High-intensity focused ultrasound for ex vivo kidney tissue ablation: influence of generator power and pulse duration.
OBJECTIVE
The therapeutic application of noninvasive tissue ablation by high-intensity focused ultrasound (HIFU) requires precise physical definition of the focal size and determination of control parameters. The objective of this study was to measure the extent of ex-vivo porcine kidney tissue ablation at variable generator parameters and to identify parameters to control lesion size.


METHODS
The ultrasound waves generated by a cylindrical piezoceramic element (1.04 MHz) were focused at a depth of 100 mm using a parabolic reflector (diameter 100 mm). A needle hydrophone was used to measure the field distribution of the sound pressure. The morphology and extent of tissue necrosis were examined at generator powers of up to 400 W (P(el)) and single pulse durations of as long as 8 seconds.


RESULTS
The two-dimensional field distribution resulted in an approximately ellipsoidal focus of 32 x 4 mm (-6 dB). A sharp demarcation between coagulation necrosis and intact tissue was observed. Lesion size was controlled by both the variation of generator power and the pulse duration. At a constant pulse duration of 2 seconds, a generator power of 100 W remained below the threshold doses for inducing a reproducible lesion. An increase in power to as high as 400 W induced lesions with average dimensions of as much as 11.2 x 3 mm. At constant total energy (generator power x pulse duration), lesion size increased at higher generator power.


CONCLUSIONS
This ultrasound generator can induce defined and reproducible necrosis in ex-vivo kidney tissue. Lesion size can be controlled by adjusting the generator power and pulse duration. Generator power, in particular, turned out to be a suitable control parameter for obtaining a lesion of a defined size.
Häcker
Axel
A
Department of Urology, University Hospital Mannheim, Faculty of Clinical Medicine Mannheim, 68135 Mannheim, Germany. axel.haecker@chir.ma.uni-heidelberg.de
Köhrmann
Kai Uwe
KU
Knoll
Thomas
T
Langbein
Sigrun
S
Steidler
Annette
A
Kraut
Oliver
O
Marlinghaus
Ernst
E
Alken
Peter
P
Michel
Maurice Stephan
MS
D000818:Animals; D066298:In Vitro Techniques; D007668:Kidney / Q000473:pathology / Q000601:surgery*; D013552:Swine; D014464:Ultrasonic Therapy / Q000295:instrumentation*; D014465:Ultrasonics