Slice-Specific Navigator Signal Separation for EPI Phase Error Correction
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Solution Overview
Problem
Current slice multiplexing methods in magnetic resonance imaging (MRI) face challenges in efficiently correcting phase errors, such as N/2 ghosts and drift, with existing methods requiring additional reference scans and increasing total scan time, especially when using echo-planar simultaneous multi-slice (SMS) techniques.
Innovation Solution
A method for slice-specific correction of scan data recorded simultaneously using an EPI SMS technique, involving recording slice separation reference scan data, generating phase-encoded navigator signals, separating them into single-slice signals, and determining slice-specific correction data to correct scan data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If slice multiplexing methods are used to record scan data for multiple slices simultaneously, then productivity is improved, but phase errors such as N/2 ghosts and drift occur in the recorded data
Solution Approach 1:
The patent separates navigator signals into individual slice-specific components using slice separation reference scan data. Each slice's navigator signal is processed independently to determine slice-specific correction data, allowing phase error correction to be applied individually to each slice while maintaining the benefits of simultaneous multi-slice recording
Solution Approach 2:
The patent introduces navigator signals as intermediary measurements that capture phase error information without affecting the main scan data acquisition. These navigator signals serve as mediators between the simultaneous multi-slice recording process and the phase error correction process, enabling correction without sacrificing scan speed
2Manufacturing precision
If additional reference scans are performed to correct phase errors, then image quality is improved, but total scan time increases
Solution Approach 1:
The patent combines the acquisition of navigator signals with the main scan data acquisition process. Navigator signals are recorded during the same RF excitation pulses and gradient switching sequences used for the actual imaging, eliminating the need for separate reference scans and avoiding additional scan time
Solution Approach 2:
The patent performs slice separation using reference scan data that is acquired once and reused for correcting multiple slices. This preliminary action of separating slice-specific navigator signals allows subsequent phase error correction to be performed efficiently without requiring additional scanning time for each correction 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 allows for high-quality image reconstruction with reduced total scan time by enabling slice-specific corrections for phase errors, avoiding the need for extensive additional reference scans and minimizing artifacts.
Implementation Method 1
high-frequency excitation pulses (RF pulses) are radiated into the examination object and the nuclear spin resonances produced are measured as so-called k-space data
Implementation Method 2
an oscillating (i.e. 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 3
one of also N different phases is applied in the phase-encoding direction to each of successive echo signals
Implementation Method 4
separating the navigator signals simultaneously recorded for the at least two slices, in each case, into single-slice navigator signals of the at least two slices using the slice separation reference scan data
Implementation Method 5
determining slice-specific correction data from the single-slice navigator signals; and correcting scan data that is to be corrected by means of the slice-specific correction data
Implementation Method 6
the actual image is mapped again but displaced by N/2 in the positive and the negative direction relative to the image matrix center, in general with different intensity
Data Source
AI summary
A technique for slice-specific correction of scan data recorded for at least two slices simultaneously of an examination object via an EPI-SMS is provided. The technique comprises recording slice separation reference scan data, generating scan data that is to be corrected, and recording phase-encoded navigator signals simultaneously for the at least two slices after an RF excitation pulse radiated into the examination object and before the recording of scan data to be corrected. The at least one navigator signal is recorded for each possible polarity and different phase-encoding of the navigator signals that is used. The technique further comprises separating the navigator signals simultaneously recorded for the at least two slices into single-slice navigator signals using the slice separation reference scan data, determining slice-specific correction data from the single-slice navigator signals, and correcting scan data that is to be corrected by means of the slice-specific correction data.