Advanced design and experimental validation of MRI contrast agents for fluid pressure mapping using microbubbles

Abstract

This work is related to monitoring fluid pressure using Magnetic Resonance Imaging or MRI and includes numerical simulations and experimental MRI. The nature of this study is such that techniques other than MRI have been extensively used to assess the contrast agent for its physical behaviour. These techniques include rheometry, light scattering, optical and scanning electron microscopy. Six MRI experiments in total were performed: The first two experiments use standard spin echo imaging techniques to test various lipid preparations which are then used as a contrast agent to pressure in a porous medium. The remaining experiments are performed using a fast imaging technique and investigate various improvements to the contrast agent which resulted in the development of an agent exhibiting an unprecedented level of sensitivity. A variety of lipid preparations are utilised throughout the experiments. Initial testing reveals that the DSPC lipid offers the greatest stability, although a fluorinated lipid is used in a later study for an improved synergy between the shell and gas microbubble components. Having assessed the microbubble stability, preparations are prepared as in the work previously published in the area. This preparation is tested in two porous media to investigate the sensitivity of the contrast agent to changes in pressure. A sensitivity of 20% signal change per bar is found in porous media although a drift of 11%h-1 is also observed. An improved preparation was then developed by using an alternative polysaccharide gel, gellan gum