MRI RF Phase Estimation Using Multiple Transmit Configurations
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Solution Overview
Problem
Current MRI technologies face challenges in accurately estimating the absolute phase of radiofrequency (RF) fields, particularly for transmit and receive coils, which affects image quality, RF safety, and the determination of electromagnetic properties, due to limitations in existing phase estimation methods that often rely on approximations and assumptions, leading to inaccuracies in coil sensitivity and phase distribution.
Innovation Solution
A method and system for determining the absolute phase of RF transmit and receive fields by using multiple transmit configurations to acquire complex k-space data, transforming it into images, and estimating the absolute phase maps, which can improve image quality, RF shimming, and the estimation of electromagnetic properties by providing accurate spatial distribution of RF fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phase-constrained parallel MRI algorithms are used to reduce noise amplification, then image reconstruction quality is improved, but accurate spatial phase distribution is required which increases system complexity
Solution Approach 1:
The patent introduces an intermediary calibration process using phantom objects to measure and store phase distribution characteristics. This intermediary measurement system acts as a mediator between the complex parallel MRI reconstruction algorithms and the actual imaging process, providing pre-characterized phase information that simplifies the reconstruction process while maintaining high image quality.
Solution Approach 2:
The patent performs preliminary phase calibration measurements using phantom objects before actual patient imaging. The phase distribution characteristics are measured and stored in advance, allowing the clinical imaging process to benefit from these pre-characterized parameters without requiring complex real-time phase calculations during the actual scan.
2Productivity
If higher acceleration factors are applied to reduce scan time, then productivity is improved, but signal-to-noise ratio decreases due to reduced k-space samples
Solution Approach 1:
The patent incorporates feedback mechanisms where the measured phase distribution from calibration phantoms is used to correct and refine the parallel imaging reconstruction process. This feedback loop allows the system to compensate for the noise amplification inherent in high acceleration factor imaging by using the pre-measured phase characteristics to optimize the reconstruction algorithm parameters.
3Device complexity
If approximate methods are used to estimate RF field phase, then device complexity is reduced, but measurement precision deteriorates due to reliance on assumptions
Solution Approach 1:
The patent implements a self-service approach where the system automatically performs calibration measurements using phantom objects to characterize its own phase distribution. Rather than relying on theoretical assumptions or external reference systems, the MRI system uses its own hardware and measurement capabilities to generate accurate phase maps, making the system self-calibrating and eliminating the need for complex external calibration equipment.
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 enables precise estimation of absolute phases, enhancing image quality, increasing acceleration factors, and improving RF safety by providing accurate electromagnetic property mapping, thus overcoming the limitations of existing methods.
Implementation Method 1
exciting nuclear spins in magnetic resonance (MR) nuclei using at least two transmit configurations of the transmit coil, and detecting first MR signals and second MR signals arising from exciting nuclear spins in MR nuclei
Data Source
AI summary
Methods and apparatuses for determining spatial distribution of an absolute phase of RF transmit field B1+ and/or RF receive field B1− in an MRI system are described herein. An example method can include selecting a transmit coil for which to measure the absolute phase of the RF transmit field B1+, exciting nuclear spins in MR nuclei using at least two transmit configurations of the transmit coil, and detecting first and MR signals arising from exciting nuclear spins in MR nuclei using first and second transmit configurations, respectively. The method can also include acquiring first and second sets of complex k-space data from the first and second MR signals, respectively, and estimating an absolute phase B1+ map of the transmit coil using the first set of complex k-space data and the second set of complex k-space data.