邱甲军 吴跃 惠孛 刘彦伯

摘 要：图像纹理增强过程中容易丢失平滑区域纹理细节，而分数阶微分增强虽然能够非线性保留平滑区域纹理细节，但对频率分辨率敏感。针对这个问题，提出一种基于小波变换的分数阶微分纹理增强算法，应用于平扫计算机断层扫描（CT）图像的肝脏肿瘤区域的纹理增强。首先，通过小波变换将图像感兴趣区分解成多个子带分量;其次，基于分数阶微分定义构造一个带补偿参数的分数阶微分掩膜;最后，使用该掩膜与每个高频子带分量进行卷积并利用小波逆变换重组图像感兴趣区。实验结果表明，该方法在使用较大分数阶次显著增强肿瘤区域的高频轮廓信息的同时，有效地保留了低频平滑的纹理细节：增强后的肝细胞癌区域与原区域相比，信息熵平均增加36.56%，平均梯度平均增加321.56%，平均絕对差值平均为9.287;增强后的肝血管瘤区域与原区域相比，信息熵平均增加48.77%，平均梯度平均增加511.26%，平均绝对差值平均为14.097。

关键词：纹理增强;小波变换;分数阶微分;肝细胞癌;肝血管瘤;计算机断层扫描图像

中图分类号：TP391.4

文献标志码：A

文章编号：1001-9081（2019）04-1196-05

Abstract： Smooth texture details are easily lost in the process of image texture enhancement. Although fractional-order differential enhancement can preserve the texture details of smooth regions nonlinearly， it is sensitive to frequency resolution. Focusing on this problem， a fractional differential texture enhancement algorithm based on wavelet transform was proposed and applied to texture enhancement of liver tumor regions in plain Computed Tomography （CT） images. Firstly， wavelet transform was used to decompose the image region of interest into multiple subband components. Then， a fractional differential mask with compensation parameter was constructed based on fractional-order differential definition. Finally， the mask was used to convolve with each high frequency subband component respectively， and the image region of interest was recombined by using reverse wavelet transform. The experimental results show that the algorithm effectively preserves the low-frequency smooth texture details while observably enhances the high-frequency contour information of the tumor region by a relatively large fractional order： compared with the original region， the enhanced hepatocellular carcinoma region has the information entropy increased by 36.56% averagely， the average gradient increased by 321.56% averagely， and the mean absolute difference of 9.287 averagely; compared with the original region， the enhanced hepatic hemangioma region has the information entropy increased by 48.77% averagely， the average gradient increased by 511.26% averagely， and the mean absolute difference of 14.097 averagely.

Key words： texture enhancement; wavelet transform; fractional differential; hepatocellular carcinoma; hepatic hemangioma; Computed Tomography （CT） image

0 引言

在医学图像处理中，纹理是放射组学中一种重要的定量数据特征，丰富的纹理代表了大量非可视数据[1]。在肝脏肿瘤的计算机辅助诊断系统中，基于计算机断层扫描（Computed Tomography， CT）图像纹理的分类识别是一种可行的辅助诊断方法[2]，但CT扫描中不同的参数设置、容积效应，以及病灶本身在病理组织上的复杂性，使得感兴趣区的图像解释比较困难，因此纹理增强成为放射组学中模式识别、图像恢复等诸多领域的一种重要手段[3-4]。……