Journal: Nano letters

Article Title: Polypyrrole Coated Perfluorocarbon Nanoemulsions as a Sono-Photoacoustic Contrast Agent

doi: 10.1021/acs.nanolett.7b02845

Figure Lengend Snippet: The image panels compare the images and contrast enhancement from (A) photoacoustic (PA) imaging and sono-photoacoustic (SPA) images at (B) low pressure versus (C) high pressure. Images were acquired using a 3 MHz burst from a linear array (ATL L7-4) paired with a custom 1 mm × 15 mm bifurcating optical fiber bundle used to deliver laser pulses (see in panel D). The timing of the laser shot relative to the ultrasound acquisition was controlled using a programmable ultrasound system. Color images were normalized to the maximum signal in panel C and superimposed on gray scale ultrasound (US) images. The four samples from left to right are cellulose, PPy particles in water (8.1 nM), and PFP PPy emulsion contrast agent (0.65 pM), and the tube containing DI water. Cellulose provided the greatest US scattering within the tube (gray scale). Although a PA signal was produced by both the PPy particles as well as the PPy coated emulsions, only the PPy coated emulsions produced an SPA signal. Conventional US and PA imaging provides a linear signal that scales with transmitted signal intensity and absorbed energy density, respectively, which is removed from the SPA images (seen comparing panels A and B). For PPy emulsions, when the combined energy from the laser and US exceeds the cavitation threshold, the contrast agent vaporizes to produce a non-linear signal. The non-linear SPA contrast enhancement from the PPy coated PFP emulsions were compared against PA contrast imaging of PPy particles (no PFC core) (see panel E). PA imaging contrast enhancement has no dependence on transmitted acoustic pressure (R2 = 0.0009), while SPA imaging shows a near linear increase in contrast enhancement with increasing pressure (R2 = 0.94). The low contrast obtained from the SPA contrast agent relative to the PA agent at pressures under 0.4 MPa is due to the much lower concentration of SPA agents than PA agents. The additional signal seen in some of the ultrasound images as well as the SPA contrast image (panel D) is from an internal acoustic reflection from the tube.

Article Snippet: To mimic a clinical situation, a linear array transducer (ATL L7-4, 128 elements, Philips, Bothell, WA, USA) controlled by a programmable ultrasound scanner (Vantage 128, Verasonics, Redmond, WA, USA) was used both to excite the contrast agent and detect relevant US signals.

Techniques: Imaging, Emulsion, Produced, Concentration Assay