iMSDE MRI Sequence for Vessel Wall Imaging
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Solution Overview
Problem
Current black-blood imaging techniques, such as in-flow saturation and double inversion recovery, are limited by blood replenishing rate and prone to plaque-mimicking artifacts, especially in 3-D imaging applications with stagnant or slow-flowing blood, and are sensitive to local magnetic field inhomogeneities, leading to signal loss.
Innovation Solution
The improved motion-sensitization driven equilibrium (iMSDE) sequence is introduced, featuring a second 180-degree refocusing pulse and additional motion sensitization gradients, which maximizes the first gradient moment to enhance flow suppression while being less sensitive to B1 inhomogeneities, allowing for consistent blood suppression in larger volumes and 3-D imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional black-blood imaging techniques (IS or DIR) are used, then blood suppression is achieved, but plaque-mimicking artifacts occur due to insufficient suppression in stagnant or slow-flowing blood
Solution Approach 1:
The patent replaces the blood replenishing rate-based mechanism (IS/DIR techniques) with a flow-dephasing mechanism using motion-sensitizing gradients. This substitutes the temporal blood replacement approach with a spatial phase dispersion approach, where flowing blood is suppressed through phase incoherence rather than replenishment rate limitations.
Solution Approach 2:
The patent changes the fundamental parameter for blood suppression from preparation time (TEprep) to gradient moment (m1). By optimizing the first gradient moment of the motion-sensitizing gradient pair, the technique achieves superior blood suppression independent of blood replenishing rate, thereby eliminating plaque-mimicking artifacts.
2Reliability
If MSDE technique is used to achieve superior blood suppression, then flow suppression is improved, but signal loss occurs due to sensitivity to B1 inhomogeneity
Solution Approach 1:
The patent introduces a B1-insensitive refocusing pulse as an intermediary element between the motion-sensitizing gradients and signal acquisition. This refocusing pulse acts as a mediator that recovers signal lost to B1 inhomogeneity while preserving the flow suppression effect, thereby reducing signal loss without compromising flow suppression capability.
3Volume of moving object
If larger imaging volume is used for 3-D imaging, then isotropic voxel size is achieved, but blood suppression becomes insufficient in regions with stagnant or slow-flowing blood
Solution Approach 1:
The patent segments the blood suppression mechanism into two independent components: flow dephasing (achieved through motion-sensitizing gradients) and signal recovery (achieved through B1-insensitive refocusing). This segmentation allows the technique to maintain effective blood suppression across large imaging volumes by applying gradient moments that are independent of imaging size, while the refocusing pulse ensures signal recovery regardless of flow state.
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 iMSDE sequence provides improved immunity to B1 inhomogeneities, maintaining signal levels even under non-ideal conditions, and offers superior blood suppression in 3-D imaging, enabling clearer visualization of atherosclerosis plaques and vessel walls with reduced artifacts.
Implementation Method 1
The flow sensitizing gradient pair can introduce phase dispersion among moving spins, while maintaining the phase coherence of stationary spins
Implementation Method 2
the DIR technique and its variations achieve BB imaging by inverting the out-of-slice blood signal with a 180 degree pulse
Implementation Method 3
The iMSDE sequence thus includes a group of four RF pulses, as well as additional magnetic gradient pulses that are not included in the conventional MSDE sequence. The scheme for placing sensitization gradients, G(u), employed, is selected to maximize the first gradient moment (m1) within the fixed TEprep interval
Data Source
AI summary
An improved motion-sensitization driven equilibrium (iMSDE) sequence based upon an MLEV-4 sequence is used for black-blood vessel wall imaging. The MSDE pulse pattern that is used us a preparation sequence for other procedures employed to acquire images has been modified to produce the iMSDE sequence by the addition of a second 180 degree refocusing pulse and two motion sensitization gradients. The iMSDE sequence thus includes a group of four radio frequency (RF) pulses, as well as additional magnetic gradient pulses that are not included in the conventional MSDE sequence. Computer simulations indicate that this new pulse sequence is substantially more immune to local B1 inhomogeneity than conventional sequences. In vivo experiments have demonstrated significant signal improvement at high first-order moments (m1) conditions compared to the traditional MSDE sequence.