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Robust watermarking with oblivious detection is essential to practical copyright protection of digital images. Effective exploitation of the characteristics of human visual perception to color stimuli helps to develop the watermarking scheme that fills the requirement. In this paper, an oblivious watermarking scheme that embeds color watermarks in color images is proposed. Through color gamut analysis and quantizer design, color watermarks are embedded by modifying quantization indices of color pixels without resulting in perceivable distortion. Only a small amount of information including the specification of color gamut, quantizer stepsize, and color tables is required to extract the watermark. Experimental results show that the proposed watermarking scheme is computationally simple and quite robust in face of various attacks such as cropping, low-pass filtering, white-noise addition, scaling, and JPEG compression with high compression ratios.

Purpose: Functional magnetic resonance imaging with BOLD contrast is widely used for detecting brain activity in the cortex. Recently, several studies have described anisotropic correlations of resting‐state BOLD signals between voxels in white matter (WM). These local WM correlations have been modeled as functional‐correlation tensors, are largely consistent with underlying WM fiber orientations derived from diffusion MRI, and appear to change during functional activity. However, functional‐correlation tensors have several limitations. The use of only nearest‐neighbor voxels makes functional‐correlation tensors sensitive to noise. Furthermore, adjacent voxels tend to have higher correlations than diagonal voxels, resulting in orientation‐related biases. Finally, the tensor model restricts functional correlations to an ellipsoidal bipolar‐symmetric shape, and precludes the ability to detect complex functional orientation distributions (FODs). Methods: We introduce high‐angular‐resolution functional‐correlation imaging (HARFI) to address these limitations. In the same way that high‐angular‐resolution diffusion imaging (HARDI) techniques provide more information than diffusion tensors, we show that the HARFI model is capable of characterizing complex FODs expected to be present in WM. Results: We demonstrate that the unique radial and angular sampling strategy eliminates orientation biases present in tensor models. We further show that HARFI FODs are able to reconstruct known WM pathways. Finally, we show that HARFI allows asymmetric "bending" and "fanning" distributions, and propose asymmetric and functional indices which may increase fiber tracking specificity, or highlight boundaries between functional regions. Conclusions: The results suggest the HARFI model could be a robust, new way to evaluate anisotropic BOLD signal changes in WM. [ABSTRACT FROM AUTHOR]

Purpose: Numerous studies have adopted resting‐state functional MRI methods to infer functional connectivity between cortical regions, but very few have translated them to the spinal cord, despite its critical role in the central nervous system. Resting‐state functional connectivity between gray matter horns of the spinal cord has previously been shown to be detectable in humans and nonhuman primates, but it has not been reported previously in rodents. Methods: Resting‐state functional MRI of the cervical spinal cord of live anesthetized rats was performed at 9.4 T. The quality of the functional images acquired was assessed, and quantitative analyses of functional connectivity in C4‐C7 of the spinal cord were derived. Results: Robust gray matter horn‐to‐horn connectivity patterns were found that were statistically significant when compared with adjacent control regions. Specifically, dorsal–dorsal and ventral–ventral connectivity measurements were most prominent, while ipsilateral dorsal–ventral connectivity was also observed but to a lesser extent. Quantitative evaluation of reproducibility also revealed moderate robustness in the bilateral sensory and motor networks that was weaker in the dorsal–ventral connections. Conclusions: This study reports the first evidence of resting‐state functional circuits within gray matter in the rat spinal cord, and verifies their detectability using resting‐state functional MRI at 9.4 T. Magn Reson Med 79:2773–2783, 2018. © 2017 International Society for Magnetic Resonance in Medicine. [ABSTRACT FROM AUTHOR]

Purpose In principle, MR methods that exploit magnetization transfer (MT) may be used to quantify changes in the molecular composition of tissues after injury. The ability to track such changes in injured spinal cord may allow more precise assessment of the state of neural tissues. Methods Z-Spectra were obtained from the cervical spinal cord before and after a unilateral dorsal column lesion in monkeys at 9.4T. The amplitudes of chemical exchange saturation transfer (CEST) and nuclear Overhauser enhancement (NOE) effects from multiple proton pools, along with nonspecific semisolid MT effects from immobile macromolecules, were quantified using a five-peak Lorenzian fitting of each Z-spectrum. Results Abnormal tissues/cysts that formed around lesion sites exhibited relatively low correlations between their Z-spectra and that of normal gray matter (GM). Compared with normal GM, cysts showed strong CEST but weak semisolid MT and NOE effects after injury. The abnormal tissues around lesion sites were heterogeneous and showed different regional Z-spectra. Different regional correlations between proton pools were observed. Longitudinally, injured spinal cord tissue exhibited remarkable recovery in all subjects. Conclusion Characterization of multiple proton pools from Z-spectra permitted noninvasive, regional, quantitative assessments of changes in tissue composition of injured spinal cord over time. Magn Reson Med 79:1070-1082, 2018. © 2017 International Society for Magnetic Resonance in Medicine. [ABSTRACT FROM AUTHOR]