MR System Phase Error Correction Using Spatially Selective RF Pulses
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Solution Overview
Problem
Magnetic resonance (MR) systems face challenges in correcting phase errors in multidimensional, spatially-selective RF excitation pulses, leading to artifacts and instability, especially in repeated imaging sequences where system parameters are difficult to maintain stability, and existing calibration techniques are time-consuming and complex.
Innovation Solution
A method and MR system that radiate multidimensional, spatially-selective RF excitation pulses using excitation gradient fields, acquire calibration gradient echoes, determine phase responses and shifts, calculate and apply phase and time corrections to correct phase errors, and adapt calibration parameters for precise phase error correction during the measurement sequence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multidimensional, spatially-selective RF excitation pulses are used to shorten measurement time, then productivity is improved, but phase errors and artifacts increase due to system inaccuracies
Solution Approach 1:
The patent applies preliminary calibration before the actual measurement sequence to determine correction values for phase errors. The calibration process radiates test RF excitation pulses, acquires calibration data, and calculates correction values that are stored and applied during subsequent measurements. This preliminary action prepares the system in advance to compensate for phase errors, allowing the use of multidimensional RF excitation pulses without suffering from their inherent phase inaccuracies.
2Measurement precision
If conventional calibration techniques are applied to correct phase errors, then measurement precision is improved, but calibration time increases significantly
Solution Approach 1:
The patent extracts only the essential calibration information needed for phase error correction by focusing on specific calibration gradient echoes and k-space lines. Instead of performing comprehensive system calibration, the method selectively acquires calibration data at key points (e.g., center k-space line) and extracts phase error parameters directly relevant to the RF excitation pulses. This extraction approach maintains correction accuracy while dramatically reducing calibration time.
Solution Approach 2:
The patent applies partial calibration by performing correction only for the specific phase errors affecting the RF excitation pulses, rather than calibrating the entire MRI system. The calibration is performed once at the beginning of the measurement sequence and then reused for multiple subsequent excitations. This partial action approach provides sufficient correction for the intended application without the time cost of exhaustive calibration.
3Measurement precision
If repeated imaging sequences are performed to improve data quality, then measurement precision is improved, but system parameter stability deteriorates over time
Solution Approach 1:
The patent performs preliminary calibration at the beginning of the measurement sequence to establish baseline correction values before system drift occurs. These correction values are then applied consistently across multiple repeated imaging sequences. By preparing the correction parameters in advance and reusing them throughout the measurement sequence, the method maintains phase accuracy even as system parameters naturally drift over time during repeated excitations.
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 continuous correction of phase errors, improving the accuracy of MR imaging by reducing artifacts and maintaining system stability throughout the measurement sequence, even with time-dependent errors, and reduces the time required for calibration.
Implementation Method 1
radiation of a multidimensional, spatially-selective RF excitation pulse using associated excitation gradient fields to excite a transversal magnetization
Implementation Method 2
acquisition of a number of calibration gradient echoes of the excited transversal magnetization using associated positive and negative calibration gradient fields
Data Source
AI summary
In a method and magnetic resonance system to correct phase errors in multidimensional, spatially selective radio-frequency excitation pulses in a pulse sequence used to operate the system to acquire magnetic resonance data, a multidimensional, spatially selective radio-frequency excitation pulse is radiated and multiple calibration gradient echoes are acquired. A phase correction and a time correction of the multidimensional, spatially selective radio-frequency excitation pulse is then calculated.