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The solution of Bloch equations for flowing spins during a selective pulse using a finite difference method.
C Yuan1, G T Gullberg, D L Parker
1Department of Radiology, University of Utah, Salt Lake City 84132.
Medical Physics
|November 1, 1987
Summary
Flowing spins during selective pulses cause signal loss in magnetic resonance imaging (MRI). This study quantifies these perturbations using a finite difference method, crucial for developing new MRI techniques to reduce artifacts.
Area of Science:
- Medical Imaging
- Biophysics
- Magnetic Resonance Imaging
Background:
- Selective pulses in MRI modulate signal intensity and phase, causing signal loss in vessels.
- Existing flow compensation methods address constant velocity flow during gradients, not during selective pulses.
- Understanding spin behavior during selective pulses is key to improving MRI.
Purpose of the Study:
- To quantify amplitude and phase perturbations for spins flowing during selective radiofrequency (rf) pulses.
- To investigate the impact of flow velocity on these perturbations.
- To provide a basis for developing novel flow compensation strategies in MRI.
Main Methods:
- Solving Bloch equations for flowing spins during a 90-degree selective pulse using a finite difference method.
- Analyzing the resulting magnetization distribution and phase shifts.
- Comparing results for flowing spins versus stationary spins.
Main Results:
- Flowing spins exhibit shifted, expanded, and distorted slice profiles compared to stationary spins.
- Significant phase shifts and residual phase errors occur, worsening with higher flow velocities.
- Current flow compensation schemes are ineffective for spins flowing during selective rf pulses.
Conclusions:
- Accurate modeling of spin behavior during selective pulses is essential for MRI.
- Understanding these flow dynamics is critical for designing effective pulse sequences.
- Developing new flow compensation methods is necessary to reduce artifacts and enhance MR angiography.