Nuclear magnetic resonance signal from flowing nuclei in rapid imaging using gradient echoes

TLDR

The study models NMR signal from flowing nuclei using laminar and plug‑flow equations and validates them experimentally with a 0.15 T FLASH sequence across varying flip angles and flow rates. Theoretical predictions show that the rate of approach to steady‑state governs flow enhancement, and experimental data confirm the model’s accuracy until turbulence begins.

Abstract

A theoretical description of the nuclear magnetic resonance (NMR) signal from flowing nuclei has been developed for rapid imaging sequences that use small flip angles and gradient refocused echoes. Both laminar and plug flow models have been considered and formulas derived relating mean image signal intensity to flip angle, pulse sequence repetition interval ( T R ), and flow velocity. It is shown that the rate of approach to steady‐state conditions determines the degree of flow enhancement. Experimental measurements have been performed on a flow phantom in a whole‐body NMR imaging system operating at 0.15 T using the spoiled FLASH sequence with different radiofrequency pulse flip angles and flow rates. There is excellent agreement between the experimental results and the theoretical predictions up to the onset of turbulence.