Turbospin Echo MRI Sequence With Variable Flip Angles
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Solution Overview
Problem
Existing magnetic resonance imaging (MRI) techniques using two- and three-dimensional spin echo sequences with longer echo trains suffer from increased T2 weighting, which worsens T1 contrast, and previous methods to mitigate this have been ineffective in preventing T2 weighting.
Innovation Solution
A method involving a restoration pulse chain after refocusing pulses, which aligns magnetization opposite to the main magnetic field before the next excitation pulse, combined with a partial Fourier technique to reduce echo train length and minimize T2-weighted signal portions, and magnetization preparation to achieve consistent signal levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If longer echo trains with multiple refocusing pulses are used to shorten acquisition time, then productivity is improved, but T1 contrast deteriorates due to increased T2 weighting
Solution Approach 1:
The patent applies parameter changes by systematically varying the flip angles of refocusing pulses within the echo train according to a predetermined pattern. This optimization of pulse parameters maintains T1 contrast while enabling longer echo trains for faster acquisition. The flip angle modulation compensates for T2 weighting effects that would otherwise degrade T1 contrast in fast spin echo sequences.
Solution Approach 2:
The patent implements dynamics by making the refocusing pulse flip angles variable rather than constant. The flip angles dynamically change throughout the echo train according to a specific pattern, allowing the sequence to adapt and maintain optimal T1 contrast weighting across multiple echoes while achieving faster imaging through extended echo trains.
2Productivity
If refocusing pulses with variable flip angles are used in three-dimensional spin echo imaging, then productivity is improved through longer echo trains, but T2 weighting increases and worsens T1 contrast
Solution Approach 1:
The patent optimizes the flip angle parameters of refocusing pulses to minimize T2 weighting effects. By carefully selecting and varying the flip angles according to a predetermined pattern, the sequence maintains signals that are predominantly T1-weighted even through long echo trains, thereby reducing the harmful T2 weighting that would otherwise contaminate the T1 contrast.
Solution Approach 2:
The patent converts the potentially harmful effect of multiple refocusing pulses (which normally increase T2 weighting) into a benefit by using variable flip angles. The variable flip angle scheme exploits the pulse train structure to maintain T1 contrast while achieving the speed benefits of long echo trains, effectively turning the echo train length from a source of T2 weighting into a means for faster imaging with preserved T1 contrast.
3Manufacturing precision
If magnetization is inverted before refocusing pulses in prior art methods, then some T2 weighting mitigation is achieved, but increasing T2 weighting cannot be fully prevented with long echo trains
Solution Approach 1:
The patent applies preliminary action by inverting the magnetization before the refocusing pulse train, similar to prior art, but combines this with variable flip angle refocusing pulses. This preliminary inversion prepares the magnetization state to maximize T1 contrast, while the subsequent variable flip angle pulses maintain this contrast throughout the echo train, achieving both T1 contrast preservation and reduced acquisition time.
Solution Approach 2:
The patent enhances the preliminary action approach by making the refocusing pulses dynamic with variable flip angles. This dynamic adjustment of pulse parameters throughout the echo train maintains optimal T1 contrast weighting from the inverted magnetization state, preventing the signal from becoming T2-weighted even as the echo train progresses, thereby achieving fast imaging without contrast degradation.
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 effectively suppresses T2 weighting, enhancing T1 contrast in MRI images, particularly in fast spin echo imaging sequences, allowing for better differentiation between tissues like white and grey brain matter with reduced acquisition time.
Implementation Method 1
method for generating T1-weighted images of an examination subject by means of magnetic resonance
Implementation Method 2
the magnetization of the examination subject is excited with an RF excitation pulse
Implementation Method 3
A number N of RF focusing pulses with variable flip angles is subsequently radiated to generate a plurality of spin echoes
Implementation Method 4
this restoration pulse chain of RF pulses influences the magnetization such that the magnetization is aligned opposite to the direction of the basic magnetic field by the restoration pulse chain
Implementation Method 5
The basic magnetic field B0 (also called a polarization field) is typically generated so as to be aligned in the positive z-direction
Data Source
AI summary
In a method in the form of a turbo spin echo imaging sequence with long echo trains and optimized T1 contrast for generation of T1-weighted images of an examination subject by magnetic resonance, magnetization in the examination subject is excited with an RF excitation pulse, a number N of RF refocusing pulses with variable flip angle are radiated to generate multiple spin echoes for an excitation pulse, a restoration pulse chain is activated after switching of the N refocusing pulses and before the next RF excitation pulse. The restoration pulse chain influences the magnetization such that the magnetization is aligned opposite to the direction of the basic magnetic field by the restoration pulse chain before the next RF excitation pulse.