MRI Frequency Map Acquisition via Multi-Echo Sequences
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Solution Overview
Problem
Magnetic resonance imaging (MRI) systems face challenges in obtaining high-quality images due to inhomogeneous static magnetic fields, particularly in moving objects like the heart, thorax, and abdomen, where position changes and velocity-induced errors complicate the determination of shim field strengths required for shimming.
Innovation Solution
The method involves generating first and second spin populations within MRI pixels with different phase histories using specific radio frequency pulses and gradients, allowing for the acquisition of a frequency map during a single pulse sequence, which can be used to determine magnetic field strength variations and correct for inhomogeneities without the need for multiple acquisitions, thus reducing errors from position and velocity changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency maps are obtained using multiple acquisitions to improve accuracy, then measurement precision is improved, but time consumption increases and position changes between acquisitions introduce velocity-induced errors
Solution Approach 1:
The patent applies preliminary action by acquiring all necessary frequency map data within a single heartbeat cycle before position and velocity changes can introduce errors. The multi-echo pulse sequence is designed to capture multiple frequency measurements in rapid succession, establishing the frequency map before the object moves to a different position or velocity state.
Solution Approach 2:
The patent implements continuity of useful action by using a continuous multi-echo pulse sequence that acquires frequency data throughout the entire heartbeat cycle without interruption. This continuous acquisition ensures that all measurements are taken under the same positional and velocity conditions, eliminating errors that would arise from position changes between separate acquisitions.
2Manufacturing precision
If multiple acquisitions are used to determine shim field strengths, then shimming accuracy is improved, but the object may move to different positions between acquisitions introducing errors
Solution Approach 1:
The patent uses preliminary action by determining all shim field strengths from frequency data acquired within a single heartbeat cycle, before the object can move to a different position. This ensures that all shimming calculations are based on measurements taken when the object is in the same positional state, eliminating position consistency errors.
Solution Approach 2:
The patent merges multiple frequency measurements into a single integrated frequency map by combining data from multiple echoes acquired within one heartbeat. This consolidation allows all shimming parameters to be determined from a unified data set taken at a single position, improving reliability while maintaining accuracy.
3Productivity
If rapid single-acquisition frequency map acquisition is used, then time consumption is reduced and position consistency is maintained, but measurement precision may be compromised
Solution Approach 1:
The patent applies periodic action by using a multi-echo pulse sequence that periodically samples the frequency within a single heartbeat cycle. Multiple echoes are acquired at different time points during the heartbeat, providing multiple measurements that improve precision while maintaining the rapid single-acquisition approach and preventing position changes.
Solution Approach 2:
The patent uses preliminary action by completing all frequency measurements within the first heartbeat cycle, establishing an accurate frequency map before any position or velocity changes occur. This preliminary acquisition ensures both high precision through multiple measurements and high productivity by completing everything in one rapid scan.
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 the rapid acquisition of accurate frequency maps that are insensitive to position changes and movement, allowing for effective shimming of the magnetic field within a single heartbeat, thereby improving image quality and reducing errors in MRI imaging of challenging anatomical regions.
Implementation Method 1
When subjected to the static magnetic field, MRI active nuclei, e.g., hydrogen nuclei, precess at frequencies proportional to the strength of the magnetic field. MRI signals are obtained from the precessing nuclei.
Implementation Method 2
MR imagers generally include shim magnets that generate shim fields used to reduce variations in the static magnetic field. The shim magnets are typically electromagnets so that the strength of the shim fields can be controlled electronically.
Implementation Method 3
generating first and second spin populations within each of a plurality of pixels of a slice, wherein the first and second spin populations are generated with different phase histories. The methods include acquiring MRI signals from the first and second spin populations of each pixel at different times
Implementation Method 4
subjecting the slice to a first radio frequency (RF) pulse, subjecting the slice to a second RF pulse, and at a time between the first and second RF pulses, subjecting the slice to a dephasing gradient
Data Source
AI summary
A magnetic resonance imaging (MRI) method includes generating first and second spin populations within each of a plurality of pixels of a slice of an object. These spin populations have different phase histories. For each pixel, MRI signals from those spin populations are acquired at different times These MRI signals can then be used to determine a field strength difference between different pixels of the slice.