Focused liver ablation by cavitation in the rabbit: a potential new method of extracorporeal treatment.

Abstract

A new device was used to achieve focused tissue ablation by shockwave induced cavitation. The device produced a half cycle of negative pressure followed by a shock wave, thus enhancing cavitation. Twenty eight New Zealand rabbits were treated. Therapeutic ultrasound was targeted at the centre of the liver under ultrasound guidance. The focal volume was scanned with a computer operated x-y-z micropositioner. The number and frequency of bursts as well as the distance between two x-y-z displacements were preselected. The relation of tissue ablation seen to preselected parameters, effects on surrounding tissues, biological side effects, and mode of healing were studied. Macroscopy, planimetry, and quantitative microscopy were used. Focused and homogeneous tissue ablation was achieved within well defined limits. Maximal tissue ablation was seen in the centre of the target. Liver surrounding the target remained unaffected. Lesions were made of a-cellular spots surrounded by disorganised rims of necrotic hepatocytes; 24 hours after treatment, the changes (mean (SEM)) in alanine transaminase and haemoglobin were +225 (36)% and -2-4 (2)% respectively. Serum transaminases, haemoglobinaemia, and packed cell volume were normal 21 days after treatment and the target area was replaced by a fibrous scar. It is concluded that ultrasound cavitation may achieve extracorporeal intrahepatic tissue ablation inside a predetermined target. This technique should now be tested in an animal hepatic tumour model. (Gut 1994; 35: Recurrences can now be detected at early stages with the help of modern diagnostic methods.5 Hence, it seems reasonable to contemplate a minimally invasive method providing radical and selective cancer destruction, which could be applied to such tumours with some benefit. It was our hypothesis that acoustic cavitation induced by shock waves could be such a method. Cavitation is defined as the non-linear oscillation and collapse ofgas bubbles suspended in a liquid under the influence of acoustic (mechanical) pressure waves$'0; the expansion of bubble nuclei results from a depression within the medium and their collapse may be induced by a sudden compression wave after expansion." It has been shown that cavitation, when occurring at an interface near a cell membrane for example, was deleterious to biological media through mechanical, non-thermal effects. 12-18 We showed the feasibility of radical tissue destruction in the rabbit liver in vivo by a concomitant administration of focused extracorporeal electrohydraulic shock waves with intravascularly infused gas microbubbles.'9 Our results showed improvement shortcomings, however, which made the method inapplicable to the human or even to animal models of tumours without an unacceptable toxicity: tissue ablation was not focused, non-homogeneous, and needed an invasive and potentially toxic intra-arterial infusion of gas microbubbles to be efficient. Our objectives were thus to perfect the method to enhance cavitation, eradicate bubble injection, and to improv...

Medical applications and bioeffects of extracorporeal shock waves

“…Recently, a piezoelectric device has been described which generated tensile waves more efficiently, thus eliminating the need for additional gas bubble injection (Prat et al 1994). It was designed for maximal tissue damage in order to remove tumors, and tightly packed cavitation lesions were produced in the focus.…”

“…This led to the postulate that the generation of different waveforms enhances the cavitation effects, and shock wave sources which differ from those used for fragmentation should be developed for tumor therapy (Delius et al 1989). The effect of the first of these generators (Feigl et al 1992;Prat et al 1994) on solid tumors should be known in the near future.…”

Distinct Sensitivity of Normal and Malignant Cells to Ultrasound in Vitro

“…Ultrasound is a nonionizing modality of irradiation that is widely used at various frequencies and intensities for diverse purposes, including diagnostic applications, sterilization, and hygiene (1)(2)(3)(4)(5)(6)(7). Furthermore, ultrasound is being used for therapeutic purposes such as urological applications, surgical interventions, angioplasty, lithotripsy, and tooth cleaning (8)(9)(10)(11)(12)(13).…”

Development of a PVDF low-cost shock-wave hydrophone

“…It has been shown that cavitation, when occurring at an interface near a cell membrane, for example, was deleterious to biological media through mechanical, nonthermal effects [6], [7]. More recently, shock wave-induced cavitation was used to achieve focused tissue destruction of malignant tumors of the liver [8]. Optimization of these clinical processes and/or study of physical properties of shock waves clearly require quanti -~ tative measurements of the relevant shock wave parameters temporally and spatially.…”