MRI Radial Sampling Blade Shift Correction
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Solution Overview
Problem
Current MRI techniques using radial sampling methods fail to accurately correct positional relationships between blades in k-space, leading to artifacts and uneven brightness due to undistinguished static and dynamic errors, especially in regions with low static magnetic field homogeneity and local sensitivity distributions of reception RF coils.
Innovation Solution
The method involves pre-measurement to separate factors shifting echo signal positions in k-space, calculating and applying shift amounts for each blade, using readout gradient magnetic field pulses with varying polarities to correct for dynamic errors, and reflecting these corrections in the reconstruction process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If radial sampling method is used to acquire images, then imaging speed and coverage are improved, but artifacts and uneven brightness occur due to improper positional relationship between blades in k-space
Solution Approach 1:
The patent applies preliminary action by performing pre-measurement to calculate shift amounts before actual image acquisition. The system measures and stores correction values for static errors in advance, then applies these corrections during the radial sampling process to prevent artifacts and uneven brightness while maintaining high imaging speed.
Solution Approach 2:
The patent implements feedback by using the calculated shift amounts from pre-measurement to correct the positional relationships of blades in k-space during image reconstruction. The system continuously refines the positioning of radial samples based on measured deviations, ensuring accurate blade alignment and eliminating artifacts.
2Device complexity
If shift amount calculation is performed without distinguishing static and dynamic errors, then processing complexity is reduced, but correction accuracy deteriorates leading to inappropriate positional relationships between blades
Solution Approach 1:
The patent applies segmentation by dividing the total shift amount into two distinct components: static error (common to all blades) and dynamic error (specific to each blade). This segmentation allows the system to calculate and correct each type of error separately using appropriate methods, significantly improving correction accuracy while managing processing complexity through structured separation.
Solution Approach 2:
The patent implements local quality by applying different correction strategies to different types of errors. Static errors are corrected using a global shift amount calculated from phase distribution, while dynamic errors are corrected using blade-specific shift amounts. This localized approach ensures each error type receives the most appropriate correction method.
3Loss of time
If conventional shift correction method is applied in regions with low static magnetic field homogeneity, then processing time is reduced, but artifact generation increases due to dominant static errors
Solution Approach 1:
The patent applies preliminary action by performing pre-measurement in regions with low static magnetic field homogeneity to accurately characterize static errors before image acquisition. The system stores correction values for these regions and applies them during reconstruction, preventing artifact generation while maintaining efficient processing time.
Solution Approach 2:
The patent implements feedback by using measured static error characteristics from pre-measurement to continuously correct blade positioning in regions with low magnetic field homogeneity. This feedback mechanism ensures that dominant static errors are properly compensated, eliminating artifacts while maintaining processing efficiency.
4Area of stationary object
If radial sampling is performed with multiple blades, then k-space coverage is improved, but positional relationship errors between blades increase leading to image quality deterioration
Solution Approach 1:
The patent implements feedback by calculating shift amounts for each blade based on phase distribution measurements and using these corrections to adjust blade positions in k-space during reconstruction. This feedback mechanism ensures that even with multiple blades covering extensive k-space areas, the positional relationships remain accurate and artifacts are minimized.
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 the acquisition of high-quality images even in challenging conditions by accurately correcting positional relationships and reducing artifacts and uneven brightness.
Implementation Method 1
The readout gradient magnetic field pulse generates a magnetic field gradient in an arbitrary direction in order to generate a magnetic field intensity gradient in the static magnetic field space
Implementation Method 2
The MRI apparatus is an apparatus that measures an NMR signal generated by atomic nucleus spin comprising tissue of an object
Implementation Method 3
Since the atomic nucleus spin performs precession at a frequency according to a gradient magnetic field intensity and the magnetic rotation ratio
Implementation Method 4
an echo signal can be decomposed into a component of each frequency i.e., position by measuring an NMR signal (echo signal) in a state where a readout gradient magnetic field pulse was applied to perform frequency analysis represented by the Fourier transform
Data Source
AI summary
The present invention obtains high-quality images even in a case of measurement with a radial sampling method. For this purpose, pre-measurement is performed to extract only a component different for each blade from among shift amounts from among echo signals, and a shift amount in k-space of an echo signal by the said component is reflected to a reconstruction process. In the pre-measurement, echo signals are obtained respectively by applying readout gradient magnetic field pulses that change the polarity to the positive and negative and that have the same pulse shape as readout gradient magnetic field pulses to be used in an image acquisition sequence. A shift amount is obtained for each axis of X, Y, and Z of an MRI apparatus as a variation amount of a phase difference between both the echo signals.