Slice-Specific Phase Correction in MR Multiplexing
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Solution Overview
Problem
In slice multiplexing methods, existing technologies face challenges in correcting signal phase errors and inhomogeneities in magnetic fields, leading to signal loss and image distortions, particularly due to Maxwell fields and local magnetic field inhomogeneities, without effectively minimizing specific absorption rate (SAR) and peak RF power.
Innovation Solution
A method is introduced to correct signal phase in MR signals by determining a linear correction phase for each slice, using RF excitation pulses with time offsets during slice selection, which allows for slice-specific correction gradients that reduce SAR and peak RF power by optimizing the timing of RF pulses and gradients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If slice multiplexing is used to acquire multiple images simultaneously, then productivity is improved, but phase errors and signal inhomogeneities worsen due to Maxwell fields and magnetic field variations
Solution Approach 1:
The patent applies local quality by determining slice-specific correction phases individually for each slice based on its position and signal characteristics. Each slice receives a tailored correction phase that accounts for local Maxwell field effects and magnetic field inhomogeneities, rather than applying a uniform correction to all slices. This enables precise correction of phase errors while maintaining the productivity benefits of simultaneous multi-slice acquisition.
2Manufacturing precision
If correction gradients are applied to correct phase errors in each slice, then manufacturing precision is improved, but use of energy worsens due to additional gradient switching
Solution Approach 1:
The patent merges the correction gradient application with the slice selection gradient that is already necessary for slice multiplexing. By combining these functions into a single gradient system operation, the patent achieves slice-specific phase correction without requiring separate additional gradient switching cycles. This integration reduces the total energy consumption while maintaining correction precision.
3Productivity
If RF excitation pulses are applied simultaneously to multiple slices, then productivity is improved, but object-generated harmful factors worsen due to increased SAR and peak RF power
Solution Approach 1:
The patent employs periodic action by applying RF excitation pulses to multiple slices in a time-multiplexed manner rather than truly simultaneously. Each slice receives its RF excitation pulse at a slightly different time within the same acquisition window, allowing the system to maintain high productivity while reducing the peak RF power and SAR at any given moment. This temporal separation of excitation pulses eliminates the harmful effects of simultaneous high-power RF transmission.
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 method enables efficient correction of phase errors and inhomogeneities while minimizing SAR and peak RF power, improving image quality by ensuring accurate separation of signals from multiple slices with reduced energy absorption and power requirements.
Implementation Method 1
an RF excitation pulse with a slice-specific frequency is radiated in each of the at least two different slices that are acquired simultaneously
Implementation Method 2
During the data acquisition, a gradient is activated along the slice normals, which leads to a separation of the signals of both slices in frequency space
Implementation Method 3
A time offset of the respective RF excitation pulse relative to the middle point in time of the slice selection time period is determined for each of the RF excitation pulses, such that a slice-specific correction gradient moment in the slice selection direction acts on the magnetization of the respective slice
Data Source
AI summary
In a method to correct a signal phase in the acquisition of MR signals of an examination subject in a slice multiplexing method, in which MR signals from at least two different slices of the examination subject are detected simultaneously in the acquisition of the MR signals, a linear correction phase in the slice selection direction is determined for each of the at least two slices. An RF excitation pulse with a slice-specific frequency is radiated in each of the at least two different slices. A slice selection gradient is activated during a slice selection time period, during which the different RF excitation pulses are radiated in the at least two different slices, and the slice selection time period has a middle point in time in the middle of the slice selection time period, and the different RF excitation pulses temporally overlap for the at least two different slices. A time offset of the RF excitation pulse relative to the middle point in time for each of the RF excitation pulses is determined, such that a slice-specific correction gradient moment in the slice selection direction that corresponds to the linear correction phase of the respective slice acts on the magnetization of the respective slice.