Magnetic Resonance Transmit Pulse Bandwidth Expansion
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Solution Overview
Problem
Magnetic resonance systems with limited controller bandwidth struggle to output dynamic pulses with high bandwidths correctly, leading to distortion or shutdown when frequency-modulated pulses exceed the controller's capacity.
Innovation Solution
A controller varies the oscillator control signal to generate transmit pulses with larger bandwidths by modulating both amplitude and frequency signals, allowing for the expansion of the controller's bandwidth to accommodate higher bandwidth pulses, enabling correct output of pulses like the hyperbolic secant and frequency offset corrected inversion pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If frequency-modulated pulses with high bandwidth are used, then the transmit pulse bandwidth is increased, but the controller bandwidth becomes insufficient causing distortion or shutdown
Solution Approach 1:
The transmit pulse generation is segmented into two independent components: a base signal p(t) with limited bandwidth that the controller can handle, and a frequency/phase modulation signal s=exp(iΦ(t)) with oscillator-controlled bandwidth. This segmentation allows each component to operate within its respective bandwidth limits while their product achieves the desired high bandwidth transmit pulse.
Solution Approach 2:
The solution moves from a single-dimensional amplitude control approach to a two-dimensional approach by introducing frequency/phase modulation as an additional dimension. The transmit pulse is expressed as p(t)·s where p(t) handles amplitude and the oscillator-controlled s handles frequency/phase, effectively adding a temporal frequency dimension to the signal generation.
2Speed
If the controller bandwidth is increased to handle high bandwidth pulses, then the controller complexity increases
Solution Approach 1:
An oscillator is introduced as an intermediary component between the controller and the modulator. The controller generates a low-bandwidth base signal, the oscillator generates a frequency signal with the desired bandwidth characteristics, and these two combine in the modulator to produce the final high-bandwidth transmit pulse. This intermediary approach allows the controller to remain simple while achieving high bandwidth output.
3Productivity
If multiple magnetic resonance antennas are operated simultaneously in array configuration, then the productivity is increased, but the required pulse bandwidth exceeds controller capability
Solution Approach 1:
The system dynamically adjusts the frequency/phase characteristics of the transmit pulses through oscillator control signals Φ(t) that can vary over time. This dynamic control allows the same hardware to support multiple antenna elements with different frequency requirements simultaneously, enabling array operation without requiring static, overly broad bandwidth allocation.
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
Enables the controlled generation and output of transmit pulses with larger bandwidths than the base signal, maintaining distortion-free transmission even when the controller's bandwidth is restricted, allowing for efficient operation of multiple magnetic resonance antennas in array configurations.
Implementation Method 1
The modulation is determined by an oscillator control signal Φ(t)... the controller may control a frequency of the frequency signal exclusively using the oscillator control signal... the controller may exclusively control a phase position of the frequency signal using the oscillator control signal
Implementation Method 2
The base signal and the frequency signal are fed to a modulator within a conversion device. The modulator modulates the frequency signal to a high frequency base pulse with the aid of the basis signal
Implementation Method 3
The power amplifier amplifies the base pulse to the transmit pulse
Implementation Method 4
The demodulator may demodulate the transmit pulse to a lower frequency signal with the aid of the frequency signal
Data Source
AI summary
A controller of a magnetic resonance system outputs a low frequency base signal to a conversion device. While outputting the base signal to the conversion device, the controller outputs an oscillator control signal to an oscillator. The oscillator outputs a frequency signal corresponding to the oscillator control signal to the conversion device. The conversion device converts the frequency signal into a high frequency transmit pulse with the aid of the base signal and outputs the transmit pulse to a magnetic resonance transmit antenna. The magnetic resonance transmit antenna applies a high frequency field corresponding to a transmit pulse to an examination volume of the magnetic resonance system. The controller varies the oscillator control signal output to the oscillator while outputting the base signal to the modulator. The transmit pulse) has a larger bandwidth than the base signal.