A two-dimensional ͑2D͒ gold nanostructure is used to optically generate high frequency ultrasound. The structure consists of 2D arrangements of gold nanoparticles, sandwiched between a transparent substrate and a 4.5 m thick polydimethylsiloxane ͑PDMS͒ layer. The acoustic signal displays significant improvements compared to a bulk black PDMS films ͑the current state of the art͒ at frequencies from 50 to 100 MHz. The high optical extinction ratio of the gold nanostructure provides a convenient method to construct an integrated transmit/receive optoacoustic array. These results show that a 2D gold nanostructure can be used to produce high frequency arrays for ultrasound imaging.
A broadband all-optical ultrasound transducer has been designed, fabricated, and tested for high-resolution ultrasound imaging. It consists of a two-dimensional gold nanostructure on a glass substrate, followed by a 3μm polydimethylsiloxane layer and a 30nm gold layer. The signal to noise ratio of a pulse-echo signal is over 10dB in the far field of the transducer, where the center frequency is 40MHz with −6dB bandwidth of 57MHz. The potential for high-frequency ultrasound arrays using this technology is demonstrated using multiple measurements from the transducer to image a 25μm diameter wire.
Optical detection of ultrasound is a promising technique for high frequency imaging arrays. Detection resolution approaches the optical resolution, which can be on the order of the optical wavelength. We describe here an optical technique for ultrasound detection based on a thin ͑10 m͒ Fabry-Perot étalon optimized for high resolution imaging. The signal to noise ratio ͑SNR͒ approaches that of an ideal piezoelectric transducer over a 100 MHz bandwidth. Array functionality is demonstrated by scanning a probe beam along a line. Thermoelastic excitation was applied to generate acoustic waves in a test phantom containing a single "pointlike" source. An image of the source was reconstructed using signals acquired from the étalon detector array.
Humans can voluntarily attend to a variety of visual attributes to serve behavioral goals. Voluntary attention is believed to be controlled by a network of dorsal frontoparietal areas. However, it is unknown how neural signals representing behavioral relevance (attentional priority) for different attributes are organized in this network. Computational studies have suggested that a hierarchical organization reflecting the similarity structure of the task demands provides an efficient and flexible neural representation. Here we examined the structure of attentional priority using functional magnetic resonance imaging. Participants were cued to attend to location, color, or motion direction within the same stimulus. We found a hierarchical structure emerging in frontoparietal areas, such that multivoxel patterns for attending to spatial locations were most distinct from those for attending to features, and the latter were further clustered into different dimensions (color vs motion). These results provide novel evidence for the organization of the attentional control signals at the level of distributed neural activity. The hierarchical organization provides a computationally efficient scheme to support flexible top-down control.
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