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Robinson JW. et al., 2023: Performance of brushite plaster as kidney stone phantoms for laser lithotripsy.

Robinson JW, Marom R, Ghani KR, Roberts WW, Matzger AJ.
Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109, USA.
Division of Endourology, Department of Urology, University of Michigan, Ann Arbor, MI, 48109, USA.
Department of Urology, Tel Aviv Medical Center, Tel Aviv, Israel.
Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA.
Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109, USA.
Macromolecular Science and Engineering Program, University of Michigan, Ann Arbor, MI, 48109, USA.

Abstract

Artificial phantoms used in photothermal near-infrared laser lithotripsy research generally fail to mimic both the chemical and the physical properties of human stones. Though high-energy, 1 J pulses are capable of fracturing hard human stones into several large fragments along natural boundaries, similar behavior has not been observed in commonly used gypsum plasters like BegoStone. We developed a new brushite-based plaster formulation composed of ≈90% brushite that undergoes rapid fracture in the manner of human stones under fragmentation pulse regimes. Single-pulse (1 J) ablation crater volumes for phantoms were not significantly different from those of pure brushite stones. Control over crater volumes was demonstrated by varying phosphorous acid concentration in the plaster formulation. Fragmentation of cylindrical brushite phantoms was filmed using a high-speed camera which demonstrated rapid fragmentation in < 100 µs during the bubble expansion phase of a short pulse from a high-powered Ho:YAG laser (Lumenis Pulse 120 H). The rapid nature of observed fracture suggests increasing laser pulse energy by increasing laser pulse duration will not improve fragmentation performance of laser lithotripters. Brushite plaster phantoms are a superior alternative to gypsum plasters for laser lithotripsy research due to their better mimicry of stone composition, controllable single-pulse crater volumes, and fragmentation behavior.

Urolithiasis. 2023 Dec 7;52(1):10. doi: 10.1007/s00240-023-01505-8. PMID: 38060010



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Comments 1

Peter Alken on Thursday, 11 April 2024 11:00

New lasers for lithotripsy are welcomed with enthusiasm until a more widespread clinical application shows not expected drawbacks. In this context the properties of artificial stones for in vitro experiments gain new interest (1). The authors of the present paper used phosphate-containing material that has been applied to bone and tooth repair. It should better mimic true human stones than the frequently used plaster or BEGO (2) phantoms.
Procedures to produce the phantoms of different compositions produced with brushite powder among other components are described in detail in the paper and extensively in the supplementary material.
The title of the paper may suggest that it deals with brushite stones. However, as the authors state
“Though these brushite phantoms have superior properties compared to available artificial options, greater porosity in plaster phantoms is a clear area for improvement. Besides different crystallite size and orientation, SEM images show pores on the order 10 μm diameter which appear as darker spots in survey images. The introduction of pores during plaster setting is inevitable as the excess water required for processing leaves voids upon evaporation.” and “In contrast, human brushite stones are formed entirely in solution and slow crystal growth and dissolution–re-deposition of growing crystals allows stones to form without obvious pores”. It may be impossible to grow renal stones in a few days which in the human take years to develop (3)

1 Ballesta Martinez B, et al. Radiological Density, Atomic Numbers, and Stone Fragmentation of Bego Stones Used for Research on Endourology: Comparison to Real Urinary Stones. J Endourol. 2024 Jan 9. doi: 10.1089/end.2023.0091.
2 Liu Y, Zhong P (2002) BegoStone—a new stone phantom for shock wave lithotripsy research (L). J Acoust Soc Am 112:1265–1268. https:// doi. org/ 10. 1121/1. 15019 05
3 Kok DJ, et al. Timelines of the "free-particle" and "fixed-particle" models of stone-formation: theoretical and experimental investigations. Urolithiasis. 2017 Feb;45(1):33-41. doi: 10.1007/s00240-016-0946-x.

Peter Alken

New lasers for lithotripsy are welcomed with enthusiasm until a more widespread clinical application shows not expected drawbacks. In this context the properties of artificial stones for in vitro experiments gain new interest (1). The authors of the present paper used phosphate-containing material that has been applied to bone and tooth repair. It should better mimic true human stones than the frequently used plaster or BEGO (2) phantoms. Procedures to produce the phantoms of different compositions produced with brushite powder among other components are described in detail in the paper and extensively in the supplementary material. The title of the paper may suggest that it deals with brushite stones. However, as the authors state “Though these brushite phantoms have superior properties compared to available artificial options, greater porosity in plaster phantoms is a clear area for improvement. Besides different crystallite size and orientation, SEM images show pores on the order 10 μm diameter which appear as darker spots in survey images. The introduction of pores during plaster setting is inevitable as the excess water required for processing leaves voids upon evaporation.” and “In contrast, human brushite stones are formed entirely in solution and slow crystal growth and dissolution–re-deposition of growing crystals allows stones to form without obvious pores”. It may be impossible to grow renal stones in a few days which in the human take years to develop (3) 1 Ballesta Martinez B, et al. Radiological Density, Atomic Numbers, and Stone Fragmentation of Bego Stones Used for Research on Endourology: Comparison to Real Urinary Stones. J Endourol. 2024 Jan 9. doi: 10.1089/end.2023.0091. 2 Liu Y, Zhong P (2002) BegoStone—a new stone phantom for shock wave lithotripsy research (L). J Acoust Soc Am 112:1265–1268. https:// doi. org/ 10. 1121/1. 15019 05 3 Kok DJ, et al. Timelines of the "free-particle" and "fixed-particle" models of stone-formation: theoretical and experimental investigations. Urolithiasis. 2017 Feb;45(1):33-41. doi: 10.1007/s00240-016-0946-x. Peter Alken
Monday, 20 May 2024