CEST Imaging Frequency Drift Correction via Phase Difference
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Solution Overview
Problem
Magnetic resonance CEST imaging is affected by frequency drift of the main magnetic field, leading to overestimation or underestimation of CEST effects and reduced fat suppression efficiency, which compromises the robustness and repeatability of the imaging process.
Innovation Solution
A method and apparatus for real-time frequency drift correction using free induction decay signals or gradient echo signals, where phase differences are calculated and used to adjust the center frequency of the magnetic resonance device, ensuring effective fat signal suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If post-processing methods are used to correct frequency drift, then frequency drift correction is achieved, but fat suppression efficiency decreases resulting in higher fat signals
Solution Approach 1:
The patent applies preliminary action by performing frequency drift correction at the beginning of the imaging sequence using a field map acquired before the actual CEST imaging. This pre-correction ensures that subsequent fat suppression techniques work effectively without being compromised by frequency drift, thereby eliminating the trade-off between frequency drift correction and fat suppression efficiency
Solution Approach 2:
The patent introduces an intermediary approach by using a field map as a mediator to characterize frequency drift. This field map is then used to adjust the imaging parameters and correct frequency drift effects, allowing both frequency drift correction and fat suppression to be achieved simultaneously without direct conflict
2Measurement precision
If MTRasym analysis is used to extract CEST effect, then CEST effect extraction is achieved, but sensitivity to frequency drift increases leading to overestimation or underestimation
Solution Approach 1:
The patent implements feedback by using the field map to continuously monitor and characterize frequency drift, then applying this information to correct the CEST imaging data. This feedback mechanism allows MTRasym analysis to remain sensitive to CEST effects while compensating for frequency drift, thereby maintaining both extraction accuracy and reliability
Solution Approach 2:
The patent applies parameter changes by adjusting the center frequency and bandwidth parameters based on the field map measurements. This dynamic parameter adjustment allows the imaging sequence to adapt to frequency drift conditions, maintaining accurate CEST effect extraction while reducing sensitivity to drift-induced errors
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 corrects frequency drift in real-time, enhances the robustness and repeatability of magnetic resonance CEST imaging, and improves the clinical diagnostic value by maintaining accurate fat suppression.
Implementation Method 1
controlling a CEST imaging system to emit a radio-frequency pulse with a flip angle less than 90° to excite a target slice
Implementation Method 2
acquiring a single line of free induction decay signals
Implementation Method 3
dividing the acquired free induction decay signals into odd-numbered lines and even-numbered lines, and dividing an inter-line phase difference between the odd-numbered lines and the even-numbered lines by the sampling period to obtain a value of the main magnetic field frequency drift
Implementation Method 4
adjusting the center frequency of the magnetic resonance device in real time according to the obtained value of the main magnetic field frequency drift
Data Source
AI summary
Disclosed is a method and apparatus for frequency drift correction of magnetic resonance CEST imaging, and a medium and an imaging device. The method comprises the following steps: firstly, in the frequency drift correction module, exciting a target slice by using a small flip-angle radio-frequency pulse, and acquiring a single line of free induction decay signals or two lines of non-phase encoding gradient echo signals; secondly, respectively calculating a value of the main magnetic field frequency drift according to phase information and an acquisition time of the single line of free induction decay signals or the two lines of non-phase encoding gradient echo signals; then adjusting the center frequency of the magnetic resonance device in real time according to the calculated value of the main magnetic field frequency drift, and achieving the real-time correction of main magnetic field frequency drift; and finally, performing CEST imaging.