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The ultrasound contrast microbubbles have shown a great ability to produce nonlinear oscillations in response to acoustic excitation which results in the generation of harmonics and subharmonics of the excitation. The subharmonic response of ½ order changes significantly with a change in hydrostatic pressure in the physiological range. This property is being investigated for subharmonic aided pressure estimation (SHAPE), a noninvasive alternative to current methods for vascular pressure measurement in critical organs. In this study, the ambient pressure sensitivity of the subharmonic response of microbubbles with different gas cores and shells was investigated over 25–700 kPa acoustic pressure and the hydrostatic pressure range of 0–25 kPa. The subharmonic showed different trends of increase and decrease with hydrostatic pressure. The sensitivity has shown gradual change over time which was observed to be related to the hydrostatic pressure magnitude and the gas core. These findings could help to calibrate the SHAPE.

Microbubbles have been widely used as contrast agents for ultrasound imaging. They are also being investigated for therapeutic applications including as a vehicle for ultrasound activated targeted drug delivery. Here the effects of the shell chemistry on the acoustic response and dissolution behavior of microbubbles have been investigated. Microbubbles encapsulated by a lipid shell (DPPC and DPPE-PEG2000) were prepared with different PEG molar ratios (0% to 20%) investigating their concentration, size distribution, stability and material properties. Note that different PEG concentrations were previously shown to result in different PEG surface configuration: mushroom for lower PEG concentrations and brush for higher ones. The microbubbles in the brush regime seem to generate higher fundamental and subharmonic scattering components at 2.25 MHz excitation, while the higher harmonics seems unaffected. Microbubbles in the mushroom regime showed different dissolution behavior with longer growth period before dissolution. This is believed to be resulted from a less permeable shell in comparison to shells in brush regime. The relation between acoustic response, dissolution behavior and material properties of the shell will be discussed.

Abstract. Er 3+ -Yb 3+ co-doped titanium dioxide upconversion nanoparticles were synthesized by sol-gel method. White upconversion emissions were observed after excitation of nanoparticles with 980 nm Near-Infrared laser diode. Upconversion emissions consist of red (640-690 nm), green (520-570 nm), and blue (408 nm) emissions. Ultraviolet upconversion emissions were also detected with wavelength about 210 nm. Ultraviolet emissions are probably the results of relaxation from 2 I 13=2 (220 nm) and 2 L 15=2 (210 nm) states to 4 I 15=2 . Visible and ultraviolet emissions of these nanoparticles can be used in photodynamic therapy. High penetration of Near-Infrared light into the body tissue makes these nanoparticles appropriate for aiming tumors in deeper tissues in comparison with older methods of photodynamic therapy.