Comparative Study of Pulsed Versus Continuous High-Intensity Focused Ultrasound Ablation Using In Vitro and In Vivo Models.

OBJECTIVES

To compare the efficacy of pulsed high-intensity focused ultrasound (PHIFU) versus continuous high-intensity focused ultrasound (CHIFU) ablation at identical doses.

METHODS

Continuous and pulsed HIFU (1200 J) at duty cycles (DCs) of 60% and 20% were examined for their capacity to ablate bovine liver tissue in vitro and rabbit liver tissue in vivo. After ablation, grayscale changes and pathologic characteristics were observed or measured, and the tissue necrosis volume, energy efficiency factor, and average grayscale density were calculated.

RESULTS

The pulsed mode generated greater liquefaction necrosis. An inconspicuous grayscale change was observed for PHIFU at a DC of 20% in some samples, which appeared as an elliptical cavity. The energy efficiency factor of PHIFU at a DC of 60% was significantly lower than that of CHIFU, as observed both in vitro and in vivo (P < .05). The grayscale value and average grayscale density in response to CHIFU were significantly greater than those in response to PHIFU (60% or 20%; P < .05). Histopathologic analysis revealed liquefaction necrosis in all PHIFU groups.

CONCLUSIONS

At identical doses, compared with CHIFU, a single session of PHIFU can generate liquefaction necrosis and at a higher DC can improve ablation efficiency. This increased efficacy of PHIFU may involve enhancement of tissue destruction by cavitation effects and a reduction in the obstruction effect of endogenous microbubbles through cavitation effects or a more effective diffusion of heat.