A conjugate gradient weighted least squares reconstruction method with region of interest correction for cone-beam rotational computed laminography

Cone-beam rotational computed laminography (CL) is a highly effective inspection technique for non-destructive testing of objects with a large aspect ratio, such as printed circuit boards (PCB) and insulated gate bipolar transistors (IGBT). However, when scanning objects with a large aspect ratio, the projection data may become truncated, resulting in region of interest (ROI) artifacts in the reconstructed image and reducing the contrast of the reconstructed image. To address this issue, we have proposed a weighted factor that considers the length of the ray within the reconstructed volume and the distance between the X-ray source and the detector bin position. We have also developed a method called ROI conjugate gradient weighted least squares (ROI-CGWLS) to suppress ROI artifacts and enhance the contrast of the reconstructed image in Cone-beam rotational CL. Both simulation and real PCB experimental results demonstrate the effectiveness of the proposed ROI-CGWLS method in suppressing ROI artifacts and improving image contrast and resolution compared to other classical reconstruction methods.