目的 弥散加权成像（DWI）作为一种新型医学影像成像技术，已逐渐成为诊断心脏、大脑、肾脏、肝脏等器官中的神经、纤维组织病变的重要方法和手段。与传统的核磁共振（MRI）成像相比，通过使用不同的扩散方向矢量，在不同的扩散参数下，DWI图像呈现的灰度信息也有所不同。目前尚无相关文献提出针对DWI图像版权信息进行有效保护的相关研究。方法 为有效保护病人的DWI图像版权信息，提出一种基于DWI图像的整数小波变换域（IWT）统计直方图的鲁棒水印算法。该算法首先通过最大类间方差分割算法和面积控制阈值获取指定断层中带有弥散梯度方向图像的前景区域，作为待嵌入区域。对待嵌入区域使用整数小波变换获取低频子带系数，利用固定步长对低频子带系数进行统计，生成统计直方图，对统计直方图相邻簇的比值关系进行修改用于水印嵌入；最后提出DWI表观系数与弥散张量成像（DTI）中弥散张量值的可逆关系构建可逆密钥，利用该密钥将嵌入水印后的DWI图像再次加密，从而有效保护DWI图像的版权信息。结果 实验结果表明该算法引入的水印信息对DWI图像中的纤维参数改变量极小。在纤维方向和平均弥散程度改变个数上，本文算法与文献方法相比，分别降低了100多个和30多个；在可视质量上，本文算法提高约8 dB。在高斯噪声、小角度旋转等攻击中，本文算法能够提供较高的提取水印准确率。结论 本文算法对医生诊断的影响在可接受的范围内，且在感兴趣区域遭受各种常见攻击时，具有较高的安全性和鲁棒性。

Objective Diffusion weight imaging (DWI), as a new medical imaging technique, transforms the diffusion motion of water molecules in tissues into grayscale or other parameter information of an image by applying multi-directional diffusion magnetic sensitive gradients under each diffusion sensitive gradient. This technique can be used for the auxiliary diagnosis of living heart myocardial fiber modeling, brain fiber, lesions of the central nervous system, liver fibrosis, and other diseases. With the popularization of telemedicine diagnostic technology, an increasing amount of DWI data are being used for remote diagnosis and scientific research. DWI images, which are originally stored and used on a single machine in a hospital, must be transmitted and used over the network. Many scholars have proposed many watermarking algorithms for protecting medical images, such as the reversible watermarking algorithm, robust reversible watermarking algorithm, and zero-watermarking algorithm. The advantage of the reversible algorithm is that it can be completely used for nondestructive image recovery. The robustness of the reversible watermarking algorithm is too weak to guarantee the existence of the reversible watermark when embedded images are attacked intentionally or unintentionally. Therefore, some researchers propose the robust reversible watermarking algorithm. The robust reversible watermarking algorithm could restore an original picture when no attack occurs and could draw embedded watermarking. It ensures that its robust reversible performance should carry additional information. Thus, it must consume a large amount of transmission bandwidth. Some robust reversible watermarks are constructed by dual watermarking, and they depend on one another's information to extract the watermarks. To protect medical images by other methods, some researchers use the zero-watermarking algorithm, which is different from the traditional method that embeds information into images. The zero-watermarking algorithm can retrieve internal features from data to build binary watermarking and then save it in a third-party application. When the image is used by other people without the license, we could use zero-watermarking to prove copyright. Thus, the zero-watermarking algorithm, as a non-embedded algorithm, cannot actively complete the protection of property information. The robust watermarking algorithm plays an irreplaceable role in ensuring that the medical image watermarking information has certain robustness. To prevent unauthorized DWI images from being used or tampered with, this study proposes a robust watermarking algorithm based on DWI images. Method The algorithm initially obtains specified slips by the maximum inter-class variance segmentation algorithm and area control threshold to ensure that the selected slice has a sufficient embedding area because the tip and the bottom of the heart are unsuitable for embedding. The foreground region with a diffusion gradient direction image is prepared for embedding. We obtain the low-frequency sub-band coefficient by using integer wavelet transform in the default region. Then, we count the low frequency and analyze the low sub-frequency coefficient by using the fixed step length; the low sub-frequency coefficient follows the characteristics of the coefficient of DWI images. The ratio relation of adjacent clusters in the histogram subject area is adjusted for watermark embedding. Finally, we propose to design the quantitative reversible relationship between apparent DWI coefficients, with diffusion tensor imaging (DTI) as the key. We use this key to encrypt a DWI image after embedding the watermark to effectively protect the copyright information of the DWI image. Result The algorithm can maintain its robustness and reduce the change in the DTI parameters in the experiment on robustness and changes in the parameters of DTI after embedding. The proposed algorithm also has excellent robustness in attack experiments, such as those involving Gaussian noise, contrast expansion, and small angle rotation. In the experiment on parameter change measurement before and after embedding, the algorithm is greatly reduced the volume of change in isotropic and fiber main direction of the myocardial fiber. In our proposed method, the main direction of the fiber is reduced by more than 100, and the average change of the mean diffusivity is reduced by more than 30 in the same database. In the visual quality of the algorithm, the peak signal-to-noise ratio is approximately 8 dB higher than that specified in the comparative literature. Conclusion An embedded selection feedback mechanism is proposed to carry out the selection of watermark embedding according to actual embedding demands. Then, the statistical histogram of the sub-band coefficient is constructed by specifying the fixed step length according to the characteristics of the wavelet transform coefficient of the DWI image. Finally, the reversible key algorithm based on the quantitative relationship between DWI and DTI is constructed. Experiments show that this algorithm can be applied to the watermark embedding of dispersion weighted imaging and can satisfy fiber direction as little as possible.