Flow-Encoded MRI Eddy Current Reduction via Preliminary Parameter Calibration
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Solution Overview
Problem
Eddy current fields induced during phase-contrast flow measurements in magnetic resonance imaging lead to image distortions and reduced precision due to noise phenomena, particularly aliasing and phase convolution, which are difficult to compensate, especially in fast imaging sequences with short repetition rates.
Innovation Solution
A method is introduced where preliminary recordings with varying imaging sequence parameter values are used to acquire flow-encoded candidate datasets from a calibration region, allowing for the selection of parameters that minimize background phase contrast and reduce noise effects from eddy currents, without requiring complex models or additional phantom measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If flow-encoding gradients are used in phase-contrast flow measurements, then velocity encoding capability is achieved, but eddy current fields are induced causing image distortions and reduced measurement precision
Solution Approach 1:
The patent applies preliminary action by performing a preliminary recording before the actual flow measurement to determine optimal imaging sequence parameter values. This preliminary step allows the system to pre-calculate and pre-set parameters that will minimize eddy current effects during the subsequent measurement, thereby improving velocity measurement precision while reducing image distortions.
Solution Approach 2:
The patent utilizes parameter changes by varying imaging sequence parameter values in the preliminary recording to identify the optimal set of parameters. By systematically changing parameters such as gradient strength, timing, and other sequence settings, the system determines the combination that minimizes eddy current formation, thus resolving the contradiction between achieving velocity encoding and avoiding eddy current-induced distortions.
2Productivity
If fast imaging sequences with short repetition rates are used, then imaging speed is improved, but eddy current effects become more complex and difficult to compensate
Solution Approach 1:
The patent applies preliminary action by performing a preliminary recording before the actual flow measurement to determine optimal imaging sequence parameter values. This preliminary step allows the system to pre-calculate and pre-set parameters that will minimize eddy current effects during the subsequent measurement, thereby improving velocity measurement precision while reducing image distortions.
Solution Approach 2:
The patent applies self-service by using the preliminary recording itself to provide the information needed for optimization. The preliminary recording automatically generates data about eddy current effects under specific sequence parameters, and the system uses this self-generated information to select optimal parameters without requiring external phantom measurements or complex manual calibration procedures.
3Ease of operation
If conventional MR measurement sequences are used, then standard imaging is achieved, but phase information is discarded or computed with anatomical images rather than used for flow measurement
Solution Approach 1:
The patent applies universality by making the phase information serve multiple functions. The same phase data that could be used for conventional anatomical imaging is also utilized for flow measurement purposes. By determining optimal sequence parameters through preliminary recording, the system enables the phase information to effectively encode velocity data while maintaining compatibility with standard imaging operations.
Solution Approach 2:
The patent utilizes parameter changes by modifying the imaging sequence parameters based on results from the preliminary recording. These parameter adjustments optimize the phase information encoding for flow measurement while preserving the ability to perform standard anatomical imaging, thus preventing loss of phase information utility without compromising ease of operation.
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 effectively minimizes noise effects from eddy currents, enhancing the accuracy and precision of flow-encoded magnetic resonance imaging by setting optimal imaging sequence parameter values before the actual imaging, thus reducing image distortions and improving the reliability of velocity measurements.
Implementation Method 1
The aforementioned eddy current fields, also referred to as eddy currents, occur during the measurement due to currents induced in the conducting parts of the magnet housing by the switching of the gradient magnetic fields.
Implementation Method 2
In the presence of gradient fields that vary over time, a magnetization moved in the external B0-field picks up a phase. This can be used to encode velocities.
Data Source
AI summary
In a method and magnetic resonance (MR) apparatus for establishing imaging sequence parameter values with a reduced eddy current formation for flow-encoded magnetic resonance imaging, a number of different flow-encoded candidate raw datasets are acquired by executing a flow-encoded gradient measurement sequence with different imaging sequence parameter values from a test or calibration region of an examination object. Flow-encoded candidate image datasets are reconstructed from the different flow-encoded candidate raw datasets. A flow-encoded candidate image dataset is selected as a function of a background phase contrast established in a phase-contrast image assigned to the respective flow-encoded candidate image dataset. The imaging sequence parameter values assigned to the flow-encoded candidate image dataset are selected as parameter values for an imaging sequence for subsequent diagnostic flow-encoded magnetic resonance imaging.