Registration between 2D and 3D Ultrasound Images to Track Liver Blood Vessel Movement.

BACKGROUND: For the accurate positioning of surgical tools, conventional intraoperative navigation systems have been developed to recognize the relationship between target positions and the tools. However, since an internal organ is deformed during the operation, registration between realtime two-dimensional (2D) ultrasound images and three-dimensional (3D) CT or MRI images is not always effective. Therefore, this study developed image registration between 2D and 3D ultrasound images considering deformation for tracking target vessel movement in the liver. METHODS: 3D ultrasound image was obtained in advance with 3D coordinates, including the target vessel. Then real-time 2D images and ultrasound probe position were simultaneously acquired using a 3D position sensor. We applied multiple image resolution registration, where rapid and fine optimizations can be expected at higher and lower levels, respectively. Meanwhile, the gradient descent method was adopted for the optimization, which determines the relative arrangements to obtain maximum similarity between 2D and 3D images. We experimentally established resolution level parameters using a phantom before applying it to track liver blood vessel movements in a normal healthy subject. RESULTS: Comparing the 2D images and the registered images, although the approach has some limitations in tracking large displacement, we confirmed that the cross-section of the target blood vessel was clearly visualized. CONCLUSION: This method has the potential for an ultrasound therapy targeting blood vessels under natural respiration conditions.

Grain boundary sliding in pure and segregated bicrystals: a molecular dynamics and first principles study.

Sliding behaviors of Σ9(221) grain boundary bicrystals have been investigated in pure metals (Al, Ag, Au, Cu, Pt and Co) and in segregated metals (Cu segregated by Al, Ag, Au, Pt and Co) by molecular dynamics simulations and first-principles calculations. The grain boundary energy, the atomic size and the electronegativity of the segregated elements were not critical for the occurrence of grain boundary sliding. On the other hand, the sliding rate increased as the minimum charge density decreased at the bond critical point. This was the case for both pure grain boundary models and segregated grain boundary models. Therefore, it seems that the sliding rate depends on atomic movement at sites with minimum charge density, irrespective of the elements involved and of the presence of segregated atoms.