Imaging Conditions in Moving Grid Technique for Reduction of Grid Line Artifacts
Antiscatter grids are considered an indispensable tool to improve image contrast and even decrease imaging doses if they are properly selected and installed specifically for the imaging system. However, the most critical problem remaining as an obstacle for their successful use in digital x-ray imaging is probably the the observation of the grid line artifacts such as a moire pattern and a shadow of grid strips themselves in x-ray images, resulting in a risk of misdiagnosis by physicians.
Grid strips can be seen in x-ray images when the detector resolution is comparable or higher than the grid spacing. Moire pattern, a wavy shadow of the grid strips usually having a low frequency, is easily observed in digital x-ray images due to inadequate sampling of the grid strips by the detector pixels. We have previous found that moire free images could be produced through frequency synchronization between the grid and the detector, possibly by adjusting the magnification of the grid strips. However, complete matching of the grid frequency to the detector frequency is often impractical.
In order to find a practical solution against the grid line artifacts, we revisited the moving grid technique, which was originally proposed by Potter in 1920, in which the grid moves during the exposure to blur out the shadow of the grid strips. We implemented a simple and useful moving grid analysis code, JPI iTom™, and performed systematic simulation works to investigate proper imaging conditions in the moving grid technique for the reduction of the grid line artifacts. The framework of the code takes as parameters grid pitch, grid strip width, detector pixel size and exposure time, and allows for variation in grid moving velocity. We also performed experimental works and compared the results to the simulated ones to demonstrate the effectiveness of the code.