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Research Papers

Evolution of Acoustically Vaporized Microdroplets in Gas Embolotherapy

[+] Author and Article Information
Adnan Qamar

Department of Biomedical Engineering,  University of Michigan, Ann Arbor 48109, MI, USA; Physical Sciences and Engineering Division,  King Abdullah University of Science and Technology, Thuwal, 23955-6900, KSA

Zheng Z. Wong, Joseph L. Bull

Department of Biomedical Engineering,  University of Michigan, Ann Arbor 48109, MI

J. Brian Fowlkes

Department of Radiology,  University of Michigan, Ann Arbor 48109, Michigan, USA

J Biomech Eng 134(3), 031010 (Mar 27, 2012) (13 pages) doi:10.1115/1.4005980 History: Received June 02, 2011; Revised December 23, 2011; Posted February 13, 2012; Published March 27, 2012; Online March 27, 2012

Acoustic vaporization dynamics of a superheated dodecafluoropentane (DDFP) microdroplet inside a microtube and the resulting bubble evolution is investigated in the present work. This work is motivated by a developmental gas embolotherapy technique that is intended to treat cancers by infarcting tumors using gas bubbles. A combined theoretical and computational approach is utilized and compared with the experiments to understand the evolution process and to estimate the resulting stress distribution associated with vaporization event. The transient bubble growth is first studied by ultra-high speed imaging and then theoretical and computational modeling is used to predict the entire bubble evolution process. The evolution process consists of three regimes: an initial linear rapid spherical growth followed by a linear compressed oval shaped growth and finally a slow asymptotic nonlinear spherical bubble growth. Although the droplets are small compared to the tube diameter, the bubble evolution is influenced by the tube wall. The final bubble radius is found to scale linearly with the initial droplet radius and is approximately five times the initial droplet radius. A short pressure pulse with amplitude almost twice as that of ambient conditions is observed. The width of this pressure pulse increases with increasing droplet size whereas the amplitude is weakly dependent. Although the rise in shear stress along the tube wall is found to be under peak physiological limits, the shear stress amplitude is found to be more prominently influenced by the initial droplet size. The role of viscous dissipation along the tube wall and ambient bulk fluid pressure is found to be significant in bubble evolution dynamics.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematics of the gas embolotherapy procedure

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Figure 2

Schematics of the experimental setup

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Figure 3

Bubble evolution at different time for Ro  = 12.23 μm

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Figure 4

Experimental (left) and computational (right) bubble evolution for Ro  = 7.81 μm

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Figure 5

Experimental (left) and computational (right) bubble evolution for Ro  = 10.93 μm

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Figure 6

Experimental (left) and computational (right) bubble evolution for Ro  = 14.39 μm

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Figure 7

Bubble evolution comparisons from experimental, theoretical and computational approach for (a) Ro  = 7.81 μm, (b) Ro  = 10.93 μm and (c) Ro  = 14.39 μm. Note that the computations are stopped at t = 0.00015 s, based on test runs that showed the asymptotic stage was reached by this time.

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Figure 8

Variation of (a) Peak pressure and (b) Peak shear stress on the tube wall for different initial droplet size

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Figure 9

Variation of (a) Peak pressure and (b) Peak shear stress on the tube wall for different initial droplet size

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Figure 10

Percentage Energy conversion in ADV for Ro  = 10.93 μm

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Figure 11

Effect of tube length on expansion ratio for Ro  = 10.93 μm

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Figure 12

Effect of ambient pressure on expansion ratio for Ro  = 10.93 μm

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