EPI-SMS Navigator Correction for Slice-Specific Phase Errors
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Solution Overview
Problem
Existing methods for correcting phase errors in echo-planar simultaneous multi-slice magnetic resonance imaging (EPI SMS) are inefficient, requiring additional reference scans and increasing total scan time, and cannot provide slice-specific corrections for phase displacements and drift effects.
Innovation Solution
A method involving the recording of navigator signals using a bipolar readout gradient for each slice, followed by Fourier transformation to determine slice-specific correction data, allowing for efficient correction of phase errors without additional reference scans.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional reference scans are performed to correct phase errors, then correction precision is improved, but total scan time increases
Solution Approach 1:
The patent combines the reference scan and navigator signal acquisition into a single integrated process. Navigator signals are recorded during the actual scan for each slice, eliminating the need for separate reference scans. This merging approach maintains correction precision while reducing total scan time.
Solution Approach 2:
The method uses navigator signals acquired during the scan itself to perform self-correction of phase errors. Each slice's navigator signals provide the necessary information for slice-specific correction without requiring external reference data, enabling the system to correct its own errors efficiently.
2Device complexity
If global correction methods are used for phase errors, then device complexity is reduced, but manufacturing precision of slice-specific corrections deteriorates
Solution Approach 1:
The patent divides the correction process into slice-specific segments. Each slice has its own navigator signals recorded and processed independently, allowing precise correction for each slice while maintaining manageable complexity through modular processing of individual slice data.
Solution Approach 2:
The method applies local quality correction by using slice-specific navigator signals to determine correction factors tailored to each slice's actual conditions. This ensures high precision for each slice rather than applying a uniform global correction that cannot account for slice-specific variations.
3Productivity
If navigator signals are recorded for each slice simultaneously, then productivity is improved, but measurement precision of slice-specific phase errors deteriorates
Solution Approach 1:
The patent segments the simultaneously acquired navigator signals by slice using slice selection encoding. This allows multiple slices to be scanned efficiently in parallel while maintaining the ability to separately analyze and correct phase errors for each slice based on its specific navigator signal characteristics.
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
Enables high-quality image reconstruction with slice-specific corrections for phase errors and drift effects, reducing total scan time and minimizing artifacts.
Implementation Method 1
an oscillating, that is bipolar, readout gradient is used in which each change of the polarization direction of the gradient refocuses the transverse magnetization as far as the T2* decay allows, and thereby generates a gradient echo
Implementation Method 2
determining single-slice navigator signals by applying a Fourier transform to the mean navigator signal of the second polarity and a navigator signal of the first polarity
Data Source
AI summary
In a method for slice-specific correction of scan data recorded for at least two slices simultaneously of an examination object using an EPI-SMS technique, navigator signals encoded in a slice selection direction using a bipolar readout gradient for the at least two slices temporally after a RF excitation pulse radiated into the examination object and temporally before the recording of scan data to be corrected may be simultaneously recorded. Mean navigator signal(s) from at least two of the recorded navigator signals of a same polarity may be determined. Single-slice navigator signals may be determined based on the mean navigator signal and a navigator signal having been recorded with the same polarity as the mean navigator signal(s), but with a different slice selection encoding. Slice-specific correction data from the single-slice navigator signals may be determined, and scan data may be corrected based on the slice-specific correction data.