Dixon Turbo Spin Echo Image Sharpness via Gradient Inversion
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Solution Overview
Problem
Dixon Turbo Spin Echo sequences in magnetic resonance imaging suffer from a lack of image sharpness due to exponential signal decline and long echo train lengths, leading to reduced image quality.
Innovation Solution
The method involves acquiring MR data using two echo trains with partial or complete inversion of gradient moments, allowing for the combination of echoes to compensate for T2 relaxation-induced filtering effects, thereby improving image sharpness. This is achieved by synchronizing gradient moments between echo trains and reconstructing images from both sets of data, ensuring that neither echo train scans the same k-space region twice.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a long echo train is used in Dixon Turbo Spin Echo sequences, then the scanning efficiency is improved, but the image sharpness deteriorates due to exponential signal decline
Solution Approach 1:
The k-space is divided into two segments scanned by two separate echo trains. The first echo train scans k-space lines with phase-encoding gradient moments following a first predetermined sequence, while the second echo train scans k-space lines with phase-encoding gradient moments following a second predetermined sequence that is at least partially inverted relative to the first. This segmentation allows each echo train to contribute to different portions of k-space, compensating for signal decline while maintaining overall scanning efficiency.
Solution Approach 2:
The phase-encoding gradient moment sequence of the second echo train is at least partially inverted relative to the first echo train. Specifically, if the first sequence is GM1(1) to GM1(EZL), the second sequence is GM2(1) to GM2(EZL) where GM2(i) corresponds to GM1(EZL-i+1) for at least some values of i. This inversion ensures that k-space lines acquired with stronger signals in the first echo train are combined with corresponding lines from the second echo train, compensating for T2 relaxation effects and improving image sharpness.
2Speed
If the echo train length is increased to reduce scan time, then the scanning speed is improved, but the point spread function spreads out causing loss of sharpness
Solution Approach 1:
The scanning process is segmented into two echo trains, each with its own phase-encoding gradient moment sequence. By distributing the k-space coverage across two sequences and combining the results, the effective point spread function is sharpened while maintaining the long echo train length needed for fast scanning.
Solution Approach 2:
The inverted phase-encoding gradient moment sequence in the second echo train counteracts the spreading effect of the long echo train length. The inversion ensures that signal intensity variations across the echo train are compensated when combining data, preserving point spread function sharpness despite the extended echo train duration.
3Device complexity
If gradient moments are not inverted between echo trains, then the sequence complexity is reduced, but the filtering effects of T2 relaxation cannot be compensated
Solution Approach 1:
The phase-encoding gradient moment sequence of the second echo train is at least partially inverted relative to the first. This inversion, while increasing sequence complexity, enables compensation for T2 relaxation filtering effects. The inverted sequence ensures that k-space lines are acquired with complementary signal characteristics, allowing reconstruction of sharper images with reduced T2 weighting.
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
The approach enhances image sharpness by compensating for the filtering effects of T2 relaxation, resulting in improved MR image quality by reducing the filter effect and maintaining identical recording conditions for both echo trains.
Implementation Method 1
The signal strength of the echoes diminishes exponentially within an echo train according to the function e−t/T2 (with T2 being the spin-spin relaxation time or transverse relaxation time)
Implementation Method 2
MR data are acquired that relate to the predetermined volume segment of an examination subject with a first echo train... during time intervals during which nuclear spins of two predetermined substances inside the volume segment are in phase
Data Source
AI summary
In a magnetic resonance (MR) method and apparatus, first and second MR data are acquired from respective echo trains with gradient moments of one echo train being in a sequence that is an inversion of at least a portion of the sequence of gradient moments in the second echo train. The MR signals are acquired from at least two substances in a volume of a subject, so that the relaxation of the respective nuclear spins influences the manner by which the first and second data are entered into k-space, so that when an image is reconstructed, the filter effect induced by such relaxation is compensated for.