RF Pulse Distortion Compensation in MRI Scanners
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Solution Overview
Problem
Magnetic resonance imaging (MRI) systems face distortion in radiofrequency (RF) pulses, leading to undesired excitation of slices and artifacts in images due to differences between designed and amplified RF pulses, which current technologies fail to adequately address.
Innovation Solution
A system and method that utilize processors to obtain and modify time-domain waveforms for RF pulses in MRI scanners, compensating for distortion by determining a modified waveform based on the designed and output waveforms, ensuring closer alignment with execution capabilities and reducing sidebands to improve slice excitation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a radiofrequency power amplifier (RFPA) is used to amplify the RF pulse, then the power and voltage of the RF pulse are increased to drive the RF coils, but the waveform of the amplified RF pulse becomes distorted and deviates from the designed waveform
Solution Approach 1:
The system performs preliminary characterization of the RFPA by measuring its actual output waveform in response to a designed RF pulse waveform. This measured waveform is stored and used to create a lookup table that maps desired waveforms to compensating waveforms, enabling the system to pre-correct for amplifier distortion before actual imaging pulses are generated
Solution Approach 2:
The system transforms the measured time-domain waveforms into frequency-domain representations using Fourier transforms. By operating in the frequency domain, the system can more effectively identify and correct waveform distortions, then transform the corrected frequency-domain waveform back to the time domain for application to the RF coils
2Illumination intensity
If the amplified RF pulse with distortion is applied to the RF coils, then the magnetic field is generated with sufficient magnitude, but undesired slices are excited causing artifacts in the MRI image
Solution Approach 1:
The system uses a feedback mechanism where the actual output waveform of the RFPA is measured and used to determine a compensating waveform. This compensating waveform is then applied to the RFPA input to counteract the distortion, creating a closed-loop system that ensures accurate slice excitation while maintaining sufficient magnetic field magnitude
Solution Approach 2:
The system creates a lookup table that stores the relationship between desired RF pulse waveforms and the actual waveforms produced by the RFPA. This lookup table serves as a reference copy that can be used to quickly determine the appropriate compensating waveform for any desired excitation pattern without requiring real-time measurement and correction
Data Source
AI summary
A method for modifying RF pulse infidelity is provided. The method may include obtaining a designed time-domain waveform. The method may also include directing a radio frequency power amplifier (RFPA) of a magnetic resonance imaging (MRI) scanner to generate an output RF pulse based on the designed time-domain waveform. The method may also include measuring an output time-domain waveform of the output RF pulse. The method may also include determining, based on the designed time-domain waveform and the output time-domain waveform, a modified time-domain waveform corresponding to an excitation RF pulse. The method may also include directing the MRI scanner to generate, using a waveform generator and the RFPA and based on the modified time-domain waveform, the excitation RF pulse to excite one or more slices of an object in an MRI scan.