Effects of physiologic waveform variability in triggered MR imaging: theoretical analysis

Area of Science:

• Medical Imaging
• Biophysics
• Signal Processing

Background:

• Triggered magnetic resonance (MR) imaging assumes periodic physiologic waveforms (cardiac, respiratory).
• Real-world physiologic waveforms exhibit variability, violating this periodicity assumption.
• This variability can cause image artifacts and inaccurate velocity/flow rate estimations.

Purpose of the Study:

• To analyze the effects of physiologic waveform variability in triggered MR imaging.
• To propose a model treating waveform variability as motion waveform modulation.
• To predict and explain artifacts and errors in velocity/flow rate measurements.

Main Methods:

• Analysis of triggered MR imaging with focus on amplitude modulation of velocity waveforms.
• Application of Fourier and modulation theory.
• Utilizing (k,t)-space principles to derive artifact appearance and error predictions.
• Simulations and experimental validation.

Main Results:

• Physiologic waveform variability leads to amplitude and phase modulation of transverse magnetization.
• Artifacts in triggered MR images, including ghost overlap, were derived and predicted.
• Errors in time-averaged and instantaneous velocity estimates were quantified.
• Simulations and experiments confirmed theoretical predictions.

Conclusions:

• Physiologic waveform variability is a significant factor affecting triggered MR imaging accuracy.
• Modeling variability as motion waveform modulation provides a framework for understanding and mitigating artifacts.
• The findings improve the reliability of velocity and flow rate estimations in MR imaging.