Diagnostic imaging of molecular-targeted nanorods simultaneously exposed to light and sound

Light-absorbing nanorods can be used to improve the signal-to-noise ratio of the thermoelastic emissions from tissue that are used in photoacoustic imaging. As nanorods can be functionalised to selectively target cancer cells, which could then be used to identify and/or destroy them through the formation of ultrasonically driven vapour bubbles. Heating the nanorods with a laser whilst they are simultaneously under tension from a ultrasound field results in a significant reduction in the fluence and pressure thresholds required for bubble formation. A custom build 96-channel diagnostic ultrasound system (4 MHz) was used in conjunction with a nanosecond pulse laser (850 nm) to B-mode image both transparent and turbid tissue-mimicking phantoms, which have been doped with gold nanorods (surface plasmon resonance 850 nm). For a mechanical index of 0.93 (1.86 MPa) and laser fluence of 16 mJ/cm², which are both below safety limits for diagnostic exposures, broadband emissions from the nanorod nucleated vapour bubbles were generated in both phantom types. For the turbid phantom type un-beamformed RF data was filtered using a narrowband filter to remove both the fundamental and second harmonic components of the ultrasound to show only the broadband emissions generated by the inertial collapse of the vapour bubbles. This demonstrates how this technique could be used for the diagnostic imaging of molecular-targeted nanorods.