Thomas GPL. et al., 2020: Confocal lens focused piezoelectric lithotripter

Friday, 10 July 2020

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Thomas GPL, Chapelon JY, Birer A, Inserra C, Lafon C.
INSERM, LabTAU, F-69003 Lyon, France; Université Lyon 1, Univ Lyon, F-69003 Lyon, France.
INSERM, LabTAU, F-69003 Lyon, France.

Abstract

This work focuses on the evaluation of a type of piezoelectric lithotripter with similar dimensions of a commercial lithotripter and composed of either 3 or 4 large lens focused piezoelectric transducers set either in a confocal coplanar C-shape or a confocal spherical shape. Each transducer is made with a 92 mm diameter 220 kHz flat piezoelectric ceramic disc and a 3D printed acoustic lens. Both confocal setups pressure field were measured with a fiber optic hydrophone, and in vitro fragmentations of 13 mm diameter and 14 mm length cylindrical model stones were done in a 2 mm mesh basket. The acoustic characterization of the three transducers confocal setup revealed a disc shaped focal volume, with a 2.2 mm width on one axis and a 9.6 mm width on the other, and a peak positive pressure of 40.9 MPa and a peak negative pressure of -16.9 MPa, while the focus of the four transducers confocal setup was similar to a traditional narrow focus high pressure lithotripter with a focus width of 2.1 mm, and a peak positive pressure of 71.9 MPa and peak negative pressure of -24.3 MPa. Both confocal setups showed in vitro fragmentation efficiency close to a commercial electroconductive lithotripter.
Ultrasonics. 2020 Apr;103:106066. doi: 10.1016/j.ultras.2020.106066. Epub 2020 Jan 10. Epub 2020 Jan 10. PMID: 32028115

Comments 1

Othmar Wess on Friday, 10 July 2020 10:30

Shock wave lithotripsy (SWL) is a proven non-invasive treatment modality since 1980. Different shock wave generation principles (electro-hydraulic, electro-magnetic and piezo-electric) are successfully established in the lithotripter market. Piezo-electric shock wave generation require multiple small piezo-elements, usually arranged at the inner surface of a quite bulky spherical bowl.
This paper develops two alternative configurations reducing the numbers of piezo-elements to three, in a second version to four flat, circular elements with a diameter of 92 mm. Each element is attached to an acoustic lens. The C-configuration is designed to partially fit on the side of a patient and provides a treatment depth of 100 mm whereas the spherical configuration has a focussing distance of 134 mm. Both distances are in the lower range of commercial lithotripters. As expected, the focus of the C-configuration has a shape of a thin disc due to the different length and width of the configuration.
It is not clear what advantages the reported configurations feature. Perhaps the reduced number of piezo-elements and the way they can be arranged may offer intermediate space for in-line ultrasound localization or other instruments useful for lithotripsy.
The fragmentation performance is similar to other commercial lithotripters. The unusually high second and third peak of the pressure curve is assumed to reduce focal cavitation but needs further exploration.

Shock wave lithotripsy (SWL) is a proven non-invasive treatment modality since 1980. Different shock wave generation principles (electro-hydraulic, electro-magnetic and piezo-electric) are successfully established in the lithotripter market. Piezo-electric shock wave generation require multiple small piezo-elements, usually arranged at the inner surface of a quite bulky spherical bowl. 
This paper develops two alternative configurations reducing the numbers of piezo-elements to three, in a second version to four flat, circular elements with a diameter of 92 mm. Each element is attached to an acoustic lens. The C-configuration is designed to partially fit on the side of a patient and provides a treatment depth of 100 mm whereas the spherical configuration has a focussing distance of 134 mm. Both distances are in the lower range of commercial lithotripters. As expected, the focus of the C-configuration has a shape of a thin disc due to the different length and width of the configuration. 
It is not clear what advantages the reported configurations feature. Perhaps the reduced number of piezo-elements and the way they can be arranged may offer intermediate space for in-line ultrasound localization or other instruments useful for lithotripsy. 
The fragmentation performance is similar to other commercial lithotripters. The unusually high second and third peak of the pressure curve is assumed to reduce focal cavitation but needs further exploration.

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