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Abstract: The control plane techniques based on the Generalized Multi-Protocol Label Switching (GMPLS) and Path Computation Element (PCE) architectures are promising candidates for potential industrial deployment in Wavelength Switched Optical Networks (WSON), because they can greatly reduce operational expenses and improve the network intelligence. Moreover, link failures have a critical effect on WSON, since a single failure may result in the loss of a huge amount of data. In light of this, in this paper, we detail the design and implementation of a GMPLS control plane, with PCE-based, impairment-aware, full restoration capability for translucent WSON. We investigate the enabling techniques for such a PCE/GMPLS control plane by surveying a series of solutions, and, based on these enabling techniques, we present an experimental demonstration of service recovery for uncompressed video stream in a GMPLS controlled WSON with PCE-based full lightpath restoration. We also quantitatively evaluate the performance of the PCE-based full restoration, and compare it with the PCE-based pre-planned restoration and the PCE-based pre-computed dynamic restoration in terms of signaling latency and restorability. To the best of our knowledge, it is the first time that the PCE-based full restoration is experimentally investigated on an actual GMPLS controlled WSON testbed, which is beneficial for verifying the overall feasibility and efficiency of the proposed solutions, obtaining valuable insights for its future deployment in a real operational scenario, and providing active contribution in support of the on-going Internet Engineering Task Force (IETF) standardization activities. [Copyright &y& Elsevier]

Abstract: In this paper, we present the correction of the geometric distortion measured in the clinical magnetic resonance imaging (MRI) systems reported in the preceding paper (Part I) using a 3D method based on the phantom-mapped geometric distortion data. This method allows the correction to be made on phantom images acquired without or with the vendor correction applied. With the vendor''s 2D correction applied, the method corrects for both the “residual” geometric distortion still present in the plane in which the correction method was applied (the axial plane) and the uncorrected geometric distortion along the axis normal to the plane. The evaluation of the effectiveness of the correction using this new method was carried out through analyzing the residual geometric distortion in the corrected phantom images. The results show that the new method can restore the distorted images in 3D nearly to perfection. For all the MRI systems investigated, the mean absolute deviations in the positions of the control points (along x-, y- and z-axes) measured on the corrected phantom images were all less than 0.2 mm. The maximum absolute deviations were all below ∼0.8 mm. As expected, the correction of the phantom images acquired with the vendor''s correction applied in the axial plane performed equally well. Both the geometric distortion still present in the axial plane after applying the vendor''s correction and the uncorrected distortion along the z-axis have all been “restored.” [Copyright &y& Elsevier]

A phantom that can be used for mapping geometric distortion in magnetic resonance imaging (MRI) is described. This phantom provides an array of densely distributed control points in three-dimensional (3D) space. These points form the basis of a comprehensive measurement method to correct for geometric distortion in MR images arising principally from gradient field non-linearity and magnet field inhomogeneity. The phantom was designed based on the concept that a point in space can be defined using three orthogonal planes. This novel design approach allows for as many control points as desired. Employing this novel design, a highly accurate method has been developed that enables the positions of the control points to be measured to sub-voxel accuracy. The phantom described in this paper was constructed to fit into a body coil of a MRI scanner, (external dimensions of the phantom were: 310 mm × 310 mm × 310 mm), and it contained 10,830 control points. With this phantom, the mean errors in the measured coordinates of the control points were on the order of 0.1 mm or less, which were less than one tenth of the voxel''s dimensions of the phantom image. The calculated three-dimensional distortion map, i.e., the differences between the image positions and true positions of the control points, can then be used to compensate for geometric distortion for a full image restoration. It is anticipated that this novel method will have an impact on the applicability of MRI in both clinical and research settings, especially in areas where geometric accuracy is highly required, such as in MR neuro-imaging. [Copyright &y& Elsevier]