Au nanocages with an edge length of ~50 nm were prepared in a two-step process. First, Ag nanocubes were prepared by a modified polyol process. 1 6.0 mL of ethylene glycol (EG, J.T.Baker 9300-01 Lot C42B27) was added to a glass vial and heated at 152 °C for 1 hour while being stirred with a Teflon-coated magnetic stir bar at 260 rpm. 90 µL of a 3 mM sodium sulfide (J. T. Baker 3910)-EG solution was then injected into the vial. After 8.5 minutes, 1.5 mL of a PVP (20 mg/mL, J. T. Baker, cat. no. 3910, MW = 29,000) solution in EG was injected into the vial. Immediately thereafter, 0.50 mL of a AgNO 3 (48 mg/mL, Sigma-Aldrich 209139) solution in EG was injected into the vial. A series of color changes were observed over the next 12 minutes, with the reaction being stopped by cooling the vial to room temperature after the reaction media appeared opaque, green-ochre when viewed head-on and ruddy-red when viewed from the top. Plating was observed on the vial walls. The quenched reaction media was then diluted twice its volume with acetone and the Ag nanocubes were collected by centrifugation.The Ag nanocubes were resuspended in water and washed an additional 3 times then stored in 4 mL of deionized water for future use.

Nanoparticles have been designed and applied as contrast enhancers in various optical imaging techniques, such as optical coherence tomography, fluorescence imaging, and optical reflectance microscopy. As an emerging hybrid imaging modality, photoacoustic imaging (PAI) has also benefited from the application of these nanoparticle-based contrast agents. We review this rapidly growing field and describe the applications of nanoparticles in PAI. Particular focus is given to nanoparticles whose absorption mechanism is based on surface plasmon resonance, including gold nanoshells, nanorods, and nanocages. Dye-embedded nanoparticles are also reviewed. Specifically, the design and application of each nanoparticle-based contrast agent in relation to the field of PAI are detailed.

Understanding the behavior of cavitation bubbles driven by ultrasonic fields is an important problem in biomedical acoustics. Keller-Miksis equation, which can account for the large amplitude oscillations of bubbles, is rederived in this paper and combined with a viscoelastic model to account for the strain-stress relation. The viscoelastic model used in this study is the Voigt model. It is shown that only the viscous damping term in the original equation needs to be modified to account for the effect of elasticity. With experiment determined viscoelastic properties, the effects of elasticity on bubble oscillations are studied. Specifically, the inertial cavitation thresholds are determined using R max / R 0 , and subharmonic signals from the emission of an oscillating bubble are estimated. The results show that the presence of the elasticity increases the threshold pressure for a bubble to oscillate inertially, and subharmonic signals may only be detectable in certain ranges of radius and pressure amplitude. These results should be easy to verify experimentally, and they may also be useful in cavitation detection and bubble-enhanced imaging.

Abstract. Photoacoustic tomography ͑PAT͒ is applied to image the brain cortex of a monkey through the intact scalp and skull ex vivo. The reconstructed PAT image shows the major blood vessels on the monkey brain cortex. For comparison, the brain cortex is imaged without the scalp, and then imaged again without the scalp and skull. Ultrasound attenuation through the skull is also measured at various incidence angles. This study demonstrates that PAT of the brain cortex is capable of surviving the ultrasound signal attenuation and distortion caused by a relatively thick skull.