Computed tomography (CT) is an imaging modality widely used for medical diagnosis and treatment. CT images are often corrupted by undesirable artifacts when metallic implants are carried by patients, which creates the problem of metal artifact reduction (MAR). Existing methods for reducing the artifacts due to metallic implants are inadequate for two main reasons. First, metal artifacts are structured and non-local so that simple image domain enhancement approaches would not suffice. Second, the MAR approaches which attempt to reduce metal artifacts in the X-ray projection (sinogram) domain inevitably lead to severe secondary artifact due to sinogram inconsistency. To overcome these difficulties, we propose an end-to-end trainable Dual Domain Network (DuDoNet) to simultaneously restore sinogram consistency and enhance CT images. The linkage between the sinogram and image domains is a novel Radon inversion layer that allows the gradients to back-propagate from the image domain to the sinogram domain during training. Extensive experiments show that our method achieves significant improvements over other single domain MAR approaches. To the best of our knowledge, it is the first end-to-end dual-domain network for MAR.

Hydrogels are three-dimensional porous polymeric networks prepared by physical or chemical cross-linking of hydrophilic molecules, which can be made into smart materials through judicious chemical modifications to recognize external stimuli; more specifically, this can be accomplished by the integration with stimuli-responsive polymers or sensing molecules that has drawn considerable attention in their possible roles as sensors and diagnostic tools. They can be tailored in different structures and integrated into systems, depending on their chemical and physical structure, sensitivity to the external stimuli and biocompatibility. A panoramic overview of the sensing advances in the field of hydrogels over the past several decades focusing on a variety protocols of hydrogel preparations is provided, with a major focus on natural polymers. The modifications of hydrogel composites by incorporating inorganic nanoparticles and organic polymeric compounds for sensor applications and their mechanisms are also discussed.

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