Abstract. Image resolution in 4D-CT is a crucial bottleneck that needs to be overcome for improved dose planning in radiotherapy for lung cancer. In this paper, we propose a novel patch-based algorithm to enhance the image quality of 4D-CT data. Our premise is that anatomical information missing in one phase can be recovered from complementary information embedded in other phases. We employ a patch-based mechanism to propagate information across phases for reconstruction of intermediate slices in the axial direction, where resolution is normally the lowest. Specifically, structurally-matching and spatially-nearby patches are combined for reconstruction of each patch. For greater sensitivity to anatomical nuances, we further employ a quad-tree technique to adaptively partition each slice of the image in each phase for more fine-grained refinement. Our evaluation based on a public 4D-CT lung data indicates that our algorithm gives very promising results with significantly enhanced image structures.
Introduction4D-CT is becoming increasingly popular in lung cancer treatment for providing respiratory-related information that is essential for guiding radiation therapy effectively. However, due to the risk of radiation [1], only a limited number of CT segments are usually acquired, which often results in very low resolution along the inferior-superior direction. This low-resolution (LR) data are usually plagued with visible imaging artifacts such as vessel discontinuity and partial volume effect. More importantly, insufficient resolution further distorts the shape of a tumor. This distortion might finally interfere with optimal dose planning. Super-resolution (SR) reconstruction is an effective approach for improving image resolution. Classical SR methods can be divided into two major categories: interpolation-based and model-based. The main advantage of interpolation-based methods is their simplicity. However, blurred edges and undesirable artifacts are inevitable. Currently, more attention has been directed to model-based SR approach. The general assumption of model-based SR approaches is that the LR image is a degraded version