Methane Sulfonation via a Free-Radical Mechanism by Trifluoroacetylsulfuric Acid.

Using trifluoroacetyl sulfuric acid (TFAOSO3H), we discovered a new methane activation method and revealed its radical pathway under mild conditions. Upon the addition of a radical initiator with methane, the crude solution of TFAOSO3H developed the methyltrifluoroacetylsulfate radical ((TFAO)CH3S(OH)O2•). The resulting (TFAO)CH3S(OH)O2• behaved as a critical radical propagator for carbon-hydrogen bond activation, culminating in successful methane sulfonation. With 9.5 mol % of K2S2O8, TFAOSO3H and methane were selectively converted to methanesulfonic acid in 94 and 86% conversion yields, respectively.

Enhancement of Cardiomyogenesis in Murine Stem Cells by Low-Intensity Ultrasound.

OBJECTIVES: Low-intensity ultrasound (LIUS) has been shown to enhance bone and cartilage regeneration from stem cells. The ease of its incorporation makes it an attractive mechanical stimulus for not only osteogenesis and chondrogenesis, but also cardiomyogenesis. However, to date, no study has investigated its effects on cardiomyogenesis from embryonic stem cells. METHODS: In this study, murine embryonic stem cells were differentiated via embryoid body formation and plating, and after 3 days they were subjected to daily 10 minutes of LIUS treatment with various conditions: (1) low-pulsed (21 mW/cm2 , 20% duty cycle), (2) low-continuous, (3) high-pulsed (147 mW/cm2 , 20% duty cycle), and (4) high-continuous LIUS. RESULTS: Low-pulsed and high-continuous LIUS had improved beating rates of contractile areas as well as increased late cardiac gene expressions, such as α- and ß-myosin heavy chain and cardiac troponin T, showing its benefits on cardiomyocyte differentiation. Meanwhile, an early endodermal marker, α-fetoprotein, was significantly attenuated after LIUS treatments. CONCLUSIONS: With these observations, it is demonstrated that LIUS simulation could enhance cardiomyogenesis from embryonic stem cells and increase its selectivity toward cardiomyocytes by reducing spontaneous differentiation.

Reducing lesion aberration by dual-frequency focused ultrasound ablations.

Discrepancies between hyperecho-predicted necrosed volume in ultrasound (US) images and the actual size of a thermal lesion might cause incomplete ablation or damage normal structures during high intensity focused US (HIFU) ablations. A novel dual-frequency sonication procedure is proposed to reduce this discrepancy. HIFU transducers of either 1 or 3.5 MHz were applied to transparent tissue-mimicking phantoms and ex vivo bovine liver samples. A diagnostic probe and a charge-coupled device (CCD) camera were used to record lesion formation in real time, allowing for comparison of the sizes of the hyperechoes in US images and the protein denaturing area on optical images. Bovine liver specimens were segmented to reveal the lesion's terminal sizes. Differences between actual lesion volume and hyperechoes in US images were demonstrated to be dependent on acoustic frequency and intensity. At a low frequency (1 MHz), the hyperechoes appeared to be larger than the actual volume, but the difference decreased with the duration of ablation. In contrast, at a high frequency (3.5 MHz), the hyperechoes were smaller for ablations lasting longer than 10 s. Moreover, given certain low-intensity conditions, lesions were formed without detectable hyperechoes (3.5 MHz), or hyperechoes appeared before a visible lesion was formed (1 MHz). Dual frequency sonications (low frequency followed by high frequency) produce more stable and larger lesions, and with less position shift, which might be useful for designing future ablation strategies.

Shifting the Split Reflectors to Enhance Stone Fragmentation of Shock Wave Lithotripsy.

Shock wave lithotripsy (SWL) has been used widely in urology for about three decades to treat kidney calculi. Technical development to improve performance (i.e., stone fragmentation efficiency) is continuous. Low-pressure wide-focus lithotripters have already achieved promising results. In this study, the lithotripter field and profile of lithotripter shock waves were changed simultaneously using a cost-effective and convenient design. An intact parabolic reflector was split into four pieces, and each part was moved individually. By shifting the split reflectors, the focused acoustic beams were separated. As a result, the beam width in the focal region could be increased. Both numerical models of wave propagation using a k-wave approach and hydrophone measurements showed similar pressure waveforms at the focus and the distributions along and transverse to the lithotripter axis. The increase of the shifting distance from 0 mm to 7 mm resulted in the increase of -6 dB beam width from 7.1 mm to 13.9 mm and location of tensile peak on axis moving from z = -14 mm to 1 mm. The Lithotripters at 10 kV (intact reflector) and at 12 kV with the split reflectors shifted by 5 mm were compared with each other because of their similar peak positive pressures at the focus (8.07 MPa ± 0.05 MPa vs. 7.90 MPa ± 0.11 MPa, respectively). However, there were significant differences in their positive beam width (8.7 mm vs. 10.2 mm), peak negative pressure (-6.34 MPa ± 0.04 MPa vs. -7.13 MPa ± 0.13 MPa), the maximum tensile stress (7.55 MPa vs. 8.95 MPa) and shear stress (6.1 MPa vs. 7.76 MPa) in a 10-mm diameter spherical stone and bubble collapse time (127.6 µs ± 5.4 µs vs. 212.7 µs ± 8.2 µs). As a result, stone fragmentation efficiency was enhanced about 1.8-fold (57.9% ± 4.6% vs. 32.2% ± 5.6%, p < 0.05) when shifting the split reflectors. These results suggest that this new reflector design could change the characteristics of the lithotripter field and increase stone fragmentation efficiency.

Suppressing bubble shielding effect in shock wave lithotripsy by low intensity pulsed ultrasound.

Extracorporeal shock wave lithotripsy (ESWL) has been used as an effective modality to fragment kidney calculi. Because of the bubble shielding effect in the pre-focal region, the acoustic energy delivered to the focus is reduced. Low pulse repetition frequency (PRF) will be applied to dissolve these bubbles for better stone comminution efficiency. In this study, low intensity pulsed ultrasound (LIPUS) beam was aligned perpendicular to the axis of a shock wave (SW) lithotripter at its focus. The light transmission was used to evaluate the compressive wave and cavitation induced by SWs without or with a combination of LIPUS for continuous sonication. It is found that bubble shielding effect becomes dominated with the SW exposure and has a greater significant effect on cavitation than compressive wave. Using the combined wave scheme, the improvement began at the 5th pulse and gradually increased. Suppression effect on bubble shielding is independent on the trigger delay, but increases with the acoustic intensity and pulse duration of LIPUS. The peak negative and integral area of light transmission signal, which present the compressive wave and cavitation respectively, using our strategy at PRF of 1 Hz are comparable to those using SW alone at PRF of 0.1 Hz. In addition, high-speed photography confirmed the bubble activities in both free field and close to a stone surface. Bubble motion in response to the acoustic radiation force by LIPUS was found to be the major mechanism of suppressing bubble shielding effect. There is a 2.6-fold increase in stone fragmentation efficiency after 1000 SWs at PRF of 1 Hz in combination with LIPUS. In summary, combination of SWs and LIPUS is an effective way of suppressing bubble shielding effect and, subsequently, improving cavitation at the focus for a better outcome.

Single-element ultrasound transducer for combined vessel localization and ablation.

This report describes a system that utilizes a single high-intensity focused ultrasound (HIFU) transducer for both the localization and ablation of arteries with internal diameters of 0.5 and 1.3 mm. In vitro and in vivo tests were performed to demonstrate both the imaging and ablation functionalities of this system. For imaging mode, pulsed acoustic waves (3 cycles for in vitro and 10 cycles for in vivo tests, 2 MPa peak pressure) were emitted from the 2-MHz HIFU transducer, and the backscattered ultrasonic signal was collected by the same transducer to calculate Doppler shifts in the target region. The maximum signal amplitude of the Doppler shift was used to determine the location of the target vessel. The operation mode was then switched to the therapeutic mode and vessel occlusion was successfully produced by high-intensity continuous HIFU waves (12 MPa) for 60 s. The system was then switched back to imaging mode for residual flow to determine the need for a second ablation treatment. The new system might be used to target and occlude unwanted vessels such as vasculature around tumors, and to help with tumor destruction.