Configuration space representation of MRI sequences

Abstract

Purpose: Local solutions provide little intuition about the contrast, generated by MRI sequences with unbalanced gradients. A configuration space representation of the spin density allows to formalize signal localization and thereby overcome these limitations. Theory and Methods: The continuous configuration model (CCM) constitutes a Fourier integral decomposition of the spin density, such that intrinsic tissue properties are separated from accumulated effects due to gradients and/or bulk off-resonance. Thereby, any set of local dynamic equations is automatically transformed into a corresponding set of differential equations between configurations. Results: The CCM generalizes the Fourier-based EPG formalism such that it becomes applicable to arbitrary MRI sequences. It enables a rigorous and concise treatment of signal localization (selective excitation, spatial encoding), inhomogeneous broadening and motion. Applied to frequency swept NMR, a close connection between SWIFT and SSFP sequences can be found. Conclusion: The CCM allows to view arbitrary MRI sequences from a signal processing perspective, which might simplify the development and optimization of novel imaging strategies.