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Abstract²This paper seeks to define the mechanisms by which the human motor system finds optimal reaching solutions, when one of the arm joints is locked in place. Specifically, the paper studies how people solve the problem of motion planning when they lose the ability to move their elbow joint. Our hypothesis is based on the idea that the governing rules of motion planning will be consistent even under the given joint constraint, i.e. the hand will follow the shortest path with a bell±shaped velocity profile, while reaching from a start to an end position. We present an experimental protocol with human subjects to compare their hand paths with the geodesic curve in Euclidean space. The speed profiles of these trajectories are also compared to the modified output of the so±called minimum jerk model of Flash and Hogan.Our results indicate that arm reaching paths with an elbow joint constraint at a certain angle closely follow the geodesic and has a bell shaped speed profile. The future work involves extending this research to the shoulder and wrist joints.

We have investigated the combination of high intensity focused ultrasound (HIFU) and ethanol injection for ablation treatment of anaplastic thyroid cancer, a highly aggressive form of thyroid cancer characterized by >80% mortality within months. The suspension of FB1 anaplastic thyroid cancer cells (100 μl, 2.7 million cells/ml) were placed in a 0.2 ml thin-wall PCR tube and then exposed to HIFU alone, ethanol alone, or ethanol + HIFU. The focused ultrasound signal was generated by a 1.1 MHz transducer with acoustic power ranged from 4.1 W to 12.0 W. Ethanol was diluted in the FB1 cell growth medium to the concentration of 2%, 4%, or 10% (v/v) and applied to the cells before HIFU exposure. The viability of the cells was measured by flow cytometry and trypan blue exclusion 2, 24, and 72 h post-treatment. The exposure of FB1 cells to HIFU alone greatly reduced the number of viable cells immediately after treatment; however, their proliferation rate remained high. On the other hand, both the viability and proliferation rate significantly decreased in the cells treated with both ethanol and HIFU. In conclusion, percutaneous ethanol injection (PEI) and HIFU have a synergistic effect on anaplastic thyroid cancer ablation.

We have investigated the combined effect of HIFU and ethanol injection on the temperature rise and cavitation in porcine liver tissues and on the viability and proliferation rate of HepG2 liver cancer cells. Tissues were injected with 95% ethanol before being subjected to the HIFU beam generated by a 1.1 MHz transducer with acoustic power ranged from 1.17 W to 20.52 W. Cavitation events and the temperature in and around the focal zone were measured by a passive cavitation detector and type K thermocouples, respectively. In the cell study, 100 μl of HepG2 cell suspension (2.7 million cells/ml) was placed in a 0.2 ml thin-wall PCR tube. Ethanol 2% or 4% in the cell growth medium was added to the cell suspension, and the cells were then exposed to HIFU for 30 s. The data of these experiments show that the pre-treatment of tissues with ethanol reduces the threshold power for inertial cavitation and increases the temperature rise. Both the viability and proliferation rate were significantly decreased in cells treated with ethanol and HIFU, as compared to individual treatments. The results of our study indicate that ethanol injection and HIFU have a synergistic effect on liver cancer ablation.

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