Histotripsy excitation sequences optimized for bubble cloud formation using shock scattering

A method of treating tissue with ultrasound energy, comprising the steps of:

• transmitting a first pulse of a Histotripsy excitation sequence from an ultrasound therapy transducer, the first pulse comprising an initiation pressure waveform configured to produce at least one bubble in the tissue;
• during a life-cycle of the at least one bubble, transmitting a second pulse of the Histotripsy excitation sequence from the ultrasound therapy transducer, the second pulse comprising a scattering pressure waveform configured to interact with the at least one bubble, the scattering pressure waveform configured to become a shocked focal pressure waveform in the tissue having a shocked positive pressure half cycle and a shocked negative pressure half cycle, the shocked positive pressure half cycle being configured to impinge on the at least one bubble and to scatter, invert, and constructively interfere with the shocked negative pressure half cycle to form a negative pressure half cycle waveform;
• and
• producing cavitation nuclei near the at least one bubble with a shock scattering mechanism between the positive pressure half cycle waveform and the at least one bubble.

A method of delivering ultrasound energy to tissue, comprising the steps of:

• delivering a first pulse of a Histotripsy excitation sequence from an ultrasound therapy transducer, the first pulse comprising an initiation pulse configured to provide at least 5 MPa of peak negative pressure to produce at least one bubble in the tissue;
• delivering a second pulse of the Histotripsy excitation sequence from the ultrasound therapy transducer, the second pulse comprising a first scattering pulse configured to interact with the at least one bubble within 5 μs to 200 μs of the initiation pulse;
• and
• producing a cavitation cloud of nuclei near the at least one bubble with a shock scattering mechanism between the first scattering pulse and the at least one bubble.