Sirilawan Tohnak, 78-309 General Purpose South Building, School of ITEE, The University of Queensland, Brisbane QLD 4072, Australia.
Dentomaxillofac Radiol. 2011 Mar;40(3):184-90. doi: 10.1259/dmfr/25260548.
Metal artefacts can seriously degrade the visual quality and interpretability of dental CT images. Existing image processing algorithms for metal artefact reduction (MAR) are either too computationally expensive to be used in clinical scanners or effective only in correcting mild artefacts. The aim of the present study was to investigate whether it is possible to improve the efficacy of the computationally efficient projection-correction approach to MAR by exploiting the spatial dependency or autocorrelation between adjacent CT slices.
A new projection-correction algorithm [MAR by sequential substitution (MARSS)] was developed based on the idea that the corrupted portions of the projection data can be substituted with the corresponding portions from an unaffected adjacent slice. The performance of MARSS was evaluated relative to the projection-correction method of Watzke and Kalendar using a two-alternative forced choice (2AFC) visual trial involving 20 observers and 20 clinical CT data sets.16
The Cochran Q test revealed no significant difference in the responses across all observers. The data were then pooled and analysed using a one-tailed exact binomial test. This revealed that the proportion of responses in favour of MARSS was significant (P < 2.2 × 10(-16)). A second Cochran Q test revealed no significant difference in the responses across all images.
It is possible to improve the efficacy of projection correction by exploiting spatial autocorrelation. The 2AFC results suggest that the proposed MARSS algorithm outperforms competing computationally efficient algorithms in terms of reducing metal artefacts whilst at the same time preserving/revealing anatomic detail.
金属伪影会严重降低牙科 CT 图像的视觉质量和可解释性。现有的用于减少金属伪影（MAR）的图像处理算法要么计算成本过高，无法在临床扫描仪中使用，要么只能有效纠正轻度伪影。本研究旨在探讨是否可以通过利用相邻 CT 切片之间的空间相关性或自相关性来提高计算效率高的投影校正方法对 MAR 的有效性。
基于从无伪影相邻切片中替换投影数据的受污染部分的思想，开发了一种新的投影校正算法[MAR 通过顺序替换（MARSS）]。使用涉及 20 名观察者和 20 个临床 CT 数据集的二项式选择（2AFC）视觉试验，相对于 Watzke 和 Kalendar 的投影校正方法评估了 MARSS 的性能。
Cochran Q 检验表明，所有观察者的反应均无显着差异。然后将数据汇总并使用单侧精确二项式检验进行分析。这表明，赞成 MARSS 的比例具有显着性（P <2.2×10（-16））。第二个 Cochran Q 检验表明，所有图像的反应均无显着差异。
通过利用空间自相关性，可以提高投影校正的有效性。 2AFC 结果表明，与竞争的计算效率高的算法相比，所提出的 MARSS 算法在减少金属伪影的同时，在保留/揭示解剖细节方面表现更好。
