Dr. Igor Mastikhin
Professor, Director of Graduate Studies
Magnetic Resonance Imaging
I apply Magnetic Resonance methods to studies of materials and processes with short signal lifetimes. I am interested in two areas of NMR and MRI applied to materials science: two-phase media and portable NMR instrumentation/applications.
1) Two-phase media (microbubbles, microdroplets) and how to measure themquantitatively with MRI: MRI can be sensitive to a wide variety of physical and chemicalparameters. This very sensitivity, however, can be an obstacle in realistic two-phase flows: themagnetic susceptibility difference between the gas and liquid will generate magnetic fieldgradients at the gas-liquid boundary, precluding quantitative studies. We can, however, exploitthe bubble-generated gradients to our advantage: motion of water in the bubble vicinity will reduce its relaxation times. Information on the void fraction and average bubble size can be extracted from relaxation measurements. Both a spatially resolved mapping of the medium (if you do MRI, preferably a single-point based one) and a fast bulk measurements can be performed.
In the field of acoustic cavitation where a strong sound wave generates violently collapsing, chemically active gaseous bubbles, we have investigated cavitationboth at macro- and microscales, obtaining 3D information on the void fraction and mobility ofliquid in vicinity of cavitation bubbles. Measurements of velocity fields of cavitating mediademonstrated how bubble interactions determine the energy transfer from the acoustic field viathe bubbles to the liquid motion. Details of this transfer were further studied with the newlydeveloped approach where we measured turbulent motion spectra by scanning liquid motionwith oscillating magnetic field gradients at a wide frequency range. A very different perspective on cavitation processes can be obtained by measuring the NMRsignal from the gas dissolved in the liquid prior to cavitation. The 19F NMR and MRI offluorinated gases yields estimates of average residence times of gas molecules in bubbles andprovides information on interaction between the cavitation bubble clouds and with the liquid.
2) My other research interests are in the development of portable, unilateral NMR instruments with controlled parameters (sensitive volume size and location, magnetic field gradient) (incollaboration with Drs. B.J.Balcom and B.Colpitts), and how to use them to measure variousinteresting and useful things. Over several years, our then graduate student A.Marble has beenvery successful in this development that resulted in several research papers and patents; he was the recipient of the 2007 NSERC Innovation Challenge Award andthe 2008 NSERC Doctoral Prize.
Very recently, we decided to use portable NMR to measure small-amplitude vibrations of the medium. In MR elastography, NMR signal is sensitized to vibrations by synchronizing the vibrations with the oscillating magnetic field gradients. In the most basic portable NMR, magnetic field gradients are permanent: you just do measurements in the presence of a stray field of an array of permanent magnets, so you don't really have control over the gradients per se. You can, however, control the spin phase by flipping it with RF pulses, so we generated an "effective" square-wave gradient, a la Stepisnik-Callaghan, by using the CPMG 180-pulse train. The resulting sensitivity to ~100-nm amplitude vibrations can be improved further and, unlike the conventional MR elastography where you need a big MRI scanner, the NMR sensor can fit into your palm.
Arbabi, A., Hall, J., Richard, P., Wilkins, S., Mastikhin, I.V.
"MR relaxometry of micro-bubbles in the vertical bubbly flow at a low magnetic field (0.2 T) ", Journal of Magnetic Resonance (2014) 249, 16-23.
Mastikhin, I., Barnhill, M.
"Sensitization of a stray-field NMR to vibrations: A potential for MR elastometry with a portable NMR sensor", Journal of Magnetic Resonance (2014) 248, 1-7.
Mastikhin, I.V. and Arbabi, A.
"Transiently Porous Medium: Magnetic Resonance Imaging Studies of Acoustic Cavitation", Microporous and Mesoporous Materials (2013) 178, 41704.
Arbabi, A., Mastikhin, I. V. Magnetic susceptibility-based Magnetic Resonance estimation of micro-bubble size for the vertically upward bubbly flow. J Magn Reson 225, 36-45 (2012).
Mastikhin, I. V., Hetherington, N. L., Emms, R. Oscillating gradient measurements of fast oscillatory and rotational motion in the fluids. J Magn Reson 214, 189–199 (2012).
Mastikhin, I. V., Arbabi, A., Newling, B., Hamza, A., Adair, A. Magnetic resonance imaging of velocity fields, the void fraction and gas dynamics in a cavitating liquid. ExpFluids 52, 95–104 (2012).
Mastikhin, I. V., Newling, B. MRI measurements of an acoustically cavitated fluid in a standing wave. Phys. Rev. E 72, 056310 (2005).
Mastikhin, I. V., Newling, B. Dynamics of dissolved gas in a cavitating fluid. Phys. Rev. E 78, 066316 (2008).
Marble, A., Mastikhin, I. V., Colpitts, B., Balcom, B. An analytical methodology for magnetic field control in unilateral NMR. J Magn Reson 174, 78–87 (2005).
Marble, A., Mastikhin, I. V., Colpitts, B., Balcom, B. A constant gradient unilateral magnet for near-surface MRI profiling. J Magn Reson 183, 228–234 (2006).
Marble, A., Mastikhin, I. V., Colpitts, B., Balcom, B. A compact permanent magnet array with a remote homogeneous field. J Magn Reson 186, 100–104 (2007).Marble, A., Mastikhin, I. V., Colpitts, B., Balcom, B. Designing static fields for unilateral magnetic resonance by a scalar potential approach. IEEE Transactions on Magnetics 43,1903–1911 (2007).