Wedge-Shaped Inversion Slab for Arterial Spin Labeling MRI
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Solution Overview
Problem
Conventional arterial spin labeling (ASL) techniques in MRI struggle to achieve optimal temporal signal-to-noise ratio (tSNR) due to varying velocities and geometries of feeding arteries, which prevents matching the temporal bolus width with inter-pulse spacing.
Innovation Solution
The implementation of a wedge-shaped inversion slab in MRI systems, achieved by modulating the shape and thickness of the excitation/inversion slab using a combination of conventional slice-selective adiabatic fast passage (AFP) pulses and in-plane gradient pulses, allowing for tailored inversion thickness across different arteries to match bolus width with inter-pulse spacing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional slice-selective inversion pulses with uniform thickness are used, then the inversion slab can be easily applied to all feeding arteries, but the temporal bolus width cannot be matched with inter-pulse spacing due to varying arterial velocities and geometries
Solution Approach 1:
The patent applies local quality by creating a wedge-shaped inversion slab where the thickness varies spatially across different locations. Specifically, the inversion slab has different thicknesses at different in-plane positions to match the varying velocities and geometries of feeding arteries, with thinner regions for faster arteries and thicker regions for slower arteries, thereby optimizing bolus temporal width matching locally for each artery
Solution Approach 2:
The patent introduces an additional spatial dimension to the inversion slab design by transitioning from a uniform two-dimensional slab to a three-dimensional wedge shape with varying thickness. This is achieved by modulating the slice-selective gradient to create linear variation in inversion thickness across the in-plane direction, adding a thickness dimension that enables adaptation to different arterial characteristics
2Speed
If the inversion slab thickness is increased to capture slower flowing blood, then bolus temporal width matching is improved for slow arteries, but the bolus width becomes excessively large for fast-flowing arteries
Solution Approach 1:
The wedge-shaped inversion slab implements local quality by assigning different thickness values to different spatial locations corresponding to different arteries. Faster-flowing arteries are positioned in regions with thinner inversion slabs to produce shorter bolus temporal widths, while slower-flowing arteries are positioned in regions with thicker inversion slabs to produce longer bolus temporal widths, thereby matching bolus duration to flow velocity locally
3Ease of manufacture
If uniform inversion thickness is used across all locations, then the pulse sequence is simple to implement, but optimal tSNR cannot be achieved due to mismatched bolus temporal widths
Solution Approach 1:
The patent applies dynamics by making the inversion slab thickness variable rather than static and uniform. The slice-selective gradient is modulated to create a dynamic wedge shape where the effective inversion thickness changes across the in-plane direction, allowing the system to adapt to different arterial characteristics and achieve optimal tSNR
Solution Approach 2:
The patent changes the geometric parameter of the inversion slab from uniform thickness to varying thickness. By modifying the slice-selective gradient waveform and introducing in-plane gradient modulation, the inversion slab thickness becomes a variable parameter that can be optimized for different arterial velocities and geometries, improving bolus temporal width matching
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 enhances the temporal signal-to-noise ratio (tSNR) in ASL experiments by ensuring uniform bolus temporal widths across different feeding arteries, improving the accuracy and efficiency of perfusion imaging.
Implementation Method 1
Magnetic resonance imaging (MRI) system for modifying the shape/thickness of the excitation/inversion slab
Implementation Method 2
conventional slice-selective (SS) adiabatic fast passage (AFP)
Implementation Method 3
gradient fields along mutually orthogonal x, y, or z directions to spatially select a body part for imaging
Implementation Method 4
arterial spin labeling (ASL), where the arterial blood is tagged by magnetic inversion using RF pulses
Data Source
AI summary
Techniques, systems and apparatus are described for magnetic resonance imaging by modifying the shape/thickness of an excitation/inversion slab. For instance, the inversion slab can be shaped as a wedge to improve temporal signal-to-noise ratio (tSNR) of arterial spin labeling (ASL) experiments by matching the temporal bolus width with the inter-pulse spacing in different feeding arteries. The shape/thickness of the excitation/inversion slab across the X-Y plane can be modified by modulating the movement of the “on-resonance” plane in space by the combination of conventional slice-selective (SS) adiabatic fast passage (AFP) and additional in-plane gradient pulses. Using this method, a computer can generate different shapes of the excitation/inversion slab.