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Zhang Y et al, 2016: Effects of Stone Size on the Comminution Process and Efficiency in Shock Wave Lithotripsy.

Zhang Y, Nault I, Mitran S, Iversen ES, Zhong P.
Department of Mathematics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
Department of Statistical Science, Duke University, Durham, North Carolina, USA.
Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina, USA.

Abstract

The effects of stone size on the process and comminution efficiency of shock wave lithotripsy (SWL) were investigated in experiments, numerical simulations and scale analysis. Cylindrical BegoStone phantoms with approximately equal height and diameter of either 4, 7 or 10 mm, in a total aggregated mass of about 1.5 g, were treated in an electromagnetic shock wave lithotripter field. The resultant stone comminution was found to correlate closely with the average peak pressure, P+(avg), incident on the stones. The P+(avg) threshold necessary to initiate stone fragmentation in water increased from 7.9 to 8.8 to 12.7 MPa, respectively, as stone size decreased from 10 to 7 to 4 mm. Similar changes in the P+(avg) threshold were observed for the 7- and 10-mm stones treated in 1,3-butanediol, in which cavitation is suppressed, suggesting that the observed size dependency is due to changes in stress distribution within stones of different size. Moreover, the slope of the correlation curve between stone comminution and ln(P¯+(avg)) in water increased with decreasing stone size, whereas the opposite trend was observed in 1,3-butanediol. The progression of stone comminution in SWL exhibited size-dependence: the 7- and 10-mm stones fragmented into progressively smaller pieces, whereas a significant portion (>30%) of the 4-mm stones reached a stalemate within the size range of 2.8 ∼ 4 mm, even after 1000 shocks. Analytical scaling considerations suggest size-dependent fragmentation behavior, a hypothesis further supported by numerical model calculations that reveal changing patterns of constructive and destructive wave interference and, thus, variations in the maximum tensile stress or stress integral produced in cylindrical and spherical stone of different sizes. 

Ultrasound Med Biol. 2016 Aug 8. pii: S0301-5629(16)30149-1. doi: 10.1016/j.ultrasmedbio.2016.06.018. [Epub ahead of print]

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Commentaires 1

Othmar Wess le lundi 6 mars 2017 07:27

This is a nice proof for what has been known or assumed for long. Comminution of a certain mass of stone material is more efficient and complete if the shock wave exposure is started on an intact stone instead on several fragments of identical mass.
This means in clinical routine not to force fragmentation too much at the beginning of a treatment in order to achieve big fragments soon but to weaken a stone by creating multiple internal fissure without separating single big fragments. As long as a stone is intact, a single shock wave shatters the total mass which leads to fatigue of the total stone mass, whereas after splitting, fragments are more or less acoustically separated requiring individual shock wave exposure. The reason for a different shock wave resistance of small vs. bigger particles is claimed to be the difference in stress wave generation.

These findings well agree with a previous paper published by one of the Co-Autors Pei Zhong:

J Endourol. 2006 September ; 20(9): 603–606
Progressive Increase of Lithotripter Output Produces Better in-Vivo Stone Comminution
Michaella E. Maloney, M.D.1, Charles G. Marguet, M.D.1, Yufeng Zhou, Ph.D.1,2, David E.
Kang, M.D.1, Jeffery C. Sung, M.D.1, W. Patrick Springhart, M.D.1, John Madden, M.D.3, Pei
Zhong, Ph.D.1,2, and Glenn M. Preminger, M.D.1
Comprehensive Kidney Stone Center, Division of Urology, Duke University, Durham, North Carolina.
Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina.
Department of Pathology, Duke University, Durham, North Carolina.

This is a nice proof for what has been known or assumed for long. Comminution of a certain mass of stone material is more efficient and complete if the shock wave exposure is started on an intact stone instead on several fragments of identical mass. This means in clinical routine not to force fragmentation too much at the beginning of a treatment in order to achieve big fragments soon but to weaken a stone by creating multiple internal fissure without separating single big fragments. As long as a stone is intact, a single shock wave shatters the total mass which leads to fatigue of the total stone mass, whereas after splitting, fragments are more or less acoustically separated requiring individual shock wave exposure. The reason for a different shock wave resistance of small vs. bigger particles is claimed to be the difference in stress wave generation. These findings well agree with a previous paper published by one of the Co-Autors Pei Zhong: J Endourol. 2006 September ; 20(9): 603–606 Progressive Increase of Lithotripter Output Produces Better in-Vivo Stone Comminution Michaella E. Maloney, M.D.1, Charles G. Marguet, M.D.1, Yufeng Zhou, Ph.D.1,2, David E. Kang, M.D.1, Jeffery C. Sung, M.D.1, W. Patrick Springhart, M.D.1, John Madden, M.D.3, Pei Zhong, Ph.D.1,2, and Glenn M. Preminger, M.D.1 Comprehensive Kidney Stone Center, Division of Urology, Duke University, Durham, North Carolina. Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina. Department of Pathology, Duke University, Durham, North Carolina.
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