Modified Driven-Equilibrium MRI for Faster 3D STIR Contrast
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Solution Overview
Problem
Long acquisition times and inadequate image contrast in fluid-sensitive fast- or turbo-spin-echo-based MRI with short-tau inversion recovery (STIR) sequences, particularly in 3D acquisitions, due to the slow recovery of longitudinal fluid magnetization and the need for long inversion-recovery times, which limits clinical applicability for musculoskeletal imaging.
Innovation Solution
A modified driven-equilibrium (mDE) pulse sequence is introduced, comprising a phase-shifted flip-back pulse to convert transverse magnetization of interest into positive longitudinal magnetization, aligned with the B0-field direction, within a novel MRI pulse sequence that includes an inversion-recovery pulse, image-encoding, and a modified driven-equilibrium element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a standard inversion-recovery pulse sequence is used for fluid-sensitive imaging, then fat signal suppression is achieved, but the acquisition time becomes excessively long due to slow fluid magnetization recovery
Solution Approach 1:
The driven-equilibrium element performs preliminary action by refocusing transverse magnetization and converting it to longitudinal magnetization before the next excitation pulse, preparing the fluid magnetization in advance to reduce the required waiting time for recovery
Solution Approach 2:
The invention changes the parameter of longitudinal magnetization by using a phase-shifted flip-back pulse (90° phase shift relative to refocusing pulses) that converts transverse magnetization into positive longitudinal magnetization, thereby accelerating the effective recovery of fluid signal
2Productivity
If the repetition time TR is shortened to reduce acquisition time, then productivity improves, but the fluid signal intensity decreases due to insufficient magnetization recovery
Solution Approach 1:
The driven-equilibrium element ensures continuity of useful action by continuously converting transverse magnetization to longitudinal magnetization throughout the TR period, maintaining fluid signal enhancement even with shortened repetition times
Solution Approach 2:
By changing the phase of the flip-back pulse to 90° relative to refocusing pulses, the invention transforms the action of the RF pulse train from converting longitudinal to transverse magnetization into converting transverse to longitudinal magnetization, thereby enhancing fluid signal at shorter TR times
3Loss of time
If a standard driven-equilibrium element is added to accelerate fluid magnetization recovery, then acquisition time is reduced, but the fluid signal contrast deteriorates because transverse magnetization is converted to negative longitudinal magnetization
Solution Approach 1:
The invention applies the inversion principle by changing the phase of the flip-back pulse from the standard configuration to a 90° phase shift, which inverts the direction of conversion from producing negative longitudinal magnetization to producing positive longitudinal magnetization, thereby restoring fluid signal contrast
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 mDE pulse sequence enhances longitudinal magnetization of fluids, improving image contrast and reducing acquisition time, making it suitable for clinical applications, especially in 3D STIR imaging of musculoskeletal systems.
Implementation Method 1
The present invention concerns an MRI method for improving an MRI signal for a magnetization of interest... performing, by the MRI system, an MRI pulse sequence containing three consecutive radio frequency (RF) elements... a third element that is a modified driven-equilibrium (mDE) pulse sequence configured for achieving a conversion of a transverse magnetization component of the magnetization of interest into positive longitudinal magnetization, aligned with the positive z-axis and the B0-field direction
Implementation Method 2
a first element that is an inversion-recovery pulse sequence characterized by a time of inversion (recovery) TI... The characteristic recovery time, T1, of low-viscous fluids, is in the range of several seconds at the field strength of clinical scanners
Data Source
AI summary
A method and a magnetic resonance imaging (MRI) system improve an MRI signal from a magnetization of interest. The method includes performing an MRI pulse sequence containing three consecutive radio frequency (RF) elements, namely, a first element that is an inversion-recovery pulse sequence characterized by a time of inversion, a second element that is an image-encoding pulse sequence starting at the time of inversion with an excitation RF pulse followed by an image-encoding gradient and a data sampling. The second element is followed by a third element. An MRI signal generated by the object and sampled by image readout blocks applied to the object by the MRI system during each repetition time, is acquired. From the MRI signal, an image of the object is reconstructed. The third element is a modified driven-equilibrium (mDE) pulse sequence configured for achieving a conversion of a transverse magnetization component.