MRI Slice-Select Pulse Design Using Variable-Rate Scaling
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Solution Overview
Problem
Magnetic resonance imaging (MRI) slice-select pulses can be loud, causing patient discomfort and acoustic noise, and existing methods to reduce noise often increase minimum echo time or narrow pulse bandwidth, which are not applicable during RF excitation, inversion, or refocusing pulses.
Innovation Solution
A variable-rate principle is applied to design slice-select pulses by scaling down RF and gradient waveforms during the beginning and end of the pulse with broadened time increments and scaling up in the middle with narrowed time increments, resulting in quieter pulses with rounder gradient corners while maintaining identical on-resonance slice profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If gradient slew rate and amplitude are reduced to make slice-select pulses quieter, then acoustic noise is reduced, but pulse length increases and minimum echo time increases
Solution Approach 1:
The patent applies dynamic rescaling of gradient waveforms using time-varying scaling factors that modify gradient amplitude and slew rate dynamically throughout the pulse duration. This allows the gradient to be quieter during periods when high slew rate is not critical for maintaining slice profile fidelity, while preserving performance where it matters most.
Solution Approach 2:
The patent changes the parameters of the gradient waveform by applying scaling factors that modify amplitude, slew rate, and timing characteristics. These parameter transformations allow the gradient to achieve lower acoustic noise levels while maintaining the necessary slice selection performance through computational optimization.
2Object-affected harmful factors
If gradient amplitude is reduced to make slice-select pulses quieter, then acoustic noise is reduced, but pulse bandwidth becomes narrower
Solution Approach 1:
The patent uses dynamic scaling factors that vary throughout the pulse duration to adjust gradient amplitude. This dynamic approach allows the system to reduce overall gradient amplitude for noise reduction while compensating at critical time points to maintain the necessary bandwidth and slice profile precision.
Solution Approach 2:
The patent transforms the gradient waveform parameters through scaling operations that preserve the essential bandwidth characteristics while reducing peak amplitudes. The scaling factors are optimized to maintain frequency content necessary for slice selection while lowering the amplitude that generates acoustic noise.
3Duration of action of moving object
If VERSE is applied to multidimensional selective excitation pulses to optimize bandwidth, then pulse length is reduced, but gradient amplitude requirements increase
Solution Approach 1:
The patent combines VERSE with dynamic scaling, allowing the gradient waveform to be compressed in time (reducing pulse length) while the scaling factors dynamically manage the amplitude peaks. This ensures that gradient amplitude never exceeds system limits while achieving the shortened pulse duration.
Data Source
AI summary
A system, non-transitory computer-readable medium, and method of designing quiet variable-rate MRI slice-select pulses includes creating discretized first slice-select constant-amplitude gradient and RF waveforms, associating discretized time points having a first constant time increment with the first waveforms, selecting a scaling function that smooths the gradient waveform when multiplied together, multiplying the gradient and RF waveforms by the corresponding value of the scaling function to create second gradient and RF waveforms, dividing the time increment between the discretized time points by the corresponding value of the scaling function to create a remapped time increment, cumulatively summing the remapped time increments to create a remapped time scale, interpolating the second gradient and RF waveforms along the remapped time scale to form final gradient and RF waveforms, and providing the final gradient and RF waveforms for incorporation into an MRI pulse sequence.