Target Audience

Beginning or advanced researchers interested in getting to know a promising alternative imaging method for measuring diffusion in challenging body regions.

Abstract

Diffusion-weighted (DW) MRI is a powerful modality for studying microstructure in normal and pathological tissues [1]. In most cases, and certainly in clinical applications, echo planar imaging (EPI) [2] is the method of choice for performing rapid in vivo diffusion measurements. Still, SE-EPI is prone to display several image artifacts; particularly with respect to chemical shift offsets, geometric distortions and blurring derived from field inhomogeneities. Those limitations have led to searches of other single-scan “ultrafast” MRI methods capable to overcome motion and local field heterogeneities during an experiment that aims to measure μm-sized random displacements. In this educational talk, we will discuss the physical principles of novel single-shot techniques based on SPatio-temporal ENcoding (SPEN), originally developed by Pro. Lucio Frydman for acquiring arbitrary 2D NMR spectra, which can overcome B0 and local field heterogeneities. SPEN’s principles differ from conventional Fourier Transform (FT) methods, allowing it to operate at higher effective bandwidths than SE-EPI, providing a significant reduction in image distortions arising from field inhomogeneities, eddy currents, and common heterogeneous chemical environments [3]. The talk will cover the formalism for analyzing diffusion experiments based SPEN data, which takes into account the concomitant effects of adiabatic pulses, imaging as well as diffusion gradients, and of the cross-terms between them [4]. Moreover, attention will center on SPEN’s capability to reduce the effects of heterogeneities by operating in a so‐called “full refocusing” mode, whereby spin echoes refocusing T2* effects arise throughout the course of the data acquisition—rather than at a single time instant. Resolution improvements will also be exemplified as a result of SPEN’s built‐in capability to target restricted FOVs, free from folding artifacts, all of which are relevant for high definition diffusion experiments. Finally, multiple examples of successful diffusion experiments will be discussed such as DWI and DTI in human and rodent brains, characterization of breast cancer, dynamics of placental flow during pregnancy, and real-time imaging of small animals in high and ultrahigh magnetic fields.

Acknowledgements

No acknowledgement found.