Microbubble formation as tissue necroses. As the ablation continues the microbubbles identify the periphery of the tissue necrosed. This should ideally be an extra 2cm cuff around the visible periphery of the original tumour. The first centimetre to treat non visible spread throughout liver tissue, the next centimetre to treat any microscopic growth outside the original perceived boundary. The hyperechoic cloud recedes and is replaced by a heterogenous, echogenic mass of tissue.