技术说明：用于X射线计算机断层扫描及其他应用的类似发射期望最大化算法
Technical Note: Emission expectation maximization look-alike algorithms for x-ray CT and other applications.
作者信息
Zeng Gengsheng L
机构信息
Department of Engineering, Weber State University, Ogden, UT, 84408, USA.
Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, 84108, USA.
出版信息
Med Phys. 2018 Jul 2. doi: 10.1002/mp.13077.
PURPOSE
In emission tomography, the expectation maximization (EM) algorithm is easy to use with only one parameter to adjust - the number of iterations. On the other hand, the EM algorithms for transmission tomography are not so user-friendly and have many problems. This paper develops a new transmission algorithm similar to the emission EM algorithm.
METHODS
This paper develops a family of emission-EM-look-alike algorithms by expressing the emission EM algorithm in the additive form and changing the weighting factor. One of the family members can be applied to transmission tomography such as the x-ray computed tomography (CT).
RESULTS
Computer simulations are performed and compared with a similar algorithm by a different group using the transmission CT noise model. Our algorithm has the same convergence rate as theirs, and our algorithm provides better contrast-to-noise ratio for lesion detection.
CONCLUSIONS
For any noise variance function, an emission-EM-look-alike algorithm can be derived. This algorithm preserves many properties of the emission EM algorithm such as multiplicative update, non-negativity, faster convergence rate for the bright objects, and ease of implementation.
目的
在发射断层扫描中，期望最大化（EM）算法易于使用，只需调整一个参数——迭代次数。另一方面，用于透射断层扫描的EM算法对用户不太友好且存在诸多问题。本文开发了一种类似于发射EM算法的新透射算法。
方法
本文通过将发射EM算法以加法形式表示并改变加权因子，开发了一族类似发射EM的算法。该族算法中的一个成员可应用于透射断层扫描，如X射线计算机断层扫描（CT）。
结果
进行了计算机模拟，并使用透射CT噪声模型与另一组的类似算法进行比较。我们的算法与他们的算法具有相同的收敛速度，并且在病变检测方面提供了更好的对比度噪声比。
结论
对于任何噪声方差函数，都可以推导出一种类似发射EM的算法。该算法保留了发射EM算法的许多特性，如乘法更新、非负性、对明亮物体更快的收敛速度以及易于实现。
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