Single excitation multiple image RARE (SEMI-RARE): ultra-fast imaging of static and flowing systems

This paper describes the development and application of a new rapid, full k-space acquisition imaging pulse sequence based on the rapid acquisition with relaxation enhancement (RARE) methodology. We have termed this pulse sequence single excitation multiple image RARE (SEMI-RARE). We demonstrate the application of SEMI-RARE to the visualisation of a static liquid phantom and it is shown that up to 120 images can be acquired from a single excitation. By exploiting the inherent relaxation and diffusion contrast within the series of images, the SEMI-RARE provides an ultra-fast method for characterising the spatial distribution of chemical species and phases within complex systems. The pulse sequence is then applied to the study of single- and two-phase flow in a single narrow tube of inner diameter 2.9mm. In particular, it is shown that 8 two-dimensional slice-selective images for two-phase bubble-train flow in a single tube can be acquired from a single excitation at effective echo-times of 37, 109, 181, 253, 325, 397, 469, and 541ms. The visualisation enables the determination of gas/liquid bubble sizes and velocities during two-phase flow. We also report the first direct evidence, obtained from magnetic resonance measurements, of liquid re-circulation zones associated with bubble-train flow. The robustness of the SEMI-RARE technique makes it an attractive fast imaging technique for the study of multi-phase flow phenomena, which are often characterised by large variations in magnetic susceptibility, and are of widespread interest in chemical engineering.