Acoustic-transfection technique has been developed for the first time. We have developed acoustic-transfection by integrating a high frequency ultrasonic transducer and a fluorescence microscope. High frequency ultrasound with the center frequency over 150 MHz can focus acoustic sound field into a confined area with the diameter of 10 μm or less. This focusing capability was used to perturb lipid bilayer of cell membrane to induce intracellular delivery of macromolecules. Single cell level imaging was performed to investigate the behavior of a targeted single-cell after acoustic-transfection. FRET-based Ca<sup>2+</sup> biosensor was used to monitor intracellular concentration of Ca<sup>2+</sup> after acoustic-transfection and the fluorescence intensity of propidium iodide (PI) was used to observe influx of PI molecules. We changed peak-to-peak voltages and pulse duration to optimize the input parameters of an acoustic pulse. Input parameters that can induce strong perturbations on cell membrane were found and size dependent intracellular delivery of macromolecules was explored. To increase the amount of delivered molecules by acoustic-transfection, we applied several acoustic pulses and the intensity of PI fluorescence increased step wise. Finally, optimized input parameters of acoustic-transfection system were used to deliver pMax-E2F1 plasmid and GFP expression 24 hours after the intracellular delivery was confirmed using HeLa cells.
A dual-element needle transducer for intravascular ultrasound imaging has been developed. A low-frequency element and a high-frequency element were integrated into one device to obtain images which conveyed both low- and high-frequency information from a single scan. The low-frequency element with a center frequency of 48 MHz was fabricated from the single crystal form of lead magnesium niobate-lead titanate solid solution with two matching layers (MLs) and the high frequency element with a center frequency of 152 MHz was fabricated from lithium niobate with one ML. The measured axial and lateral resolutions were 27 and 122 μm, respectively, for the low-frequency element, and 14 and 40 μm, respectively, for the high-frequency element. The performance of the dual-element needle transducer was validated by imaging a tissue-mimicking phantom with lesion-mimicking area, and ex vivo rabbit aortas in water and rabbit whole blood. The results suggest that a low-frequency element effectively provides depth resolved images of the whole vessel and its adjacent tissue, and a high-frequency element visualizes detailed structure near the surface of the lumen wall in the presence of blood within the lumen. The advantages of a dual-element approach for intravascular imaging are also discussed.
Clutter noise is an important challenge in photocoustic (PA) and ultrasound (US) imaging as they degrade the image
quality. In this paper, the short-lag spatial coherence (SLSC) imaging technique is used to reduce clutter and side lobes
in PA images. In this technique, images are obtained through the spatial coherence of PA signals at small spatial
distances across the transducer aperture. The performance of this technique in improving image quality and detecting
point targets is compared with a conventional delay-and-sum (DAS) beamforming technique. A superior contrast,
contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) are observed when SLSC imaging is employed. Point
spread function of point targets shows an improved spatial resolution and reduced side lobes when compared with DAS
beamforming. Also shown is the impact of increasing the number of frames on which SLSC is applied. The results show
that contrast, CNR, and SNR are improved with increasing number of frames.