光谱法分析迭代重建过程中的滤波

Analyzing the Methods to Smooth Field Reconstructed by Algebraic Reconstruction Technique with Spectroscopy

应用光谱法讨论了滤波器及其滤波方案对重建效果的影响。数值模拟重建场,应用光谱法分析了1/4,1/5,1/8均值滤波器,1/5中值滤波器,1/3行、列滤波器,在内嵌、外置等情况下对代数迭代重建的场滤波效果的影响。结果发现:用代数迭代法重建的场含有较大噪声,需要平滑处理;采用1/4,1/5或1/8均值滤波器仅对迭代结果滤波,会严重降低重建精度;采用1/4,1/8均值滤波器内嵌在迭代过程中按一定的迭代次数滤波,可以在一定程度上改善重建精度;采用1/5中值滤波器内嵌在迭代过程中比相应的均值滤波器重建效果更好;内嵌1/5中值滤波器和均值滤波器交替滤波,效果比单一的滤波器滤波更好。采用不同的滤波器和滤波方案对重建结果的影响差别较大。

The effects of filters and filtering methods on the field reconstructed by algebraic reconstruction technique （ART） is discussed with spectroscopy. The field to be constructed was simulated with numerical simulation technique. The effects of many kinds of filters and filtering methods on the field reconstructed by ART were analyzed with spectroscopy. The filters used included quarter, fifth, eighth averaging filter, fifth center filter, and third row, column filter. The filtering methods included filter being inserted in the iterating process or set at its end. The averaging filter mentioned above meant that the value was acquired from the average of the four data, named quarter averaging filter, and so on. The fifth center filter meant that the value was acquired from the center, the third one in ascendant or descendant sequence of the five data. As a result, the authors found that a larger difference existed in the effects of different filters and filtering methods on the reconstructed field. First, the field reconstructed by ART contained much big noise and needed to be smoothed. Secondly, the reconstructive accuracy declined much when an averaging filter, such as quarter, fifth or eighth filter, was only set at the end of iterating process. Thirdly, the accura- cy could be improved a little with a quarter or eighth averaging filter inserted in the iterating process and activated according to iterating times. Forthly, a better accuracy could be obtained with a fifth center filter inserted in the iterating process than with a fifth averaging one inserted. Fifthly, the best result in this work was obtained with a fifth averaging filter and a fifth center one inserted in the iterating process and activated alternately according to iterating times.