Related Experiment Video
Updated: Jun 10, 2026
12:18
Microwave Photonics Systems Based on Whispering-gallery-mode Resonators
Published on: August 5, 2013
Minimum envelope roughness pulse design for reduced amplifier distortion in parallel excitation
William A Grissom1, Adam B Kerr, Pascal Stang
1Department of Electrical Engineering, Stanford University, Stanford, California, USA. wgrissom@gmail.com
Magnetic Resonance in Medicine
|July 16, 2010
Summary
Parallel excitation pulse design is improved using a new technique that creates smoother pulse envelopes. This reduces amplifier distortion, offering a more cost-effective solution for advanced MRI techniques.
Area of Science:
- Magnetic Resonance Imaging (MRI)
- Radiofrequency Engineering
Background:
- Parallel excitation in MRI utilizes multiple transmit channels for spatial encoding.
- Low-cost power amplifiers in parallel excitation can cause radiofrequency pulse distortion due to nonlinear memory effects.
- Rapidly varying pulse envelopes exacerbate amplifier distortion.
Purpose of the Study:
- To introduce a novel technique for parallel excitation pulse design.
- To mitigate radiofrequency pulse distortion caused by power amplifiers.
- To enable the use of more cost-effective amplifiers in parallel excitation MRI.
Main Methods:
- Developed a pulse design technique focusing on smoother envelope generation.
- Compared experimental results of the new technique against unregularized and conventionally regularized pulses.
- Evaluated amplifier distortion in parallel excitation scenarios.
Main Results:
- Pulses designed with the new technique exhibited reduced amplifier distortion.
- Smoother pulse envelopes led to less distortion compared to conventional methods.
- Experimental validation confirmed the effectiveness of the proposed pulse design.
Conclusions:
- The novel pulse design technique effectively reduces amplifier distortion in parallel excitation.
- This method facilitates the use of lower-cost, potentially nonlinear amplifiers.
- Improved pulse design enhances the feasibility and cost-effectiveness of parallel excitation MRI.
Related Concept Videos
01:23Parallel Resonance
The parallel RLC circuit is an arrangement where the resistor (R), inductor (L), and capacitor (C) are all connected to the same nodes and, as a result, share the same voltage across them. The parallel RLC circuit is analyzed in terms of admittance (Y), which reflects the ease with which current can flow. The admittance is given by:
01:17Design Example: Vintage Mixing Console
A sound engineer at a music company recently encountered a problem. The output from their newly acquired studio's vintage mixing console was too low for the requirements of modern recording equipment. To rectify this situation, the engineer decided to design an audio pre-amplifier using an operational amplifier (op-amp) to boost the signal level.
The specifications for the pre-amplifier were clear. It needed to amplify the audio signal by a factor of 10, have an input impedance above 10...
The specifications for the pre-amplifier were clear. It needed to amplify the audio signal by a factor of 10, have an input impedance above 10...
01:23Small-Signal Analysis of MOSFET Amplifiers
In small-signal analysis, a MOSFET transistor amplifier acts as a linear amplifier when operating in its saturation region. The gate-to-source voltage (VGS) of the MOSFET is the sum of the DC biasing voltage and the small time-varying input signal. This combination sets up the operating point and modulates the drain current (ID) that flows from the drain to the source. When a small AC signal is superimposed on the DC bias voltage at the gate, the instantaneous drain current comprises three...
01:17Design Example: Underdamped Parallel RLC Circuit
Consider designing an oscillator circuit, a crucial component in various electronic devices and systems. The objective is to create an oscillator circuit with specific characteristics: a damped natural frequency of 4 kHz and a damping factor of 4 radians per second. To accomplish this, a parallel RLC circuit is employed, known for its ability to sustain oscillations at a resonant frequency. In this case, the damping factor is pivotal in achieving the desired performance.
Starting with a fixed...
Starting with a fixed...
01:17MOSFET Amplifiers
The MOSFET, when operating in its active region, functions as a voltage-controlled current source. In this region, the gate-to-source voltage controls the drain current. This principle underlies the operation of the transconductance MOSFET amplifier. The output current is directed through a load resistor to convert this amplifier into a voltage amplifier. The output voltage is then obtained by subtracting the voltage drop across the load resistance from the supply voltage. This process results...
01:17NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences
A pulse is a short burst of radio waves distributed over a range of frequencies that simultaneously excites all the nuclei in the sample. Upon passing a radio frequency pulse along the x-axis, the nuclei absorb energy corresponding to their Larmor frequencies and achieve resonance. This shifts the net magnetization vector from the z-axis toward the transverse plane. This angle of rotation of the magnetization vector, or the flip angle, is proportional to the duration and intensity of the pulse.