A technique to enhance the photoacoustic emissions from laser-heated nanoparticles is presented. Gold nanoparticle-doped phantoms are subjected to pulsed optical and ultrasound fields, resulting in bubble formation and collapse and producing strong acoustic emissions. The applied ultrasound field allows for cavitation at lower laser fluences than using light alone. The acoustic emission associated with bubble collapse well exceeds the direct photoacoustic response and is used to image a nanoparticle-doped region in a tissue phantom. The strong acoustic emission and low-threshold fluence associated with ultrasound-assisted cavitation make the technique well suited for nanoparticle-targeted biological imaging and tissue therapy.