Magneto-acousto-electrical tomography (MAET) is designed to produce conductivity images with high spatial resolution for a conducting object. In a previous study, for an irregular conductor, transverse scanning and rotational methods with a focus transducer were combined to collect complete electrical information. This kind of method, however, is time-consuming because of the transverse scanning procedure. In this study, we proposed a novel imaging method based on plane ultrasound waves and a new aspect of projection in rotational MAET. In the proposed method, we achieved the projection in each rotation angle by using plane waves rather than mechanical scanning of the focus waves along the transverse direction. Thus, the imaging time was significantly saved. To verify the proposed method, we derived a measurement formula containing a lateral integration, which built the relationship between the measurement formula and the projection under each rotation angle. Next, we constructed two different numerical models to compute magneto-acousto-electrical signals by using a finite element method and reconstructed the corresponding conductivity parameter images based on a filtered back-projection algorithm. Then, simulated signals under different signal-to-ratios (6, 20, 40, and 60 dB) were generated to test the performance of the proposed algorithm. To improve the image quality, we further analysed the influence of the filters and the frequency scaling factors embedded in the filtered back-projection algorithm. Moreover, we computed the L2norm of the error in case of different frequency scaling factors and measurement noises. Finally, we conducted a phantom experiment with a 64-element linear phased array transducer (center frequency of 2.7 MHz) and reconstructed the conductivity parameter images of the circular phantom with an elliptical hole. The experimental results demonstrated the feasibility and time-efficiency of the proposed rapid rotational MAET.
A self-healing target has been demonstrated for synchronous photo-pumping of extreme- ultraviolet lasers. The threaded, mercury-wetted copper rod, rotating in a pool of mercury, offers similar photoionization efficiency as gold targets, but without target-surface degradation. A gain coefficient of 1.4 cm-1 was obtained with mercury for the 1089 angstrom Xe2+ laser at a pump-laser intensity of 140 GW(DOT)cm-2, comparing favorably with results from gold targets.
The resonance frequencies of individual SonoVue/spl trade/ contrast agent bubbles were measured optically by recording the radius-time curves of a single microbubble at 24 different frequencies. For these experiments, the Brandaris 128 fast framing camera was operated in a special segmented mode. The resonance frequencies found for SonoVue/spl trade/ microbubbles are in good agreement with the modified Herring model for coated bubbles indicating that the shell only slightly affects the resonance frequency of this class of contrast bubbles.
Acoustic waves induced by megavoltage photon beam from a clinical linear accelerator (Linac) could provide location and dosimetric information of actual delivered radiation during the course of therapy. In this study, we investigated, for the first time, the technical feasibility of detecting the dynamic acoustic emission process induced by Linac with high SNR. A 6 MV pulsed X-ray beam produced by a Linac was used to excite the X-ray acoustic signals from the water-gelatin phantom and the carbon-gelatin phantom. The induced acoustic signals were collected with a circular plane piston, immersion hydrophone in the frequency range from 100 kHz to 1 MHz perpendicular to the incident X-ray beam direction. The signals were amplified using a preamplifier with a bandwidth of 50 KHz-5 MHz at 34 dB and sampled by a high-speed 14-Bit 100 MS/s data acquisition card. A trigger circuit was designed to synchronize the process of incident pulsed X-ray generation and emitted acoustic signal acquisition. The dynamic X-ray acoustic emission process was consecutively detected from both phantoms with high SNR. The peak amplitude shows a marked increase in the phase of X-ray irradiation and then a rapid fall-off with different dynamic acoustic signal profiles in water-gelatin phantom, suggesting the different processes of accumulation and the absorption of the X-ray energy in different phantom properties. The acoustic emission process of carbon-gelatin phantom lasted more than 5 ms induced by a single X-ray beam with 5 μs pulse width. X-ray acoustic waves detected with high SNR may be used to verify the dose distribution during radiation therapy. Moreover, it may open the opportunity of using X-ray acoustic signals emitted from the tumor to evaluate the radiation treatment efficacy.
Ultrasound mediated delivery (USMD) in the presence of microbubbles is a potentially safe and effective method for gene therapy, offering many desired characteristics such as low toxicity, potential for repeated treatment, as well as organ specificity. In this study we tested the capability of USMD to improve gene transfection to mice livers for treating a rare genetic disorder, Glycogen Storage Disease Type Ia. An image guided therapeutic ultrasound system (TIPS, Philips) was used to provide therapeutic ultrasound to mice liver under IACUC approved protocols. Anesthetized healthy mice were placed supine on a heated pad and coupled to the TIPS transducer. Therapeutic plasmid DNA (FLAG-pG6Pase) was injected and microbubbles infused via the tail vein. Treated animals (n=4) received therapeutic ultrasound pulses (1 MHz, 2.5 MPa) over the entire liver. Control animals (n=5) received pDNA but not ultrasound treatment. Post treatment the animals were left to recover and subsequently sacrificed after 5 days. Tissues from the left, middle, caudal, right anterior, and right posterior liver lobes were harvested and stored. Quantitative PCR assays were then performed on the samples to quantify gene transfection. Ultrasound treated animals showed significantly higher levels of G6Pase transfection compared to control animals (p<;0.05) in all five lobes of the liver. On average, the treated animals showed 5.4 times more pDNA accumulation in the liver compared to controls. Immunohistochemistry staining for FLAG tag showed increased transgene expression especially around the blood vessels in treated animals. No evidence of toxicity was found up to 5 days post treatment.
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