Related Experiment Video
Updated: Jan 20, 2026

Measuring the Complete-arch Distortion of an Optical Dental Impression
Published on: May 30, 2019
Iterative correction of RF envelope distortion with GRATER-measured waveforms
Vanessa L Landes1, Krishna S Nayak2
1Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, California.
Purpose:
To develop and evaluate a method for RF envelope correction without extra hardware or synchronization.
Methods:
Transmitted RF waveforms are measured through a simple pulse sequence called the gradient reversal approach to evaluate RF (GRATER). The measured RF waveforms are used to compute predistorted RF waveforms. This process is repeated until a stopping criterion is met, for example, based on pulse performance or a maximum number of iterations. Excitation profiles and simultaneous multi-slice (SMS) image quality are compared before and after RF predistortion.
Results:
The proposed method improved the accuracy of multiband RF pulses, reducing normalized root mean squared error (NRMSE) by >12-fold, and reducing spurious side-lobe excitation by >6-fold. The reduction in unwanted side-lobe signal is demonstrated using SMS bSSFP imaging at 3T in phantoms and in the heart.
Conclusion:
Iterative GRATER-based predistortion is a practical, hardware-free way to boost performance of short duration, low flip angle RF pulses, such as those used in SMS bSSFP imaging. Because of its efficiency, this technique could be included as part of an initial scan setup or for use with subsequent scans.
More Related Videos
Related Concept Videos
Effective Value of a Periodic Waveform
The effective value of a periodic current represents the direct current (DC) that conveys the same average power to a resistor as the periodic current itself. This concept is crucial when assessing AC circuits. To determine the...
Outer Layers of the Cell Envelope
Distance Corrections
Power Factor Correction
¹H NMR: Interpreting Distorted and Overlapping Signals
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
NMR Spectrometers: Resolution and Error Correction

