MRI Phase Error Correction via Shifted Gradient Echo Template Acquisition
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Solution Overview
Problem
Conventional EPI techniques face challenges in minimizing image distortion caused by phase errors, primarily due to non-uniform static magnetic fields and eddy currents, which affect the quality of magnetic resonance imaging.
Innovation Solution
The proposed MRI apparatus and method involve acquiring multiple echo signals with shifted gradient magnetic field timings in the readout direction and using these signals to generate both phase correction data and a magnetic field correction map, allowing for the reduction of phase errors and improvement of static magnetic field uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If EPI imaging is performed with high-speed gradient magnetic field inversions, then imaging speed is improved, but phase error increases causing image distortion
Solution Approach 1:
The patent applies preliminary action by performing template shots before the main EPI imaging to measure and characterize phase errors. The phase correction data is obtained in advance through template acquisitions, allowing the main imaging to proceed without delay while still achieving correction. This separates the measurement phase from the imaging phase, enabling high-speed imaging while maintaining accuracy.
Solution Approach 2:
The patent uses an intermediary approach by introducing template shots as a mediating step between the imaging system and the main EPI acquisition. These template shots serve as intermediaries that capture phase error characteristics, which are then used to correct the main imaging data. This intermediary measurement allows the system to achieve both high speed and high accuracy.
2Manufacturing precision
If template shots are acquired before main imaging to correct phase errors, then image quality is improved, but total imaging time increases
Solution Approach 1:
The patent applies partial action by acquiring only the necessary template shots with minimal phase encoding steps required to characterize the phase errors, rather than performing full imaging sequences. This partial acquisition provides sufficient correction data without the time penalty of complete imaging, optimizing the balance between correction quality and time efficiency.
3Manufacturing precision
If phase correction is applied to remove eddy magnetic field effects, then image distortion is reduced, but correction complexity increases
Solution Approach 1:
The patent segments the phase correction process into distinct components: template shot acquisition, phase error measurement, and application of correction data. By dividing the correction process into separate manageable steps, the system reduces the perceived complexity while achieving comprehensive phase correction for both static field non-uniformity and eddy current effects.
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 reduces image distortion caused by phase errors, enhancing the quality of MRI images by correcting for both static field non-uniformities and eddy current-induced errors, leading to more precise imaging.
Implementation Method 1
a static magnetic field for holding a predetermined magnetic field for a long period of time
Implementation Method 2
magnetic resonance imaging which magnetically excites nuclear spin of an object set in a static magnetic field with an RF pulse having the Larmor frequency and reconstructs an image based on MR signals generated due to the excitation
Implementation Method 3
EPI is a high speed imaging method that involves consecutively inverting a gradient magnetic field at high speed for each nuclear magnetic excitation to cause consecutive echoes
Implementation Method 4
the phase error component due to the causes other than the non-uniformity of the static magnetic field is selectively extracted and used as phase correction data
Data Source
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AI summary
According to one embodiment, an MRI apparatus (20) includes a first acquisition unit, a second acquisition unit and a correction unit (100). The first and second acquisition units produce a plurality of echo signals by performing echo signal acquisition sequence of EPI including application of a gradient magnetic field in a phase encoding direction, and acquire the plurality of echo signals as first and second template data, respectively. The second acquisition unit acquires the second template data under a sequence in which start timing of application of a gradient magnetic field in a readout direction is shifted from the case where acquisition of the first template data is performed. The correction unit (100) corrects phase error included in the echo signals by using the first and second template data.