Resolution enhancement of lung 4D-CT data using multiscale interphase iterative nonlocal means

• Published in: Medical physics (Lancaster) Vol. 40; no. 5; pp. 051916 - n/a
• Main Authors: Zhang, Yu, Yap, Pew-Thian, Wu, Guorong, Feng, Qianjin, Lian, Jun, Chen, Wufan, Shen, Dinggang
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01.05.2013
• Subjects: 60 APPLIED LIFE SCIENCES; ALGORITHMS; cancer; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Computed tomography; Computerised tomographs; computerised tomography; COMPUTERIZED TOMOGRAPHY; Digital computing or data processing equipment or methods, specially adapted for specific applications; DOSIMETRY; Dosimetry/exposure assessment; FOUR-DIMENSIONAL CALCULATIONS; Four-Dimensional Computed Tomography - methods; HEALTH HAZARDS; Humans; Image data processing or generation, in general; Image enhancement; IMAGE PROCESSING; image reconstruction; INTERPOLATION; ITERATIVE METHODS; lung; Lung - diagnostic imaging; lung 4D‐CT; LUNGS; medical image processing; Medical image reconstruction; Medical imaging; nonlocal means; Numerical approximation and analysis; PEAKS; Pneumodyamics, respiration; RADIATION DOSES; RADIATION PROTECTION AND DOSIMETRY; radiation therapy; RADIOLOGY AND NUCLEAR MEDICINE; RADIOTHERAPY; Reconstruction; resolution enhancement; SENSITIVITY; SIGNAL-TO-NOISE RATIO; SPATIAL RESOLUTION; tumours; X‐ray imaging; nonlocal means; lung 4D-CT; resolution enhancement
• ISSN: 0094-2405; 2473-4209; 1522-8541; 2473-4209
• DOI: 10.1118/1.4802747

Purpose: Four-dimensional computer tomography (4D-CT) has been widely used in lung cancer radiotherapy due to its capability in providing important tumor motion information. However, the prolonged scanning duration required by 4D-CT causes considerable increase in radiation dose. To minimize the radiation-related health risk, radiation dose is often reduced at the expense of interslice spatial resolution. However, inadequate resolution in 4D-CT causes artifacts and increases uncertainty in tumor localization, which eventually results in extra damages of healthy tissues during radiotherapy. In this paper, the authors propose a novel postprocessing algorithm to enhance the resolution of lung 4D-CT data. Methods: The authors' premise is that anatomical information missing in one phase can be recovered from the complementary information embedded in other phases. The authors employ a patch-based mechanism to propagate information across phases for the reconstruction of intermediate slices in the longitudinal direction, where resolution is normally the lowest. Specifically, the structurally matching and spatially nearby patches are combined for reconstruction of each patch. For greater sensitivity to anatomical details, the authors employ a quad-tree technique to adaptively partition the image for more fine-grained refinement. The authors further devise an iterative strategy for significant enhancement of anatomical details. Results: The authors evaluated their algorithm using a publicly available lung data that consist of 10 4D-CT cases. The authors’ algorithm gives very promising results with significantly enhanced image structures and much less artifacts. Quantitative analysis shows that the authors’ algorithm increases peak signal-to-noise ratio by 3–4 dB and the structural similarity index by 3%–5% when compared with the standard interpolation-based algorithms. Conclusions: The authors have developed a new algorithm to improve the resolution of 4D-CT. It outperforms the conventional interpolation-based approaches by producing images with the markedly improved structural clarity and greatly reduced artifacts.