1. A method of imaging a blood vessel, the method comprising: delivering a bubble-based contrast agent within the vessel; positioning at least one ultrasound device in the vicinity of the bubble-based contrast agent within the vessel; delivering a first burst of ultrasound energy directed at the bubble-based contrast agent to excite the bubble-based contrast agent, the first burst of energy comprising a first low-frequency component and a first high-frequency component, the first high-frequency component and the first low-frequency component having a first relative timing; and delivering a second burst of ultrasound energy directed at the excited bubble-based contrast agent, the second burst of energy comprising a second low-frequency component and a second high-frequency component, the second high-frequency component and the second low-frequency component having a second relative timing; receiving one or more return signals from the high-frequency ultrasound energy of the first and second bursts; and processing the one or more return signals to obtain a first image of the excited bubble-based contrast agent, wherein the first and second relative timings are different.