Electromagnetic energy is applied to thereby oscillate a bubble that is then insonified to produce an echo (260) for reception and analysis to afford imaging of the region of the bubble. To create the bubble, the energy may be applied to a nano particle (232) of a contrast agent whose consequent internal nano- or micro-bubbles offer, with novel pulsing techniques, greater sensitivity, and which can permeate outside vasculature (216) prior to being energized thereby affording quantification of vascular permeability and delivery of targeting molecules. The particle can include an absorbing and an evaporating parts, the irradiation (204), as by near-infrared laser, causing the phase change that gives rise to the bubble. The echo may occur in response to ultrasound interrogation (220) of the activated contrast agent, which could entail pulse inversion, power modulation or contrast pulse sequence imaging, with persistence processing. The contrast agent might be mixed with microbubble based ultrasound contrast agent to facilitate the timing of bubble activation.