RF Half-Pulse Sequences for UTE Slice Selection
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Solution Overview
Problem
Current MRI technologies face challenges in imaging tissues with short T2 relaxation times due to signal loss and out-of-slice signal contamination, leading to inadequate in-plane resolution and image artifacts, especially when varying slice thickness requires recalibration.
Innovation Solution
The method involves determining the shape and duration of slice select RF half pulses based on desired slice thickness, maintaining a consistent gradient amplitude and trajectory through excitation k-space, and using a windowed Sinc function to optimize RF pulse shape and duration, allowing for variable slice selection without significant signal contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional RF pulse sequences are used for slice selection, then slice thickness can be controlled, but out-of-slice signal contamination occurs leading to image artifacts
Solution Approach 1:
The RF pulse sequence is segmented into two separate half-pulses: a first half-pulse for initial excitation and a second half-pulse for refocusing. This segmentation allows precise control of the slice selection profile while minimizing out-of-slice signal contamination, as each half-pulse can be independently optimized for its specific function in the UTE sequence.
Solution Approach 2:
The patent applies different pulse shapes and durations to different portions of the excitation process. The first half-pulse uses a specific shape optimized for initial slice selection, while the second half-pulse uses a different shape optimized for refocusing. This local optimization of pulse characteristics reduces artifacts while maintaining accurate slice thickness control.
2Duration of action of moving object
If pulse amplitude is rapidly ramped up and down to achieve short pulse durations, then equipment constraints are met, but trapezoidal pulse shapes result in reduced imaging precision
Solution Approach 1:
The patent dynamically adjusts the RF pulse shape and duration based on the desired slice thickness and imaging parameters. Rather than using fixed trapezoidal pulses, the system dynamically generates optimized half-pulse sequences that adapt to specific imaging requirements, maintaining both short duration and high precision.
Solution Approach 2:
The invention changes multiple pulse parameters simultaneously including amplitude, duration, shape, and timing of the half-pulses. By optimizing these parameters together rather than independently, the system achieves both short pulse durations (meeting equipment constraints) and high image quality (reducing artifacts).
3Adaptability or versatility
If slice thickness is varied to image different tissues, then imaging versatility improves, but recalibration is required reducing productivity
Solution Approach 1:
The patent develops a universal half-pulse sequence framework that can image different tissues and slice thicknesses without requiring recalibration. The same basic pulse sequence structure serves multiple functions by simply adjusting pulse parameters, eliminating the need for time-consuming recalibration when changing imaging conditions.
Solution Approach 2:
The system performs preliminary optimization of the half-pulse sequences for a range of slice thicknesses and tissue types. This preliminary preparation allows the system to quickly switch between different imaging conditions without recalibration, as the optimized pulse parameters are pre-determined and stored for rapid deployment.
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 enables accurate T2-weighted imaging with reduced artifacts and improved in-plane resolution for tissues with short T2 relaxation times, allowing for precise diagnostics without the need for extensive recalibration with varying slice thickness.
Implementation Method 1
the frequency spectrum encompassing their Larmor frequency, or the frequency of their precessing nuclear spins
Implementation Method 2
A series of gradient fields are produced by a set of gradient coils located around the subject. The gradient fields encode positions of individual plane or volume elements (pixels or voxels) in two or three dimensions.
Implementation Method 3
An RF coil is employed to produce an RF excitation field. This RF field perturbs the spins of some of the gyromagnetic nuclei from their equilibrium directions, causing the spins to precess around the axis of their equilibrium magnetization.
Implementation Method 4
During this precession and during relaxation, RF signals are emitted by the spinning, precessing nuclei and are detected by either the same transmitting RF coil, or by a separate coil.
Data Source
AI summary
The present embodiments are directed towards artifact reduction in slice select pulse sequences utilized in ultra short echo time imaging sequences. In one embodiment, a method includes determining a desired slice select thickness, determining a radiofrequency pulse shape and duration based upon the desired slice select thickness while maintaining a desired relationship between excitation k space and radiofrequency amplitude, and determining radiofrequency scaling based on the determined radiofrequency pulse shape and duration.