Three-dimensional optoacoustic monitoring of lesion formation in real time during radiofrequency catheter ablation.

INTRODUCTION: Due to lack of reliable imaging contrast from catheter radiofrequency ablation (RFA) lesions, the vast majority of current procedures rely on indirect indicators of ablation activity, resulting in a significant number of arrhythmia reoccurrences after RFA procedures and the need for repeat surgeries. The objective of this work is to develop an accurate method for on-the-fly assessment of the durability and size of lesions formed during RFA procedures. METHOD AND RESULTS: Radiofrequency catheter ablation on freshly excised porcine ventricular myocardial tissue was optoacoustically monitored by means of pulsed-laser illumination in the near-infrared spectrum. Lesion formation during ablation was captured at a rate of 10 Hz with a 256-detector optoacoustic imaging probe. Postablated samples were imaged using multispectral excitation in the wavelength range 740-860 nm to determine the lesion contrast spectrum. Tomographic reconstruction was performed to generate 3-dimensional images of the lesions, which were compared to photographs depicting the final ablated tissue samples. Video-rate 3-dimensional tomographic reconstructions depict formation of the lesion with high contrast and spatial resolution. The size and geometry of the lesion was shown to be in excellent agreement with the histological examinations. The wavelength dependence of the lesion contrast shows a contrast peak near 780 nm. CONCLUSION: Deep-tissue 3-dimensional monitoring of RFA lesion generation in real time was demonstrated for the first time in this work. The results suggest the potential of optoacoustic monitoring for providing critical feedback on lesion position and size during radiofrequency catheter ablation, improving safety and efficacy of these treatments.

Shock tube measurements of the rate constant for the reaction ethanol + OH.

The overall rate constant for the reaction ethanol + OH → products was determined experimentally from 900 to 1270 K behind reflected shock waves. Ethan(18)ol was utilized for these measurements in order to avoid the recycling of OH radicals following H-atom abstraction at the ß-site of ethanol. Similar experiments were also performed with unlabeled ethan(16)ol in order to infer the rate constant that excludes reactivity at the ß-site. The two data sets were used to directly infer the branching ratio for the reaction at the ß-site. Experimental data in the current study and in previous low-temperature studies for the overall rate constant are best fit by the expression koverall = 5.07 × 10(5) T[K](2.31) exp(608/T[K]) cm(3) mol(-1) s(-1), valid from 300 to 1300 K. Measurements indicate that the branching ratio of the ß-site is between 20 and 25% at the conditions studied. Pseudo-first-order reaction conditions were generated using tert-butylhydroperoxide (TBHP) as a fast source of (16)OH with ethanol in excess. (16)OH mole fraction time-histories were measured using narrow-line width laser absorption near 307 nm. Measurements were performed at the linecenter of the R22(5.5) transition in the A-X(0,0) band of (16)OH that does not overlap with any absorption features of (18)OH, thus producing a measurement of the (16)OH mole fraction that is insensitive to the presence of (18)OH.

Shock tube measurements of the tert-butanol + OH reaction rate and the tert-C4H8OH radical ß-scission branching ratio using isotopic labeling.

The overall rate constant for the reaction tert-butanol + OH → products was determined experimentally behind reflected shock waves by using (18)O-substituted tert-butanol (tert-butan(18)ol) and tert-butyl hydroperoxide (TBHP) as a fast source of (16)OH. The data were acquired from 900 to 1200 K near 1.1 atm and are best fit by the Arrhenius expression 1.24 × 10(-10) exp(-2501/T [K]) cm(3) molecule(-1) s(-1). The products of the title reaction include the tert-C4H8OH radical that is known to have two major ß-scission decomposition channels, one of which produces OH radicals. Experiments with the isotopically labeled tert-butan(18)ol also lead to an experimental determination of the branching ratio for the ß-scission pathways of the tert-C4H8OH radical by comparing the measured pseudo-first-order decay rate of (16)OH in the presence of excess tert-butan(16)ol with the respective decay rate of (16)OH in the presence of excess tert-butan(18)ol. The two decay rates of (16)OH as a result of reactions with the two forms of tert-butanol differ by approximately a factor of 5 due to the absence of (16)OH-producing pathways in experiments with tert-butan(18)ol. This indicates that 80% of the (16)OH molecules that react with tert-butan(16)ol will reproduce another (16)OH molecule through ß-scission of the resulting tert-C4H8(16)OH radical. (16)OH mole fraction time histories were measured using narrow-line-width laser absorption near 307 nm. Measurements were performed at the line center of the R22(5.5) transition in the A-X(0,0) band of (16)OH, a transition that does not overlap with any absorption features of (18)OH, hence yielding a measurement of (16)OH mole fraction that is insensitive to any production of (18)OH.

Rate constant measurements for the overall reaction of OH + 1-butanol → products from 900 to 1200 K.

The rate constant for the overall reaction OH + 1-butanol → products was determined in the temperature range 900 to 1200 K from measurements of OH concentration time histories in reflected shock wave experiments of tert-butyl hydroperoxide (TBHP) as a fast source of OH radicals with 1-butanol in excess. Narrow-linewidth laser absorption was employed for the quantitative OH concentration measurement. A detailed kinetic mechanism was constructed that includes updated rate constants for 1-butanol and TBHP kinetics that influence the near-first-order OH concentration decay under the present experimental conditions, and this mechanism was used to facilitate the rate constant determination. The current work improves upon previous experimental studies of the title rate constant by utilizing a rigorously generated kinetic model to describe secondary reactions. Additionally, the current work extends the temperature range of experimental data in the literature for the title reaction under combustion-relevant conditions, presenting the first measurements from 900 to 1000 K. Over the entire temperature range studied, the overall rate constant can be expressed in Arrhenius form as 3.24 × 10(-10) exp(-2505/T [K]) cm(3) molecule(-1) s(-1). The influence of secondary reactions on the overall OH decay rate is discussed, and a detailed uncertainty analysis is performed yielding an overall uncertainty in the measured rate constant of ±20% at 1197 K and ±23% at 925 K. The results are compared with previous experimental and theoretical studies on the rate constant for the title reaction and reasonable agreement is found when the earlier experimental data were reinterpreted.

Experimental determination of the high-temperature rate constant for the reaction of OH with sec-butanol.

The overall rate constant for the reaction of OH with sec-butanol [CH(3)CH(OH)CH(2)CH(3)] was determined from measurements of the near-first-order OH decay in shock-heated mixtures of tert-butylhydroperoxide (as a fast source of OH) with sec-butanol in excess. Three kinetic mechanisms from the literature describing sec-butanol combustion were used to examine the sensitivity of the rate constant determination to secondary kinetics. The overall rate constant determined can be described by the Arrhenius expression 6.97 × 10(-11) exp(-1550/T[K]) cm(3) molecule(-1) s(-1), valid over the temperature range of 888-1178 K. Uncertainty bounds of ±30% were found to adequately account for the uncertainty in secondary kinetics. To our knowledge, the current data represent the first efforts toward an experimentally determined rate constant for the overall reaction of OH with sec-butanol at combustion-relevant temperatures. A rate constant predicted using a structure-activity relationship from the literature was compared to the current data and previous rate constant measurements for the title reaction at atmospheric-relevant temperatures. The structure-activity relationship was found to be unable to correctly predict the measured rate constant at all temperatures where experimental data exist. We found that the three-parameter fit of 4.95 × 10(-20)T(2.66) exp(+1123/T[K]) cm(3) molecule(-1) s(-1) better describes the overall rate constant for the reaction of OH with sec-butanol from 263 to 1178 K.

High-temperature rate constant determination for the reaction of OH with iso-butanol.

This work presents the first direct experimental study of the rate constant for the reaction of OH with iso-butanol (2-methyl-1-propanol) at temperatures from 907 to 1147 K at near-atmospheric pressures. OH time-histories were measured behind reflected shock waves using a narrow-linewidth laser absorption method during reactions of dilute mixtures of tert-butylhydroperoxide (as a fast source of OH) with iso-butanol in excess. The title reaction's overall rate constant (OH + iso-butanol →(k(overall)) all products) minus the rate constant for the ß-radical-producing channel (OH + iso-butanol →(k(ß)) 1-hydroxy-2-methyl-prop-2-yl radical + H(2)O) was determined from the pseudo-first-order rate of OH decay. A two-parameter Arrhenius fit of the experimentally determined rate constant in the current temperature range yields the expression (k(overall) - k(ß)) = 1.84 × 10(-10) exp(-2350/T[K]) cm(3) molecule(-1) s(-1). A recommendation for the overall rate constant, including k(ß), is made, and comparisons of the results to rate constant recommendations from the literature are discussed.

Quenching of nonlinear photoacoustic signal generation in gold nanoparticles through coating.

The photoacoustic signal generated from specific gold nanoparticles increases nonlinearly with respect to fluence. We demonstrate experimentally that this nonlinear behavior can be quenched with a particle coating, and present a theoretical analysis to explain this behavior. This effect has the potential to be developed into a photoacoustic-based biochemical sensor.

Kinetic and Mechanistic Investigation of the Photocatalyzed Surface Reduction of 4-Nitrothiophenol Observed on a Silver Plasmonic Film via Surface-Enhanced Raman Scattering.

Hot electrons generated by photoinduced plasmon decay from a plasmonic metal surface can reduce 4-nitrothiophenol (4-NTP) to 4-aminothiophenol (4-ATP). Compared to the reduction with a reducing agent such as sodium borohydride, surface-enhanced Raman scattering (SERS) measurements were performed here to elucidate the complex molecular mechanism of the reduction in the presence of halide ions and hydrogen ions. The SERS measurements were performed using a simply prepared silver plasmonic film (AgPF), which enables monitoring of the reaction under different conditions at a solid-liquid surface and eliminates the need for the use of a reducing agent. As the concentration of H+ and Cl- could be controlled, the observation of the reaction under a systematic set of conditions was possible. Based on the kinetic traces of the intermediates, a reaction mechanism for the 4-NTP to 4-ATP reduction is suggested. Rate constants for the individual reactions are presented that fit the measured kinetic traces, and the role of hydrogen in each reaction step is characterized. This work provides clarification on the molecular transformation directly using protons as the hydrogen source and demonstrates an effective method of applying a simple and low-cost silver surface catalyst for SERS studies. Moreover, the monitoring of Cl--concentration-dependent spectra provides insight into the hot-electron conversion process during the photoreduction and strongly supports the formation of AgCl for the activation of H+.

Real-time monitoring of incision profile during laser surgery using shock wave detection.

Lack of sensory feedback during laser surgery prevents surgeons from discerning the exact location of the incision, which increases duration and complexity of the treatment. In this study we demonstrate a new method for monitoring of laser ablation procedures. Real-time tracking of the exact three dimensional (3D) lesion profile is accomplished by detection of shock waves emanating from the ablation spot and subsequent reconstruction of the incision location using time-of-flight data obtained from multiple acoustic detectors. Here, incisions of up to 9 mm in depth, created by pulsed laser ablation of fresh bovine tissue samples, were successfully monitored in real time. It was further observed that, by utilizing as little as 12 detection elements, the incision profile can be characterized with accuracy below 0.5 mm in all three dimensions and in good agreement with histological examinations. The proposed method holds therefore promise for delivering high precision real-time feedback during laser surgeries.