A method of contrast agent based active ultrasound imaging applied to a subject's vasculature to which a contrast agent mixture of (i) a nanoparticle-based contrast medium that comprises nanoparticles and (ii) an additional contrast agent has already been introduced into a target region of the vasculature, the method comprising: - detecting an inflow of the additional contrast agent of the contrast agent mixture in the vasculature of said target region; the additional contrast agent comprising a microbubble-based ultrasound contrast agent that includes microbubbles, - wherein detecting an inflow of the additional contrast agent of the contrast agent mixture in the vasculature of said target region comprises detecting an inflow of the microbubbles of the microbubble-based ultrasound contrast agent in the vasculature of said target region, and - wherein applying of pulsed electromagnetic energy to the nanoparticle-based contrast medium is commenced responsive to detecting the inflow of the microbubbles of the microbubble-based ultrasound contrast agent in the vasculature of said target region; - applying pulsed electromagnetic energy to the nanoparticle-based contrast medium located in said target region (i) to cause a phase change in an evaporation part of the nanoparticles that produces bubbles and (ii) to further produce oscillating bubbles (ii)(a) from the bubbles produced by the phase change in the evaporation part of the nanoparticles (ii)(b) in response to an ongoing on and off energy absorption of an absorbing part of the nanoparticles in response to applying the pulsed electromagnetic energy, wherein the oscillating bubbles resonate at a frequency that is detectable by an interrogating ultrasound of an active ultrasound imaging of the vasculature of said target region; and - insonifying the oscillating bubbles to produce echoes for reception and analysis by the active ultrasound imaging of the vasculature of said target region, wherein the active ultrasound imaging comprises low mechanical index imaging at low power so that a destruction of the oscillating bubbles is avoided, and wherein (i) said applying of pulsed electromagnetic energy is commenced, and (ii) said low mechanical index imaging is performed, (iii) at a concurrent time in response to (iii)(a) an inflow of the nanoparticle-based contrast medium in the vasculature of said target region being detected via detecting the inflow of the additional contrast agent of the contrast agent mixture in the vasculature of said target region and (iii)(b) for which a portion of the inflow of the nanoparticle-based contrast medium detected in the vasculature of said target region has permeated outside the vasculature of said target region. - detecting an inflow of the additional contrast agent of the contrast agent mixture in the vasculature of said target region; the additional contrast agent comprising a microbubble-based ultrasound contrast agent that includes microbubbles, - wherein detecting an inflow of the additional contrast agent of the contrast agent mixture in the vasculature of said target region comprises detecting an inflow of the microbubbles of the microbubble-based ultrasound contrast agent in the vasculature of said target region, and - wherein applying of pulsed electromagnetic energy to the nanoparticle-based contrast medium is commenced responsive to detecting the inflow of the microbubbles of the microbubble-based ultrasound contrast agent in the vasculature of said target region; - applying pulsed electromagnetic energy to the nanoparticle-based contrast medium located in said target region (i) to cause a phase change in an evaporation part of the nanoparticles that produces bubbles and (ii) to further produce oscillating bubbles (ii)(a) from the bubbles produced by the phase change in the evaporation part of the nanoparticles (ii)(b) in response to an ongoing on and off energy absorption of an absorbing part of the nanoparticles in response to applying the pulsed electromagnetic energy, wherein the oscillating bubbles resonate at a frequency that is detectable by an interrogating ultrasound of an active ultrasound imaging of the vasculature of said target region; and - insonifying the oscillating bubbles to produce echoes for reception and analysis by the active ultrasound imaging of the vasculature of said target region, wherein the active ultrasound imaging comprises low mechanical index imaging at low power so that a destruction of the oscillating bubbles is avoided, and wherein (i) said applying of pulsed electromagnetic energy is commenced, and (ii) said low mechanical index imaging is performed, (iii) at a concurrent time in response to (iii)(a) an inflow of the nanoparticle-based contrast medium in the vasculature of said target region being detected via detecting the inflow of the additional contrast agent of the contrast agent mixture in the vasculature of said target region and (iii)(b) for which a portion of the inflow of the nanoparticle-based contrast medium detected in the vasculature of said target region has permeated outside the vasculature of said target region.