Robust spatially resolved pressure measurements using MRI with novel buoyant advection-free preparations of stable microbubbles in polysaccharide gels

Abstract

MRI of fluids containing lipid coated microbubbles has been shown to be an effective tool for measuring the local fluid pressure. However, the intrinsically buoyant nature of these microbubbles precludes lengthy measurements due to their vertical migration under gravity and pressure-induced coalescence. A novel preparation is presented which is shown to minimize both these effects for at least 25 minutes. By using a 2% polysaccharide gel base with a small concentration of glycerol and 1,2-Distearoyl-sn-Glycero-3-Phosphocholine coated gas microbubbles, MR measurements are made for pressures between 0.95 and 1.44 bar. The signal drifts due to migration and amalgamation are shown to be minimized for such an experiment whilst yielding very high NMR sensitivities up to 38% signal change per bar.

Non-Cartesian sampled centric scan SPRITE imaging with magnetic field gradient and B0(t) field measurements for MRI in the vicinity of metal structures

“…However high-pressure MRI has been rare due to a low signal-to-noise ratio which results from a low filling factor and the restricted volume of commonly employed high-pressure cells [2][3][4]. MRI experiments [5][6][7][8] using traditional high-pressure cells [2,3], are hindered by this problem, and inefficient temperature control [2,3,9].…”

MR relaxometry of micro-bubbles in the vertical bubbly flow at a low magnetic field (0.2 T)

“…Given the limitations of the analytical approach, Monte-Carlo simulations [16,17] can probably be considered as an alternative analysis technique. However, given the nature of the simulations, their use would require mapping of all possible combinations of parameters of interest (void fraction, bubble size distributions, diffusion/dispersion, etc.)…”

“…Dharmakumar et al have derived analytical expressions which take into account the void fraction, diffusion, and average bubble radius to qualitatively explain the functional behavior of T 2 and T 2 ⁄ decays [15]. Morris et al has presented an MRI-based technique for spatially resolved pressure mapping in porous media with a multi slice multi echo pulse sequence using air-filled liposome micrometer-sized bubbles as pressure sensitive MR contrast agents [16,17]. Sukstanskii et al has provided a detailed theoretical description of the free induction decay (FID) and Spin Echo (SE) signal formation in the framework of the Gaussian phase distribution approximation for permeable and impermeable spherical and infinitely long cylindrical inclusions [18,19].…”

Magnetic susceptibility based magnetic resonance estimation of micro-bubble size for the vertically upward bubbly flow

“…This makes the presented measurement well suited for studies of micro-bubbles in cavitating media where the bubble sizes do not exceed several dozens of microns and the void fraction is on the order, or well below, of 1% for the total volume [30]. With the limitations of the analytical approach, Monte-Carlo simulations [15,16] should probably considered as an alternative technique to relate the average bubble size, dispersion, and MR relaxations at greater void fraction and air flow rates.…”

“…Morris et al has presented an MRI based technique for spatially resolved pressure mapping in porous media using a multi slice multi echo pulse sequence. They also took advantage of air-filled liposome micrometer-sized bubbles as pressure sensitive MR contrast agents in their work [15,16].…”