Official Proceedings - AIUM

American Institute of Ultrasound in Medicine Proceedings J Ultrasound Med 32(suppl):S1–S134, 201337°C and 5% O 2. After 48 hours, explants were subjected to a 7-J/cm 2impact with a customized drop tower device, and LIPUS (1 MHz, 54mW/cm 2 , and durations of 30, 60, and 90 minutes) was immediately applied.A sham group was subjected to identical procedures except LIPUSstimulation. After LIPUS stimulation, cell viability (calcein AM/ethidiumhomodimer) and oxidative stress (dihydroethidine) were imaged with confocalmicroscopy and quantified.Results—Sixty-minute LIPUS after the 7-J/cm 2 impact resultedin a significant increase in ROS production (≈2-fold) compared to thesham group. In contrast, no difference in ROS production was apparent inuninjured explants with or without LIPUS stimulation. After injury, theROS response to the LIPUS duration showed a strong linear relationship(R 2 = 0.75) with an increasing duration of stimulation inside the impactedarea, whereas such a relationship was not observed in areas adjacent tothe impact. No difference in post–24-hour chondrocyte viability was observedbetween LIPUS and sham groups.Conclusions—Our findings demonstrate that LIPUS stimulatesROS production in injured articular cartilage in a duration-dependent manner,and enhanced ROS production did not affect cell viability in cartilage.Although the exact role of enhanced ROS in response to LIPUS ininjured cartilage remains unclear, we hypothesize that the increased oxidativestress may have implications in cartilage repair processes by modulatingchondrocyte energy production, metabolism, and matrix synthesis.1543362 Microbubble and Ultrasound Enhancement of Radiation-Induced Tumor Cell Death In Vivo: ASMase DependenceGregory Czarnota, 1 * Amr Hashim, 1 Ahmed El Kaffas, 1 RaffiKarshafian, 2 Anoja Giles, 1 Sara Iradji, 1 Azza Al Mahrouki 11Radiation Oncology/Physical Sciences, Sunnybrook HealthSciences Center, Toronto, Ontario, Canada; 2 Physics, RyersonUniversity, Toronto, Ontario, CanadaObjectives—It is now appreciated that radiation not only damagesthe DNA inside tumor cells in vivo but also may act by damaging theendothelial cells of the vasculature. In this study, we tested the hypothesisthat microbubble agents in vivo may be used a priori to cause endothelialcell perturbations, thus causing “radiosensitization” of tumors.Methods—Fibrosarcoma xenograft-bearing mice (n = 200+)were exposed to combinations of ultrasound, activated microbubbles, andradiation (8 animals per group). For ultrasound treatments, animals wereexposed to a 500-kHz center frequency and 570-kPa peak negative pressurefor treatment. For treatments involving bubbles, Definity bubbles(Bristol Myers-Squibb) were administered, and for radiation treatments160-kVp x-rays were used at doses of 2 and 8 Gy. Representative tumorsections were examined using immunohistochemistry. Clonogenic assaysand growth delay studies were also carried out. Experiments were carriedout in ASMase +/+ and –/– mice to investigate endothelial cell apoptosiseffects.Results—Analyses indicated a synergistic increase in tumorcell kill due to vascular disruption that was ASMase dependent, causedby the combined therapies that increased when microbubbles were usedin conjunction with radiation, with increases of cell kill from 5% to >50%with combined single treatments. Immunohistochemistry indicated endothelialcell apoptosis and activation of the ceramide cell death pathwayto be caused by microbubbles. Multiple treatments indicated a better therapeuticoutcome with multiple treatments combining both modalities comparedto single-modality treatments.Conclusions—Radiation effects were synergistically enhancedby using microbubbles to perturb tumor vasculature prior to the administrationof radiotherapy. Analyses indicated activation of ceramide-mediatedapoptotic cell death in endothelial cells leading to vasculardisruption in tumors. This led to profoundly enhanced tumor cell deatheven after 1 combined treatment using a 2-Gy radiation dose. This workforms the basis for ultrasound-induced spatial targeting of radiotherapyenhancement.1540684 On the Acceleration of Ultrasound Thermal Therapy byPatterned Acoustic Droplet VaporizationOliver Kripfgans, 1 * Mario Fabiilli, 1 Scott Swanson, 1 CharlesMougenot, 2 Paul Carson, 1 Man Zhang, 1 J. Brian Fowlkes 11Radiology, University of Michigan, Ann Arbor, Michigan USA;2Philips Healthcare, Toronto, Ontario, CanadaObjectives—High-intensity focused ultrasound (HIFU), an establishedmethod for treating cancer and hyperplasia, often suffers fromuneven heating and requires in general long treatment times for large targetvolumes. In situ gas bubbles have become more accepted as energyconversion agents for HIFU. If carefully controlled, these agents increaselesion sizes dramatically.Methods—Emulsions of perfluorocarbon droplets (lipid coated,C 5F 12, Ø 2.0 ± 0.1 µm, ≈99% < 8 µm Ø) were used to create thermal agentsin polyacrylamide phantoms. The emulsion concentration in the gel was3 × 10 5 droplets/mL. This corresponds to a volume fraction of 1 ppm(vol/vol). The samples were placed in thermal contact with a heating systemto maintain 35°C. Egg white was incorporated to allow for visual inspectionof the phantoms after acoustic exposure from a Philips Sonallevemagnetic resonance–guided focused ultrasound system (1.5 T) using a256-element phased array with a 120-mm focal length. At a transmit centerfrequency of 1.45 MHz, maximum electronic steering of 10 mm wasachieved at a depth of 10 cm. In situ temperature monitoring limited focalheating to 75°C. Lesion sizes were measured as a function of appliedacoustic power. Acoustic trenches were created to accelerate thermal therapy,in which individual lesions were spaced 5.5 mm apart to create 25-mm-diameter spiral patterns.Results—Single HIFU exposures in droplet-laden phantomsresulted in lesions of 2 to 5 mm in diameter. Rapid repetition of electronicallysteered therapy pulses (40 pulses/s) allowed for the generation of homogeneousand contiguous composite lesions at a rate >1 mL/s. Foracoustic power levels ranging from 40 to 300 W (acoustic), lesion volumesincreased by a factor of at least 15 when comparing lesion volumesin phantoms with droplets to without droplets. With the use of acousticdroplet vaporization (ADV) and the resulting trench, a uniform ablationvolume of 15 mL was achieved in 15 seconds; without ADV,