基于稀疏重建的磁共振图像尖峰噪声消除方法

磁共振图像K空间中的尖峰噪声会严重影响图像质量.该文在磁共振图像压缩感知的共轭梯度重建法的基础上,提出一种新的利用磁共振图像稀疏性进行尖峰噪声修复的方法.传统的共轭梯度重建是通过小波域迭代进行的,对于K空间的尖峰噪声的消除不是最适合.首先提出压缩感知的K空间重建算法,该算法与小波域重建等效.在此基础上,提出可以较好地修复尖峰噪声的K空间部分重建算法.即在迭代过程中,以图像的稀疏性作为约束条件,仅修改尖峰噪声所遮盖区域的数据,其他位置的数据保持不变.该算法与传统的插值算法及共轭梯度算法相比,能够更好地修复K空间尖峰噪声点,减少图像伪影,同时降低了对尖峰噪声定位准确性的要求.     

气泡微液底层蒸干特性分析

本文从气泡微液底层的流动特性出发，利用Ｈａｌｌｉｎａｎ和Ｅｒｖｉｎ模型对微层蒸干的Ｓｔｒａｕｂ判据进行了理论分析，证实了临界蒸干半径与湿润性有关，同时指出微层蒸发中起关键作用的是膨胀压力而不是表面张力梯度。     

EFFECT OF CONTENT OF CHLORIDE IONS IN SILVER BROMIDE ON THE ADSORPTION AND SENSITIZATION OF DYES

The adsorption and spectral sensitization of different types of dyes (cationic, anionic cyanine andmerocyanine) on silver chlorobromide were investigated by clectrochemical method, FT-IR and modelPhotographic emulsion. It has been found that addition of chloride ions can enhance the adsorption ofdyes and improve the ability of spectral sensitization. Different behaviors in adsorption and spectralsensitization appeared in different types of dyes depending on the structures and electric charges ofdyes. Merocyanine dye has the best adsorption and remarkable spectral sensitization ability on silverchlorobromide in comparison with other cyanine dyes. Experimental results also showed that there wasa good correlativity between adsorption behavior of dyes obtained by electrochemical method and spec-tral sensitization in model photographic emulsion, and the adsorption complex composed of dye andsilver halide was electro-inert but photo-active. The mechanism of spectral sensitization with variousdyes has been dis     

压缩感知同步扫描重建及其采样方案的研究

压缩感知(compressed sensing,CS)-磁共振成像(magnetic resonance imaging,MRI)技术使用随机欠采样的k空间数据来重建图像,大大提高了成像速度.但典型的CS重建很费时,这也是CS-MRI临床应用的主要障碍之一.针对这一问题,该文提出了在扫描时同步进行CS图像重建的方案.在同步重建的过程中,可以实时显示重建图像的结果,用户可以根据图像质量来决定何时终止扫描,这样可以在节约扫描和重建时间的同时,更好地控制图像质量.由于预先无法确定最终的采样率,因此传统的变密度随机采样方法并不完全适用.该文设计了适用于同步重建过程的采样模式生成方案,同时提出了分段采样方法,把采样过程分为两个阶段,不同阶段使用不同的概率密度函数(probability density function,PDF)确定待采样的相位编码行.模拟实验的结果表明,与使用单一密度函数的采样方案相比,分段采样方案能够在整个同步扫描重建过程中始终获得更好的图像.