Magnetic resonance imaging (MRI) is a revolutionary tool in medical imaging, which plays an important role in clinical diagnosis. Compressive sensing (CS) has shown great potential in significantly reducing the acquisition time of MRI scanning. However, how to improve the reconstruction quality with limited k-space data is still a challenge. MRI images are featured with large area of smooth regions, sharp edges and rich textures. Motivated by these facts, we propose a nonlocal autoregressive model (NAM) for CS MRI reconstruction. Nonlocal similarity between image patches is exploited as a regularization term to constrain the nonlocal feature in MRI images, which is very helpful in preserving edge sharpness. While an autoregressive regularization term is employed to describe the linear correlation between neighboring pixels, which preserves more spatial details. Different from previous work, we reconstruct an MRI image patch utilizing correlations both among patches and among neighboring pixels. Extensive experimental results demonstrate that our method outperforms mainstream methods in MRI reconstruction in terms of both subjective quality and objective quality.
A 2D high-precision motion unit plays an important role in an automatic optical inspection (AOI) system, and its
positioning accuracy and speed have an decisive effect on the inspection accuracy, efficiency and stability of the AOI
system, but the present AOI systems cannot ensure the high speed and high-precision at the same time. To solve this
problem, an automatic optical platform is developed, using the whole-closed-loop, fast, high-precision positioning
technology to construct the mathematical models of its motion control unit, including models of current loop, velocity
loop and position loop from inside to outside. Experiments were made on the motion platform using a laser
interferometer. Experimental results show that the 2D motion platform can be used to reach a scanning speed of 20m/s
and a positioning accuracy of 9ìm in a work area of 300mm * 3000mm with a load of 5kg.