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, the first high-frequency component being delivered while the bubble-based contrast agent is being exited by the first low-frequency component; 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 the second high-frequency component being delivered while the bubble-based contrast agent is being exited by the second low-frequency component; 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, the low-frequency components have a frequency of less than 5 MHz, and the high-frequency components have a frequency of greater than 15 MHz.