Multiband Sweep Imaging With Fourier Transformation Bandwidth
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Solution Overview
Problem
Current MRI techniques for imaging short T2 signals are limited by insufficient excitation and acquisition bandwidths, leading to incomplete resolution of short T2 signals and off-resonance artifacts, particularly due to hardware constraints such as RF amplifier power limitations and gradient coil inductance.
Innovation Solution
The implementation of a multiband sweep imaging with Fourier transformation (MB-SWIFT) method, which uses a series of spaced radiofrequency pulses to simultaneously excite multiple resonance frequencies, allowing for increased excitation and acquisition bandwidths while efficiently using transmitter power and enhancing sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the excitation bandwidth is increased to resolve short T2 signals, then the detection capability improves, but the RF amplifier power requirements increase beyond hardware limits
Solution Approach 1:
The patent divides the excitation process into multiple frequency-swept segments instead of using a single broadband pulse. Each segment excites a specific frequency range, and the segments are combined to achieve comprehensive coverage. This segmentation allows the system to achieve high detection capability without requiring excessive peak RF power from the amplifier.
Solution Approach 2:
The patent employs periodic frequency sweeping across multiple cycles to excite different resonance frequencies. By distributing the excitation energy across periodic cycles rather than concentrating it in a single pulse, the system achieves comprehensive frequency coverage while maintaining RF amplifier power within hardware limits.
2Measurement precision
If the readout bandwidth is increased to capture short T2 signals, then the signal resolution improves, but the gradient coil inductance prevents sufficient ramping speed
Solution Approach 1:
The patent applies the excitation pulse before activating the readout gradients, rather than simultaneously. This preliminary action allows the excitation to occur without interference from gradient switching, and the signal is then captured during the gradient ramp-up phase. This sequencing overcomes the limitation imposed by gradient coil inductance while maintaining high signal resolution.
3Measurement precision
If longer frequency swept pulses are used to increase excitation bandwidth, then the bandwidth coverage improves, but the pulse duration increases reducing temporal resolution
Solution Approach 1:
The patent segments the frequency sweep into multiple shorter pulses rather than using one long continuous sweep. Each pulse covers a portion of the total frequency range, and the segments are applied in sequence. This approach achieves comprehensive bandwidth coverage while keeping individual pulse durations short, thereby maintaining temporal resolution.
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
MB-SWIFT achieves higher flip angles and improved sensitivity for both fast and slow relaxing spins, enabling more comprehensive imaging of short T2 signals with reduced power deposition and artifacts, thus overcoming the limitations of existing methods.
Implementation Method 1
SYSTEMS AND METHODS FOR MULTIBAND SWEEP WITH FOURIER TRANSFORMATION
Implementation Method 2
applying a sweeping frequency excitation... the sweeping frequency excitation comprising a plurality of spaced apart radio frequency (RF) excitation pulses
Implementation Method 3
acquiring a time domain signal during the duration, the time domain signal being based on evolution of the spins
Data Source
AI summary
Systems and methods for magnetic resonance imaging (“MRI”) using a frequency swept excitation that utilizes multiple sidebands to achieve significant increases in excitation and acquisition bandwidth are provided. The imaging sequence efficiently uses transmitter power and has increased sensitivity as compared to other techniques used for imaging of fast relaxing spins. Additionally, the imaging sequence can provide information about both fast and slow relaxing spins in a single scan. These features are advantageous for numerous MRI applications, including musculoskeletal imaging, other medical imaging applications, and imaging materials.