the time required for longitudinal magnetization recovery, allowing the water reference scan to be completed quickly and interleaved within the MRS sequence without extending the total repetition time.
Solution Approach 2:
The low flip-angle pulse provides just enough signal intensity for accurate phase and B0 correction without requiring full magnetization saturation. This partial action is sufficient for the reference purpose while minimizing the time cost and allowing faster repetition.
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 faster MRS acquisition with a total repetition time of 1500-2000 ms and more accurate phase and B0 correction, while maintaining a high signal-to-noise ratio, reducing the impact of system instability and phase distortion.
Implementation Method 1
Magnetic resonance (MR) is a known technique that is useful in medical diagnostics
Implementation Method 2
A magnetic resonance sequence is implemented with a low flip-angle excitation pulse for the reference sub-sequence, minimizing delay and using the recovering water signal as a reference
Data Source
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AI summary
A magnetic resonance (MR) sequence (14)is performed, including: applying a preparatory MR sub-sequence (S prep )providing water signal suppression; performing a magnetic resonance spectroscopy (MRS) sub-sequence (S MRS )after applying the preparatory MR sub-sequence to acquire H MRS data with water signal suppression; and performing an MR reference sub-sequence (S Ref )to acquire MR reference data. The MR reference sub-sequence is performed after the MRS sub-sequence. Phase and B0 correction of the H MRS data with water signal suppression are performed using the MR reference data to generate corrected MRS data. The excitation pulse (g)of the MR reference sub-sequence has a flip angle of less than or equal to o, and more preferably has a flip angle of less than or equal to 3 o.In some embodiments the MR sequence has a total repetition time (TR) of 2000 msec or less.